Current Activities on Solid Oxide Cells at DLR Asif Ansar, Rmi - - PowerPoint PPT Presentation

Current Activities on Solid Oxide Cells at DLR

Asif Ansar, Rémi Costa, Michael Hörlein, and Günter Schiller German Aerospace Center Institute of Engineering Thermodynamics Stuttgart, Germany

• Brief Introduction of DLR-ITT
• Metal Supported Cell Concepts for SOC
• Plasma spray concept
• EVOLVE concept
• SOEC activities
• Hi2H2 project
• Degradation study
• Solar fuels
• Conclusion

Outline

Aeronautics Space Transport Energy Space Agency Project Management Agency

DLR German Aerospace Center

Research Institution

> 7500 employees across 32 institutes and facilities

Institute of Engineering Thermodynamics

• Prof. Dr. André Thess

Administration

Jörg Piskurek Thermal Process Technology

• Dr. A. Wörner

Staff: About 190 in Stuttgart, Köln, Hamburg and Ulm Yearly budget: About 18 Mio. EUR including 50% third party funding „... innovative solutions for sustainable and environmentally friendly energy storage and conversion processes ...“

Computational Electrochemistry

• Prof. A. Latz

System Analysis and

• Techn. Assessment
• Dr. C. Schillings /
• C. Hoyer-Klick (komm.)

Electrochemical Energy Technology

• Prof. A. Friedrich

R&D of efficient electrochemical energy storage and conversion 5 Fields of Research Solid Oxide Cells Realization of durable, powerful and cost effective SOFC-stacks Polymer Electrolyte Fuel Cells Improvement of longevity and reliability with regard to electric mobility and residential power supply Lithium Metal and Lithium Ion Batteries Development of mobile energy storages Modeling & Simulation Improvement of the efficiency factor, longevity and costs of fuel cells and batteries Electrochemical Systems Development of efficient and effective, multifunctional fuel cells systems for stationary and mobile applications

Electrochemical Energy Technology

Generations of planar SOFCs

1st gen. 2nd gen. 3rd gen.

ESC

Limited power density Fuel flexibility Robustness Stationary Transportation High power density Fuel flexibility Sulfur poisoning Thermal cycling Redox Cycling Stationary Transportation High power density Fuel flexibility Sulfur poisoning Thermal cycling Redox Cycling Stationary Transportation

ASC MSC

Electrolyte Cathode Anode

Bipolar plate Bipolar plate porous metallic substrate anode electrolyte contact layer cathode current collector cathode active layer protective coating not used air

• xygen/air

air channel fuel channel fuel brazing not used fuel + H O

2

(not in scale)

Plasma Spray for Functional Layers Compact design with thin sheet ferritic substrates and interconnects 100 cm² foot print Counter flow stamped gas manifold Welded substrate with the interconnect Brazing or Glass Seal as joining of repeat units

Cathode 20 µm Electrolyte 35 µm Anode 35 µm Substrate

Metal Supported SOFC

Functional Principle of DC Plasma

Powder Jet

Substrate Plasma Gun Particle Melting and Acceleration

Particle Impingement Plasma Gases

Ar H2 N2 He

Splat Layering

Coating

Particle Injection

Vortrag > Autor > Dokumentname > Datum

MSC Cell

12.5 cm² cell at 800°C; H2/N2 and air

10-Cell Stack

100 cm² cells at 800°C; H2/N2; air

MSC-10-31, 800°C, 27h 10H2+10N2/ 20 Luft (SLPM) P1: Kennlinie nach Aufheizen, KL1

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 100 200 300 400 500

Stromdichte i [mA/cm²] Zellspannung U [V]

200 400 600 800

Leistungsdichte p [mW/cm²]

OCV Zelle 10: 1,019 V Zelle 9: 1,006 V Zelle 8: 1,007 V Zelle 7: 1,001 V Zelle 6: 1,006 V Zelle 5: 1,016 V Zelle 4: 1,022 V Zelle 3: 1,005V Zelle 2: 1,013V Zelle 1: 1,014 V

