Electronic structure modification of CoP for enhanced acidic hydrogen evolution activity and stability

With the global transition toward sustainable energy, the development of efficient and durable electrocatalysts for the hydrogen evolution reaction (HER) under acidic conditions is essential for practical hydrogen production. Although platinum-based catalysts exhibit outstanding HER activity, their scarcity and high cost severely hinder large-scale deployment in proton exchange membrane (PEM) water electrolysis. As a result, considerable efforts have been devoted to developing earth-abundant alternatives. Among them, cobalt phosphide (CoP) has emerged as one of the most promising non-noble-metal catalysts owing to its favorable electrical conductivity and intrinsic catalytic activity. However, achieving simultaneously high activity and long-term durability in acidic media remains a major challenge. In particular, the insufficient hydrogen adsorption capability of CoP limits reaction kinetics, while the harsh acidic and strongly reductive operating environment can induce excessive reduction and structural degradation of active metal centers, resulting in a pronounced activity-stability trade-off. Therefore, developing effective strategies to regulate the electronic structure of CoP and overcome this fundamental limitation is of great scientific and technological significance. Herein, bismuth (Bi) doping is selectively introduced as an effective strategy to modulate the electronic structure of CoP for enhanced acidic hydrogen evolution. The resulting optimal Bi-CoP/CC catalyst exhibits significantly improved HER activity, delivering an overpotential of 83 mV at 10 mA cm −2 and a small Tafel slope of 33 mV dec −1 , outperforming pristine CoP. Moreover, it exhibits remarkably improved catalytic stability, with only a 4 mV loss in performance after 140 h of continuous operation. Experimental results and further density functional theory (DFT) calculations reveal that Bi doping increases the Co oxidation state while decreasing the P valence, which strengthens Co-P d – p orbital hybridization, optimizes hydrogen adsorption kinetics, and reinforces metal-ligand bonding, thereby accounting for the enhanced activity and stability. Furthermore, a proton exchange membrane water (PEM) electrolyzer assembled with Bi-CoP/CC as the cathode and IrO 2 supported on Pt-Ti felt as the anode exhibits a cell voltage of 1.683 V at 500 mA cm −2 and maintains stable operation for over 140 h at 60 °C. These results demonstrate the practical applicability of the Bi-engineering strategy under industrially relevant operating conditions. More importantly, this work establishes a clear correlation between electronic structure regulation and the simultaneous enhancement of catalytic activity and durability. Our findings provide valuable guidance for overcoming the activity-stability trade-off in acidic CoP HER electrocatalysts and can be extended to other non-precious transition-metal compounds, offering a general strategy for the development of high-performance PEM electrolyzers. Bi engineering reconstructs the electronic structure of CoP by strengthening Co–P d – p hybridization, overcoming the activity–stability trade-off for efficient and durable acidic HER. Download: Download high-res image (292KB) Download: Download full-size image