Abstract
The performance of fixed-gas unitized regenerative fuel cells (FG-URFCs) are limited by the bifunctional activity of the oxygen electrocatalyst. It is essential to have a good bifunctional oxygen electrocatalyst which can exhibit high activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this regard, Pt-Pb(2)Ru(2)O(7-x) is synthesized by depositing Pt on Pb(2)Ru(2)O(7-x) wherein Pt individually exhibits high ORR while Pb(2)Ru(2)O(7-x) shows high OER and moderate ORR activity. Pt-Pb(2)Ru(2)O(7-x) exhibits higher OER (η(@10mAcm-2) = 0.25 ± 0.01 V) and ORR (η(@-3mAcm-2) = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO(2), η(@10mAcm-2) = 0.35 ± 0.02 V) and ORR (Pt/C, η(@-3mAcm-2) = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-Pb(2)Ru(2)O(7-x) shows a lower bifunctionality index (η(@10mAcm-2, OER)(-) η(@-3mAcm-2, ORR)) of 0.56 V with more symmetric OER-ORR activity profile than both Pt (>1.0 V) and Pb(2)Ru(2)O(7-x) (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-Pb(2)Ru(2)O(7-x) and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/g(cat)(-1) at 1.8 V and 56 ± 2 A/g(cat)(-1) at 0.9 V under electrolyzer mode and fuel-cell mode, respectively. The FG-URFC shows a round-trip efficiency of 75% at 0.1 A/cm(-2), underlying improvement in AEM FG-URFC electrocatalyst design.