Hydrogen Energy Future PDF

8/3/2019 Hydrogen Energy Future PDF

1/48

U.S. Department of Energy

Hydrogen Program

www.hydrogen.energy.gov

Hoe &O Ee Fe


2/48

|

HydrOgEn & Our EnErgy FuturE

U.S. Department of Energy

Hydrogen Programwww.hydrogen.energy.gov

u.S. depame o Ee


3/48

|

www.hoe.ee.ov

Hoe & O Ee Fe

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.1

Hydrogen An Overview .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.3

Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.5

Delivery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.15

Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.19

Application and Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.25

Saety, Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.33

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.35

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.39

u.S. depame o Ee


4/48

|


u.S. depame o Ee


5/48

www.hoe.ee.ov

Introduction

Hydrogen holds the potential to provide clean, sae, aordable,

and secure energy rom abundant domestic resources.

In 2003, President George W. Bush announced the Hydrogen Fuel Initiative to

accelerate the research and development o hydrogen, uel cell, and inrastruc

ture technologies that would enable hydrogen uel cell vehicles to reach the

commercial market in the 2020 timerame. The widespread use o hydrogen

can reduce our dependence on imported oil and benet the environment by

reducing greenhouse gas emissions and criteria pollutant emissions that aect

our air quality.

The Energy Policy Act o 2005, passed by Congress and signed into law by

President Bush on August 8, 2005, reinorces Federal government support or

hydrogen and uel cell technologies. Title VIII, also called the Spark M. MatsunagaHydrogen Act o 2005 authorizes more than $3.2 billion or hydrogen and uel

cell activities intended to enable the commercial introduction o hydrogen uel

cell vehicles by 2020, consistent with the Hydrogen Fuel Initiative. Numerous

other titles in the Act call or related tax and market incentives, new studies,

collaboration with alternative uels and renewable energy programs, and broad

ened demonstrationsclearly demonstrating the strong support among members

o Congress or the development and use o hydrogen uel cell technologies.

In 2006, the President announced the Advanced Energy Initiative (AEI) to

accelerate research on technologies with the potential to reduce near-term oiluse in the transportation sectorbatteries or hybrid vehicles and cellulosic

ethanoland advance activities under the Hydrogen Fuel Initiative. The AEI

also supports research to reduce the cost o electricity production technologies

in the stationary sector such as clean coal, nuclear energy, solar photovoltaics,

and wind energy.

Energy Security

The increasing demand or gasoline and diesel uel used to power our cars and

trucks makes our nation more dependent on oreign sources o oil. More thanone-hal o the petroleum consumed in the United States is imported, and that

percentage is expected to rise to 68% by 2025.1 The U.S. transportation sector

relies almost exclusively on rened petroleum products, accounting or over

two-thirds o the oil used.2 Our increasing dependence on oreign sources o

oil makes us vulnerable to supply disruptions and price fuctuations that occur

outside o our country.

) u.S. depame o Ee, Ee

Iomaio Amiisaio, AalEe Olook 005, (Feba

005), 7.

) Oak rie naioal Laboao,

taspoaio Ee daa Book:

Eiio , (decembe 00), table

. Wol Peolem Pocio,

97-00, -.

u.S. depame o Ee Iocio |


6/48


In the short term, conservation and the use o highly ecient hybrid-electric

vehicles (HEVs) can slow the overall rate o growth o oil consumption

Hybrid-electric vehicle technology is becoming commercially competitive in

Introduction

) u.S. Eviomeal Poecio

Aec, Ai tes: Six Picipal

Pollas, (..), eieve

Sepembe 5, 005, om hp://

www.epa.ov/aies/sixpoll.hml;

a u.S. Bea o he Cess global

Poplaio Pole 00, table A-

Poplaio b reio a Co:

950-050, 5.

todays consumer market, and additional research is ocused on making hybrid

batteries, electronics, and materials more aordable. But over the long term

when projected increases in the number o cars on the road and vehicle-miles

traveled are taken into account, HEV use alone will not reduce oil consumption

below todays level.

In addition to the increased use o biouels, like ethanol, and plug-in hybrid

vehicles technology, using hydrogen as an energy carrier can provide the United

States with a more ecient and diversied energy inrastructure. Hydrogen is a

promising energy carrier in part because it can be produced rom dierent and

abundant resources, including ossil, nuclear, and renewables. Using hydrogenparticularly or our transportation needs, will allow us to diversiy our energy

supply with abundant, domestic resources and reduce our dependence on

oreign oil.

Environmental Benefts

Air quality is a signicant national concern. The U.S. Environmental Protection

Agency estimates that about 50% o Americans live in areas where levels o

one or more air pollutants are high enough to aect public health and/or

the environment3. In addition, the combustion o ossil uels accounts or themajority o anthropogenic greenhouse gas emissions (primarily carbon dioxide

or CO2) released into the atmosphere. The largest sources o CO

2emissions are

the electric utility and transportation sectors.

Fuel cells use hydrogen to create electricity, with only heat and water as byprod

ucts. When used to power a vehicle, the only output rom the tailpipe is water

vaporno greenhouse gas or criteria emissions. To realize the environmental

benets o hydrogen, however, we must consider the ull uel cycle (also called

well-to-wheels)rom energy source to hydrogen production to end-use

Producing hydrogen rom renewable sources or nuclear energy yields virtuallyzero greenhouse gas emissions. Hydrogen produced rom coal, when combined

with capture and sequestration o the byproduct carbon dioxide, also results in

virtually no greenhouse gas emissions.

| Iocio u.S. depame o Ee


7/48

www.hoe.ee.ov

Hydrogen An Overview

Hydrogen can power cars, trucks, buses, and other vehicles, as

well as homes, ofces, actories, and even portable electronic

equipment, such as laptop computers.

What is Hydrogen?

Hydrogen, chemical symbol H, is the simplest element on earth. An atom o

hydrogen has only one proton and one electron. Hydrogen gas is a diatomic

moleculeeach molecule has two atoms o hydrogen (which is why pure

hydrogen is commonly expressed as H2). At standard temperature and pres

sure, hydrogen exists as a gas. It is colorless, odorless, tasteless, and lighter

than air.

Like electricity, hydrogen is an energy carrier(not an energy source), meaning

it can store and deliver energy in an easily usable orm. Although abundant

on earth as an element, hydrogen combines readily with other elements and is

almost always ound as part o some other substance, such as water (H2O), or

hydrocarbons like natural gas (which consists primarily o methane, with the

chemical ormula, CH4). Hydrogen is also ound in biomass, which includes all

plants and animals.

How is Hydrogen Currently Used?

The United States currently produces about nine million tons o hydrogen per

year.4 This hydrogen is used primarily in industrial processes including petroleum

rening, petrochemical manuacturing, glass purication, and in ertilizers. It is

also used in the semiconductor industry and or the hydrogenation o unsaturated

ats in vegetable oil.

Only a small raction o the hydrogen produced in the United States is used

as an energy carrier, most notably by the National Aeronautics and Space

Administration (NASA). This could change, however, as our nations leaders

look to increase our energy security by reducing our dependence on imported

oil and expanding our portolio o energy choices. Hydrogen is the optimum

choice or uel cells, which are extremely ecient energy conversion devices

that can be used or transportation and electricity generation.

Hydrogen molecule (H2)

How Mch is nie Millio

tos o Hoe?

Eoh o el appoximael

millio hoe cas

Soce: dOE reco 50, www.hoe.

ee.ov/poam_ecos.hml

) naioal Acaem o Scieces/naioal reseach Cocil, the

Hoe Ecoom: Oppoiies,

Coss, Baies, a r&d nees,

pae 7.

u.S. depame o Ee Hoe - A Oveview |


8/48


U.S. Department o Energy (DOE) HydrogenProgram: Implementing the Presidents

Hydrogen Fuel Initiative

Hydrogen - An Overview

Under the Presidents Hydrogen Fuel Initiative, the DOE Hydrogen Program

works in partnership with industry, academia, national laboratories, and other

ederal and international agencies to do the ollowing:

Overcome technical barriers through the research and development o

hydrogen production, delivery, and storage technologies, as well as uel cel

technologies or transportation, distributed stationary power, and portable

power applications;

Address saety concerns and acilitate the development o model codes andstandards;

Validate hydrogen and uel cell technologies in real-world conditions; and

Educate key target audiences who can acilitate the near-term use o hydrogen

as an energy carrier.

| Hoe - A Oveview u.S. depame o Ee


9/48

www.hoe.ee.ov

Hydrogen can be produced using diverse, domestic resources at

both central and distributed production acilities.

Production

Basics

Although hydrogen is the most abundant element in the universe, it does not

naturally exist in its elemental orm on Earth. Pure hydrogen must be produced

rom other hydrogen-containing compounds, such as ossil uels, biomass, or

water. Each production method requires a source o energy, i.e., thermal (heat),

electrolytic (electricity), or photolytic (light) energy. Researchers are developing a

wide range o technologies to produce hydrogen in economical, environmentally

riendly ways so that we will not need to rely on any one energy resource. The

great potential or diversity o supply is an important reason why hydrogen is

such a promising energy carrier.

