Fuel Cell Lecture dr. li

7/27/2019 Fuel Cell Lecture dr. li

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Fuel Cell Basic

How Fuel Cells work

Applications of Fuel Cell Experiment Setup

Fuel CellFuel Cell

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work with a PEM (proton exchange

membrane) electrolyzer and a PEM fuel cell

to study the electrochemistry of water

electrolysis

how much power it takes to generate a

meaningful quantity of hydrogen (10 cm^3)

how efficient the electrolyzer is

measure the breakdown voltage of water

Power output from the fuel cell

Laboratory Objectives


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What is a Fuel Cell

A Fuel Cell is an electrochemical device that

combines hydrogen (and oxygen) to produce

electricity, with water and heat as its by-product.

Fuel (H2) + O2 / Catalyst (H2)O + Heat

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How a Fuel Cell work

A Fuel Cell consists of two catalyst coated electrodes

surrounding an electrolyte

One electrode is an anode and the other is a cathode

The process begins when Hydrogen molecules enter the

anode


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The catalyst coating separates hydrogens negatively charged

electrons (e-) from the positively charged protons (H+)

The electrolyte allows the protons to pass through to the

cathode, but not the electrons

Instead the electrons are directed through an external circuit

which creates electrical current

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While the electrons pass through the external circuit,

oxygen molecules pass through the cathode on the

other side of the fuel cell

There the oxygen and the protons combine with the

electrons after they have passed through the external

circuit

When the oxygen and the protons combine with the

electrons it produces water and release heat


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Fuel Cells Concept

Individual fuel cells can then be placed in a series

to form a fuel cell stack

The stack can be used in a system to power a

vehicle or to provide stationary power to a

building

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Fuel Cells Concept


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Hydrogen Generation and applications

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Types of Fuel Cells

Type Efficiency(%) Operating Temp

Solid Oxide 45-65 800-1000

Molten Carbonate 50 650

Phosphoric Acid 40 200

Alkaline 50-60 80

Direct Methanol 40 80

Polymer (PEM) 40 50


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Benefits

Low / Zero Emissions

Based on measured data, a fuel cell power plant may

create less than one ounce ofpollution per1,000

kilowatt-hours of electricity (25 pounds for Conventional

systems) -- Clean Energy

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Benefits

High Efficiency (for power output) 2nd law ?

Quiet

Fuel Flexible (Next slide)

Combine with wind power and solar power

Lightweight battery alternative

Wide Range of Applications

High Quality, Reliable Power


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Applications

Transportation All major automakers are working to commercialize a fuel cell car

Automakers and experts speculate that a fuel cell vehicle will becommercialized by 2012, others later

50 fuel cell buses are currently in use in North and South America,Europe, Asia and Australia

Trains, planes, boats, scooters, forklifts and even bicycles areutilizing fuel cell technology as well

Ford Hyundai Toyota

HondaGM

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Applications Honda

TOYOTA FCHV-adv


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Hyundai's zero-emissions ix35 Fuel Cell is

similar in performance to the petrol version

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Applications

Stationary Power Stations

Over 2,500 fuel cell systems have been installedall over the world in hospitals, nursing homes,hotels, office buildings, schools and utility power

plants

Most of these systems are eitherconnected tothe electric grid to provide supplemental powerand backup assurance or as a grid-independentgenerator for locations that are inaccessible bypower lines


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Applications

Telecommunications Due to computers, the Internet and sophisticated

communication networks there is a need for an

incredibly reliable power source

Fuel Cells have been proven to be 99.999% reliable

Micro Power Consumer electronics could gain drastically longer

battery power with Fuel Cell technology Cell phones can be powered for 30 days without

recharging

Laptops can be powered for 20 hours without recharging

2020

Thermodynamics analysis

Gibbs function (g) : property defined in

terms of properties

U: internal energy

H: Enthalpy

T: Absolute temperature

S: Final entropy

P: Absolute pressure

V: Final volume

TsPVU

Tshg


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The change in Gibbs free energy, G, in a

reaction can be thought of as the maximum

amount of work obtainable from a reaction.

For example, in the oxidation of glucose, the

change in Gibbs free energy is G = 686 kcal =

2870 kJ.

(n=number of electrons released at the anode

F=Faraday constant, = electric potential) nFG

STHG

Thermodynamics

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Electrolysis of Water

The amount power must be supplied by the

battery is actually the change in the Gibbs

function G = H - TSElectrical Energy input


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Electrolysis of Water

Electrolysis of WaterH20 H2+1/2O2 (T=298K, P=1 atm)

H=285.83 kJ

TS = 48.7 kJ (S = 130.68+ 0.5 x 205.14 - 69.91, T=298 K)

G = H - TS =285.83 kJ-48.7 kJ=237.1kJ

Theoretical Electrical Energy input for Electrolysis of Water :

G =237.1kJ

H2O H2 0.5 O2 Change

Enthalpy -285.83 kJ H = 285.83 kJ

Entropy 69.91 J/K 130.68 J/K 0.5 x 205.14 J/K TS = 48.7 kJ

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Hydrogen Fuel Cell

The theoretical efficiency of a fuel cell is

The overall system efficiency

( : the reform efficiency (hydrocarbon),

: the DC/AC convert efficiency)

fcH

G

max

CRfc

R

C

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Example Hydrogen and oxygen are combined in a fuel cell to produce

electrical energy in a fuel cell. This process is presumed to be

at 298K and one atmosphere pressure. For the ideal case,

determine the efficiency of fuel energy converted to electrical

energy.

G =

H - T

S = -285.83 kJ + 48.7 kJ = -237.1 kJ H = 285.83 kJ

83%x100%8237.1/285.max

fcH

G


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work with a PEM electrolyzer and a PEM fuel

cell to study the electrochemistry of water

electrolysis how much power/time it takes to generate a

meaningful quantity of hydrogen (10 cm^3)

measure the breakdown voltage of water

Voltage and Power output from the fuel cell

Laboratory Objectives


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Fuel Cell Lecture dr. li

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