Professor Nigel Brandon OBE FREng

Chair, Sustainable Development in Energy

Director, Energy Futures Lab

RCUK Energy Senior Research Fellow

www.imperial.ac.uk/energyfutureslab

SOFCs for power plants – current status and future

perspectives

- Established in 2005 to promote and stimulate multi-disciplinary energy research.

- Research budget of £50M pa for energy research, one third from industry.

- ~370 projects & 600 research staff and PhD students undertaking energy research.

Integrating Themes

-Energy systems engineering

-Energy policy

-Energy business

-Energy in society

The Energy Future Lab| Integrates across Science, Engineering, Policy and Business in

the energy sector

Energy Technologies

-Fuel cells and batteries

-Bio-energy

-Hydrogen

-Solar

-Carbon capture and storage

-Oil and gas

-Smart grids

-Transport

-Nuclear fission and fusion

-Future fuels

-Electric and hybrid vehicles

-Green aviation

Introduction

• What is a Solid Oxide Fuel Cell?

• Why Solid Oxide Fuel Cells?

• SOFC technology overview.

•SOFC-GT hybrids for distributed generation.

•SOFC mCHP for highly distributed systems.

• Some key challenges and opportunities

• Summary.

Introduction to Fuel Cells

H2

H2

H2

H2

H2

O2

O2

O2

O2

O2

Fluid-Flow Plate (FFP)Flow Channel

Membrane Electrode Assembly (MEA)/Positive - Electrolyte - Negative (PEN)

AnodeCathode

O22H2

4H+

4e-

2H O250 m

200 m

10 m

Catalyst

GDL

Mem

braneC

ath

ode

An

od

e

2H O2

2H2

2O2-

15 m

50 mca. 1000 m

4e-

4e-

+

+

O2

4e-+

Anode: 2H + 2O 2

2- 2H O + 4e2

-

Cathode: O + 4e2

-2O

2-

Anode: 2H24H + 4e

+ -

Cathode:4H + O + 4e+ -

2 2H O2

PEMFCSOFC

Electrolyte

CathodeAnode

20 m

Solid Oxide Fuel Cell Proton Exchange

Membrane Fuel Cell

•Cell Voltage is given by:

Ecell = E - h - IRcell

Ecell voltage of cell

E Nernst (OCV) voltage

h sum of overpotentials

IRcell ohmic cell resistance

Cell and Stack Characteristics

Schematic Solid Oxide Fuel Cell System

Fuel Processing Options

Thermodynamic predictions of

the equilibrium composition for

methane fed at different

temperatures and steam-to-

carbon ratios. The combined

CH4 + H2O input amount is 1

kmol in each case.

UK: Share of fuels contributing to primary energy supply

Source: UK Energy Sector Indicators. 2008. DECC.

2007 UK CO2 emissions were 544Mt

Heat: 39% UK CO2

Power: 33% UK CO2

Transport: 28% UK CO2

Motivation for SOFC/GT Integration

10

• High efficiency

-Electrical efficiency up to ~70%

• Environmental Attractions

-No SOx/NOx, lower CO2 emission

-Quiet

-No vibration

• Distributed power potential

-Modularity

-Siting flexibility

• Cogeneration potential

• Fuel flexibility

-Natural gas

-Biogas

-Biomass

-Coal gasification syngas

-Higher voltage-Improved power output-GT pressure ratio and inlet temperature limited by fuel cell

-kW to several hundred kW-Natural gas, biomass, gasoline…

AtmosphericPressurized

Sub DepartmentConfigurations

SOFC-GT Hybrid Cycle

11

-GT pressure independent of fuel cell pressure

-Less complex/expensive to develop and implement

-Accommodate a wider variety of GT-MW-class and multi-MW-Natural gas, syngas from coal…

