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Free keywords:
Protonic ceramic fuel cells (PCFC);
Redox cycling;
Ni-cermet anodes;
Polarization behaviour;
Environmental scanning electron microscopy (ESEM);
Barium zirconate
Abstract:
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.
