Hybrid-metal hydroxyl fluoride nanosheet arrays as a bifunctional electrocatalyst for efficient overall water splitting

Abstract

Electrochemical splitting of water to produce clean hydrogen fuel requires high-performance electrocatalysts. Here, we design and fabricate self-supported hybrid-metal hydroxyl fluoride [Co_xFe_y(OH)F] nanosheet arrays on nickel foam (NF) as an efficient bifunctional electrocatalyst through a facile one-step hydrothermal method. The experimental results demonstrate that the values of x and y in Co_xFe_y(OH)F can not only regulate the ratio value of M²⁺/M³⁺ but also control the morphology, thus providing abundant active sites for water splitting. DFT calculations further disclose that the different ratios of Co and Fe can tune the potential determining step, leading to a reduced energy barrier for electrocatalytic reactions. In particular, Co_0.21Fe_0.28(OH)F has lower charge transfer resistance, abundant active sites, and a larger electrochemical surface area, which can achieve an overpotential of 195 mV for the OER and 73 mV for the HER at a current density of 10 mA cm⁻², respectively, in 1 M KOH. It can be simultaneously used as both a cathode and anode to form a two-electrode cell for overall water splitting, which requires a low voltage of 1.53 V at 10 mA cm⁻². Further study shows that the reconstruction of the structure and morphology during the OER makes this electrocatalyst show better OER catalytic performance.