Core@shell structured NiCo@NiCoP nanorods vertically aligned on Ni foam as an efficient bifunctional electrocatalyst for overall water electrolysis

초록

The development of clean and renewable energy carrier is necessary owing to the tremendous devastation of the environment and exhaustion of fossil fuel resources. Due to high energy density and renewability of hydrogen gas, it is regarded as one of the energy alternatives to traditional fossil fuels. Electrochemical water splitting, which consists of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is considered as sustainable technology for high-purity hydrogen gas production. However, the thermodynamically sluggish kinetics of electrochemical reaction at each electrode have hampered the practical applications in the industrial fields. To overcome this issue, ruthenium and platinum based materials are generally used for electrocatalysts for improving OER and HER performances, respectively. However, their high cost, scarcity and insufficient durability have limited their large-scale applications. Recently, transition metal based oxide, sulfide, phosphide have been considered as promising electrocatalyst for water splitting owing to their remarkable advantages such as low-cost, abundance, rich redox properties, and outstanding chemical stability. Among them, transition metal phosphides (TMPs) are emerging as a promising bifunctional electrocatalyst for both of OER and HER. However, their intrinsic low electrical conductivity still remained as a challenge Herein, core-shell structured nickel cobalt alloy-nickel cobalt phosphide (NiCo@NiCoP) nanorod directly grown on nickel foam (NF) was synthesized by hydrothermal, thermal reduction, electrochemical oxidation, and phosphidation process. First, NiCo carbonate hydroxide (NiCoCH) was synthesized by hydrothermal method, and then it was calcined under the H2 flow to form NiCo alloy core. The core-shell structured NiCo@NiCo hydroxide (NiCo@NiCoOH) was obtained by electrochemical oxidation at anodic current density of 300 mA cm-2 for 60 min in 1 M KOH solution.