The overall challenge to hydrogen production is cost reduction. For transportation,

hydrogen must be cost-competitive with conventional uels and technologies

on a per-mile basis to succeed in the commercial marketplace. This means

that the cost o hydrogen (which includes the cost o production as well as

delivery to the point o use) should be between $2.00 - $3.00 per gallon gasoline

equivalent (untaxed).

Distributed and Central ProductionHydrogen can be produced in large central plants several hundred miles rom

the point o end-use; in smaller, semi-central plants within 20-100 miles o the

point o end-use; or in small distributed generation acilities located very near

or at the point o end-use.

Distributed production may be the most viable approach or expanding the use

o hydrogen in the near term because it requires less capital investment and less

delivery inrastructure. Natural gas or renewable liquid uel reorming and small-

scale water electrolysis at the point o end-use are two distributed technologies

with potential or near-term development and commercialization.

Large central hydrogen production acilities that take advantage o economies o

scale will be needed in the long term to meet the expected hydrogen demand.

Central production can use a variety o resourcesossil, nuclear, and renewable

but an inrastructure will be required to eciently and cost-eectively deliver

the hydrogen to vehicle reueling stations and other points o end-use.

Wha is a gallon

gasoline equivalent?

taspoaio els ae oe

compae base o hei

eqivalec o asolie. the

amo o el wih he ee

coe o oe allo o

asolie is eee o

as a allo asolie

eqivale (e).

u.S. depame o Ee Pocio | 5


10/48


Hydrogen production technologies all into three general categories

Thermal Processes

Electrolytic Processes

Production

Pesse Covesio Facos

1 amosphee (am) =

14.7 pos pe sqae ich (psi)

1 am =

29.92 iches o mec (i H)

1 ba =

14.5 psi

1 mea Pascal (MPa) =

10 ba =

145 psi

Seam reomi reacios

Methane:

CH

+ HO (+heat)CO + H

Propane:

C H + H O (+heat)CO + 7H 8

Gasoline:(using iso-octane and toluene as example

compounds rom the hundred or more

compounds present in gasoline)

C H + 8H O (+heat)8CO + 7H8 8

C7H

8+ 7H

O (+heat)7CO + H

Wae-gas Shi reacio:

CO + HOCO

+ H

(+small

amount o heat)

Photolytic Processes

Thermal Processes

Thermal processes use the energy in resources including natural gas, coal, or

biomass to produce hydrogen. Some thermochemical processes use heat

combined with closed chemical cycles to produce hydrogen rom eedstocks

such as water.

Thermal processes include

Natural gas reorming

Gasication

Renewable liquid uel reorming

High temperature water splitting

Natural Gas Reorming

Natural gas contains methane (CH4) that can be used to produce hydrogen via

thermal processes including steam methane reorming and partial oxidation.

Steam Methane Reforming

Hydrogen can be produced via steam reorming o uels including gasoline

propane, and ethanol (see renewable liquid reorming on page 10). But about

95% o the hydrogen produced in the United States today is made via steam

methane reorming, in which high-temperature steam (700 1000C) is used

to produce hydrogen rom a methane source such as natural gas. The methane

reacts with steam under 3-25 bar pressure in the presence o a catalyst to

produce hydrogen, carbon monoxide, and a relatively small amount o carbon

dioxide. The carbon monoxide and steam are then reacted using a catalysto produce carbon dioxide and more hydrogen. This is called the water-gas

shit reaction. In the nal process step, called pressure-swing adsorption,

carbon dioxide and other impurities are removed rom the gas stream, leaving

essentially pure hydrogen.

| Pocio u.S. depame o Ee


11/48

www.hoe.ee.ov

Production

Well-to-WheelsGreenhouseGasEmissions(g

/mile)

Current G

V

(GasolineVehicle)Future G

V

(GasolineVehicle)

CurrentGasoline HE

V

FutureGasoline HE

V

FutureNatural Gas

DistributedHydrogenFCV

FutureCentral Win

d

ElectrolysisHydrogenFCV

FutureCentra

l

Biomass HydrogenFCV

0

100

GREENHOUSE GAS EMISSIONS

200

300

400

500

Well-to-WheelsGreenhouseGasEmissions(g

/mile)

Current G

V

(GasolineVehicle)

Future G

V

(GasolineVehicle)

CurrentGasoline HE

V

FutureGasoline HE

V

FutureNatural Gas


FutureCentral Win

d


FutureCentra

l

Biomass HydrogenFCV

0

100

GREENHOUSE GAS EMISSIONS

200

300

400

500

Fie . Well-o-Wheels Ee use Fie . Well-o-Wheels geehose gas Emissio

Well-to-WheelsEnergyUse(Btu/mile)

CurrentGV

(GasolineVehicle)FutureGV

(GasolineVehicle)

CurrentGasolineHEV

FutureGasolineHEV

FutureNaturalGas


FutureCentralWind


FutureCentral

BiomassHydrogenFCV

0

1000

2000

TOTAL ENERGY USE PETROLEUM ENERGY USE

3000

4000

5000

6000

A el cell vehicle si hoe poce om aal as wol cosme 50% O a well-o-wheels basisaccoi o eehose ases emie i exaci

less ee ha a coveioal asolie vehicle a eal 5% less ee ha ei, aspoi, a si a ela el cell vehicle si hoe om

a asolie hbi elecic vehicle o a well-o-wheels basiswhich accos o aal as wol poce 50% less eehose as emissios ha a coveio

ee cosme i exaci, ei, aspoi, a si a el. asolie vehicle a 5% less ha a asolie hbi elecic vehicle.

Soce o boh es a : Department o Energy Hydrogen Program 2006

Annual Progress Report, novembe 00.Partial Oxidation

In partial oxidation, the methane and other hydrocarbons in natural gas are

reacted with a limited amount o oxygen (typically rom air) that is not enough

to completely oxidize the hydrocarbons to carbon dioxide and water. With less

than the stoichiometric amount o oxygen available or the reaction, the reac

tion products contain primarily hydrogen and carbon monoxide (and nitrogen,

i the reaction is carried out with air rather than pure oxygen), again with a

relatively small amount o carbon dioxide and other compounds. The product

gas is oten reerred to as synthesis gas or syngas, rom which hydrogen can

be separated or use.

Unlike steam reorming, which is an endothermic process that requires heat,

partial oxidation is an exothermic process that gives o heat. Typically, it ismuch aster than steam reorming and requires a smaller reactor vessel. As

illustrated in the chemical reactions (see sidebar), partial oxidation initially

produces less hydrogen per unit o the input uel than is obtained by steam

reorming o the same uel. As in steam reorming, to maximize the amount o

hydrogen produced, partial oxidation usually includes a water-gas shit reaction

to generate additional hydrogen rom the oxidation o carbon monoxide to

carbon dioxide by reaction with water (steam).

Paial Oxiaio reacios

Methane:

CH

+ OCO + H

(+heat)

Propane:

CH

8+ O

CO + H

(+heat)

Ethanol:

CH

5OH + O

CO+H

(+heat)

Gasoline:(using iso-octane and toluene as example

compounds rom the hundred or more

compounds present in gasoline)

C H + O 8CO + 9H (+heat)8 8

C7H

8+ O

7CO + H

(+heat)



12/48


Most o the hydrogen produced today in the United States is made rom natura

gas in large, central acilities. Natural gas will continue to be an important

resource or near-term hydrogen production or many reasons. It has a high

Production

Soce: u.S. depame o Ee, Oce o

Fossil Ee, hp://www.ossil.ee.ov/

poams/powessems/asicaio/

howasicaiowoks.hml,

accesse Ma 9, 00.

Coal gasicaio reacio

Chemicall, coal is a complex

a hihl vaiable sbsace. I

bimios coal, he cabo a

hoe ma be appoximael

epesee as 0.8 aoms o

hoe pe aom o cabo.

Is asicaio eacio ca be

epesee b his (balace)

eacio eqaio:

CH + O + H O 0.8

CO + CO

+ H

+ ohe species

hydrogen-to-carbon ratio (it emits less carbon dioxide than other hydrocarbons

per unit o hydrogen production) and it has an existing pipeline-based transmis

sion, distribution, and delivery inrastructure. But because natural gas resources

in the United States are limited, producing large amounts o hydrogen rom

natural gas is unsustainable or the long term, as it would essentially trade U.S

dependence on imported oil or U.S. dependence on imported natural gas.

Although natural gas reorming is relatively mature compared to other hydrogen

production technologies, the capital equipment and operation and maintenance

costs associated with distributed natural gas reorming must be reduced to make

hydrogen cost-competitive with the conventional uels we use today.

Gasifcation

Gasication is a thermal process that converts coal or biomass into a gaseous

mixture o hydrogen, carbon monoxide, carbon dioxide, and other compoundsby applying heat under pressure and in the presence o steam. Adsorbers

or special membranes can separate the hydrogen rom this gas stream, and

additional hydrogen can be generated by reacting the carbon monoxide in a

separate unit with water (orming carbon dioxide and producing hydrogen)

To be commercially viable, the capital costs o the gasier and the equipmen

to separate and puriy hydrogen must be reduced.