Heat Exchangers

Fuel Processor

Waste Heat Recycle

Heat Loss

SOFC GT

Electronic Controllers

Blowers

Generator

Sensors

Valves

Pumps

Electrodes

Electrolyte

Interconnect

Reformer

Blower

Afterburner

Compressors

Turbines

Recuperated/Intercooled

Key System Features

Thermal

Management

Control

System

10

Two Optimization Options

Efficiency

Power Density

0)/()(/)(2

0/

0/)(2)/()()/()(

0/

2

6

2

62566255

4423

2

4

2

42334

2

4242

RTdRTddkddRTddkdRTd

bydeterminedisii

dRTddkdRTdRTddkdRTdiRTdRTddkRTdd

bydeterminedisiiP

fc

P

Pfc

hh

20%

40%

60%

80%

100%Maximum Efficiency

Maximum Power

1000

2000

3000

4000

5000

6000

Pihi

Piii h

16

Zhao Y, Shah N, Brandon NP, The Development and Application of a Novel Optimisation Strategy for Solid

Oxide Fuel Cell-Gas Turbine Hybrid Cycles, Fuel Cells, 2010, Vol:10, Pages:181-193

Rolls-Royce

Mitsubishi

Siemens Westinghouse

14

Technology Status of SOFC-GT HybridTechnology Status of SOFC-GT Hybrid

Rolls-Royce data-private; Confidential

1

1-Megawatt Solid Oxide Fuel Cell System

SOFC-GT Hybrid by Rolls-Royce Fuel Cell Systems

Porous

support

Fuel

Air

Ni-YSZ anode YSZ

electrolyte

LSM-YSZ cathode

Rolls-Royce data-private; Confidential

1

1-Megawatt Solid Oxide Fuel Cell System

Final Energy Consumption of Thermal Energy in

the UK in 2006 Space heating and hot water in UK residential sector = 78Mt CO2 pa. In 2008

BERR, Energy Trends: September 2008 (Special feature – Estimates of Heat use in the UK). 2008, Department

for Business, Enterprise & Regulatory Reform (now Department of Energy and Climate Change): London, UK.

p. 31-42.

UK: Ownership of central heating

Source: GfK Home Audit from the Domestic Energy Fact File. Building Research Establishment.

Fuel

Fuel

CellFuel

Heat

Electrical

50%

40%

Energy

100%Power station

55% losses

Transmission

5% losses

Delivered

40%

Fuel Cell

10% lossesDelivered

90%

Energy

100%

Conventional

Micro-CHP

Fuel Cell Boilers for the Home (micro-CHP)

Micro-CHP Technologies

Baxi Stirling engineVaillant and Plug Power PEMFC

Ceres Power and British Gas SOFC

Honda ECOWILL ICE

Honda ECOWILL ICE with Storage

mCHP electrical efficiency against load factor

A.D. Hawkes, P. Aguiar, C.A. Hernandez-Aramburo, M.A. Leach , N.P. Brandon , T.C. Green, C.S. Adjiman. Techno-economic

modelling of a solid oxide fuel cell stack for micro CHP, J Power Sources, 156 (2006) pp. 321–333.

0 4 8 12 16 20 240

2

4

6

8

10

12

14

16

Time (Hours)

Dem

and (

kW

)

Space Heating and DHW Demand

Electricity Demand

Residential heat and power demand

Heat and Power Demand over 1 Day in a Typical UK Dwelling

Economic Drivers for m-CHP Systems

• Dwelling Annual Electricity Demand•The main value driver for micro-CHP is (the ability to displace) onsite electricity demand.

•If onsite electricity demand exists, the ability to access the value available (in displacing it) is dependent on the heat-to-power ratio (HPR) and presence of thermal demand.

0 2500 5000 7500 100000

200

400

600

800

1000

1200

IC Engine

0 2500 5000 7500 100000

200

400

600

800

1000

1200

PEMFC

0 2500 5000 7500 100000

200

400

600

800

1000

1200

SOFC

0 2500 5000 7500 100000

200

400

600

800

1000

1200

Annual Electricity Demand (kWh/year)

Maxim

um

Cost

Diffe

rence B

etw

een

Mic

ro-C

HP

Syste

m a

nd B

oiler

Syste

m (

£)

Stirling Engine

Low Thermal Demand

Average Thermal Demand

High Thermal Demand

HPR = 1

HPR = 3 HPR = 2

HPR = 8

Dwelling Annual Electricity Demand

Hawkes, AD, Staffell, I, Brett, DJL, Brandon, NP, Fuel Cells for Micro-Combined Heat and Power Generation, Energy &

Environmental Science, 2009, Vol: 2, Pages: 729 - 744

5000 10000 15000 20000 25000 300000

500

1000

1500ICE

5000 10000 15000 20000 25000 300000

500

1000

1500PEMFC

5000 10000 15000 20000 25000 300000

500

1000

1500SOFC

5000 10000 15000 20000 25000 300000

500

1000

1500

Annual Thermal Demand (kWh/year)

Annual C

O2 R

eduction w

.r.t. R

efe

rence S

yste

m (

kg C

O2/y

ear)

)

Stirling

Flat

Bungalow

Terrace

Semi-Detached

Detached

Environmental Drivers for m-CHP Systems

CO2 Reduction – Thermal Demand •CO2 reduction is dependent on ability to displace grid electricity.

