Earth-Abundant Fe and Ni Dually Doped Co₂P for Superior Oxygen Evolution Reactivity and as a Bifunctional Electrocatalyst toward Renewable Energy-Powered Overall Alkaline Water Splitting

In this paper, we report multimetallic phosphide FeNi-Co₂P as a superior alkaline oxygen evolution reaction (OER) electrocatalyst and bifunctional electrocatalyst for solar energy-powered water splitting. Fe incorporation into Ni-Co₂P leads to (i) the increased amount of high-valence Co³⁺ and Ni³⁺, (ii) the improved intrinsic activity of active centers, and (iii) the increased disorder defects in the in situ-formed oxyhydroxide species during the OER activation process. Synergistic actions among them enable the electrocatalyst’s exceptional OER activity with an overpotential of 225 ± 4 mV at 10 mA/cm², which outperforms the benchmark catalyst RuO₂ and most state-of-the-art OER electrocatalysts. Meanwhile, Fe incorporation decreases the density of states near the Fermi level, which slightly degrades the HER activity compared to the Fe-free electrocatalyst. The FeNi-Co₂P||FeNi-Co₂P and FeNi-Co₂P||Ni-Co₂P electrolyzer cells demonstrate voltages of 1.596 and 1.578 V at 10 mA/cm² for water splitting in 1 M KOH, respectively. A solar energy-powered electrolyzer cell for water splitting has been realized with the as-proposed electrocatalysts. Our results suggest that multimetallic phosphides are promising as low-cost, efficient bifunctional electrocatalysts for overall water splitting in alkaline electrolyte. Additionally, this work provides a real-world application scenario of overall water splitting for hydrogen generation by renewable energy sources.