8 | Pocio u.S. depame o Ee


13/48

www.hoe.ee.ov

Production

Coal

Coal is an abundant and relatively inexpensive domestic resource. The United

States has more proven coal reserves than any other country in the worldabouthal o the electricity produced in the United States today is generated rom

coal. It is important to note that hydrogen can be produced directly rom coal

via gasication, rather than by using coal-generated electricity to produce

hydrogen. The carbon dioxide created as a byproduct o coal gasication can

be captured and sequestered so that the process results in near-zero greenhouse

gas emissions. Coal gasication research, development, and demonstration

activities seek to ensure that coal can produce clean, aordable, reliable and

ecient electricity and hydrogen in the uture (see below).

Wha is Cabo Cape

a Seqesaio?

I hoe is o be poce om

coal, he cabo ioxie ha is also

poce i he pocess ms be

hale i a eviomeall espo

sible mae. Cabo cape a

seqesaio echoloies ae bei

evelope o sepaae cabo ioxi

a he poi o pocio a soe

(i eep eo eoloic om

ios, o example, as aal as is

soe oa) whee i ca be moi

oe a pevee om escapi.

Fege

Aoce i Feba 00, Fege is a $ billio, 0-ea

iiiaive o emosae he wols s coal-base, ea-zeo

amospheic emissios powe pla o poce elecici a

hoe. this dOE eo, alhoh o pa o he Hoe

Fel Iiiaive, sppos poam oals hoh is objecive o

esablish he echical a ecoomic easibili o co-poci

elecici a hoe om coal while capi a

seqesei he cabo ioxie. Fege will se asicaio

echolo o poce hoe iecl, which is a moe

ecie pocess o he cealize pocio o hoe ha

coal-o-elecici-o-hoe eeaio.

www.ossil.ee.ov/ee

Biomass

Biomass includes crop or orest residues; special crops grown specically or

energy use like switchgrass or willow trees; and organic municipal solid waste.

Because biomass resources oten consume carbon dioxide in the atmosphereas part o their natural growth processes, producing hydrogen through biomass

gasication may release near-zero net greenhouse gases. Improved agricultural

handling practices and breeding eorts, as well as advancements in biotechnol

ogy, can reduce the cost o biomass eedstocksand thereore reduce the cost

o hydrogenin the uture.

Biomass gasicaio reacio

Biomass, like coal, is a sbsace

o hihl vaiable chemis a

complexi. Celllose is a majo

compoe i mos biomass, alo

wih liis a ohe compos.

Celllose is a polsacchaie

ha ma be epesee o he

asicaio pocess b lcose as

a soae:

C H O + O + H O

CO + CO

+ H

+ ohe species



14/48


Renewable Liquid Fuel Reorming

Renewable liquid uels, such as ethanol or bio-oils made rom biomass resources

can be reormed to produce hydrogen in a distributed systemat reueling

Maki Liqi Fels

om Biomass

Production

Ethanol is mae b covei

he sach i co io sas a

emei he sas o poce

ehaol. Sas ca be exace

om ohe biomass esoces like

cop o oes esies hoh

a pocess ivolvi mil aci o

seam a ezme iesio.

these sas ae he emee,

poci ehaol.

Bio-oil is a oil-like liqi simila oiesel el. Whe eae wih hea,

biomass beaks ow o poce

a bio-oil.

reewable Liqi

Fel (e.., Ehaol)

reomi reacio

CH

5OH + H

O (+heat) CO + H

Hih tempeae Wae

Splii reacio Zic/

Zic Oxie Ccle Example

ZO + hea Z + O

Z + HO ZO + H

stations or stationary power sites. Biomass resources, when converted to ethanol

bio-oils, or other liquid uels, can be transported at relatively low cost to the

point o use and reormed onsite to produce hydrogen.

Reorming renewable liquids is similar to reorming natural gas. The liquid

uel is reacted with steam at high temperatures in the presence o a catalyst to

produce a reormate gas composed o mostly hydrogen and carbon monoxide

Reacting the carbon monoxide with steam in a water-gas shit reaction produces

additional hydrogen and carbon dioxide (see p.6).

Since renewable liquids consist o larger molecules with more carbon atomsthey can be somewhat more dicult to reorm than the methane in natural gas

Better catalysts will improve hydrogen yields and selectivity. And like natura

gas reorming, operation, maintenance and capital equipment costs must be

reduced and the energy eciency must be improved or the hydrogen produced

to be cost-competitive with conventional uels.

High Temperature Water Splitting

High-temperature water splitting, a longer-term technology in the early stages

o development, uses high temperatures to drive a series o chemical reactions

that produce hydrogen rom water. The chemicals are reused within each cycle

creating a closed loop that consumes only water and produces hydrogen and

oxygen. For both o the thermochemical processes described below, scientists

have identied cycles appropriate to specic temperature ranges at which hea

is available and are researching these systems in the laboratory.

High-Temperature Water Splitting Using Solar Concentrators

A solar concentrator uses mirrors and a refective or reractive lens to capture

and ocus sunlight to produce temperatures up to 2,000C. Researchers have

identied more than 150 chemical cycles that, in principle, could be used withheat rom a solar concentrator to produce hydrogen; more than a dozen o

these cycles are under active development.

One such pathway is the zinc/zinc oxide cycle, in which zinc oxide powder passes

through a reactor that is heated by a solar concentrator operating at about 1,900C

At this temperature, the zinc oxide dissociates to zinc and oxygen gas. The zinc

is cooled, separated, and reacted with water to orm hydrogen gas and solid zinc

oxide. The zinc oxide can be recycled and reused to create more hydrogen.

0 | Pocio u.S. depame o Ee


15/48

-

www.hoe.ee.ov

High-Temperature Water Splitting Using Nuclear Energy

Similarly, a nuclear reactor produces heat that can drive a series o chemical

reactions to create hydrogen by splitting water and recycling the chemical

Hih tempeae Wae

Splii reacio

Sl-Ioie Ccle Example

Production

constituents. The next-generation nuclear reactors under development could

generate heat at temperatures o 800C to 1,000C. These temperatures are much

lower than those produced by a solar concentrator, and as such, a dierent set

o chemical reactions would be used to produce hydrogen.

The sulur-iodine cycle is among the thermochemical cycles being investigated

or this purpose. Suluric acid, when heated to about 850C, decomposes to

water, oxygen, and sulur dioxide. The oxygen is removed, the sulur dioxide

and water are cooled, and the sulur dioxide reacts with water and iodine to

orm suluric acid and hydrogen iodide. The suluric acid is separated and

removed; the remaining hydrogen iodide is heated to 300C, where it breaksdown into hydrogen and iodine. The net result is hydrogen and oxygen,

produced rom waterthe suluric acid and iodine are recycled and used to

repeat the process.

Electrolytic Processes

Electrolytic processes use electricity to split water into hydrogen and oxygen in

a unit called an electrolyzer. Like uel cells (see page 25), electrolyzers consist o

an anode and a cathode separated by an electrolyte. The electrolyte determines

the type o electrolyzer and its operating conditions.

In a polymer electrolyte membrane (PEM) electrolyzer

Water at the anodereacts to orm oxygen and positively charged hydrogen

ions (protons) and electrons that fow through the external circuit;

The hydrogen ions move across the PEM to the cathode;

At the cathode, hydrogen ions combine with electrons rom the external

circuit to orm hydrogen gas.

Alkaline electrolyzers are similar to PEM electrolyzers, but instead use an alkaline

solution (o sodium or potassium hydroxide) as the electrolyte. Both PEM and

alkaline electrolyzers operate at relatively low temperatures 80-100C and

100-250C, respectively.

A solid oxide electrolyzer, which has a solid ceramic electrolyte, generates

hydrogen in a slightly dierent way and must operate at higher temperatures

HSO

+ hea a 850C

HO + SO

+ O

H O + SO + I H SO + HI

HI + heat at 300CI

+ H

Elecolsis reacios

Anode Reaction:

HOO

+ H+ + e

Cathode Reaction:

H+ + eH

CATHODE ANODE

PEM

+

Elecici i he

uie Saes

the aveae mix o ee

esoces se oa o eeae

elecici i he uie Saes is:

50% coal

20% nuclear

18% natural gas

9% renewable

3% petroleum

Soce: Ee Iomaio Amiisaio,

e eeaio, 005 aa

u.S. depame o Ee Pocio |


16/48

Other Variable Costs (including utilities) ($/kg of H )

Fixed O&M ($/kg of H )

2

2

Capital Costs ($/kg of H2) 0.33

0.04

Electricity Costs ($/kg) 0.330.04

0.58

0.33

0.040.57

0.33

0.040.55

0.33

0.040.54

0.33

0.040.53 2.81

3.28

0.52 1.88

2.35

0.94

1.41


(500-800C) or the membranes to unction properly. Solid oxide electrolyzers

can eectively use heat available at these elevated temperatures (rom various

sources, including nuclear energy) to decrease the amount o electrical energy

Production

needed to produce hydrogen rom water. In a solid oxide electrolyzer

Water at the cathodecombines with electrons rom the external circuit to

orm hydrogen gas and negatively charged oxygen ions;

The oxygen ions pass through the membrane and react at the anodeto orm

oxygen gas and give up the electrons to the external circuit.

PEM and alkaline electrolyzers can be smaller, appliance-sized equipment, and

well suited or distributed hydrogen production. The source o the required

electricityincluding its cost and eciency, as well as emissions resulting rom

electricity generationmust be considered when evaluating the benets o

hydrogen production via electrolysis.