@ 7,0 V Pstack = 250 W FU = 24,8 mol%

p U

Stromdichte@ 700mV Zelle 10: 173 mW/cm² Zelle 9: 315 Zelle 8: 324 Zelle 7: 325 mW/cm² Zelle 6: 318 Zelle 5: 324 mW/cm² Zelle 4: 329 Zelle 3: 320 mW/cm² Zelle 2: 319 Zelle 1: 320 mW/cm²

Metal Supported SOFC - Performance

MSC Cell with Suspension Plasma Spray Electrodes

Power density above 800 mW/cm² at 0.7 V 12.5 cm² cell at 800°C; H2/N2 and air

0,6 0,7 0,8 0,9 1 1,1 400 800 1200 1600 Current density / mA*cm-2 Cell voltage / V 250 500 750 1000 Power density / mW*cm

• 2

A B C D

610 mW/cm² @ 0.7V (2009- G6)

Cyclability of Metal Supported Cells

Thermal cycles MSC-02-17, 800°C 2 H2+2 N2/ 4 Air (SLPM) 458 / 1227 h

200 400 600 800 1000 1200 50 100 150 200 250 300 current density i [mA/cm²] cell voltage U [mV] 50 100 150 200 250 300 350 400 power density p [mW/cm²]

U1_start U2_start U1_end U2_end p1_start p2_start p1_end p2_end p U

Redox cycle MSC-02-17, 800°C 2 H2+2 N2/ 4 Air (SLPM) 1227 / 1517 h

200 400 600 800 1000 1200 50 100 150 200 250 300 current density i [mA/cm²] cell voltage U [mV] 50 100 150 200 250 300 350 400 power density p [mW/cm²]

U2_start U2_Redox_5 U2_Redox_20 p2_start p2_Redox_5 p2_Redox_20 p U

Redox_start cell2: 157 mW/cm² Redox_5 cell2: 177 mW/cm² Redox_20 cell2: 149 mW/cm² Redox start @ 1,4 V Pstack = 28,5 W FU = 14,1 mol% Redox 5 @ 1,4 V Pstack = 33,3 W FU = 16,6 mol% Redox 20 @ 1,4 V Pstack = 26,0 W FU = 12,9 mol%

15 thermal cycles performed, 12 down to 350 °C and 3 to ambient temperature Degradation after thermal cycles was 10.3 % 20 forced redox cycles performed with 50 ml/min O2 on the anode side per layer Increase of power density after 5 cycles (Improving contact Ni-YSZ?) Degradation of the stack was 9.1 % after 20 redox cycles

Measurement Setup for Segmented Cells

• 16 galvanically isolated segments
• Local and global i-V characteristics
• Local and global impedance measurements

Local temperature measurements Local fuel concentrations Flexible design: substrate-, anode-, and electrolyte-supported cells Co- and counter-flow

Experimental Setup for Raman Spectroscopy Measurements

Issues to be addressed for improving MSCs

• Cr-poisoning at the cathode side > Protective coating required
• Improve tolerance toward sulfur poisoning
• Lifetime of metal substrate if stationary applications are considered
• Hermetic electrolyte

Beyond the 3rd Gen. SOFC: Which materials and architecture for the next generation SO(F)C?

Metal substrate resistant toward oxidation

Al rich alloys, on the basis of MCrAl(Y) with M being Fe, Ni, Co or a mixture

Formation of an Al2O3 layer as a durable protective coating

Beyond the 3rd Generation SOFC

Hybrid current collector mechanically and chemically stable in both oxidant and reducing atmosphere

Infiltration with an electronic conductor (ideally a ceramic)

Dense La0.1Sr0.9TiO3 (800°C): sintering in H2: σtot ≈ 150 S/cm

• O. Marina et al. Solid State Ionics, 149

(2002) 21-28.

• S. Hashimoto et al. Journal of Alloys and

Compounds, 397 (2005) 245-249.

• Y. Tsvetkova et al. Materials and Design,

30 (2009) 206-209.

