Nanophase-Engineered Bifunctional Catalysts for Oxygen Electrodes in High-Performance Unitized Regenerative Fuel Cells

The development of highly efficient and durable bifunctional oxygen catalysts for high-performance unitized regenerative fuel cells (URFCs) is crucial for their practical application. Herein, the nanophase-separated ultrafine PtCoW alloy and the Ir nanocrystals covalently coupled with carbon were prepared by using a strawberry-like Ir/C hybrid as a structure-oriented template. The resultant Pt-based ternary alloy and the IrO2-covered metallic Ir feature a well-defined nanophase-separated structure with double active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In acidic environments, the bifunctional catalysts exhibit a total overpotential difference of 585 mV, showing much higher activity and stability compared with commercial Pt/C and IrO2. The outstanding bifunctional performance can be attributed to the strong particle-to-particle interaction between PtCoW and the neighboring Ir in their composite. Density functional theory calculations further confirm that the formed IrO2(100)parallel to Ir(111) epitaxial structure can lower the binding energy of reaction intermediates, thus improving OER kinetics. Moreover, the downshifted d-band center of Pt and the compressive strain in PtCoW alloy should be responsible for the remarkably enhanced ORR activity. Therefore, this work may contribute to URFC systems used as safe and efficient energy storage and conversion devices for space flights, vehicles, and stations.