Fie . Eec o Elecici Pice o disibe HoePocio Cos (assumes 1,500 GGE/day, electrolyzer systemat 76% efciency, capital cost o $250/kW)

0.04

0.33

0.59

3.75

Two electrolysis pathways with near zero greenhouse gas emissions are o

particular interest or wide-scale hydrogen production

Electrolysis using renewable sources o electricity

Nuclear high-temperature electrolysis

DistributedHydrogenCost$(Year2005/GGE)

$5.00

$4.50

$4.00

$3.50

$3.00

$2.50Soces: Solar and Wind Technologies or Hydrogen Production, Report to Congress

(ESECS EE-00), decembe 005.

Hydrogen, Fuel Cells & Inrastructure Technologies

Program, Multi-Year Research, Development and

Demonstration Plan, Planned program activities

or 2003-2010, techical Pla - Hoe

Pocio, upae novembe 00.

$2.00

$1.50

$1.00

$0.50

$0.00$0.02 $0.03 $0.04 $0.05 $0.06 $0.07 $0.08

Electricity Price ($/kWh)



17/48

www.hoe.ee.ov

Production

Among the challenges or cost-eective electrolytic production o hydrogen are

reducing the capital cost o the electrolyzerespecially lower cost anodes and

cathodesand improving the energy eciency.

Renewable Electrolysis

Electricity can be generated using renewable resources such as wind, solar,

geothermal, or hydro-electric power. Hydrogen production via renewable

electrolysis oers opportunities or synergy with variable power generation. For

example, though the cost o wind power has continued to drop, the inherent

variability o wind impedes its widespread use. Co-production o hydrogen

and electric power could be integrated at a wind arm, allowing fexibility and

the ability to shit production to match the availability o resources with the

systems operational needs and market actors.

nclea Hoe Aciviies

Haessi Hea o Poce Hoe Fom Wae

the u.S. depame o Ee is woki wih paes o emosae he

commecial-scale pocio o hoe om wae si hea om a clea

ee ssem. I aiio o he emissio-ee elecici poce b clea

eacos, some avace clea eaco esis opeae a ve hih empeaes,

maki hem well-sie o ive hihl ecie hemochemical a elecolic

hoe pocio pocesses. Majo poam elemes icle he caiae

pocio pocesses a hih empeae ieace echoloies ivolve i

copli a hemochemical o hih empeae elecolsis pla o a

avace hih-empeae eaco. Fo moe iomaio, please visi

www.e.oe.ov/hoe/hoe.hml.

Nuclear High-Temperature Electrolysis

In high-temperature electrolysis, heat rom a nuclear reactor generates high-

temperature steam that is electrolyzed to produce hydrogen and oxygen. The

higher temperature reduces the amount o electricity required to split the watermolecules. Because heat is a byproduct o nuclear electricity generation and

no greenhouse gases are emitted in the process, nuclear high-temperature

electrolysis can be an ecient method or producing hydrogen rom water.

u.S. depame o Ee Pocio |


18/48


Photolytic Processes

Photolytic processes use light energy to split water into hydrogen and oxygen

These processes are in the very early stages o research but oer long-term

Production

Scientists are researching ways in

which green algae can produce

hydrogen via photobiological

processes.

potential or sustainable hydrogen production with low environmental impact

Photolytic processes include:

Photobiological Water Splitting

Photoelectrochemical Water Splitting

Photobiological Water Splitting

In this process, hydrogen is produced rom water using sunlight and specialized

microorganisms including green algae and cyanobacteria. Just as plants produceoxygen during photosynthesis, these microbes consume water and produce

hydrogen as a byproduct o their natural metabolic processes. Photobiologica

water splitting is a long-term technology. Currently, the microbes split water at

rates too low to be used or ecient commercial hydrogen production. Scientists

are researching ways to modiy the microorganisms as well as to identiy other

naturally occurring microbes that can produce hydrogen at higher rates.

Photoelectrochemical Water Splitting

In this process, hydrogen is produced rom water using sunlight and photo-

electrochemical materialsspecialized semiconductors that absorb sunlight and

use the light energy to dissociate water molecules into hydrogen and oxygen

Currently, there are materials that can split water eciently and others tha

are durable, but to produce hydrogen or widespread use, a material must be

developed that is both ecient and durable.



19/48

www.hoe.ee.ov

The widespread use o hydrogen will require a national

inrastructure or transportation, distribution, and delivery.

Delivery

Basics

Inrastructure is required to move hydrogen rom the point o production to the

dispenser at a reueling station or stationary power site. Options and trade-os or

hydrogen delivery rom central, semi-central, and distributed production acilities

to the point o use are complexthe choice o a hydrogen production strategy

greatly aects the cost and method o delivery. For example, larger, centralized

acilities can produce hydrogen at relatively low costs due to economies o

scale, but the delivery costs are high because the point o use is arther away.

In comparison, distributed production acilities have relatively low delivery

costs, but the hydrogen production costs are likely to be higherlower volume

production means higher equipment costs on a per-unit-o-hydrogen basis.

Hydrogen has been used in industrial applications or decades, but todays

delivery inrastructure and technology are not sucient to support widespread

consumer use o hydrogen. Because hydrogen has a relatively low volumetric

energy density, its transportation, storage, and nal delivery to the point o

use comprise a signicant cost and results in some o the energy inecien

cies associated with using it as an energy carrier. Key challenges to hydrogen

delivery include reducing delivery cost, increasing energy eciency, maintaining

hydrogen purity, and minimizing hydrogen leakage. Further research is needed toanalyze the trade-os between hydrogen production and delivery options taken

together as a system. Building a national hydrogen delivery inrastructure is a

big challenge. It will take time to develop and will likely include combinations

o various technologies. Delivery inrastructure needs and resources will vary

by region and type o market (e.g., urban, interstate, or rural). Inrastructure

options will also evolve as the demand or hydrogen grows and as delivery

technologies develop and improve.

PipelinesThere are approximately 700 miles o hydrogen pipelines operating in the United

States (compared to more than one million miles o natural gas pipelines).

Owned by merchant hydrogen producers, these pipelines are located where

large hydrogen reneries and chemical plants are concentrated (or example,

in the Gul Coast region).

Inrastructure is he em se

o escibe he pipelies, cks,

ailcas, ships, a baes ha

elive el, as well as he aciliies

a eqipme eee o loa

a loa hem.

Liquid hydrogen is delivered to the

Caliornia Fuel Cell Partnership hydrog

ueling station in Sacramento.

Photo courtesy o CaFCP

u.S. depame o Ee delive | 5


20/48

hydrogen pipeline delivery inrastructure. Research is ocused on overcoming

technical concerns related to pipeline transmission, including the potential or

hydrogen to embrittle the pipeline steel and welds; the need to control hydrogen

permeation and leaks; and the need or lower cost, more reliable, and more

durable hydrogen compression technology.

One possibility or rapidly expanding the hydrogen delivery inrastructure

is to adapt part o the natural gas delivery inrastructure. Converting natura

gas pipelines to carry a blend o natural gas and hydrogen (up to about 20%

hydrogen) may require only modest modications to the pipeline; converting

existing natural gas pipelines to deliver pure hydrogen may require moresubstantial modications.

Another possible delivery process involves producing a liquid hydrogen carrier,

such as ethanol, at a central location, pumping it through pipelines to distributed

reueling stations, and processing it at the station to produce hydrogen or

dispensing. Liquid hydrogen carriers oer the potential o using existing pipeline

and truck inrastructure technology or hydrogen transport.

Trucks, Railcars, Ships, and Barges

Trucks, railcars, ships, and barges can be used to deliver compressed hydrogen

gas, cryogenic liquid hydrogen, or novel hydrogen liquid or solid carriers.

Today, compressed hydrogen can be shipped in tube trailers at pressures up

to 3,000 psi (about 200 bar). This method is expensive, however, and it is

cost-prohibitive or distances greater than about 100 miles. Researchers are

investigating technology that might permit tube trailers to operate at higher

pressures (up to 10,000 psi), which would reduce costs and extend the utility

o this delivery option.

Currently, or longer distances, hydrogen is transported as a liquid in super-insulated, cryogenic tank trucks. Gaseous hydrogen is liqueed (cooled to below

-253C/-423F) and stored at the liqueaction plant in large, insulated tanks. The

liquid hydrogen is then dispensed to delivery trucks and transported to distribu

tion sites, where it is vaporized and compressed to a high-pressure gaseous

product or dispensing. Over long distances, trucking liquid hydrogen is more

economical than trucking gaseous hydrogen because a liquid tanker truck can


Transporting gaseous hydrogen via existing pipelines is currently the lowest-cos

option or delivering large volumes o hydrogen, but the high initial capital

cost o new pipeline construction constitutes a major barrier to expanding

Delivery

Hydrogen is delivered by barge,

rail, and truck.

| delive u.S. depame o Ee


21/48

www.hoe.ee.ov

Delivery

hold a much larger mass o hydrogen than a gaseous tube trailer. But it takes

energy to liquey hydrogenusing todays technology, liqueaction consumes

more than 30% o the energy content o the hydrogen and is costly. In addition,

some amount o stored liquid hydrogen will be lost through evaporation, or

boil-o, especially when using small tanks with large surace-to-volume ratios.

