1

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Prof. Pierre Millet

University of Paris - France

In-situ electrochemical characterization

of PEM Water Electrolysis electrodes

01st International Workshop on Durability and Degradation Issues

in PEM Electrolysis Cells and its Components

Freiburg, Germany, March 11-12 2013

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Outline

I. Challenges facing PEM water electrolysis

II. Catalysts, SPEs, MEAs, cells, stacks, systems

III. Main Electrochemical Tools & Techniques

IX. Conclusions

IV. Polarization curves

V. Cyclic voltametry

VI. Electrochemical Impedance Spectroscopy

VII. Durability tests

VIII. Degradation mechanisms

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

I- From materials to processes :

challenges facing PEM WE

•• PerformancePerformance

•• DurabilityDurability

•• ReliabilityReliability

•• CostCost

•• ScaleScale--upup

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Some PEM WE specifications

Scale-up ?

Material science MEAs Mono cell Stack

Process

System

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

II- Catalysts, SPEs,

MEAs, PEM cells and stacks,

systems

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Anodic catalyst: black Ir (2.4 mg.cm−2);

Tcell = 90°C, P = 1 atm.

S = 250 cm2.

Nafion®-115 membrane.

Conventional PGM electrocatalysts

OER : Ir black

Unsupported PGM particles

Magnetron sputtering

HER : Pt black

Pt40/Vulcan XC-72

Pt/Cnano-tubes

Pt/C nanofibers

HER : supported PGM particles

2

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Non-PGM electrocatalysts

metal-oximes

M-T. Dinh Nguyen, A. Ranjbari, L. Catala, F. Brisset, P. Millet and A. Aukauloo

Implementing Molecular Catalysts for Hydrogen Production in Proton Exchange Membrane Water

Electrolysers, Coord. Chem. Review, 256 (2012) 2435 – 2444

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

MEA manufacturing

Aquivion®

Wet process Dry process

Up to 1000 cm2 MEAs

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Some cell designs

(H+, n H2O)

H2O)

H2

O2

H2O

cell thickness ≈ 4- 7 mm

Some criteria for cell design

• compacity

• reduced ohmic losses

• ease of assembly

• brittleness of cell components

DOE 1981

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

III- Main Electrochemical

Investigation Tools & Techniques

• measurement of polarisation curves

• cyclic voltametry

• electrochemical impedance spectroscopy (EIS)

• durability tests

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Typical electrochemical equipment

Lab potentiostat Potentiostat + scanner

Power potentiostat Multi potentiostat

ATEX test plateform

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Global versus local measurements

Needs of non-intrusive techniques for :

:• MEA and cell characterization & optimization

• production monitoring & quality control

• on-site diagnostic

• maintenance operations

current

Non-fragmented cell Fragmented cell

current

3

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

IV- Polarization curves

•• a a measuremeasure of of cellcell efficiencyefficiency

•• information on MEA information on MEA environmentenvironment OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Performances

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Distinct regions of polarization curves

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Cell resistance

Membrane thickness

Polarisation curve

First order derivative

≡ LF cell resistance

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Cell constituents with liquid electrolyte

(the problem of the reference electrode)

Liquid electrolyte

Pt°

Ir°

or

IrO2H2SO4

Ref2 Ref1

Polymer electrolyte

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

V- Cyclic voltametry

4

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Liquid water electrolysis cell

Pt°

Ir°

or

IrO2H2SO4

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Electrode / polymer electrolyte interfaces

Cathode probing

« In » & « ex-situ » electrodes « Ex-situ » electrodes

Anode probing

0.5 < q < 5 C.cmr-2

.2 < q < 5 C.cmr-2

Charge density is function of (i) roughness; (ii) scan rate

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Roughness factors of interfaces

In situ precipitation

1 < rf < 600

Surface coating

1 < rf < 400

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

E (V)

Interfacial kinetics: are all sites active ?

1.23 RHE

0 RHE

∆G°/2F

OER

HER

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Pt°

Ir°

or

IrO2H2SO4

Liquid electrolyte

CVs without Reference Electrode

Polymer electrolyte

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Charge density measurements

cell CVs

Charge vs. Tre

• easy to implement

• non-intrusiveCharge distribution

repeatability

Interface probing

q outer surface +

q’ inner interface

Tre + dissolved species change charge densities.

5

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Optimization of charge density distribution

before activation

after activation

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

VI- Electrochemical Impedance

Spectroscopy (EIS)

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

EIS measurements

current

Rohm Rel Rohm

ZcD Rc

ct ZaDRa

ct

Ccdl Ca

dl

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Single cell impedance

Pt°

Ir°

or

IrO2H2SO4

Liquid electrolyte

Polymer electrolyte

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Stack characterization : Z distribution

Charge transfer R

Z dispersion inside the stack

OVM - ICCPET

HEPTI RRC

Kurchatov Institute VII- Durability tests

6

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

MEA durability measurements

MEAs - 1988OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Electrodes durability measurements

(internal reference; half SPE resistance on each electrode)

MEA-1996

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Stack durability measurements

Istack (A)

TH2O (°C)

Ustack (V)

OVM - ICCPET

HEPTI RRC

Kurchatov Institute VIII- Degradation processes

Need for :

• Process monitoring

• On-site diagnostic

• Maintenance

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Some cell degradation processes

Reversible processes

• SPE poisoning

• cathode poisoning

• activity losses

• increasing SPE resistivity

observation

causes

solutions

• maintenance

• MEA treatment

Irreversible processes

• performance degradation

• increasing gas cross-permeation

• explosions, combustion

observation

causes

solutions

• activity losses (rf decrease)

• membrane thinning

• rising parasite ohmic losses

• SPE perforation

• component replacement

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Example 1 : SPE and cathode poisoning

Example 2 : activity losses

Pt/Ti interface

Roughness factor losses

SPE in contact with deionized

water circulating in SS pipes

≈ 24% SPE sites occupied by Fe3+ species

≈ 3% SPE sites occupied by Ni2+ species

≈ 1% SPE sites occupied by Cr3+ species

7

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Conclusions & perspectives

Main limitations of PEM water electrolysis

• reduced PGM contents and non-PGM catalysts

• operation at higher current densities

• better performances at higher current densities (opex)

• stationary and cycling operating conditions

• improved durability (→ 104 – 105 hr)

• scale-up (→ 102 - 103 Nm3 H2 / hr)

Some improvement targets

• cost (capex)

• durability

• scale-up

Durability : elements for accelerated stress test protocols

• load profiles combining i, T, τ

• ageing : i, T cycles

OVM - ICCPET

HEPTI RRC

Kurchatov Institute

Thanks to …

European R&D projects :GenHyPEM, ReversPEM

M.-F. Charlot DFTE. Anxolabéhère-MallartA. AukaulooA. RagupathyM.-T. Dinh-NguyenR. Guillot RXF. Brisset SEMA. RanjbariA. Villagra

Thank you for your attention !