In-situ redox cycling behaviour of NieBaZr_0.85Y_0.15O3¡δ cermet anodes for Protonic Ceramic Fuel Cells

The current work investigates the redox behaviour of peak performing NieBaZr_0.85Y_0.15O3¡δ (Ni-BZY) cermet anodes for protonic ceramic fuel cells (PCFCs) by electrochemical impedance measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Peak performing PCFC cermet anodes are documented to require much lower porosity levels than those needed in oxide-ion conducting counterparts. The polarisation behaviour of these optimised PCFC anodes is shown to be drastically impaired by redox cycling, with depletions in performance that correspond to around 80% of the original resistance values noted after the first redox cycle. The ohmic resistance (Rohmic) is also shown to be increased due to delamination at the electrode/electrolyte interface, as confirmed by postmortem microstructural analysis. In-situ measurements by environmental scanning electron microscopy (ESEM) reveal that degradation proceeds due to volume expansion of the nickel phase during the re-oxidation stage of redox cycling. The present study reveals degradation to be very fast for peak performing Ni-BZY cermets of low porosity. Hence, methods to improve redox stability can be considered to be essential before such anodes can be implemented in practical devices.