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

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 degrees C. O-2 was supplied to the cathode and the anode inlet gas mixture had a high p(H2O)/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/cm2). To investigate the effects of possible impurities in the inlet gas stream on the anode degradation, tests were setup 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 similar to 0.10 Omega cm(2) to become negligible (below 0.002 Omega cm(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 minimal/negligible anode degradation compared to tests where fuel cell testing was started immediately after initial characterization of the cells. (C) 2010 Elsevier B.V. All rights reserved.