Superconfinement Engineering of Hetero‐Nanoparticles in Ultrathin Carbon Nanosheets Enables Highly‐Efficient Water Splitting

Developing highly active and robust bifunctional electrocatalysts for overall water splitting is of great significance for the production of green hydrogen energy. Herein, heterostructured CoP/NiCoP nanoparticles that are encapsulated one-to-one in nano caves of soda-biscuit-like ultrathin carbon nanosheets (CoP/NiCoP/CMS) are prepared, using melamine-formaldehyde sponge (MS) that grew Co/NiCo hydroxides as precursor and phytic acid (PA) as phosphorus source. Especially, the PA-induced blowing behavior during pyrolysis not only transforms the 3D networks of MS into 2D ultrathin carbon nanosheets of CMS, but also achieves the uniform one-to-one superconfinement of hetero-nanoparticles within both the intralayer nanocaves and interlayer spaces of the carbon nanosheets. Benefit from the superconfinement and interface engineering, CoP/NiCoP/CMS shows low overpotentials of 247 and 124 mV at 10 mA cm^-2, as well as good stabilities toward both oxygen and hydrogen evolution reactions, respectively. Moreover, CoP/NiCoP/CMS//CoP/NiCoP/CMS electrolyzer only requires 1.56 V to achieve 10 mA cm^-2. Experimental and theoretical results demonstrate that heterojunction interfaces can well regulate the electronic structure and enhance the intrinsic activity of CoP/NiCoP/CMS, meanwhile, soda-biscuit-like architecture guarantees the compatibility of high activity and good stability. This work proposes a novel and universal strategy for designing advanced electrocatalysts for efficient overall water splitting.