Self-assembly of bimetallic polyoxometalates and dicyandiamide to form Co/WC@NC for efficient electrochemical hydrogen generation

Abstract

The design of economical and efficient electrocatalysts to replace precious platinum-based catalysts for hydrogen evolution reaction (HER) has always been an essential study direction of clean energy technology. In this work, an HER electrocatalyst (Co/WC@NC) was synthesized by pre-self assembly of polyoxometalate (Co₄P₄W₃₀), cobalt ions and dicyandiamide (DCA) via a one-step calcination process. Co/WC@NC consists of cobalt and tungsten carbide nanoparticles, which are wrapped with nitrogen-doped carbon layers. Co/WC@NC shows good HER capability with relatively low overpotentials of 142 and 158 mV with small Tafel slopes of 93 and 95 mV dec⁻¹, respectively, at a current density of 10 mA cm⁻² in acidic and alkaline solutions. Moreover, Co/WC@NC provides satisfactory durability for 24 h in both 0.5 M H₂SO₄ and 1.0 M KOH. Founded on the above results, good catalytic property of Co/WC@NC can be primarily associated with the synergy between Co and WC nanoparticles, N element doping to make adjustments for the electronic structure of carbon layers, thus speeding up the electron transfer process, as well as graphite-coated carbon layers protecting nanoparticles from oxidation, and improving stability. This study confirms the universal idea to form transition carbides for an efficient electrocatalytic production of hydrogen.