Research to improve liqueaction technology, as well as improved economies

o scale, could help lower costs (todays liqueaction units are small to meet

minimal demand). Larger liqueaction plants located near hydrogen production

acilities would also help reduce the cost o the process.

In the uture, hydrogen could be transported as a cryogenic liquid in rail cars,

barges, or ships that can carry large tanksand the larger the tank, the less

hydrogen lost to evaporation. Marine vessels carrying hydrogen would be similar

to tankers that currently carry liqueed natural gas, although better insulationwould be required to keep the hydrogen liqueed (and to minimize evaporation

losses) over long transport distances.

Additional research and analysis are needed to investigate novel liquid or solid

hydrogen carriers that can store hydrogen in some other chemical state, rather

than as ree molecules. Potential carriers include ammonia, metal hydrides (see

p.23), and carbon or other nanostructures.

Bulk Storage

A national hydrogen inrastructure may require geologic (underground) bulk

storage to handle variations in demand throughout the year. In some regions,

naturally occurring geologic ormations like salt caverns and aquier structures

might be used. In other regions, specially engineered rock caverns are a possi

bility. Geologic bulk storage is common practice in the natural gas industry.

The properties o hydrogen are dierent rom natural gas, however (hydrogen

molecules are much smaller than natural gas, or example). Further research

is needed to evaluate the suitability o geologic storage or hydrogen and to

ensure proper engineering o the storage site and hydrogen containment.

Interace with Vehicles

Technologies or storing hydrogen on-board vehicles aect the design and

selection o a hydrogen delivery system and inrastructure. To maximize overall

energy eciency, designs must avoid unnecessary energy-intensive steps, such

as liqueaction and compression, and deliver pressurized hydrogen gas directly

rom a dispenser at a reueling station.

u.S. depame o Ee delive | 7


22/48

vehicle receptacle beore any hydrogen can fow. Hydrogen dispensers are

also equipped with saety devices including breakaway hoses, leak detection

sensors, and grounding mechanisms. These controls provide additional saety

measures in the case o human error, such as a driver trying to drive away

while the dispenser is still connected to the vehicle. In todays demonstration


Reueling a vehicle with hydrogen is very similar to reueling a vehicle with

compressed natural gas (CNG). Like CNG reueling systems, hydrogen vehicle

reueling is a closed-loop system. The dispensing nozzle must lock on to the

Delivery

Reueling a hydrogen vehicle is similar programs, most hydrogen vehicles are reueled by trained personnel. This wilto reueling a natural gas vehicle. become less common as the number o demonstrations increases and hydrogen

Photo courtesy o Daimler Chrysler vehicles become available to consumers.

8 | delive u.S. depame o Ee


23/48

www.hoe.ee.ov

Storage

Compact on-board hydrogen storage systems or light-duty

vehicles are critical to the widespread use o hydrogen as an

energy carrier. Vehicles must carry enough hydrogen to travelmore than 300 miles between reuelings, without compromising

vehicle cargo capacity or passenger space.

Basics

Hydrogen has the highest energy content per unit weightbut not per unit

volumeo any uel. Its relatively low volumetric energy content poses a

signicant challenge or storage.

Under most scenarios, stationary hydrogen storage systems have less stringentrequirements than vehicular storage. Stationary systems can occupy a relatively

large area, operate at higher temperatures, and compensate or slower reuel

ing times with larger storage systems. Storage systems or vehicles, however,

ace much tougher challenges. They must operate within the size and weight

constraints o the vehicle, enable a driving range o more than 300 miles (gener

ally regarded as the minimum or widespread driver acceptance based on the

perormance o todays gasoline vehicles), and reuel at near room temperature

and at a rate ast enough to meet drivers requirements (generally only a ew

minutes). Because o these challenges, hydrogen storage research is ocused

primarily on vehicular applications.

Many consider on-board hydrogen storage to be the greatest technical chal

lenge to widespread commercialization o hydrogen uel cell vehicles. Current

approaches (see below) include compressed hydrogen gas tanks, liquid hydrogen

tanks, and hydrogen storage in materials. Researchers in government, industry,

and academia are working toward technical targets specic to the entire storage

systemwhich includes the tank, storage media, valves, regulators, piping, added

cooling capacity, and other balance-o-plant components. Research is ocused

on improving the weight, volume (gravimetric and volumetric capacity), and

cost o current hydrogen storage systems, as well as identiying and developing

new technologies that can achieve similar perormance, and at a similar cost,

as gasoline uel storage systems.

Compressed Gas

Compressing any gas allows more compact storage. Hydrogen used by industry

today is usually stored at pressures up to about 2,000 pounds per square inch

How Much is a Kilogram

o Hydrogen?

Oe kiloam o hoe coais

appoximael he same ee

as oe allo o asolie. to

achieve a 00-mile ae i he

ll specm o lih- vehicles,

appoximael 5- kiloams

(k) o hoe ms be soe

o-boa. (this ae epes

pimail o vehicle weih a

el ecoom).

u.S. depame o Ee Soae | 9


24/48


(psi) in steel cylinders or tubes on trailers. The tanks used on demonstration

hydrogen vehicles, however, must carry more hydrogen in less space and require

compressed gas storage at higher pressures.

Storage

Hoe ca be soe

as a as o liqi

Hoe molecle (H) =

Hoe aom (H) =

Compesse gas

Coeic Liqi

Lighter weight composite materials that hold hydrogen at pressures higher than

2,000 psi are being developed to reduce the weight o storage systems. These

composite tanks have an inner liner, such as a polymer, that is impermeable

to hydrogen. The liner is surrounded by a ber shell that provides strength or

high-pressure load-bearing capacity and an outer shell that provides more impact

resistance. Composite tanks or hydrogen gas at pressures o 5,000 psi (~350 bar)

and even 10,000 psi (~700 bar) are used in prototype vehicles, but they are still

much larger and heavier than what is ultimately desired or light-duty vehicles.

Two approaches are being pursued to increase the gravimetric and volumetric

storage capacities o compressed hydrogen gas tanks. The rst approach

involves cryo-compressed tanks and is based on the principle that gases, such

as hydrogen, become denser as temperature decreases. By cooling gaseous

hydrogen (or example, at 5,000 psi) rom room temperature to -196C (or

-321F, the temperature o liquid nitrogen), its volume will decrease by a actor

o about three. This reduction is somewhat oset by the increased volume o

insulation and other system components.

The term cryo-compressed also reers to a hybrid tank concept combining high-

pressure gaseous and cryogenic storage. Insulated hybrid pressure vessels are

relatively lightweight and can be reueled with either liquid hydrogen or highpressure hydrogen gas. High pressure cryogenic tanks have lower evaporative

hydrogen losses than conventional cryogenic hydrogen tanks.

A second approach involves developing conormable tanks as an alternative

to cylindrical tanks, which do not package well in light-duty vehicles. The

gasoline tanks in todays vehicles are highly conormable and take advantage

o available space. The walls o non-cylindrical high-pressure tanks, however

typically have to be thicker and heavier to contain pressure. New concepts and

geometries are being evaluated to develop structures that are capable o saely

containing the high pressures while more eciently tting into an automotivespace. In general, a key area o research required or high pressure hydrogen

tanks, including conormable tanks, is cost reduction.

Cryogenic Liquid

Liqueed hydrogen is denser than gaseous hydrogen and thereore has a higher

energy content on a per-unit-volume basis. To convert gaseous hydrogen to

0 | Soae u.S. depame o Ee


25/48

www.hyrogen.energy.gov

Storage

a liquid, it must be cooled to -253C (-423F) and must be stored in insulated

pressure vessels to minimize hydrogen loss through evaporation, or boil-o.

Hydrogen vapor that results rom boil-o is released rom the tank through

saety valves and vented into the atmosphere. Liquid hydrogen tanks can

store more hydrogen in a given volume than compressed gas tanks, but there

are trade-os. The energy requirement or hydrogen liqueaction is high, and

boil-o must be minimized (or eliminated) or the system to be cost-eective

and energy efcient.

Storage in Materials

Hydrogen also can be stored within the structure or on the surace o certain

materials, as well as in the orm o chemical compounds that undergo a reactionto release hydrogen.

Hydrogen atoms or molecules are tightly bound with other elements in a

compound (or storage material), which may make it possible to store larger

quantities in smaller volumes at low pressure and near room temperature.

Storing hydrogen in materials can occur via absorption, in which hydrogen

is absorbed directly into the storage media; adsorption, in which hydrogen is

stored on the surace o storage media; or chemical reaction. Materials used

or hydrogen storage can employ one or more o these mechanisms and may

be grouped into our general categories:

Metal HydridesCarbon-based Materials or High Surace Area SorbentsChemical Hydrogen StorageNew Materials and ProcessesMetal Hydrides

Very broadly, a hydride is a chemical compound containing hydrogen and

at least one other element (e.g., nickel). Metal hydrides can store hydrogen

via absorption.

Metal compounds with simple crystal structures orm simple metal hydrides

through absorption. Hydrogen, dissociated into hydrogen atoms, can be incor

porated into the crystal lattice ramework o atoms in the metal compound. For

example, hydrogen atoms ft in the gaps between the lanthanum and nickel

atoms in lanthanum nickel (LaNi5) to make lanthanum nickel hydride (a metal

hydride, LaNi5H

6). By adding heat, the hydrogen atoms will break loose rom

the crystal lattice and be releaseda process called desorption.

