Metal–Organic Framework–Derived Mesoporous B‐Doped CoO/Co@N‐Doped Carbon Hybrid 3D Heterostructured Interfaces with Modulated Cobalt Oxidation States for Alkaline Water Splitting

Abstract Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen‐doped carbon (NC) matrix, can mitigate the low‐conductivity and high‐agglomeration of metal‐nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)‐doped cobalt‐oxide/cobalt‐metal nanohybrids embedded in NC and grown on a Ni foam substrate (B‐CoO/Co@NC/NF) is developed as a binder‐free bifunctional electrocatalyst for alkaline water‐splitting via a post‐synthetic modification of the metal–organic framework and subsequent annealing in different Ar/H 2 gas ratios. B‐CoO/Co@NC/NF prepared using 10% H 2 gas (B‐CoO/Co@NC/NF [10% H 2 ]) shows the lowest HER overpotential (196 mV) and B‐CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307 mV at 10 mA cm −2 with excellent long‐term durability for 100 h. The best anode and cathode electrocatalyst‐based electrolyzer (B‐CoO/Co@NC/NF (Ar)(+)//B‐CoO/Co@NC/NF (10% H 2 )(−)) generates a current density of 10 mA cm −2 with only 1.62 V with long‐term stability. Further, density functional theory investigations demonstrate the effect of B‐doping on electronic structure and reaction mechanism of the electrocatalysts for optimal interaction with reaction intermediates for efficient alkaline water‐splitting which corroborates the experimental results.