Supercritical CO₂‐Directed Dual‐Defect Engineering in PtNi/C Electrocatalysts for Enhanced Hydrogen Evolution

Abstract Optimizing the electronic structure of electrocatalysts by defect engineering is a predominant strategy to enhance hydrogen evolution reaction (HER) performance, which still remains challenging. This study develops an ingenious supercritical carbon dioxide (SC CO₂)‐engineered dual‐defect strategy, synthesizing defect‐rich PtNi alloy nanocatalysts anchored on carbon supports (PtNi/C). The SC CO₂ treatment introduces defects into both the carbon matrix and PtNi nanoparticles, enhancing metal‐support interactions and optimizing electronic structures. Electrochemical evaluations demonstrate exceptional HER performance of the PtNi/C catalysts with an ultralow overpotentials of 17 mV at 10 mA cm⁻² and 119 mV at 100 mA cm⁻² in alkaline environment, outperforming the 20 wt.% Pt/C. DFT calculations elucidate that carbon and Pt vacancies synergistically lower the energy barriers for water dissociation (Volmer step), while Pt vacancies further promote the hydrogen adsorption (Tafel step), accelerating reaction kinetics. The dual‐defect architecture balances the water dissociation and hydrogen desorption, enabling outstanding HER enhancement. This work highlights SC CO₂ as a powerful tool for defect‐engineering and establishes a structure‐activity framework for advancing high‐performance HER systems.