MoRu-integrated multiphase high-entropy electrocatalysts with surface reconstruction and multi-site synergy for enhanced alkaline hydrogen evolution.

FeCoNi-based catalysts for the alkaline hydrogen evolution reaction (HER) are limited by sluggish reaction kinetics and excessively strong adsorption of hydrogen intermediates (H*). In this work, Mo and Ru were incorporated into the FeCoNi matrix via freeze-drying followed by high-temperature calcination, yielding a nitrogen-doped carbon-supported MoRuFeCoNi-based multiphase high-entropy electrocatalyst (MHEE/NC). The as-prepared catalyst features a three-dimensional (3D) porous framework with uniformly distributed metal species, in which spontaneous electron transfer occurs from Fe, Co, and Ni to Mo and Ru. Electrochemical measurements demonstrate that the optimized catalyst exhibits an overpotential of only 29 mV and a Tafel slope of 50.19 mV dec-1 at 10 mA cm-2. No noticeable performance degradation is observed after 100 h of chronopotentiometric testing. Furthermore, when assembled into an overall water-splitting system with MHEE/NC as the cathode and commercial RuO2 as the anode, the device delivers a cell voltage of 1.55 V at 10 mA cm-2. In-situ and ex-situ characterizations reveal dynamic surface reconstruction and multi-site synergistic effects. The oxide phases undergo dynamic surface reconstruction, generating a metal-rich active surface that optimizes interfacial water adsorption. Mo effectively promotes water activation and primarily accelerates the Volmer step, while metallic Ru0 species serve as the dominant active centers for H* adsorption and desorption. Consequently, the HER pathway shifts from a Heyrovsky-controlled mechanism to a mixed Volmer-Heyrovsky mechanism, in which both the Volmer and Heyrovsky steps jointly determine the reaction rate.