Towards selective test protocols for accelerated in situ degradation of PEM electrolysis cell components

Transcription

1 Towards selective test protocols for accelerated in situ degradation of PEM electrolysis cell components 1 st International Conference on Electrolysis - Copenhagen Thomas Lickert, Claudia Schwarz, Patricia Gese, Arne Fallisch, Malte Schlüter, Nicolas Höfling and Tom Smolinka Fraunhofer Institute for Solar Energy Systems ISE Copenhagen/DK,

2 AGENDA Introduction: Fraunhofer ISE and the division Hydrogen Technologies Why do we want to have accelerated stress tests (ASTs) ISE approach on AST development what are the stressors? First results from our projects Measurement equipment (test bench, test cell and materials) Voltage vs time & Vi curves (challenges on IR correction) Benefits of electrochemical impedance spectroscopy (EIS) Conclusion

3 Fraunhofer Institute for Solar Energy Systems ISE At a Glance Photovoltaics Solar Thermal Technology Fraunhofer ISE Director: Staff: ca. 1.2 Budget 216: 81 Mio. Established: 1981 Prof. H-M. Henning and A. Bett Building Energy Technology Hydrogen Technology Energy System Technology

4 Business Area Hydrogen Technologies Research topics Department Thermochemical Processes Thermochemical H 2 generation from hydrocarbons Synthesis of H 2 and CO 2 to liquid energy carriers/fuels (PtL) Catalytic evaporation of liquid hydrocarbons Department Chemical Energy Storage (Dr. Tom Smolinka) Hydrogen generation by PEM water electrolysis Energy storage in H 2 systems and redox flow batteries Power-to-Gas: Interconnection of the power and gas grid Department Fuel Cell Systems Scientific characterisation of fuel cell components Degradation research (load profile, various climates) Customer specific, self-sufficient PEM systems up to 2 kw

5 Electrolyzer hardware why do we want to have ASTs PEM-EL cells are electrochemically quite stable (required today) Degradation occurs slowly Standard materials (thick Nafion PEM) are typically used Investigation of the degredation on standard materials = cost intensive Cheaper and more efficient stacks are required in the future New materials are needed unkown degr. behavior Fast screening of these new materials how do we approch AST development?

6 Development of AST protocols Fraunhofer ISE approach Operating conditions: Stressors to be defined Current density Temperature H 2 O contamination Dynamic operation

7 Development of AST protocols Fraunhofer ISE approach Measurements 4 measurements T = 8 C using different profiles (1st measurement currently in repetition) 2x steady-state (No. 1 & 2) 2x alternating profile (No. 3 & 4) Current density [A/cm²] T = 8 C p = barg 3 A/cm² 5min 15min 5min 2.5 A/cm².3 A/cm² Test 1 Test 2 Test 3 Test A/cm² Time [min]

8 Electrolysis hardware Test bench Semi-automated test bench Process control (non automated) H 2 O circulation on both sides Temperature up to 8 C, p = barg and H 2 O circul. of.3 l/min 1 l/min Electronics (automated): Ivium multi channel potentiostat + 1 A Ivium booster (controlled by Iviumsoft) Impedance spectroscopy up i DC = 4 A/cm² (f = 1 mhz 1 khz)

9 Electrolysis hardware Test cell and materials Test cell: Polymer frame cell with Au coated flow channels (+ Au RE) Pressurized measurements up to 5 barg 23 cm² active area (1 cm² RE) Investigation of anodic and cathodic half cell potentials Cell materials: PTL: Ti powder sinter; 1 mm, 4 % porosity (Mott corp., USA) MEA: commercial; N117 based

10 Development of AST protocols Measurement results: U(t) cell i = 3 A/cm² 2.2 C1 2. C2 C3 C6 C4 C5 cell voltage [V] test bench shut down IR-corrected cell voltage Voltage decay happening in the beginning cell i = 2.5 & 3.5 A/cm² C1 C2 C6 C Block fill up water tank cell i =.3 A/cm² C4 C3 C6 C IR-corrected cell voltage cell voltage [V] C2 336 fill up water tank 2. C1 Block B6 24 measurement time [h] measurement time [h] cell voltage [V] C4 C3 IR corrected voltage 1.6 V(t) mostly nonohmic Information content limited test bench shut down fill up water tank 2.2 cell voltage [V] V(t) profile depends on current density fill up water tank C 1 C4 C3 C6 C5 C7 1.9 cell voltage IR-corrected cell voltage C measurement time [h] Block Block measurement time [h] Block

11 Development of AST protocols Measurement results: Vi curves Vi(t) changes rather small Information content limited without IRcorrection Possible MTL observed cell voltage [V] 2.4 U(i) between blocks of i = 3 A/cm² C 1 C 2 C 3 C 4 C 5 C current density [A/cm²] U(i) between blocks of i =.3 A/cm² cell voltage [V] U(i) between blocks of i = 2.5 & 3.5 A/cm² 3 C 1 C 2 C 3 C 4 C 5 C current density [A/cm²] U(i) between blocks of i =.3 & 3 A/cm² cell voltage [V] C 1 C 2 C 3 C 4 C 5 C 6 cell voltage [V] Block 7 Block current density [A/cm²] current density [A/cm²]