Nickel-free Hybrid Metal-Ceramic Supported SOFC

Use of perovskite materials at the anode and cathode, being modified by addition of suitable catalysts

High power density, sulfur resistant, fuel flexibility, thermal cycling, redox cycling Stationary applications …

Beyond the 3rd Generation SOFC

Metal Foam: NiCrAl Composition of the anode: Ce1-xGdxO2-α / La0,1Sr0,9TiO3-α Electrolyte: 8-YSZ / 10-GDC Cathode : La0,4Sr0,6Co0,2Fe0,8O3-α

Beyond the 3rd Generation SOFC

Source: Alantum Europe GmbH

Beyond the 3rd Generation SOFC

SoA MSCs DLR 2010 2014 2015 Perovskite based anode Thin film electrolyte (1 µm YSZ+ 2 µm CGO) with improved hermiticity (in collaboration with Ceraco GmbH) Manufactured in air (except PVD layer)

Beyond the 3rd Generation SOFC

50 mm x 50 mm with active surface 16 cm² P @ 0.7V and 750°C

• 340 mW /cm²
• Redox cycles tested: 10
• But… with addition of

Nickel!!! AFL: LST-CGO 50:50 modified with 5 wt% Nickel Current collector: NiCrAl + LST 50vol% - Ni 50vol%

• Issue with sulfur

poisoning still expected

Replacement of Nickel still remains challenging!

Solid Oxide Electrolysis

Advantages:

• High temperature (600 - 900°C)
• Fast reaction kinetics
• Low overvoltage
• High efficiency & high current densities
• No noble metals as catalysts
• Fuel versatility: CO2 electrolysis

 Co-electrolysis of H2O/CO2 possible  Syn-gas production  External (or internal) hydrocarbon formation Pel

+ ‐

O2

Air

H2O O2‐

Anode ‐ Oxygen electrode Cathode ‐ Fuel electrode Electrolyte

H2 e‐ e‐

Hi2H2: I-V Curves of a VPS Cell in SOFC and SOEC Mode as a Function of Temperature

0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4

• 1200 -1000 -800
• 600
• 400
• 200

200 400 600 800 1000 1200

current density/mA cm-2 cell voltage/V

• 1500
• 1250
• 1000
• 750
• 500
• 250

250 500 750 power density/mW cm-2 1 - 192h, 800°C 2 - 195h, 750°C 3 - 199h, 850°C

p(i) U(i) gas flow : 40/16//160 ml min-1 cm-2 H2/H2O//air (30% steam)

Hi2H2: Complete Test Run of a VPS Cell in Electrolysis Mode

0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 288 576 864 1152 1440 1728 2016 2304

time/hr

100 200 300 400 500 600 700 800 U/V pH2O/bar T/°C temperature voltage

• 0.3 A cm-² electrolysis

+26 mV /1000h (2,1%/1000hr) +46 mV /1000h (3,9%/1000hr)

H 2 O-ratio

varied electrolysis

voltage/V, pH2O/atm

temperature/°C

Lit: G.Schiller et al., J. Appl. Electrochem., 39, 293-301, 2009

• Improvement of performance and particularly durability (reduced degradation) by
• Development of improved materials (cathodes and anodes) for steam electrolysis
• Study of degradation behaviour and elaboration of mitigation strategies
• Integration of high-temperature heat (solar heat, waste heat from industrial processes)
• Development of operation strategies with use of integrated heat (heat management)
• Development of co-electrolysis process (steam + CO2) for production of synthetic fuels
• Development of cells for co-electrolysis operation
• Development of electrocatalysts for synthesis of liquid and gaseous fuels
• Operation at elevated pressure conditions > 10 bar
• Development of system concepts and demonstration of functionality
• Efficient operation in bi-functional mode

Development work at DLR in the frame of internal project („Future Fuels“) and in POF III phase of Helmholtz Association (HGF) with a transportable research platform („e-Xplore“)

Challenges in SOEC technology

Motivation and Objective of Systematic Degradation Study

Problem: low longevity – degradation A variety of long-term degradation data  about 3-5% / 1000h at 800°C and 80% absolute humidity (AH)  about 35% / a Different studies hard to compare! Systematic parameter study of:  Temperature T  Humidity AH  Current density i Test setup – quadruple cell measurement  Four different current densities simultaneously  Identical temperature, gas supply (and also incidents)

Solid Oxide Fuel Cells: Planar Design

Materials Cathode: (La,Sr)(Fe,Co)O3 Diffusion barrier: CGO – 1-5 µm Electrolyte: 8YSZ – 5-10 µm Anode: Ni/YSZ Anode Substrate: Ni/YSZ Interconnect: ferritic steel

