Hierarchical NiSe2 sheet-like nano-architectures as an efficient and stable bifunctional electrocatalyst for overall water splitting: Phase and morphology engineering

Designing an effective, stabilized catalyst is a key challenge to water splitting for both electrocatalytic hydrogen evolution reaction and oxygen evolution reaction. Recently, the transition metal dichalcogenide has attracted numerous attention and described as an effective and robust alternative to noble metal for hydrogen evolution and oxygen evolution. In this study, a novel structure of two-dimensional sheet-like NiSe2 nanoarchitecture integrating on three-dimensional carbon cloth has been fabricated via a facile two-step hydrothermal reaction. In addition, we research the phase structures and morphologies of nickel selenides were further controlled by adjusting the reaction temperature. Under certain conditions, orthorhombic NiSe2 nanosheets can convert into cubic NiSe2 nanosheets in solution directly. The series of nickel selenides have been investigated in detail by means of X-ray diffraction and scanning electron microscopy analyses, respectively. Electrochemical experiments show the as-prepared pure cubic phase NiSe2 nanosheets-carbon cloth achieves −10 mA cm-2 at an overpotential of 147 mV (in 0.5 M H2SO4) and 42 mV (in 1 M KOH) for hydrogen evolution reaction, respectively. NiSe2 has an extremely small overpotential of 1.531 V at 40 mA cm−2 in 1 M KOH solution for oxygen evolution reaction. A voltage of only 1.62 V is required to drive 10 mA cm−2 for the two-electrode alkaline water electrolyzer using the cubic NiSe2 nanosheets on carbon cloth as an anode and cathode. This development provides us a fascinating non-noble-metal bifunctional electrocatalyst toward overall water splitting applications.