Transition metal oxide

electrocatalysts for

ORR and OER

Andrea E. Russell

a.e.russell@soton.ac.uk

Overview

• Water electrolysers

IrxRu

1-xO

2

• XAS

Ex-situ XANES

In-situ XANES

• Air electrodes for

Zn/Air batteries

NiCo2O

4

2

2H2O

4H++ 4e

- + O

2

Water electrolysis

• Hydrogen production

O2 evolution inefficiencies

• Electrocatalysts for OER

RuO2 and IrO

2

• Limitations

Cost

Dissolution of RuO4

3

H

H

H

H

PEM

O

O

H

O

H H

O

H H

+

+

+

+

-

- -

-

Energy

grid

IrxRu

1-xO

2 catalysts

4

30 40 50 60 70 80 90 100 110

2 / o

Ir0.25

Ru0.75

O2

Ir0.50

Ru0.50

O2

Ir0.75

Ru0.25

O2

RuO2

IrO2

32 33 34 35 36 37 38

2 / o

RuO2

Ir0.25

Ru0.75

O2

Ir0.50

Ru0.50

O2

Ir0.75

Ru0.25

O2

IrO2

• XRD indicates formation of a solid solution

• Series of materials prepared by Adams Fusion method

IrxRu

1-xO

2 catalysts

5

-2.1

0.0

2.1

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

-1.2

0.0

1.2

A

E (vs. RHE) / V

B

Jgeom

etr

ic / m

A c

m-2

-1.8

0.0

1.8

-2.1

0.0

2.1

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

-1.2

0.0

1.2 C

B

j geom

etr

ic / m

A c

m-2

A

E (vs. RHE) / V

IrO2

RuO2

Ir0.75

Ru0.25

O2

Ir0.5

Ru0.5

O2

Ir0.25

Ru0.55

O2

6 0.5 M H2SO

4 on GC electrode at 295K

1.3 1.4 1.5 1.6

0

20

40

60

IrO2

Ir0.75

Ru0.25

O2

Ir0.50

Ru0.50

O2

Ir0.25

Ru0.75

O2

RuO2

J

geo

me

tric / m

A c

m-2

E (vs. RHE) / V

IrxRu

1-xO

2 catalysts

7

IrxRu

1-xO

2 catalysts

0 250 500 750 10001.35

1.40

1.45

1.50

1.55

1.60

1.65

Ce

ll p

ote

ntia

l / V

Current density / mA cm-2

IrO2

Ir0.75

Ru0.25

O2

Ir0.50

Ru0.50

O2

Ir0.25

Ru0.75

O2

RuO2

PEM water electrolysis cell running at 60 °C, 20 bar

0 100 200 300 400 500 600 7001.5

1.6

1.7

1.8

1.9

2.0

Ce

ll p

ote

ntial / V

Time / h

IrO2

Ir0.75

Ru0.25

O2

Ir0.50

Ru0.50

O2

Ir0.25

Ru0.75

O2

RuO2

1 A cm-2

X-ray absorption spectroscopy

8

Io

It

XAS measurements

Transmission: m(E) measured directly using ion chambers.

Fluoresence: refilling of core-hole detected.

 

I = I0e-m E( )x

 

m(E )x = ln I0 / I( )

 

m(E )xµ I f / I( )

X-ray absorption spectroscopy

• XAS

XANES

– electronic structure

EXAFS

– local structure

10 M. Newville - APS

22100 22110 22120 22130 22140 22150 22160-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

N

orm

alis

ed a

bsorp

tion

Energy / eV

Ru foil

Ru(acac)3

RuO2

La4.87

Ru2O

12

SrRu2O

6

KRuO4

22120 22124 22128 221320.4

0.5

0.6

Ru edge - XANES Spectra

11

Edge position shifts to higher energy with increased

oxidation state – calibration curve from reference compounds

In-situ Cell

• Stable electrochemistry

• Rapid removal of evolved gas

• Stable in 1M KOH

• Clear x-ray fluorescence path

12

13

It

Detector

Electrolyte

flow

In-situ XANES – (Ir1-x

Rux)O

2

14

Ex situ 1.0 V 1.4 V 1.7 V 1.8 V 1.0 V4.7

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

Ir L

3 e

dg

e e

ne

rgy s

hift

/ e

V

Applied potential (vs. RHE)

IrO2

Ir0.75

Ru0.25

O2

Ir0.50

Ru0.50

O2

• Ir stabilises the oxidation state of the RuOx

Ex situ 1.0 V 1.4 V 1.7 V 1.8 V 1.0 V6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

Ru K

-edge s

hift / eV

Applied potential (vs. RHE)

RuO2

Ir0.50

Ru0.50

O2

Ir0.75

Ru0.25

O2

Pyrochlores - OER

• (Na0.33

Ce0.67

)2(Ir

1-xRu

x)O

7

• Ref = (Ru0.9

Ir0.1

)O2

15 (a) OER LSV in 0.5M H2SO

4 (b) DEMS of pyrochlores during OER.

