Oriented Transformation of Co-LDH into 2D/3D ZIF-67 to Achieve Co-N-C Hybrids for Efficient Overall Water Splitting

Construction of well-defined metal-organic framework precursor is vital to derive highly efficient transition metal-carbon-based electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting. Herein, a novel strategy involving an in situ transformation of ultrathin cobalt layered double hydroxide into 2D cobalt zeolitic imidazolate framework (ZIF-67) nanosheets grafted with 3D ZIF-67 polyhedra supported on the surface of carbon cloth (2D/3D ZIF-67@CC) precursor is proposed. After a low-temperature pyrolysis, this precursor can be further converted into hybrid composites composed of ultrafine cobalt nanoparticles embedded within 2D N-doped carbon nanosheets and 3D N-doped hollow carbon polyhedra (Co@N-CS/N-HCP@CC). Experimental and density functional theory calculations results indicate that such composites have the advantages of a large number of accessible active sites, accelerated charge/mass transfer ability, the synergistic effect of components as well as an optimal water adsorption energy change. As a result, the obtained Co@N-CS/N-HCP@CC catalyst requires overpotentials of only 66 and 248 mV to reach a current density of 10 mA cm(-2) for HER and OER in 1.0 m KOH, respectively. Remarkably, it enables an alkali-electrolyzer with a current density of 10 mA cm(-2) at a low cell voltage of 1.545 V, superior to that of the IrO2@CC||Pt/C@CC couple (1.592 V).