12 Development of AST protocols Benefits of electrochemical impedance spectroscopy (1) IR correction (example: test 4) HFR needed DC signal superimposed by AC f = 1 khz Distinction between ohmic and non-ohmic contributions Ω i η η η cell voltage [V] Block 7 Block Current density Time R current density [A/cm²]

13 Development of AST protocols Benefits of Electrochemical Impedance Spectroscopy (1) Issues with IR correction by fixed f (example: test 4) Low low i (cable behavior) HFR measurement faulty Extrapolation of HFR to low i necessary Extraction of kinetic parameters (i, tafel parameters) faulty 1 khz not necessarily = HFR intercept with Re axis 1.2 differs from test to test HFR [m *cm²] IR-corrected cell voltage [V] current density [A/cm²] (IR corrected) (IR corrected) (IR corrected) (IR corrected) (IR corrected) (IR corrected) Block 7 (IR corrected) Block 8 (IR corrected) (IR corrected) log (current density) [A/cm²] 4

14 Development of AST protocols Benefits of Electrochemical Impedance Spectroscopy (1) Issues with IR correction by fixed f (example: test 4) Low low i (cable behavior) HFR measurement faulty Extrapolation of HFR to low i necessary Extraction of kinetic parameters (i, tafel parameters) faulty 1 khz not neccessarily = HFR intercept with Re-axis differs from test to test HFR [m *cm²] current density [A/cm²]

15 Development of AST protocols Measurement results: EIS Im{Z} [m cm²] -3-2 I DC = 2 A/cm² I AC = 5 % I DC T = 8 C p = 1 bar Q =.3 l/min -1 1st peak ~ 8Hz Re{Z} [m cm²] 1st peak ~ 8Hz Im{Z} [m cm²] I DC = 2 A/cm² I AC = 5 % I DC T = 8 C p = 1 bar Q =.3 l/min Peak ~ 6Hz 2nd Peak ~ 2Hz Re{Z} [m cm²] 3 Im{Z} [m cm²] I DC = 2 A/cm² I AC = 5 % I DC 8 C; 1 bar Peak ~ 8Hz 2 Im{Z} [m ] I DC = 2 A/cm² I AC = 5 % I DC T = 8 C p = 1 bar Q =.3 l/min (2 A/cm²) After (2 A/cm²) After (2A/cm²) After (2A/cm²) After (2A/cm²) After (2A/cm²) After (2A/cm²) After Block 7 (2A/cm²) Im{Z} Re{Z} [m cm²] Re{Z} [m ]

16 Development of AST protocols Benefits of Electrochemical Impedance Spectroscopy (2) Vi curve is limited in its information content Changes in the range of mfew mv (for 34 h degr. Test) Vi-curve might show MTL here Distinction between low and high frequency processes possible with EIS Compare Vi curve and 2 A/cm² (Test 3) cell voltage [V] Im{Z} [m cm²] U(i) between blocks of i = 2.5 & 3.5 A/cm² 3 C 1 C 2 C 3 C 4 C 5 C current density [A/cm²] I DC = 2 A/cm² I AC = 5 % I DC T = 8 C p = 1 bar Q =.3 l/min Peak ~ 6Hz 2nd Peak ~ 2Hz Re{Z} [m cm²] 3

17 Development of AST protocols Benefits of Electrochemical Impedance Spectroscopy (3) Main benefits Distinction between low and fast processes (not possible from Vi curve) MTL (slow process) and kinetics (fast process) can be observed more clearly Possible to extract kinetic parameters without measurements at very low current density (equivalent circuit) By capacitive behavior exchange current density i (using an equivalent circuit) Most beneficial characterisation tool for AST development

18 Development of AST protocols conclusion Status of AST development Conditions must be harsher in terms of current density dynamics Many measurements must be conducted Current density dependency rather small (for 34 h tests) Behavior at shut down need to be investigated On/off cycles to be tested

19 Acknowledgement Projects: FCH-JU: Novel and BMBF: PowerMEE FCH-JU: Novel Novel materials and system designs for low cost, efficient and durable PEM electrolysers Novel: No BMBF (germ. Gov.): PowerMEE Lifetime and performance improvement of polymer electrolyte membrane electrolyzers with high performance membrane electrode assemblies. PowerMEE:

20 Thank you for your Attention! Fotos Fraunhofer Institute for Solar Energy Systems ISE Thomas Lickert, Claudia Schwarz, Patricia Gese, Arne Fallisch, Malte Schlüter, Nicolas Höfling and Tom Smolinka