R.I. Walton et al.,

Angewandte Chemie.

2014

Pyrochlore – Ex-situ XANES

16

• Ruthenium in +4 oxidation state

• Iridium in +4.05 oxidation state

*pre-edge feature from the 1s-4d transition

Pyrochlores – In-situ XANES

• (Na0.33

Ce0.67

)2(Ir

1-xRu

x)O

7

• Increase in Ru ox. state

with increase in Ru

content

• Reduction in Ir ox. state

with increase in Ru

content

17

Zinc-air battery

18

Lee. J et al., Adv. Energy Mater., 2011, 1, 1, 34 - 50.

Electrocatalysts

19

Fuel Cells:

Acid environment

PtX particles on carbon

Metal/Air batteries:

Alkaline environment

NiCo2O

4 spinel particles

PEM Electrolyser:

Acid environment

IrxRu

1-xO

2

Catalyst Screening - RDE

• Spinels - AB2O

4

e.g. NiCo2O

4

• Perovskites – ABO3

e.g. LaNiO3

• Pyrochlores – A2B

2O

7

e.g. Pb2[Ru

2-xPb

x]O

7

20

1.3 1.4 1.5 1.6 1.7

0

25

50

75

100

j /

mA

cm

-2

E vs. RHE / V

LaNiO3

20 wt.% Pt/C

NiCo2O

4

Pb2(Ru

2-xPb

x)O

7-y

ORR comparison - RDE

21

0.6 0.7 0.8 0.9 1.0 1.1 1.2

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

j / m

A c

m-2

E vs. RHE / V

LaNiO3

20 wt.% Pt/C

NiCo2O

4

Pb2(Ru2-x

Pbx)O

7-y

NiCo2O

4

• Phase purity & crystallinity

• Surface area

22

Synthesis method BET (m2 g-1)

Co-precipitation 68.2

Citrate 51.3

Ammonia 47.5

Glycine 32.7

TD- Methanol 12.6

TD - H2 O 6.8

10 20 30 40

Inte

nsity

2 Theta / Degrees

TD-H2O

TD-methanol

Ammonia

Glycine

Citric acid

Co-precipitation

NiCo2O

4

23 10 20 30 40

Inte

nsity

2 Theta / Degrees

TD-H2O

TD-methanol

Ammonia

Glycine

Citric acid

Co-precipitation

NiCo2O

4 cycling tests

24 Price S.W.T. et al., J. Power sources, 2014, 259, 43-49

Metal nanoparticles

• Metal-oxide supported on active catalyst

RuO2 → OER

Ag → ORR

25

Ruthenium

dioxide

Silver oxide

Bulk

NiCo2O

4

RuOx Modifcation

26 2.5 mg cm-2 NiCo

2O

4 on Toray at 333K, 200 cm

-2 O

2 in 8M KOH

ORR

OER

0 500 1000 1500 2000 2500 3000 3500

0.6

0.8

1.0

1.2

1.4

1.6

1.8

E v

s. R

HE

/ V

Time /s

TD - NiCo2O

4

Co-precip - NiCo2O

4

RuOx/NiCo

2O

4

Catalyst

Composition:

RuOx 0.13 mg

NiCo2O

4 2.37 mg

10 mA cm-2 20 mA cm

-2 50 mA cm

-2

RuOx stability

27 2.5 mg cm-2 NiCo

2O

4 on Toray at 333K, 200 cm

-2 O

2 in 8M KOH

0 10 20 30 40 50 60

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

E v

s H

g/H

gO

/ V

Time / minutes

RuOx/NiCo

2O

4 1

st

RuOx/NiCo

2O

4 2

nd

RuOx/NiCo

2O

4 5

th

RuOx/NiCo

2O

4 10

th

10 mA cm-2

20 mA cm-2

50 mA cm-2

Acknowledgements

28

Members of research group:

Peter Richardson (now PDRA at Southampton)

Stephen WT Price (now at Diamond)

Stephen J Thompson (HMGCC in January)

Scott Gorman (Ilika in January)

Derek Pletcher – a retired colleague who won’t

Richard Walton - Warwick

Funded by:

EPSRC DTA & Ind. Case Studentships

EU FP7 POWAIR (C-Tech Innovation)

ITM Power

Johnson Matthey

Diamond

University of Southampton