•Ability to displace grid electricity, and thus bring about CO2

reduction, is dependent on annual thermal demand and prime mover heat-to-power ratio.

Hawkes, AD, Staffell, I, Brett, DJL, Brandon, NP, Fuel Cells for Micro-Combined Heat and Power Generation, Energy &

Environmental Science, 2009, Vol: 2, Pages: 729 - 744

Carbon Intensity of Electricity Options

marginal CO2 intensity of UK

electricity 0.69kgCO2/kWh

Ceres Power SOFC micro-CHP unit• Developed in collaboration with British Gas (with natural gas fuel) and

Calor Gas (with LPG fuel). Prototype unit now demonstrated.

• Reduces the energy bill of a customer by around 25% and saves around 1.5 tonnes of CO2 pa.

• In addition, under the new UK feed in tariff (FIT), a household installing a SOFC mCHP product will receive, for a period of ten years, a generation payment of 10p/kWh for all electricity generated plus an additional export payment of 3p/kWh for any electricity that is not consumed in the home and is fed back into the grid.

Tubular/flat tube or Planar Cell Designs

Typical planar SOFC geometries

Brett DJL, Atkinson A, Brandon NP, Skinner SJ, Intermediate temperature solid oxide fuel cells, CHEM SOC REV, 2008, Vol:37,

Pages:1568-1578

Relationship between electrolyte and temperature

Brett DJL, Atkinson A, Brandon NP, Skinner SJ, Intermediate temperature solid oxide fuel cells, CHEM SOC REV, 2008, Vol:37,

Pages:1568-1578

YSB ((Bi2O3)0.75(Y2O3)0.25); LSGMC (LaxSr1-xGayMg1-y-zCozO3; x~0.8, y~0.8, z~0.085); CGO (Ce0.9Gd0.1O1.95); SSZ

((ZrO2)0.8(Sc2O3)0.2); YDC (Ce0.8Y0.2O1.96); CDC (Ce0.9Ca0.1O1.8); YSZ ((ZrO2)0.92(Y2O3)0.08); CaSZ (Zr0.85Ca0.15O1.85).

SOFC Cathode Design

• The Three Phase Boundary

(TPB) is a zone in which the:

– open pore (reactant fluid),

– catalyst and

– electrolyte are in close contact.

• The process requires:

– flow of ions via the electrolyte,

– supply of reactant through open

pores

– reaction at the catalyst active sites

SOFC Anode Design

Illustration of the effect of extending the TPB using a MIEC electrolyte. (a)

Electrolyte / cermet anode with active TPB circled; (b) mechanism of

reaction at the TPB; (c) mechanism of reaction at the extended TPB.

Electrode Microstructure in three dimensions

TPB 2

TPB 3

TPB 1

TPB 2

TPB 3

TPB 1

Combining Modelling with Experiment

3D Reconstruction of Ni-

YSZ Anode. Ceramtec

NiO-YSZ sintered at

1350C.

100 images at 15 nm

intervals with 20 nm pixels

- 6.7 x 5 x 1.5 µm (x,y,z).

Red=YSZ; Blue=Ni.

Total TPB density = 10.4

m-2 with 63% percolated

in x-y plane and 72%

percolated in x-z plane.

Porosity = 20%.

P Shearing, Q Cai, J Golbert, V Yufit, C S Adjiman, N P Brandon, Microstructural analysis of a solid oxide fuel cell anode using

focused ion beam techniques coupled with electrochemical simulation, J Power Sources, 195 (2010) pp. 4804-4810.

Zeiss xB1540 FIB-FEG SEM, milled at 30 kV, 30 pA, imaged at 2kV in secondary

electron mode.

