Unveiling enhanced oxygen reduction activity in PtCo bimetallic solid solutions through controlled crystal strain

The development of low-cost, highly active platinum (Pt)-based electrocatalysts for oxygen reduction reaction (ORR) is crucial for widespread applications of fuel cells. An effective approach lies in alloying Pt with non-noble transition metals to modulate the physicochemical state of the Pt surface. However, fundamental challenges remain in understanding the structure-performance relationship due to the complexity of composition, crystal type, and surface structure during the alloying process. In this study, we synthesized a series of PtCo bimetallic solid solutions with varying ratios using a liquid-phase synthesis method. By exploiting the characteristics of solid solutions, the resulting PtCo bimetallic alloy maintains the face-centered cubic crystal structure of pure platinum, minimizing the complexities introduced during alloying and facilitating mechanism analysis. Furthermore, under controlled alloy composition and crystal structure, we investigated the dependence of the electrocatalytic activity for the oxygen reduction reaction on the surface strain of the platinum catalyst. The S-PtCo-SNPs cathode designed accordingly endows both proton exchange membrane fuel cell (PEMFC) (2.08 W cm⁻² at 4 A cm⁻²) and Zn-air battery (ZAB) (143.1 mW cm⁻² at 214.5 mA cm⁻²) with outstanding performance.