Hyrogen in tanks on

the srface of solis

(by adsorption) or withinsolis (by absorption)

In adsorption (A), hyrogen can be

store on the srface of a material

either as hyrogen molecles (H2) or

hyrogen atoms (H). In absorption

(B/C), hyrogen molecles issoci

ate into hyrogen atoms that are

incorporate into the soli lattice

framework this metho may make

it possible to store larger qantities

of hyrogen in smaller volmes atlow pressre an at temperatres

close to room temperatre. Finally,

hyrogen can be strongly bon

within moleclar strctres, as

chemical compons containing

hyrogen atoms (D).

A) Srface Asorption

B) Intermetallic Hyrie

C) Complex Hyrie

d) Chemical Hyrie

u.S. department of Energy Storage | 21


26/48


Advanced metal hydrides are under development with potential to store more

hydrogen than conventional or simple metal hydrides. The reactions are revers

ible, and heat or energy is released when hydrogen reacts to orm the meta

hydride. Adding heat to the hydride reverses the reaction and releases hydrogen

Sodium alanate (NaAlH4), which can store and release hydrogen, is an example

o a complex metal hydride.

Metal hydride storage materials are primarily in powder orm to increase the

surace area available or absorption. They oer great promise, but additiona

Storage

Solid Metal Hydride with

Carbon Fiber Storage Vessel.

Photo courtesy o ECD Ovonics

Ke reqiemes

o Hoe Soae

O-Boa a Vehicle

High gravimetric

and volumetric densities

(lih i weih a cosevaive i space)

Fast kinetics

(qick pake a elease)

Appropriate thermodynamics

(e.., avoable heas o hoe

absopio a esopio)

Long cycle lie or hydrogen

charging and release, durability,

and tolerance to contaminants

Low system cost, as well

as total lie-cycle cost

Minimal energy requirementsand environmental impact

Saety is a ihee

assmpio a eqieme

research is required to overcome several critical challenges including low

hydrogen capacity, slow uptake and release kinetics, and high cost. Therma

management during reueling is also a challenge, as the signicant amount o

heat released must be saely rejected or captured or use.

Carbon-Based Materials or High Surace Area Sorbents

Carbon-based materials store hydrogen via adsorption, in which hydrogen

molecules or atoms attach to the surace o the carbon nanostructure. This

category o materials, which can exist as solids and potentially as powders or

pellets, includes a range o carbon-based materials including nanotubes and

nanobers, aerogels, and ullerenes (cage-like spheres).

Carbon-based materials are still in the early stages o investigation. The ocus

o research is metal-carbon hybrid systems. Scientists are working to better

understand the mechanisms and storage capabilities o these materials andimprove the reproducibility o their measured perormance, in order to estimate

the potential to store and release adequate amounts o hydrogen under practica

operating conditions.

Metal organic rameworks (MOFs) are new, cage-like, highly porous materials

composed o metal atoms as well as organic linkers. Recent studies have shown

that certain MOFs can store hydrogen by adsorption at low temperatures. A key

ocus area or uture research is to tailor materials so hydrogen can be stored

within them at room temperature.

Chemical Hydrogen Storage

Chemical hydrogen storage describes technologies in which hydrogen is stored

and released through chemical reactions. Common reactions involve reacting

chemical hydrides with water or alcohols. Chemical hydrides can exist as liquids

or solids, and the hydrogen atoms can be bonded to metal or non-metal species

The chemical reactions needed to release the hydrogen produce a byproduct

that can be regenerated or recharged o-board the vehicle, usually by adding

| Soae u.S. depame o Ee


27/48

www.hoe.ee.ov

Storage

heat, hydrogen, and perhaps other reactants. Chemical hydride storage systems

require management o the heat produced in the hydrogen-releasing reaction, as

well as removal o the byproducts, or spent uel, created when the hydrogen

is released. Hydrolysis reactions, hydrogenation/dehydrogenation reactions,

and several new chemical approaches are under investigation.

Hydrolysis Reactions

Hydrolysis reactions involve the oxidation reaction o chemical hydrides with

water to produce hydrogen. The reaction o sodium borohydride (NaBH4)

is among the most well-studied hydrolysis reactions to date. In this system,

sodium borohydride and water react in the presence o a catalyst to produce

hydrogen as needed, along with sodium borate as the byproduct. The sodium

borate can be converted back to sodium borohydride using heat, water, andhydrogen in an o-board regeneration process. Regeneration eciency and

energy requirements are issues still to be resolved.

Another process that unctions by hydrolysis is the reaction o magnesium hydride

with water to orm magnesium hydroxide and hydrogen. Similar to the sodium

borohydride approach, water must be carried on-board the vehicle in addition

to a slurry, and the magnesium hydroxide must be regenerated o-board.

Hydrogenation/Dehydrogenation Reactions

Hydrogenation describes the process o bonding or adding hydrogen to acompound; dehydrogenation describes the removal o hydrogen. Hydrogena

tion/dehydrogenation reactions do not require water as a reactant and instead

use catalysts and heat to release hydrogen. For example, when exposed to

heat in the presence o a catalyst, decalin (C10H

18) releases hydrogen and leaves

the byproduct naphthalene (C10H

8) at roughly 200C. Research is underway to

identiy chemical hydrides that dehydrogenate at lower temperatures.

New Chemical Approaches

Other new chemical approaches are being evaluated to identiy alternatives with

higher hydrogen storage capacities, such as ammonia borane (NH3BH3). Anotherexample is the concept o reacting lightweight metal hydrides, such as LiH, NaH,

and MgH2, with methanol and ethanola process called alcoholysis. Alcoholysis

reactions could provide controlled and convenient hydrogen production (and

storage) at room temperature and below. A disadvantage, however, is that the

alcohol also needs to be carried on-board.

u.S. depame o Ee Soae |


28/48


Among the challenges to chemical hydrogen storage on-board vehicles are

waste removal and reuelingbyproducts must be purged and resh chemical

hydrides and other reactants must be put back into the vehicle. Developing

Storage

chemical hydride regeneration systems at reueling stations or transporting the

byproducts to a central regeneration site will also be a challenge. Although the

materials hydrogen storage capacity can be high and reueling with a liquid is

attractive, issues related to regeneration energy requirements, cost, and lie-cycle

impacts are key technical barriers currently under research.

New Materials and Processes

Scientists are also exploring several new materials that may have potential or

reversible hydrogen storage, including conducting polymers. Initial studies

have indicated that a signicant amount o hydrogen can be incorporated intoconducting polymer structures. These and other new concepts are yet to be

explored or their viability to vehicular hydrogen storage applications.

| Soae u.S. depame o Ee


29/48

www.hoe.ee.ov

Application and Use

Hydrogen can be converted into usable energy through uel

cells or by combustion in turbines and engines. Fuel cells now in

development will not only provide a new way to produce power,but will also signifcantly improve energy conversion efciency,

especially in transportation applications.

Overview

Hydrogen is a versatile energy carrier that can be used to power nearly every

end-use energy need. The uel cellan energy conversion device that can

eciently convert and use the power o hydrogenis key to making it happen.

Stationary uel cells can be used or backup power, power or remote locations,

distributed power generation, and cogeneration (in which excess heat releasedduring electricity generation is used or other applications). Fuel cells can power

almost any portable application that uses batteries, rom hand-held devices to

portable generators. Fuel cells can also provide primary and auxiliary power or

transportation, including personal vehicles, trucks, buses, and marine vessels.

Why Fuel Cells?

Fuel cells directly convert the chemical energy in hydrogen to electricity and

heat. Inside a uel cell, hydrogen electrochemically combines with oxygen rom

the air to create electricity, with pure water and potentially useul heat as the

only byproducts.

Hydrogen-powered uel cells are not only pollution-ree, but also can have two

to three times the eciency o traditional internal combustion technologies.

A conventional combustion-based power plant typically generates electricity

at eciencies o 33 to 35%, while uel cell systems can generate electricity

at eciencies o up to 60% (and even higher with cogeneration). In normal

driving, the gasoline engine in a conventional car is less than 20% ecient in

converting the chemical energy in gasoline into power that moves the vehicle.

Hydrogen uel cell vehicles, which use electric motors, are much more energyecient and use up to 60% o the uels energy. This corresponds to more than

a 50% reduction in uel consumption, compared to a conventional vehicle with

a gasoline internal combustion engine.6 In addition, uel cells operate quietly,

have ewer moving parts, and are well suited to a variety o applications.

Photo courtesy o General Motors

) u.S. depame o Ee,

Ee Iomaio Amiisaio,

Spplemeal tables o he Aal

Ee Olook 005, taspoaio

dema Seco, table 7, (005), 5

u.S. depame o Ee Applicaio a use | 5


30/48


Fuel Cell Basics

A single uel cell consists o an electrolyte sandwiched between two electrodes

an anode and a cathode. The power produced by a uel cell depends on severaactors, including the uel cell type, size, temperature at which it operates, and

Application and Use

pressure at which gases are supplied to the cell. A single uel cell produces 1

volt o electricity or less. To generate more electricity, individual uel cells are

combined in a series to orm a stack. (The term uel cell is oten used to reer to

the entire stack, as well as to the individual cell). Depending on the application

a uel cell stack may contain hundreds o individual cells layered together. This

scalability makes uel cells ideal or a wide variety o applications, rom laptop

computers (50-100 Watts) to homes (1-5kW), vehicles (50-125 kW), and central

power generation (1-200 MW or more).

