Structural Control of PtNi Catalysts through Precise Synthesis Conditions and Elucidation of Property Determinants by Operando XAS Analysis (Supporting Information)

PtNi alloy catalysts exhibit shape-dependent oxygen reduction reaction (ORR) activity and durability, influenced by synthesis conditions. In this study, a standardized synthesis method was developed by controlling the heating rate during nanowires (NWs) formation, yielding three distinct PtNi NW catalysts. Among these, PtNi-NW-3, featuring a rough surface with abundant high-index facets, demonstrated exceptional oxygen reduction reaction (ORR) activity and durability, achieving a mass activity of 1.06 A mg_Pt⁻¹ and a specific activity of 2.73 mA cm_Pt⁻², outperforming commercial Pt/C catalysts. The superior performance was attributed to reduced oxygen-binding energy and suppressed Pt oxidation, as revealed by operando high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). This work not only standardizes NW synthesis for improved reproducibility but also provides critical insights into the relationship between structural features and catalytic behaviours, paving the way for next-generation electrocatalysts.