The development of low-cost, stable, and robust non-noble metal catalysts for water oxidation is a pivotal challenge for sustainable hydrogen production through electrocatalytic water splitting. Currently, such catalysts suffer from high overpotential and sluggish kinetics in oxygen evolution reactions (OERs). Herein, we report a "continuous" single-crystal honeycomb-like MXene/NiFeP_x–N-doped carbon (NC) heterostructure, in which ultrasmall NiFeP_x nanoparticles (NPs) encapsulated in the NC are tightly anchored on a layered MXene. Interestingly, this MXene/NiFeP_x–NC delivers outstanding OER catalytic performance, which stems from "continuous" single-crystal characteristics, abundant active sites derived from the ultrasmall NiFeP_x NPs, and the stable honeycomb-like heterostructure with an open structure. The experimental results are rationalized theoretically (by density functional theory (DFT) calculations), which suggests that it is the unique MXene/NiFeP_x–NC heterostructure that promotes the sluggish OER, thereby enabling superior durability and excellent activity with an ultralow overpotential of 240 mV at a current density of 10 mA·cm⁻².

Rational design of electrocatalysts is important for a sustainable oxygen evolution reaction (OER). It is still a huge challenge to engineer active sites in multi-sizes and multi-components simultaneously. Here, a series of CoP nanoparticles (NPs) confined in an SiO₂ matrix (SiO₂/Co_xP) is designed and synthesized as OER electrocatalysts. The phosphorization of the hydrolyzed Co-phyllosilicate promotes the formation of ultrasmall and small Co₂P and CoP. These are firmly confined in the SiO₂ matrix. The coupling of multi-size and multi-component CoP catalysts can regulate reaction kinetics and electron transfer ability, enrich the active sites, and eventually promote the intrinsic OER activity. The SiO₂ matrix provides abundant porous structure and oxygen vacancies, and these facilitate the exposure of active sites and improve conductivity. Because of the synergy and interplay of multi-sized/component Co_xP NPs and the porous SiO₂ matrix, the unique SiO₂/CoP heterostructure exhibits low overpotential (293 ​mV@10 ​mA ​cm^-2), and robust stability (decay 12 ​mV after 5000 CV cycles, 97.4% of initial current after 100 ​h chronoamperometric) for the OER process, exceeding many advanced metal phosphide electrocatalysts. This work provides a novel tactic to design low-cost, simple, and highly efficient OER electrocatalysts.