Types o Fuel Cells

In general, all uel cells have the same basic congurationan electrolyte

sandwiched between two electrodesbut there are dierent types o uel cells

classied primarily by the kind o electrolyte used. The electrolyte determines

the kind o chemical reactions that take place in the uel cell, the operating

temperature range, and other actors that aect the applications or which the

uel cell is most suitable, as well as its advantages and limitations.

Fie . Fel Cell Compaiso Cha

Fuel Cell Common Operating System ElectricalType Electrolyte Temp. Output Efciency Applications Advantages Disadvantages

PolmeElecoleMembae(PEM)*

Soli oaic polmepol-pefoosloicaci

50 00C F


31/48

www.hoe.ee.ov

Application and Use

PEM Fuel Cells

Polymer electrolyte membrane uel cells (also called proton exchange membrane

or PEM uel cells) use a solid polymer as the electrolyte and porous carbonelectrodes containing a platinum catalyst. PEM uel cells require hydrogen,

oxygen, and water to operate. They are typically ueled with hydrogen supplied

rom storage tanks and oxygen drawn rom the air.

Compared to other kinds o uel cells, PEM uel cells operate at relatively low

temperatures, around 80C, which allows them to start quickly (less warm-up

time is needed) and results in less wear on system components. For these and

other reasons, including the ability to produce sucient power within the size

and weight constraints o a vehicle, PEM uel cells are widely regarded as the

most promising uel cells or light-duty transportation applications.

How Do They Work?

Like all uel cells, a single PEM uel cell consists o two electrodes separated

by a membrane. The polymer electrolyte membrane (PEM) is a solid organic

compound, typically the consistency o plastic wrap and thinner than a single

sheet o paper.

On one side o the cell, hydrogen gas fows through channels to the electrically

negative electrode, or anode. The anode, which is porous so that hydrogen

can pass through it, is composed o platinum (catalyst) particles uniormlysupported on carbon particles and surrounded by a thin layer o proton-conduct

ing ionomer. Hydrogen uel on the anode side moves through the electrode

and encounters the platinum catalyst, which causes the hydrogen molecules to

separate into protons and electrons. This is an oxidation reaction (see sidebar).

The PEMthe key to this uel cell technologyallows only the protons to pass

through it. While the protons are conducted through the ionomer and PEM to

the other side o the cell, the stream o negatively-charged electrons ollows

an external circuit to the cathode. This fow o electrons through the external

circuit is electricity that can be used to do work, such as power a motor.

On the other side o the cell, oxygen gas, typically drawn rom ambient air,

fows to the electrically positive electrode, or cathode. Like the anode, the

cathode is made o platinum particles uniormly supported on carbon particles

it is porous and oxygen can move through it. A reduction reaction, involving

the gaining o electrons, takes place at the cathode (see sidebar). When the

electrons (which have traveled through the external circuit) return rom doing

work, they react with oxygen and the hydrogen protons (which have moved

Chemical reacios

All elecochemical eacios,

icli hose ha ake place i

a el cell, cosis o wo sepaae

eacios: a oxiaio hal-eacio

a he aoe, a a ecio hal-

eacio a he cahoe. Oxiaio

ivolves a loss o elecos b oe

molecle, a ecio ivolves a

ai o elecos b aohe. Boh

oxiaio a ecio occ

simlaeosl a i eqivale

amos i a eacio

ivolvi eihe pocess.

Oxidation hal reaction

HH+ + e

Reduction hal reactionO

+ H+ + eHO

Fuel cell reaction

H

+ OH

O



32/48


Fel Cells geeae

Elecici, Hea, a Wae

B How Mch Wae?Hoe el cell vehicles (FCVs)

through the PEM) at the cathode to orm water. Most o the water is collected

and reused within the system, but a small amount is released in the exhaust as

water vapor (how much water?...see sidebar). Heat is generated rom this union

Application and Use

(an exothermic reaction) and rom the rictional resistance o ion transer through

the membrane. This thermal energy can be used outside the uel cell.emi appoximael he same

amo o wae pe mile as vehicles

si asolie-powee ieal

combsio eies (ICEs).

How ar will one gallon go and

how much water will it produce?

Gasoline ICE Vehicle

5 miles pe allo (mp)

allo asolie = .7 k o el

(may be represented approximately as CH2)

CH + / O CO + H O (water)

.7 k + 9. k8.5 k + .5 k

.5 k wae/5 miles =

0. k wae/mi

Hydrogen FCV

0 miles pe allo asolie

eqivale (mpe)

allo o asolie eqivale o

hoe ve eal eqals .0 k H

H

+ / OH

O (wae)

.0 k + 8.0 k9.0 k

9.0 k wae/0 miles =

0.5 k wae/mi

noe: the calclaios above assme ha aasolie ICE vehicle aveaes 5 miles pe al

lo a a hoe FCV aveaes 0 mpe

o hoe. (Oe e o hoe has he

same ee coe as a allo o asolie

[i ems o hei lowe heai vales] a is

appoximael eqal o oe k o hoe.)

the el cell is a valable ssem becase i

is . imes as ee ecie as aiioal

combsio ssems, achievi . imes as

ma miles pe allo o asolie eqivale.

Soce: Aoe naioal Laboao

H2H2

H2

Anode

Hydro

genIN

Oxyge

nIN

Heat

OUT

Polymer Electrolyte Membrane (PEM)

O2

H2

H+

H+

e

ee

H2O

Cathode

eee-

e-

H+

Water OUT

O2

O2

O2

ee

H+

ee

H2O

H2O

e

Oxygen Molecule

Hydrogen Molecule

Hydrogen Atom

Electron

Water Molecule

A Closer Look at the Details

Catalyst

Platinum-group metals are critical to catalyzing reactions in a PEM uel cell

The uel cells typically use a catalyst made o platinum powder very thinly

coated onto carbon paper or cloth. The catalyst is rough and porous to expose

the maximum surace area o the platinum to the hydrogen or oxygen. The

use o platinum adds to the cost o the system, however. Platinum catalysts

are also sensitive to poisoning by contaminants such as carbon monoxide or

sulurmolecules that can bind to the platinum and prevent it rom reacting

with hydrogen at the anode, or example. This sensitivity requires high purity

hydrogen or additional purication steps, which can add to the cost.

Membrane Electrode Assembly and Bipolar Plates

The electrodes, catalyst, PEM, and gas diusion layers (GDLs) together orm

the membrane electrode assembly, or MEA. The GDLsone next to the anode

the other next to the cathodeare usually made o a porous carbon paper

8 | Applicaio a use u.S. depam


33/48

www.hoe.ee.ov

Application and Use

or cloth about as thick as 4-12 sheets o paper. The layers must be made o aFel Cells

material like carbon that can conduct electrons leaving the anode and enteringSpecial Applicaios

the cathode. Its porous nature helps ensure eective diusion o both hydrogen

and oxygen to the entire surace area o the catalyst layers on the MEA.

The GDLs also help manage water in the uel cell. The membrane must remain

moist to operate eectively; the diusion material allows the right amount o

water vapor to reach the MEA and keep the membrane humidied. The GDL

is oten coated with Tefon to ensure that some pores in the carbon cloth (or

carbon paper) do not clog with water.

The outer-most layer o each uel cell, pressed against the surace o each GDL,

is the bipolar plate. Channels ormed into the ace o the plate provide a fow

eld, carrying the hydrogen and oxygen gases to where they are used in the

uel cell. Bipolar plates, which can be carbon composites or metal, also act as

current collectors. Electrons produced by the oxidation o hydrogen must (1)

be conducted through the anode and GDL, along the length o the uel cell

stack, and through the plate beore they can exit the cell; (2) travel through an

external circuit; and (3) re-enter the cell at the cathode.

Challenges

Reducing cost and improving durability are the two most signicant challenges

to uel cell commercialization. Fuel cell systems must be cost-competitive with,

and perorm as well or better than, traditional power technologies over the lieo the system.

Materials and manuacturing costs are currently too high or catalysts, bipolar

plates, membranes, and gas diusion layers. Today, the costs or automotive

internal combustion engine power plants are about $25-$35/kW; or trans

portation applications, a uel cell system needs to cost approximately $30/kW

(at volumes o 500,000 units per year) or the technology to be competitive.

