Ni/YSZ anode – Effect of pre-treatments on cell degradation and microstructures

Anode supported (Ni/YSZ–YSZ–LSM/YSZ) solid oxide fuel cells were tested and the degradation over hundreds of hours was monitored and analyzed by impedance spectroscopy. Test conditions were chosen to focus on the Ni/YSZ anode degradation and all tests were operated at 750 °C, a current density of 0.75 A cm−2. Oxygen was supplied to the cathode and the anode inlet gas mixture had a high p(H2O)/p(H2) ratio of 0.4/0.6. Commercially available gasses were applied. The effect of different types of pre-treatments on the Ni/YSZ electrode degradation during subsequent fuel cell testing was investigated. Pre-treatments included operating at OCV (4% and 40% H2O in H2) prior to fuel cell testing, cleaning of the inlet H2 gas at 700 °C and processing the anode half cell via multilayer tape casting. Analyses of impedance spectra showed that the increase in the charge transfer reaction resistance in the Ni/YSZ (RNi,TPB) was decreased to ¼ or less for the pre-treated and fuel cell tested cells when compared with a non-pre-treated reference tested cell; all operated at the same fuel cell test conditions. Scanning electron microscopy and image analyses for the non-pre-treated reference tested cell and selected pre-treated cells showed significant differences in the area fractions of percolating nickel both in the active anode and support layer.

Research highlights▶ Decreased Ni/YSZ anode degradation upon OCV pre-treatment. ▶ Decreased Ni/YSZ anode degradation upon high temperature gas cleaning. ▶ Decreased Ni/YSZ anode degradation upon applying multilayer tape casting production. ▶ Preservation of Ni percolation network by pre-treatment of Ni/YSZ anode.