ulrich.vogt@empa.ch

W. JU, M. HEINZ, D. BURNAT, C. BATTAGLIA,

U. F. VOGT*

EMPA

MATERIALS SCIENCE AND TECHNOLOGY

MATERIALS FOR ENERGY CONVERSION

CH-8600 DÜBENDORF

SWITZERLAND

ALKALINE WATER ELECTROLYSIS: MEMBRANE DEVELOPMENT & CHARACTERIZATION

~ 1800 : Electrolytic Water splitting (Ritter, Nicholson, Carlisle)

1834 : First use of the term «electrolysis» by Faraday

1900 : Oerlikon (Zürich) introduces first bipolar electrolyzer (2.5 V)

1939 : First 10’000 Nm3/h (900kg/h) electrolyzer

1949 : Zdansky pressure electrolyzer for Lonza

1951 : First commercial 30 bar electrolyzer (Lurgi)

1967 : Zero-Gap Design

HISTORY OF WATER ELECTROLYSIS: KNOWN FOR OVER 200 YEARS

Lurgi-Zdansky prototype

alkaline electrolyser, 1949

Hydrogen Report Switzerland 2010/2011

Water electrolysis accounts for ca. 5% of hydrogen production

Most of hydrogen is used on side for the production of

Ammonia (Haber Bosch Process)

Conversion of heavy petroleum sources by hydrocracking

Cooling of generators

steel & glass manufacturing

Diaphragm to separate H2 and O2,

conduction of OH- via KOH

in open pore network

Working conditions: 32 bar, 85°C, 25wt% KOH

Production rate: 760 m³/h H2 , equ. to 3.3 MWel

Energy Consumption: 4,3 - 4,6 kWh/m³ H2

H2 purity: 99.8 - 99.9 vol%, O2 purity: 99.3 - 99.6 vol%

556 cells, cell =1.6 m, length: 12 m, weight: 90 t

100 installed units worldwide Souorce: IHT 8th International Symposium Hydrogen & Energy, 16.-21. February 2014, Zhaoquing, China

Electrolyser , Giovanola SA, Monthey, CH, Sapphire production

1) bipolar plates

2) electrode meshes

3) separator membrane

4), 5) H2 and O2 ducts

6) electrolyte ducts

Source: Svein Sunde, NTNU, Trondheim, Halder Topse Catalysis Forum, 2006

Zero-gap geometry

Alkaline Water Electrolysis:

H2O H2 + ½ O2

ALKALINE WATER ELECTROLYSIS

Materials and system development:

Developing diaphragms with high ionic conductivity

Using highly active electrocatalysts for the OER and HER

Avoiding surface blockage by generated gas bubbles

ALKALINE WATER ELECTROLYZER

𝜺𝟐𝟓°𝑪

= 𝟏.𝟐𝟑 𝑽

𝑬𝒄𝒆𝒍𝒍

Energy loss:

Ionic resistance (membrane, KOH)

Activation energy

Gas-bubble resistance

Electronic resistance

E

I

DIAPHRAGMS FOR ALKALINE

ELECTROLYSER

Alkaline Water Electrolysis

High OH- conductivity via KOH in open pore

network during gas production

Chemical and mechanical stability

separator thickness (2.5 mm)

operating temperature (max. 85)

c(KOH) (25wt% - 35wt%)

Asbestos is banned by law since 1990

REPLACEMENT OF ASBESTOS DIAPHRAGMS

diaphragm to separate H2 and O2

Conduction of OH- via KOH in open pores

Zero-gap geometry

56% porosity of Asbestos

membrane Mg3Si2O5(OH)4

Mg3Si2O5(OH)4 Chrysotile Asbestos CaSiO3 Wollastonite (Mg,Fe)2SiO4 Olivine BaSO4 barite 99% purity

www.webmineral.com

BaTiO3 98% purity, perovskite str., electroceramics ZrO2 3YSZ (TOSOH), technical ceramics, SOFC

Synthetic based fillers

Mineral base fillers

ALTERNATIVE HYDROPHILIC FILLER MATERIALS

MINERALS AS FILLER: THERMODYNAMIC MODELING (GEMS)

Low pH: congruent dissolution

High pH: (a, b, c) Si ions increases , Ca, Mg drops precipitation of portlandite & brucite

Barite shows higher stability, no secondary phases formed

Calculations of the

influence of pH on the

concentration of different

Ions for:

a) wollastonite

b) forsterite

c) Chrysotile

d) Barite

@ 85°C, pH 9.6 - 13

The equilibrium phases are

indicated by gray and orange bars

Corrosion Experiments of Mineral Fillers, 85°C, 25 wt% KOH

Concentrations of Si, Mg, Ca, and Ba leached from forsterite, wollastonite, chrysotile and barite

in 5.5 M KOH solution at 85 C as a function of time.

Dotted lines represent the logarithmic function, drawn as a guide to the eye only.

Burnat et al. Journal of Power Sources 291 (2015) 163-172

concentration of ions from leaching experiments, measured by ICP-OES

relative mass loss of leached minerals

(Mg-Olivine)

MEMBRANE PRODUCTION BY PHASE INVERSION

2. tape casting (Si-Coated PET film or weaved reinforcement)

1. polysulfone + filler particles + solvent

Polysulfone + BaSO4 (barite) + NMP

3. Phase inversion process – immersion precipitation in H2O coagulation bath

Source: Membranes for Membrane Reactors, John Wiley & Sons, Ltd, 2011.