For stationary systems, the acceptable price point is considerably higher

$400-$750/kW is considered necessary or widespread commercialization

($1,000/kW or initial early adopter applications). (Data current as o March

2007. For the most up-to-date numbers, please reer to the Hydrogen Program

Multi-Year Research, Development, and Demonstration Planwww.eere.energy.

gov/hydrogenanduelcells/mypp/)

In addition to cost-related challenges, adequate uel cell system durability has

not been established. To be considered ready or widespread use in transporta

tion, uel cell power systems must demonstrate durability and reliability similar

Fel cells o ceai special o

iche applicaios ae commeciall

available oa. Fel cells se i

o-aspoaio applicaios

ca help evelop maaci

capabiliies a a spplie base while

aspoaio el cells ae e

evelopme. these applicaios

icle powe eeaio:

I emoe locaios whee he

elecici i is o accessible

Whee poable powe is eee

a coscio sies, isea o

eeaos, a campos,

o fexible a moveable powe

Fo ok lis isie

waehoses a ohe

ioo eviomes

Fo smalle applicaios,

sch as lapops a cellphoes, ha picall

se baeies

Fo axilia powe applicaios,

sch as powei he

cabi o a 8-wheele

while he eie is

o i

Fo isa emeec backp

powe o sppleme he i,

whee cosa powe is eqie

a places sch as baks, hospials

a elecommicaios owes



34/48


Hbi elecic a el cell

vehicles shae echoloies

to todays automotive engines. Specically, this means a 5,000-hour operating

liespan (the equivalent o 150,000 miles) and the ability to perorm over the

ull range o dynamic vehicle operating conditions, including temperatures

Application and Use

techoloies evelope o oas

asolie hbi-elecic vehicles ca

help acceleae he evelopme

o el cell vehicles. Fo example,

hbi vehicles se elecic moos

o poplsio a eqie avace

ive cool elecoics a

sowae, mch like el cell vehicles.

Fhe eseach will impove he

aoabili a peomace o

hbi echolo available o

cosmes i he ea-em aalso avace el cell echolo

evelopme o he lo-em.


and climates (various degrees o humidity and ambient temperatures o -40C

to +40C, or example). Requirements or stationary applications are slightly

dierent because the associated duty cycles are less demanding. To compete

with other distributed power generation systems, stationary uel cells mus

demonstrate more than 40,000 hours (nearly 5 years) o reliable operation

in ambient temperatures o -40C to +50C to be considered ready or the

mainstream market.

For both transportation and stationary applications, research is needed to identiy

and develop new materials to reduce the cost and extend the lie o uel cel

stack components. Low cost, high volume manuacturing processes will alsohelp to make uel cell systems competitive with traditional technologies.

the Soli Sae Ee Covesio Alliace

Focsi o Soli Oxie Fel Cell r&d

the Soli Sae Ee Covesio Alliace (SECA) is a joi oveme-is

eo le b he u.S. depame o Ee o ece cos a achieve echolo

beakhohs i soli oxie el cells (SOFCs), pimail se o elecic ili a

saioa applicaios. SECA aims o evelop -0kW SOFCs b 00 ha ca be

mass-poce i mola om (he echolo will he be scale-p o seve as

bili blocks o Fege-pe plas o moe o Fege, see pae 9).

SECA el cells will be se o a wie ae o applicaios, icli axilia

powe a combie hea a powe. Fo eaile poam oals, eqiemes,

milesoes, a aciviies, please visi www.seca.oe.ov.

0 | Applicaio a use u.S. depam


35/48

www.hoe.ee.ov

Application and Use

Frequently Asked Question: When Can I Buy One?

The answer to that question depends on what you want to buy.

The widespread use o hydrogen as an energy carrier requires a combination

o technological breakthroughs, market acceptance, and large investments in a

national hydrogen energy inrastructure. This evolutionary process will happen

over decades, wherein hydrogen will phase in as the technologies and their

markets are ready.

Fuel cells or some portable and small stationary applications are available to

commercial customers today. Fuel cell vehicles and hydrogen ueling stations

are also operating in certain parts o the country as part o demonstration

programs, although hydrogen uel cell vehicles ace greater technical challenges

that extend the timeline or their commercial market introduction.

Government, industry, and others continue to research, develop, and validate

hydrogen and uel cell technologies to meet specic technical targets based

on customer requirements or cost and perormance. As uel cells or portable

and stationary applications begin to penetrate the market, experience will be

gained in uel cell manuacturing, standards or hydrogen transport and storage

containers, and integration with the electricity grid that will support the expanded

use o hydrogen in all sectors o the economy and help integrate hydrogen into

our nations energy portolio.

u.S. depame o Ee Applicaio a use |


36/48


Application and Use

techolo Valiaio o a Lae Scale: the naioal Hoe Leai demosaio

I Mach 005, he u.S. depame o Ee (dOE) aoce he naioal Hoe Leai demosaio, a iqe

collaboaio o aomobile a ee is paes, hei spplies, a he eeal oveme o evalae hoe

el cell vehicle a iasce echoloies oehe i eal-wol coiios a assess poess owa echolo

eaiess o he commecial make. Is is povii hal he cos o he emosaio.

the leai emosaio will valiae hoe el cell echolo aais aes o el cell abili a eciec,

vehicle ae, a hoe el cos. I will also help ese seamless ieaio o vehicle a iasce ieaces.

Learning Demonstration Projects

the naioal Hoe Leai demosaio cel ivolves he wok o he ollowi o eams opeai el cell

vehicles a hoe eli saios o collec aa boh i coolle es coiios a o he ope oa i a vaie o

eoaphic aeas a climaes.

Chevo Copoaio is bili hoe eli saios i ohe a sohe Calioia a i Michia; Hai-Kia Moo

Compa is woki i paeship wih Chevo o es vehicles wih el cells maace b uie techoloies Copoaio.

daimleChsle is esi vehicles wih Balla Powe Ssems el cells; he vehicles will eel a hoe saios bil b

pojec pae BP i ohe a sohe Calioia a i Michia.

Fo Moo Compa is esi vehicles wih Balla el cells; he vehicles will eel a hoe saios bil b pojec

pae BP i ohe Calioia a Michia, as well as Floia.

geeal Moos Copoaio is esi vehicles wih is ow el cell echolo i paeship wih Shell Hoe, LLC,

which is bili hoe eli saios i seveal locaios: new yok, deoi, Calioia, a Washio, d.C.

Project Outcomes

the naioal Hoe Leai demosaio will help dOE ie is hoe a el cell compoe a maeialseseach a ma also cove ew echical challees ha have o e bee cosiee. Becase compoe aa

ahee i he emosaio will be obaie om a ieae ssem a e eal opeai coiios, sakeholes

will have he iomaio he ee o valiae dOE ecoomic, ee, a eviomeal moels/aalses, as well as

echolo sas impoa o csome eqiemes (vehicle el ecoom, el cell eciec/abili, eeze sa abili,

hoe cos, a opeai ae). B ivolvi majo sakeholes who will be esposible o bii vehicle a

ee echoloies o cosmes, he emosaio also povies a eal eviome o he shai o sae, coes, a

saas isses acoss eams, as well as a oppoi o has-o pblic ecaio ha ca ioce cosmes o hei

e ee opios.

| Applicaio a use u.S. depam


37/48

www.hoe.ee.ov

Saety, Codes and Standards

The United States saely produces and uses more than nine million

tons o hydrogen each year, primarily in controlled industrial

environments. Hydrogen can be used saely in consumer environments as well, when users understand its basic properties and

observe guidelines.

Hydrogen Saety

Like gasoline or natural gas, hydrogen is a uel that must be handled appropriately.

The characteristics o hydrogen are dierent rom those o other uels, but it

can be used as saely as other common uels when guidelines are observed.

Hydrogen has a number o properties that are advantageous with regard tosaety. It is much lighter than air and has a rapid diusivity (3.8 times aster

than natural gas), which means that when released in an open environment,

it disperses quickly into a non-fammable concentration. Hydrogen rises at a

speed o almost 20 meters per second, twice as ast as helium and six times

aster than natural gas.

With the exception o oxygen, any gas can cause asphyxiation in high enough

concentrations. But because hydrogen is buoyant and disperses rapidly, it is

less likely to be conned than other gases and thereore poses less risk as

an asphyxiant.

Hydrogen is non-toxic and non-poisonous. It will not contaminate groundwater

and is a gas under normal atmospheric conditions with a very low solubility

in water. A release o hydrogen is not known to contribute to atmospheric

pollution or water pollution.

Hydrogen is odorless, colorless, and tasteless, and thus undetectable by human

senses. By comparison, natural gas is also odorless, colorless, and tasteless,

but industry adds a sulur-containing odorant to make it readily detectable by

people. Odorants are not added to hydrogen because currently, there is no

known odorant light enough to travel with hydrogen or disperse in air atthe same rate. Odorants also contaminate uel cells. Industry considers these

properties when designing structures where hydrogen is used or stored and

includes redundant saety systems that include leak detection sensors and

ventilation systems.


u.S. depame o Ee Sae, Coes a Saas |


38/48


Hydrogen burns with a pale blue, nearly invisible, fame. Hydrogen fames also

have low radiant heat compared to hydrocarbon fames. Detection sensors buil

into hydrogen systems can quickly identiy any leak and eliminate the potential

Saety, Codes, and Standards

Wha ae Coes

a Saas?

Moel bili coes ae

ielies o he esi o he

bil eviome (bilis a

aciliies, o example). Coes

ae eeall aope b local

jisicios, heeb achievi

oce o law. Coes oe ee o

o ivoke saas o eqipme

se wihi he bil eviome.

Saas ae les, ielies,

coiios, o chaaceisics o

pocs o elae pocesses, a

eeall appl o eqipme ocompoes. Saas achieve a

elao-like sas whe he

ae eee o i coes o hoh

oveme elaios.

or undetected fames. Since hydrogen fames emit relat

Hydrogen Energy Future PDF

Documents

Transcript of Hydrogen Energy Future PDF