I-V Curves at 750 °C as a Function of Steam Content

(Flow rates: 2 l/min H2/H2O, 3 l/min air)

0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 ‐1,5 ‐1 ‐0,5 0,5 1 1,5 Cell Voltage / V Current density / A*cm‐2

750°C ‐ 7%AH 750°C ‐ 40%AH 750°C ‐ 60%AH 750°C ‐ 80%AH

I-V Curves at 800 °C as a Function of Steam Content

(Flow rates: 2 l/min H2/H2O, 3 l/min air)

0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 ‐1,5 ‐1 ‐0,5 0,5 1 1,5 Cell Voltage / V Current density / A*cm‐2

800°C ‐ 7%AH 800 C ‐ 40%AH 800°C ‐ 60%AH 800°C ‐ 80%AH

Degradation Measurements

Degradation Measurements

Impedance analysis – equivalent circuit High freq. (105 Hz) Low freq. (0.5 Hz)

• L1: High frequency interference (~ 105 Hz)
• R0: Ohmic resistance (~ 105 Hz)
• R1: Fuel electrode process A (~ 104 Hz)
• R2: Fuel electrode process B (~ 103 - 104 Hz)
• R3: Oxygen electrode process (~ 102 Hz)
• R4: Fuel electrode mass transport (~ 101 Hz)
• A. Leonide, V. Sonn, A. Weber, and E. Ivers‐Tiffée

Journal of The Electrochemical Society, 155 (1) B36‐B41 (2008)

L1 R0 R1 R2 R3 R4

R0 R1 R3 R2 R4

Degradation Measurements

Change of each resistive process with time Bias: 0.5 A/cm2

Degradation Measurements

Relative change in resistance / A.U. Time / d

Post mortem Analysis (SEM)

Solely reduced 1000 h @ OCV 1000 h @ 1.5 A/cm2 Ohmic resistance:

• Weakening of YSZ|CGO|LSCF interface
• Visible cracks probably formed during sample preparation along weakened

microstructure

Post mortem Analysis (SEM)

Solely reduced 1000 h @ OCV 1000 h @ 1.5 A/cm2 Fuel electrode:

• Change in microstructure
• Likely due to Ni-coarsening
•  decrease TPB
• Decreased percolation ?

Post mortem Analysis (SEM)

Solely reduced 1000 h @ OCV 1000 h @ 1.5 A/cm2 Oxygen electrode:

• No obvious change in microstructure
• Appearance of brittleness
• Degradation due to change in perovskite stoichiometry close to surface

 Sr-rich surface layer?

• Difficult to measure surface sensitively with high focus XPS

Post mortem Analysis (SEM)

Solely reduced 1000 h @ OCV 1000 h @ 1.5 A/cm2 Diffusion barrier layer:

• No reaction between Sr and Zr (or generally

LSFC with YSZ)

• General Sr-enrichment at CGO|YSZ interface
• Ce depletion at CGO|YSZ interface

DLR Internal Project: SF, TT, VT, AT

• Objective:
• Production of synthetic liquid hydrocarbons

through solarthermal and solarelectrical processes

• Duration: 2015-2017

Future Fuels: TP 3 Solar Fuels

Syn-gas

Solar Fuels

High performance radiator Receiver Latent heat storage SOEC-Stack Heat Steam CO2 Water, CO2 Radiation Syn-Fuels Analysis Modelling Simulation Evaluation Application

Conclusion

• Plasma sprayed metal supported cell technology has been

developed

• Stability of ferritic stainless steel against corrosion remains an issue

for long-term operation.

• Use of perovskite as current collector and anodic electro-catalysts

are still challenging because of the reduced electronic conductivity and the stringent manufacturing parameters required for high performance

• Current and future SOEC activities in cell degradation, co-

electrolysis and synthetic fuel production

Acknowledgment

I‘d like to thank my co-workers Dr. Asif Ansar, Dr. Rémi Costa and PhD student Michael Hörlein for their scientific work as well as all other members of my group for their strong effort. Financial support from Helmholtz Association in the frame of the Helmholtz Energy Alliance „Stationary electrochemical solid state storage and conversion“ is gratefully acknowledged.