T

ºC

RHF

Ω cm-2

RMF

Ω cm-2

RLF

Ω cm-2

1000 0.076 0.857 0.161

900 0.387 1.365 0.138

800 0.803 1.543 0.1690.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

0.000

0.002

0.004

0.006

0.008

0.010

0.012

y=0.076x

y=0.387x

y=0.803x

800 oC

900 oC

1000 oC

Over-

pote

ntial (V

)

Current density (A/cm2)

Exchange Current per unit TPB length

800 °C: 9.4×10-11 A/μm

900 °C: 2.14×10-10 A/μm

1000 °C: 1.22×10-9 A/μm

Model and experiment – an first step

3.5 4.0 4.5 5.0 5.5 6.0 6.5

-0.5

0.0

0.5

1.0

1000 C

900 C

800 C

Zim

g [

Oh

m c

m-2]

Zreal

[Ohm cm-2]

97 % H2 , 3 % H

2O

P Shearing, Q Cai, J Golbert, V Yufit, C S Adjiman, N P Brandon, Microstructural analysis of a solid oxide fuel cell anode using

focused ion beam techniques coupled with electrochemical simulation, J Power Sources, 195 (2010) pp. 4804-4810.

Electrode Thickness Investigation – current density

The current density

reaches a maximum at a

different thickness as a

function of overpotential.

At over potential of 400

mV, active electrode

thickness = 9 µm

At over potential of 300

mV, active electrode

thickness =12 µm

At over potential of 50-

200 mV, active electrode

thickness =15-18 µm0 2 4 6 8 10 12 14 16 18 20 22 24

0

1

2

3

4

5

6

400 mV

300 mV

200 mV

100 mV

50 mV

Curr

ent

density (

A/c

m2)

Electrode thickness (µm)

T=1073 K; Ionic conductivity: 4.28×10-6 S/μm

PH2:PH20=1; Electronic conductivity: 2.4 S/μm

Exchange current : 9.4×10-11 A/μm

Binary diffusion coeff: 8.28x10-4 m2 s-1

Case 1: 21% Porosity VNi: VYSZ=1.3

Electrode Thickness Investigation

0 2 4 6 8 10 12 14 16 18

02

46

8

0

2

4

6

8

xy

z

0

1

2

3

4

5

6

7

8

9x 10

-6×10-6 A/µm3×10-2 A/cm3The 3D map of current density distribution in the electrode of Case 1. x is the electrode

thickness dimension, y and z dimensions form the cross section of the electrode. At x=0

is the interface of current collector with the electrode, and at x=18, the interface of the

electrode with the electrolyte.

A A

200

σP1

(MPa)

0YSZ Phase

Ni Phase

FEM analysis of 3D electrode structures

(ScanFE V3.1, Simpleware Ltd, UK). The FE model consisted of 285,000 four-

node tetrahedral elements (Abaqus type C3D4)

R Clague, P Shearing, PD Lee, Z Zhang, DJL Brett, AJ Marquis, NP Brandon, Stress analysis of SOFC anode microstructure reconstructed from focused

ion beam tomography, J Power Sources (2011) in press.

1. Manufacture Cell2. Electrochemical

Characterisation

3. Microstructural

Characterisation

4. Simulation5. Validate & Re-

iterate

Summary

•SOFC offer improved efficiency, and hence reduced carbon

emissions, using a wide range of fuels, and over a wide range of

power levels, with a strong fit with distributed power generation.

•Key SOFC challenges in the near term are related to demonstrating

durable fuel cell system performance under real world operating

conditions, and a number of programmes are under way around the

world to do this.

•Future challenges lie in enabling operation on renewable and/or

lower carbon fuels, continuing to reduce device cost, and further

extending device performance and lifetime.

•At the 100 MWe’s scale SOFC technology can contribute to CCS

schemes, and syngas production from CO2 and steam by electrolysis

using renewable energy.

Konda N, Shah N, Brandon NP, Optimal transition towards a large-scale hydrogen

infrastructure for the transport sector: The case for the Netherlands, INT J HYDROGEN

ENERGY, 2011, Vol:36, Pages:4619-4635

Thank you

n.brandon@imperial.ac.uk

www.imperial.ac.uk/energyfutureslab