Unveiling the Optimal Interfacial Synergy of Plasma‐Modulated Trimetallic Mn‐Ni‐Co Phosphides: Tailoring Deposition Ratio for Complementary Water Splitting

Designing highly active, durable, and nonprecious metal‐based bifunctional electrocatalysts for overall water electrolysis is of urgent scientific importance to realize the sustainable hydrogen production, which remains a grand challenge. Herein, an innovative approach is demonstrated to synthesize flower‐like 3D homogenous trimetallic Mn, Ni, Co phosphide catalysts directly on nickel foam via electrodeposition followed by plasma phosphidation. The electrochemical activity of the catalysts with varying Mn:Ni:Co ratios is assessed to identify the optimal composition, demonstrating that the equimolar trimetallic phosphide yields an outstanding HER catalytic performance with a current density of 10 mA cm −2 at an ultra‐low overpotential of ~14 mV, outperforming the best reported electrocatalysts. This is asserted by the DFT calculations, revealing strong interaction of the metals and the P atom, resulting in enhanced water activation and optimized G H * values for the HER process. Moreover, this optimal composition appreciably catalyzes the OER by exposing more intrinsic active species in‐situ formed on the catalyst surface during the OER. Therefore, the Mn 1 ‐Ni 1 ‐Co 1 ‐P‐(O)/NF catalyst exhibits a decreased overpotential of ~289 mV at 10 mA cm −2 . More importantly, the electrocatalyst sustains perfect durability up to 48 h at a current density of 10 mA cm −2 and continued 5000 cycling stability for both HER and OER. Meanwhile, the assembled MNC‐P/NF||MNC‐P/NF full water electrolyzer system attains an extremely low cell voltage of 1.48 V at 10 mA cm −2 . Significantly, the robust stability of the overall system results in a remarkable current retention of ~96% after a continuous 50‐h run. Therefore, this study provides a facile design and a scalable construction of superb bifunctional ternary MNC‐phosphide electrocatalysts for efficient electrochemical energy production systems.