In-situ growth of VS4 nanorods on Ni-Fe sulfides nanoplate array towards achieving a highly efficient and bifunctional electrocatalyst for total water splitting

In order to improve the catalytic activity of fully hydrolytic electrocatalysts, it becomes extremely important to design water electrolytic catalytic materials with electrocatalytic defects, high charge transfer rates and large catalytic specific surface areas. Herein, we synthesize a sea urchin-like three-dimensional (3D) nanosheet array of NiFeVSx@NF via in-situ growth of VS4 nanorods on Ni-Fe Layered double hydroxides nanoplate array and utilize it as a bifunctional catalyst for monolithic hydrolysis by a two-step hydrothermal processes and one-step high-temperature sulfidation treatment. By doping with vanadium, V elements with different valence states are generated during the catalytic process, which can co-operate with the high valence Fe and Ni elements to further enrich the active sites for oxygen evolution reaction (OER). Thus, the NiFeVSx@NF shows excellent catalytic activity with overpotentials of 259 mV for OER in KOH (1.0 M) solution at current densities of 10 mA cm−2. Meanwhile, the strong coupling synergy between the three metal sulfides NiS2, Fe9S11 and VS4 and the synergistic effect with the conductive substrate nickel foam (NF) results in an abundance of oxygen vacancies which enhance the performance of the HER. As a result, the NiFeVSx@NF shows excellent catalytic activity with overpotentials of 127 mV for HER and exhibits a high long-term stability. In addition, the unique self-supporting sea urchin structure not only provides a large catalytic surface area but also facilitates the penetration of the electrolyte during the catalytic reaction, so that a low cell potential of only 1.60 V is required for the NiFeVSx@NF||NiFeVSx@NF electrolyzer to obtain a current density of 10 mA cm−2. Therefore, this study provides a new idea for the preparation of self-supporting structural composites.