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 Ca _(2) Ru _(2) O _(7) pyrochlore catalysts is affected by the addition of carbonate to the aqueous KOH (1 mol dm ~(?3) ) electrolyte. The parent Ca _(2) Ru _(2) O _(7) catalyst has been previously reported to be selective towards the generation of CO _(3) ~(2?) on the reaction of O _(2) with CO _(2) (in the presence of H _(2) O) 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 _(3) ~(2?) conduction through the AAEM (for potential CO _(2) utilisation). Rotating ring disk electrode (RRDE) voltammetry was used to probe the ORR behaviours of Ca _(2) Ru _(2? x ) Bi _( x ) O _(7? y ) 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 Ca _(2) Ru _(2) O _(7) (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 _(3) ~(2?) in the O _(2) -saturated KOH (1 mol dm ~(?3) ) electrolyte appeared to improve kinetic performance of the Bi-doped pyrochlore catalysts (the effect being greatest with the x = 0.75 catalyst).