control of structure, strain and chemistry: a route to designer ......control of structure, strain...

Control of structure, strain

and chemistry: a route to

designer fuel cell interfaces

H2FC SUPERGEN Research Forum1st Sept 2016

Control of structure, strain and chemistry: a

route to designer fuel cell interfaces

Team

PI Prof Stephen Skinner, Imperial College London

CoI Prof Mary Ryan, Imperial College London

CoI Prof John Jilner, Imperial College London

CoI Dr David Payne, Imperial College London

CoI Dr C. Nicklin, Diamond Light Source

CoI Dr Ainara Aguadero, Imperial College London

Partners

International institute for carbon-neutral energy research, Japan

AFC Energy, UK

Massachusetts Institute of Technology, USA

Kyushu University



Main objectives of the project

1- Determine surface structure and chemistry of air electrode environment

interfaces under operating conditions

2- Relate catalytic activity to surface structure and cation segregation effects

3- Probe strain and structure at buried interfaces (electrolyte/electrode)

4- Design and manufacture electrode structures with 2D and/or 3D engineered

interfaces



Work Package 1 (WP1) – Cathode/Environment interfaces

Analyse the factors governing the catalytic activity of both TPB and MEIC

air electrodes as bi-functional catalysts

Work Package 2 (WP2) – Electrode-Electrolyte: towards

understanding buried interfaces in devices

Explore the link between the transport processes detailed in WP1 and

the assembly of tailored microstructures (WP3)

Work Package 3 (WP3) – Engineered 2D and 3D Interfaces

Offer new routes and alternate/improved cell morphologies



Year 1 Year 2 Year 3 Year 4

WP1 - Cathode Interfaces (PDRA1) Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q16

Deposition of Thin Films (PLD, MBE etc) Surface characterization of films Kinetic studies using isotopic tracers LEIS & HiPPES of LSM & LSCF films In-situ DC measurements in films (FIB-SIMS) Character. of thin film heterostructures (STM/STS) WP2 – Buried Interfaces (PDRA2) Development of in-situ sample stage Deposit YSZ/STO, YSZ/LSM & CGO/LSCF films Electrochemical charac. of films XANES/CTR/HiPPES In-situ growth and monitoring of films (MBE) WP3 - Engineered Interfaces (PDRA3) Evaluation of templating methods Development of MBE techniques Evaluation of microstructure of deposited electrodes Testing at AFC Energy 3D Printing of structures WP4 - Dissemination Website development & Outreach Milestones & Deliverables Annual Reports Applications to Diamond Light Source Special Issue: J. Mater Chem. Collaborative exchange visit (MIT/Kyushu/AFC)

WP1: Cathode interfaces: SrCoO3- polymorphs

6

Synthesis via a citrate route. Highly reactive precursors calcined at 900 C

Slow cooling Hexagonal phase (H) Sr6Co5O15

De la Calle et al. Solid State Comm 2008 (10) 1924

200 400 600 800 1000

0.000

0.003

0.006

0.009

0.012

0.015

0.018

L/L

0T (ºC)

SrCoO3-

Transition to

cubic phaseCubic perovskite (C)Hexagonal (H)

- Outstanding performance of the cubic phase- Need to stabilise cubic phase at room temperature without detrimental of transport properties

Tailoring properties with subtle changes in the

composition

7

Slight doping on the cobalt positions

SrCo1-xBxO3- ( B= Sb, Mo and x = 0.05,

0.1, 0.15 and 0.2) allow the stabilization

of a perovskite 3C-arrangement

Change of symmetry form tetragonal to

cubic for x<0.2

(Co,Sb)2

Co1 O1

O2

O3

Co

Sr

0,05 0,10 0,15 0,20 0,253,8

3,9

7,7

7,8

7,9

a,c

(Å

)

x

a

C

P4/mmm Pm-3m

P4/mmm Pm-3m

40 60 80 100 120 140-1000

-500

0

500

1000

1500

2000

2500

3000

3500

4000

Inte

nsity (

a.u

.)

