Macroporous Array Induced Multiscale Modulation at the Surface/Interface of Co(OH)2/NiMo Self‐Supporting Electrode for Effective Overall Water Splitting

Abstract Outstanding electrocatalysts for high‐efficiency water splitting demand not only the high intrinsic activity determined by the electronic structure but also a favorable mass transfer (electrolyte diffusion and bubble desorption) and strong structural stability. Here, a 3D core–shell electrocatalyst consisting of Co(OH) 2 cavity array‐encapsulated NiMo alloy on the flexible carbon cloth substrate (Co(OH) 2 /NiMo CA@CC) is proposed. Density functional theory reveals that coupling NiMo with Co(OH) 2 can better optimize the water adsorption/dissociation and hydrogen adsorption energies in hydrogen evolution reaction, and also accelerate the kinetics of oxygen evolution reaction. Based on this, the open porous structure of the outer Co(OH) 2 cavity array further promotes the diffusion of the electrolyte into the heterogeneous interface between NiMo and Co(OH) 2 , significantly shortening the electron transfer pathways and exposing multiple active sites. In addition, the macroporous array structure accelerates the bubble evolution and desorption process, thus ensuring a rapid mass transfer. When served as bifunctional electrocatalysts toward alkaline overall water splitting, Co(OH) 2 /NiMo CA@CC delivers a current density of 10 mA cm −2 at a low cell voltage of 1.52 V. Results support the multiscale optimization of the surface/interface engineering induced by the macroporous array.