Ultrathin Two-Dimensional Cobalt-Organic Framework Nanosheets as an Effective Electrocatalyst for Overall Water Splitting Under Alkaline Conditions

•One–pot synthesis of ZIF-67 nanosheets with exposure (211) facet without using any surfactant molecules.•Green synthesis of ZIF-67 nanoparticles without using any organic solvents.•Determination of electronic band structures of both ZIF-67 nanosheets and ZIF-67 nanoparticles experimentally.•Study of OER and HER on the surface ZIF-67 nanosheets with exposure (211) facet.•Study of HER on the surface of ZIF-67 nanoparticles.