2 (º)

SrCo0.95

Mo0.05

O3-

NPD,RT = 1.91Å

P4/mmm


composition: thermal expansion

8

Regular variation of the thermal expansion along the SrCo1-xSbxO3- (0.05 x 0.2)

series without the presence of the abrupt changes observed in the undoped

compound

0 200 400 600 800 1000-0,05

0,00

0,05

0,10

0,15

0,20

0,25

T (ºC)

L

/Lo (

%)

+ Sb

“H” SrCoO3-

0 200 400 600 800 1000

0.000

0.005

0.010

0.015

x = 0.05

x = 0.2

L/L

0

T (ºC)

x = 0.1

x = 0.15SrCo1-x

SbxO

3-


composition: electrical conductivity

9

Increase of the electrical conductivity at intermediate temperatures (T

800 C) due to the stabilization of a 3D perovskite-like structure at RT

The highest conductivity value is presented by the x = 0.05 sample,

reaching a maximum of 505 Scm-1 at 400 C

100 200 300 400 500 600 700 800 900 10000

50

100

150

200

250

300

350

400

450

500

550

(

Scm

-1)

T (ºC)

x = 0

x = 0,05

x = 0,1

x = 0,15

x = 0,2X=0.05

X=0.1

X=0.15

X=0.2X=0

T (ºC)

100 300 500 700 900

(S

·cm

-1)

100

200

300

400

500

0

SrCo1-xSbxO3-

200 400 600 800 1000

97.0

97.5

98.0

98.5

99.0

99.5

100.0 SrCo0,95

Sb0,05

O3-

Temperature (ºC)

TG

(%

)

Air

-200

-150

-100

-50

0

50

100

150

200

DT

A (

V)

J. Power Sources, 192, 132, 2009

Chem. Mater., 19, 6437, 2007

Compressive strain:

substrate lattice parameter

<

thin film lattice parameter

Tensile strain:

substrate lattice parameter

>

thin film lattice parameter

Thin film layer

Single crystal

substrate

SrCo0.95Sb0.05O3-d was chosen as optimum material from bulk studies

Strained materials: Can we tune the surface defect

structure of the catalysts?

In order evaluate the effect of the surface composition under operation

condition thin films of these materials were grown under different strains

SrCo0.95Sb0.05O3- thin films : Strain tuning

-10

-8

-6

-4

-2

0

2

4

6

8

10

MgO

LSGMSTO

LSAT NGO

LAO

Si GDC

YSZCompressive

Str

ain

Substrates

Tensile0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

2Theta (°)

0.1

3

1

3

10

3

100

3

1000

3

10000

3

100000

3

1000000

Inte

nsit

y (

co

un

ts)

Thickness =30nm

SrCo0.95Sb0.05O3- thin films : Strain tuning

STO (103)

SrCo0.95Sb0.05O3-

(106)

LSAT (103)

SrCo0.95Sb0.05O3-

(106)

NGO (103)

SrCo0.95Sb0.05O3-

(106)

In-plane tensile

In-plane compressive

In-plane compressive

LSAT STO

SrCo0.95Sb0.05O3- thin films : AFM

NGO

SrCo0.95Sb0.05O3- thin films : Anisotropic strain

• SCSO/STO in-plane tensile

• SCSO/NGO in plane compressive

• Strain effect on the electronic conductivity

• SCSO/LSAT different activation energy Ea

of the electrical conductivity- effect of tetragonality?

• Possible under-stoichiometry of Sb in the thin film

SrCo0.95Sb0.05O3- thin films : Electrical

conductivity

(Co,Sb)2

Co1 O1

O2

O3

WP2-Buried interfaces: polar and non polar

terminations

LaAlO3n-type; metallic

p-type; insulating

WP2-Buried interfaces: Low energy ion

scattering

WP2-Buried interfaces: crystal truncation

rods

surfbulksum FFF

)(216

2

02

2

2

1

1

jjj

j

lzkyhxiunitcellbulk

j

QB

ju

ilu

j

jilj

ubulk

eefF

eeFeeFF

)(2mod

16 2

2

jjj

j

lzkyhxiel

surface

j

QB

jjsurf eefF

WP2-Buried interfaces-CTR different

reciprocal lattice indices

S. S. Pramana et al., Phys Rev B. Under Review, 2016.

10

100

1000

10000

100000

0 0.5 1 1.5 2 2.5 3 3.5

F (a

.u.)

L

Fraw

bulk-Al terminated

bulk-La terminated

refined surface occupancy

optimised fit - relaxationand occupancy

WP2-Buried interfaces

WP2-Buried interfaces

control of structure, strain and chemistry: a route to designer ......control of structure, strain...

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