Three-dimensional flower-like Ni–S/Co-MOF grown on Ni foam as a bifunctional electrocatalyst for efficient overall water splitting

Poor conductivity of the metal-organic frameworks (MOFs) limits their applications in overall water splitting. Surface sulfur (S) doping transition metal hydroxides would effectively improve the conductivity and adjust the electronic structure to generate additional electroactive sites. Herein, we fabricated a Ni-S/Co-MOF/NF catalyst by electroplating a Ni-S film on the 3D flower-like Co-MOF. Because the 3D flower-like structures are covered in Ni foam, the high exposure of active sites and good conductivity are obtained. Moreover, the synergistic effect between Ni-S and Co-MOF contributes to the redistribution of electrons in the catalyst, which can then optimize the catalytic performance of the material. The obtained 3D flower-like Ni-S/Co-MOF/NF demonstrates excellent activity toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in 1 M KOH, which only requires a low overpotential of 248 mV@10 mA cm^-2 for the OER and 127 mV@10 mA cm^-2 for the HER, respectively. At a current density of 10 mA cm^-2, the Ni-S/Co-MOF/NF‖Ni-S/Co-MOF/NF requires a low cell voltage of 1.59 V to split overall water splitting.