Rare‐Earth Oxychlorides as Promoters of Ruthenium Toward High‐Performance Hydrogen Evolution Electrocatalysts for Alkaline Electrolyzers

Abstract Developing efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline environments is vital for hydrogen production, owing to the extra water dissociation and hydroxyl desorption steps. Here, rare‐earth oxychlorides (REOCl) are proposed as innovative promoters for ruthenium as HER electrocatalyst in alkali. The lamellar structure of REOCl with weakly bond [Cl] layers can facilitate the formation of an internal electric field that enhances interphase charge transfer. Taking ruthenium/ neodymium oxychloride (Ru/NdOCl) composites as a case study, sub ≈4 nm Ru nanoparticles are successfully embedded into NdOCl crystals through a rapid self‐exothermic process, and the highly‐coupled Ru−Cl/O−Nd interfaces are observed as metallic Ru particles with the edge of the NdOCl lamellar layers, where the [Nd2O2] and [Cl] layers act as the negative and positive charge transfer channels, respectively. The enhanced charge transfer between REOCl and Ru makes the highly‐coupled Ru/REOCl catalysts show better electrocatalytic activity than both the benchmark Pt and Ru catalysts in alkaline electrolyte. This work will encourage more novel promoters for electrocatalysis and other emerging technologies.