Gas Diffusion Electrodes

Transcription

1 Thessaloniki ISE 55 th anual meeting 2004 Gas Diffusion Electrodes Production, Characterisation and Performance Dr. H.-J. Kohnke, J. Helmke Gaskatel GmbH Holländische Str. 195 Kassel / Germany

2 Products H 2 Reference Electrode HydroFlex AFC & AEL EloFlux Gas Diffusion Electrode BiPlex

3 Production Mixing process Hydrophobic binder: PTFE, PP or PE Catalysts nickel, silver, carbon, Platinum, Cobalt, manganese hydrophilic or hydrophobic Variable energy input Additional pore formers Rolling Process Dry process up to 12 m² per hour Continious production up to several 100 meters Variable speed, pressure, thickness and temperature Additional device for adding a current collector Additional device for adding a gas diffusion layer

4 Characterisation Adjust the right temperature! Adjust the right pressure differences! Test various electrolytes! Wait for the equilibrium time! Mechanical & electrical parameters Thickness Weight E-Modul Electrical resistance in plane and through plane contact restistance? Fluid mechanical parameters Bubble-Point, filling pressure Gas Permeability dry and wet Wettability / contact angle Elektrochemical parameters (half cell, membrane contact) Open circuit voltage Tafel -Slope (CV curve) ph value of the electrode

5 Analysis-Database Every electrode recorded in database. Every parameter recorded in database. Fast graphical correlation between all parameters. On-line update with characterisation data by wire. Data base includes: Raw material parameters (catalyst loading, grain size, shape, density ) Production parameters (pressure, temperature,.) Characterisation parameters (mechanical, electrical, electrochemical) Data base enabled: Managment of huge quantities of datas Acquisition of datas by extern instruments Exchange of measured datas to the data base Fast optimisation of GDE s

6 Electrolyte uptake [mg/cm³] Analysis example Graphical correlation by database: Silflon catalyst Octan KOH Electrode density [mg/cm³]

7 Current [A/cm²] Activation limitation Pt and Ag cathodes: fuel cell & chlor alkaline electrolyser 0,00-0,05 Pt/C in H 3 PO 4 80 C Ag in KOH at 20 C Ag in KOH at 60 C -0,10-0,15-0,20-0,25-0,30 0,5 0,6 0,7 0,8 0,9 1 1,1 Potential vs H 2 [V]

8 Current [A/cm²] Gas diffusion limitation Ag cathode in KOH: fuel cell & chlor alkaline electrolyser 0,00-0,05 Oxygen air -0,10-0,15-0,20-0,25-0,30 0,5 0,6 0,7 0,8 0,9 1 1,1 Potential vs H 2 [V]

9 Current [A/cm²] Electrolyte limitation Carbon cathode in KOH: fuel cell & H 2 O 2 production 0,00-0,05-0,10-0,15-0,20-0,25-0,30 0,5 0,6 0,7 0,8 0,9 1,0 1,1 Potential vs H 2 [V] 1 st scan 5 th scan 10 th scan 20 th scan

10 Electrolyte-pressure Limited electrolyte diffusion: Fluid overpressure in pore system Flooding of the gas pore system destruction of the catalyst material

11 Power [W/cm²] Hydrophil/Hydrophob Pt/C in H 3 PO 4 fuel cell: Variation of support 0,40 0,35 0,30 SHB in air SHB in oxygen XC72 in air XC72 in oxygen 0,25 0,20 0,15 0,10 0,05 0, Temperature [ C]

12 Current [A/cm²] Corrosion -0,05 Carbon cathode in KOH: corrosion at current collector 0,00-0,10-0,15-0,20-0,25-0,30 0,5 0,6 0,7 0,8 0,9 1,0 1,1 Potential vs H 2 [V] Silver plated nickel Fresh nickel Old nickel

13 Current [A/cm²] Bi-funtional electrode Co 3 O 4 /C in KOH: Oxygen production and consumption 0,15 0,10 0,05 0,00-0,05 0,5 0,7 0,9 1,1 1,3 1,5 1,7 1,9-0,10-0,15 Potential vs H 2 [V]

14 Resumé Production of any kind of GDE is simple Production of one GDE with balanced limitations is difficult Testing of GDE parameters is simple Finding the right test procedure is difficult Detecting one limiting parameter of a good GDE is simple Finding the limitting parameter in a manifold (i.e. electrolyte) is difficult. GDE will have a bigger market in fuel cells, electrolysers, sensors GDE production has to be less expensive