Electrochemical phenomena in MEA electrodes

The numerous measurements of I-V-characteristics and impedance spectra on symmetrical cells and MEAs with different types of electrodes have been carried out at different temperatures using various gas compositions to characterize the performance of the electrolyte supported cells (ESC). The tests have been performed in ceramic housing in absence of any contamination sources resulting from experimental setup. The cathodic and anodic reaction steps have been investigated as a function of gas composition. It was found that the cathode polarization can be described by three processes: (i) oxygen adsorption on the cathode surface, (ii) oxygen diffusion to the three phase boundary followed by electrochemical reaction and (iii) oxygen transfer into electrolyte. In the MEA impedance spectra mainly the processes (i) and (ii) were observed. For B-doped LSM based cathodes the impact of oxygen adsorption on the total polarization resistance was reduced. In the anode the number of observed processes depends strongly on the art of the used anode and on the fuel humidification level. The Ni/YSZ anodes have mainly two arcs in impedance spectra connected with (i) hydrogen adsorption on Ni surface and (ii) diffusion of adsorbed species and formation of water. In the ceria based anodes the additional electrochemical reaction on ceria has been seen. With both anodes the ASR below 0.2 Omega cm² at 850°C for 10Sc1CeSZ based ESCs is achieved.