High-performance AEM unitized regenerative fuel cell using Pt-pyrochlore as bifunctional oxygen electrocatalyst.

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-PbRuO is synthesized by depositing Pt on PbRuO wherein Pt individually exhibits high ORR while PbRuO shows high OER and moderate ORR activity. Pt-PbRuO exhibits higher OER (η = 0.25 ± 0.01 V) and ORR (η = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO, η = 0.35 ± 0.02 V) and ORR (Pt/C, η = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-PbRuO shows a lower bifunctionality index (η η) of 0.56 V with more symmetric OER-ORR activity profile than both Pt (>1.0 V) and PbRuO (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-PbRuO and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/g at 1.8 V and 56 ± 2 A/g 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, underlying improvement in AEM FG-URFC electrocatalyst design.