Ni/YSZ electrode degradation studied by impedance spectroscopy. Effects of gas cleaning and current density

摘要

Anode supported (Ni/YSZ-YSZ-LSM/YSZ) solid oxide fuel cells were tested and the degradation over time was monitored and analyzed by impedance spectroscopy. Test conditions were chosen to focus on the anode degradation and all tests were operated at 750 °C. O_2 was supplied to the cathode and the anode inlet gas mixture had a high p(H_2O)/p(H_2) ratio of 0.4/0.6. Commercially available gasses were applied. Cells were tested over a few hundred hours applying varying current densities (OCV, 0.75 A/cm~2 and 1 A/cm~2). To investigate the effects of possible impurities in the inlet gas stream on the anode degradation, tests were set-up both with and without gas cleaning. Gas cleaning was done by passing the H_2 over porous nickel at room temperature. It was found that cleaning of the inlet H_2 gas more than halved the anode degradation under current load. For tests at OCV the increase in the Ni-YSZ charge transfer reaction resistance changed from ～ 0.10 Ωcm~2 to become negligible (below 0.002 Ωcm~2) upon applying H_2 gas cleaning over the couple of hundred of hours of testing. Both for tests with and without H_2 gas cleaning applied, it was surprisingly found that operating the solid oxide fuel cells at OCV prior to fuel cell testing provided fuel cell tests with minimalegligible anode degradation compared to tests where fuel cell testing was started immediately after initial characterization of the cells.