Topochemical Domain Engineering to Construct 2D Mosaic Heterostructure with Internal Electric Field for High-Performance Overall Water Splitting

Rational design of bifunctional two-dimensional (2D) heterostructures with excellent activity and durability remains a great challenge for electrocatalytic water splitting. Herein, we propose a topochemical domain engineering to realize 2D mosaic heterostructures with ultrafine phosphide nanodomains highly dispersed on the surface of Ru doped CoMoO₄ nanosheets (denoted as Ru-CMOP), which are vertically interconnected on the conductive skeleton assembling a 3D array structure. The as-prepared Ru-CMOP electrocatalyst exhibits excellent activity and long-term stability with the overpotentials of 114 and 286 mV at 100 mA cm⁻² for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH solution, respectively, outperforming most reported metal phosphide-based bifunctional heterostructures. Moreover, an assembled electrolyzer using the Ru-CMOP as anode and cathode simultaneously delivers cell voltages of 1.697 V and 1.828 V to achieve 100 mA cm⁻² and 500 mA cm⁻², respectively, with outstanding durability at 250 mA cm⁻² for 120 h. Density functional theory calculations and experimental results indicate that the strongly coupled heterointerfaces with built-in electric field can facilitate electron transfer while multi-porous nanosheet arrays contribute to active sites exposure and mass/gas transport, thereby synergistically accelerating the reaction kinetics. Additionally, combining with a commercial silicon photovoltaic solar cell, the electrolyzer can be efficiently and robustly established, demonstrating the great potential for practical photovoltaic-electrolysis applications.