Co-doped NiP2 as an efficient and robust bifunctional electrocatalyst for overall water splitting in alkaline electrolytes and seawater

Abstract

The development of efficient and durable bifunctional electrocatalysts is crucial for overall water splitting in alkaline electrolytes/seawater, but these electrocatalysts face the dual challenges of unbalanced reaction kinetics and insufficient operational durability. Herein, we report a Co-doped NiP₂ catalyst (Co₈-NiP₂) that achieves remarkable bifunctional performance and durability for overall water splitting. The Co₈-NiP₂ electrolyzer requires low cell voltages of only 1.54 V in 1 M KOH and 1.56 V in alkaline seawater at 10 mA cm⁻² and maintains operation for over 500 h at 300 mA cm⁻² with negligible degradation. Density functional theory (DFT) calculations revealed that optimal Co doping modulates the electronic structure of NiP₂ by downshifting the Ni d-band center to simultaneously enhance the kinetics of both the hydrogen and oxygen evolution reactions. Moreover, the high Cl* adsorption energy on Co₈-NiP₂ ensures excellent durability in seawater environments. This work further establishes the correlation between the seawater concentration and the performance, defining its operational limits in relation to structural stability and performance. This study provides valuable insights into the electronic-structure regulation strategy for designing efficient and stable electrocatalysts suitable for complex real-world applications.