Catalyzing overall water splitting at an ultralow cell voltage of 1.42 V via coupled Co-doped NiO nanosheets with carbon

A hybrid structure constructed by Co-doped NiO and carbon on nickel foams could be employed as bifunctional electrocatalyst for both anode and cathode towards overall water splitting, enabling an alkaline electrolyzer with a current density of 10 mA cm−2 at an ultralow cell voltage of 1.42 V. [Display omitted] •An efficient bifunctional electrocatalyst of Ni0.82Co0.18O@C/NF was developed.•The catalyst towards overall water splliting could achieve 10 mA cm–2 at an ultralow voltage of 1.42 V.•The peformace can be attributed to the synergism of geometric engineering and electronic modulation. The development of nonprecious, highly active and robust bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions via water splitting is of primary significance, but still remains challenging. Herein, we develop a three-dimension (3D) heterostructured catalyst (Ni0.82Co0.18O@C/NF) by coupling of ultrathin Co-doped NiO (Ni0.82Co0.18O) nanosheets and carbon on nickel foam (NF) with synergism of geometric engineering and electronic modulation. Benefiting from the unique 3D configuration, highly exposed active sites and the synergistic effect of the active Ni0.82Co0.18O and the carbon, the catalyst exhibits exceptional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance with low overpotentials and Tafel slopes and excellent stability in alkaline media. Specifically, the Ni0.82Co0.18O@C/NF employed as catalyst for both anode and cathode enables an alkaline electrolyzer to achieve a current density of 10 mA cm−2 by a cell voltage of only 1.42 V, which is not only much lower than that of the integrated performance of the commercial noble Pt/C and IrO2/C catalyst couple (∼1.61 V), but also superior to most reported results to date. Our finding may provide a new opportunity to design advanced bifunctional catalysts toward practical overall water splitting.