Modulating Water Splitting Kinetics via Charge Transfer and Interfacial Hydrogen Spillover Effect for Robust Hydrogen Evolution Catalysis in Alkaline Media

Designing and synthesizing advanced electrocatalysts with superior intrinsic activity toward hydrogen evolution reaction (HER) in alkaline media is critical for the hydrogen economy. Herein, a novel Ir@Rhene heterojunction electrocatalyst is synthesized via epitaxially confining ultrasmall and low‐coordinate Ir nanoclusters on the ultrathin Rh metallene accompanying the formation of Ir/IrO(2) Janus nanoparticles. The as‐prepared heterojunctions display outstanding alkaline HER activity, with an overpotential of only 17 mV at 10 mA cm(−2) and an ultralow Tafel slope of 14.7 mV dec(−1). Both structural characterizations and theoretical calculations demonstrate that the Ir@Rhene heterointerfaces induce charge density redistribution, resulting in the increment of the electron density around the O atoms in the IrO(2) site and thus delivering much lower water dissociation energy. In addition, the dual‐site synergetic effects between IrO(2) and Ir/Rh interface trigger and improve the interfacial hydrogen spillover, thereby subtly avoiding the steric blocking of the active site and eventually accelerating the alkaline HER kinetics.