Sintering aid (ZnO) effect on proton transport in BaCe0.35Zr0.5Y0.15O3-δ and electrode phenomena studied by distribution function of relaxation times

In this work, we have employed an evolutionary programming technique to analyse the impedance spectroscopy (IS) of a ceramic proton conductor BaCe0.35Zr0.5Y0.15O3-delta(BCZY) to study its proton transport properties as well as the electrode reactions kinetics at the Pt vertical bar BCZY interface. The distribution functions of relaxation times (DFRT) obtained from the impedance analysis were used to evaluate the physical parameters such as relaxation time constant, resistance, reactance/capacitance, conductivities, activation energies, grain-boundary space charge potential Phi(0, T), and electrode polarization resistance. The effect of ZnO sintering aid (2 wt%) on charge-transfer processes at bulk, grain boundaries and Pt vertical bar BCZY interface were thoroughly studied. Phi(0, T) is increased and grain-boundary conductivity (sigma(gb)) is decreased by an order of magnitude due to the presence of Zn at the grain boundaries, whereas bulk properties appear to be unchanged. Variation in sgb with temperature is explained by correlating the grain-boundary capacitance (sigma(gb)), relaxation time (tau(gb)), space charge effect, and the defect associations (eg, Y-OH). The anodic functions, for example, hydrogen oxidation kinetics at the electrode (Pt) surface and Pt-BCZY interface, are explained through the symmetrical cell study and the behavior of relaxation time constants (tau) with temperature.