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Revealing the effect of the cell voltage and external conditions on the characteristics of protonic ceramic fuel cells

The effect of the cell voltage and external conditions on the characteristics of protonic ceramic fuel cells is theoretically elucidated taking into account the non-uniform distribution of charge carriers along and across the oxide membrane with proton and hole conductivity. The interdependence of this distribution and gas phase composition along the cathode and anode gas channels is a fundamental feature of fuel cells based on proton-conducting oxides. To address this issue, a novel computational method is proposed to determine the current densities and effective characteristics of the fuel cells operating on wet hydrogen and oxygen. It is shown that the effective proton conductivity can either increase or decrease with increasing the cell voltage depending on the fuel and oxidant humidity. In contrast, the effective hole conductivity drastically increases with increasing the cell voltage for any realistic gas phase compositions, thereby reducing the proton transport number and faradaic efficiency. It is demonstrated that the fuel cell parameters (partial conductivities, transport numbers, EMF, etc.) can be noticeably different under open circuit and operating conditions. The established relationships between the cell voltage, parameters of the inlet gas phases and output characteristics can be used as a guide to enhance the performance of protonic ceramic fuel cells.