Phase inversion – Process in which polymer solution is converted into two phases:

- Solid polymer rich phase (rigid structure) - Polymer lean phase (pores)

Membrane thickness:

0.2 – 1.5 mm

CONTINUOUS PILOT DIAPHRAGM PRODUCTION @ CILANDER

Manufacturing of 0.4 m width diaphragm

Source: Burnat et al. Composite membranes for alkaline electrolysis based on polysulfone and mineral fillers, Journal of Power Sources, (291), 2015, pp.163-172

(I) – skin layer; polymer rich,

quite dense, develops first

(gas separation properties)

(II) – bulk microstructure;

very porous, less polymer,

develops after the skin layer,

mainly mechanical properties

MICROSTRUCTURAL FEATURES OF THE MEMBRANE

CAPILLARY FLOW POROMETRY

Liquid (Porofil) membrane

P

N2

Sketch of the measuring cell for CFP (capillary flow porometry )

Defines pore size distribution of percolating pores (effective for the mass transport)

The higher the BP pressure – the better the physical gas separation

a) differential flow distribution through the percolating pore network

b) determination of the largest, medium and smallest pore sizes for various membranes located within the top layer

Source: Burnat et al. Composite membranes for alkaline electrolysis based on polysulfone and mineral fillers, Journal of Power Sources, (291), 2015, pp.163-172

𝑅𝑀 = 𝑅𝐸+𝑀 − 𝑅𝐸

𝜌𝑀 =

1

𝐾𝐸+𝑀−

1

𝐾𝐸 𝐿𝐸+𝑀

𝐿𝑀+

1

𝐾𝐸 Ω𝑐𝑚

where KE+M is the conductivity including the membrane, KE conductivity without membrane, L the distance between the electrodes, LM the thickness of the membrane

Measured as zero-bias, provides a fingerprint of electrical performance of the membrane

ZERO-BIAS RESISTIVITY MEASUREMENT

a) Schematic representation of top layer (Lt) and bulk microstructure (Lb) ratios for membranes of

various thicknesses

b) Influence of membrane thickness on total resistivity

Ratio between the skin layer and bulk microstructure changes variation in resistivity

Top skin layer has resistivity 2 orders of magnitude higher!

Source: Burnat et al. Composite membranes for alkaline electrolysis based on polysulfone and mineral fillers, Journal of Power Sources, (291), 2015, pp.163-172

𝜌𝑀 = (𝑹𝒕+𝑹𝒃)𝐴

𝐿𝑀=

𝝆𝒕𝑳𝒕 + 𝝆𝒃(𝐿𝑀 − 𝑳𝒕)

𝐿𝑀= 𝝆𝒃 + (𝝆𝒕 − 𝝆𝒃)

𝑳𝒕

𝐿𝑀

ρ = 5 Ω·cm

VARIATION OF TOTAL RESISTIVITY AS A FUNCTION OF THICKNESS

Good electrical performance and high bubble points can be achieved

MEMBRANE POROSITY VS. RESISTIVITY

Source: Burnat et al. Composite membranes for alkaline electrolysis based on polysulfone and mineral fillers, Journal of Power Sources, (291), 2015, pp.163-172

66 68 70 7252

54

56

58

60

62

64

54 56 58 60 62 644.0

4.5

5.0

5.5

6.0

To

tal p

oro

sity / %

NMP / vol%

a)

me

mb

rane

resis

tivity

cm

Porosity / %

M14

M16

M21

b)

(Zirfon)

influence of NEP content on porosity influence of porosity on resistivity

- Zirfon 500utp membrane as reference

Determined by the Zero-bias resistivity measurement method

Nitidor Pilot Electrolyser, 0.2 Nm3/h, 5 cells, 117 mm

Voltammetric results of Barite based Diaphragms

LAB-SCALE 1 CELL ELECTROLYSER

LAB-SCALE ALKALINE WATER ELECTROLYSER

• Lab-scale Electrolyser

• Specifications:

• Pressure: 30 bar

• Temperature: 80 °C

• Electrode area: 19.6 cm2

• Current density: 500 mA/cm2

• Complete in-house development

20

LAB-SCALE ALKALINE WATER ELECTROLYSER

LAB-SCALE ALKALINE WATER ELECTROLYSER

Electrolysis cell

LabVIEW interface

For electrolyser adjustment: Diaphragm: Zirfon 500utp Electrodes: Nickel plates

LAB-SCALE ALKALINE WATER ELECTROLYSER

Voltammetric curves measured with Zirfon 500utp diaphragm and Nickel plates

Pressure effect on cell voltages

30 °C increasing pressures

80 °C increasing pressures

Pressure effect on cell voltages not very pronounced

LAB-SCALE ALKALINE WATER ELECTROLYSER

Voltammetric curves measured with Zirfon 500utp diaphragm and Nickel plates

Temperature effect on cell voltages

1 bar increasing temperature

30 bar increasing temperature

Temperature effect on cell voltages very pronounced

SUMMARY & OUTLOOK

25

Chemical stable membrane based on polysulfone & BaSO4 filler

Top surface layer significantly contributes to membrane resistivity ~2 orders of magnitude higher than bulk.

Labscale electrolyser suitable for electrode & membrane characterization

Ongoing work: electrode- and catalyst development

CTI Project NMAE: New membranes for Alkaline Electrolysis

SI/50076

European Project ELYGRID, FCH-JU: High Pressure Alkaline

Electrolysis

BFE P&D Project PALE: Laboratory alkaline electrolyser test

bench for high pressure and temperature

Swiss electric project: Alkaline Electrolysis for renewable

energy generation: Membrane Development for Industrial

Electrolyser

ACKNOWLEDGEMENT

26

© Daimler

THANK YOU FOR YOUR ATTENTION!

FOR A SUSTAINABLE FUTURE