Effect of carbonate anions on Bi-doped Ca2Ru2O7 pyrochlores that are potential cathode catalysts for low temperature carbonate fuel cells

摘要

This ex situ electrochemical study investigates how the oxygen reduction reaction (ORR) on Bi-doped CaRuO pyrochlore catalysts is affected by the addition of carbonate to the aqueous KOH (1 mol dm) electrolyte. The parent CaRuO catalyst has been previously reported to be selective towards the generation of CO on the reaction of O with CO (in the presence of HO) at the cathode of low temperature alkaline polymer electrolyte fuel cells containing alkaline anion-exchange membranes (AAEM): a target is to develop low temperature carbonate fuel cells involving CO conduction through the AAEM (for potential CO utilisation). Rotating ring disk electrode (RRDE) voltammetry was used to probe the ORR behaviours of Ca RuBiO catalysts with x = 0.25, 0.5, 0.75, and 1. The results show that as more Bi was doped into the pyrochlore catalysts, the poorer the on-set potentials compared to the parent CaRuO (which itself yielded a poorer on-set potential to a benchmark Pt black catalyst). Higher levels of Bi-doping tended to reduce n values with higher levels of peroxide generated: all of the pyrochlore catalysts tested gave higher peroxide yields compared to the Pt black benchmark. However, the presence of CO in the O -saturated KOH (1 mol dm) electrolyte appeared to improve kinetic performance of the Bi-doped pyrochlore catalysts (the effect being greatest with the x = 0.75 catalyst).