Crystalline‐Amorphous Interface‐Triggered Electron Redistribution on Copper(II) Sulfide@Metal (Ni, Co, and Fe) Oxyhydroxides for Ultra‐Efficient Overall Water/Seawater Splitting

CuS@MOOH (M = Ni, Co, and Fe) with crystalline–amorphous interfaces are obtained via a multi-step liquid-phase synthesis strategy. These interfaces facilitate the electron filling of Cu's 3d orbitals, thereby reducing the energy barrier for *H adsorption for HER. Positively-charged MOOH (M³⁺/M⁴⁺) optimizes oxygen-intermediates adsorption to boost OER. An electrolyzer with CuS@CoOOH-6 electrodes exhibits ultra-stable efficiency (96.9%) over 72 h at only 1.52 V.

Abstract

Rearranging the electronic orbitals of metal sites through interface engineering is the breakthrough for achieving high efficiencies in hydrogen/oxygen evolution reactions (HER/OER) on bimetallic catalysts. Here, via a multistep liquid-phase synthesis strategy, the crystalline-amorphous (c-a) interface is built by coating amorphous oxyhydroxide layer on the surface of crystallized copper(II) sulfide (CuS@MOOH, M = iron (Fe), cobalt (Co) and nickel (Ni)) with an internal cavity. For HER, c-a interface facilitates the electron filling of the 3d orbitals of Cu, thereby enhancing the coordination between Cu sites (Cu²⁺/Cu⁺) and *H and reducing the energy barrier for *H adsorption. For OER, c-a interface triggers electronic rearrangement in the 3d orbitals of M sites, prompting electron transition from the t2g orbitals to the eg orbitals to achieve a half-filled state, optimizing the oxygen-intermediates adsorption on M sites (M³⁺/M⁴⁺). Among CuS@MOOH, the as-marked CuS@CoOOH-6 exhibits the best activities with ultra-low overpotentials of 62 mV (HER) and 136 mV (OER). Only 1.52 V is sufficient to power the electrolyzer with CuS@CoOOH-6-based cathode/anode, maintaining a ultra-stable efficiency (96.9 %) over 72 h. Notably, CuS@CoOOH-6 also exhibits impressive activity/durability for natural seawater electrolysis. This study enhances understanding of the properties and electronic structure of the c-a interface for water splitting.