Bifunctional Electrode Design Targeting Co-Enhanced Kinetics and Mass Transport for Hydrogen and Water Oxidation Reactions

Abstract

Bifunctional catalysts based on noble metals have achieved practical-level performances in round-trip energy conversion systems. However, the required amount of noble metals should be substantially reduced via a new catalyst design that can pursue the synergy of the constituent materials' intrinsic properties and architectural maneuver over reactant/product transport. In this study, cross-stacked Ir and Pt nanowires resolved the bottlenecks of two reactions essential for the hydrogen-based energy system: i) hydrogen spillover phenomenon between Pt and Ir nanowires to expedite the hydrogen oxidation reaction and ii) spacing Ir nanowires sufficiently to enhance the mass transport of the oxygen evolution reaction. Simultaneously accommodating the different strategies within the single catalyst layer, a new horizon to design a bifunctional electrode is proposed with the high performance of polymer electrolyte membrane unitized regenerative fuel cells: 47% of round-trip efficiency at 0.5 A cm(-2) with total noble metal loading < 0.3 mg cm(-2).