In-situ redox cycling behaviour of Ni–BaZr0.85Y0.15O3−δ cermet anodes for Protonic Ceramic Fuel Cells

• Impact of redox cycling on polarisation behaviour of Ni-BZY cermet anodes for PCFCs.
• Environmental scanning electron microscopy (ESEM) study of redox cycling in Ni-BZY anodes.
• Fast degradation issues noted with ∼80% performance depletion after a single redox cycle.

The current work investigates the redox behaviour of peak performing Ni–BaZr0.85Y0.15O3−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.

The percentage change in the high frequency polarization resistance, R2, the low frequency polarization resistance, R3, and the ohmic resistance, Rohmic, as a function of redox cycling for 40 vol% Ni-BZY cermet anode measured at 600 °C.Figure optionsDownload as PowerPoint slide