Hydrogen evolution catalysis at a liquid-liquid interface by WC/NiOx and WC/CoOx

Abstract

Developing Pt-free catalysts for the hydrogen evolution reaction (HER) is important for sustainable hydrogen production. Here, tungsten carbide (WC)-based hybrid catalysts containing nickel oxide (NiOx) or cobalt oxide (CoOx) surface species were synthesized via a colloidal route and evaluated for decamethylferrocene (DMFc)-driven HER at a water/1,2-dichloroethane (DCE) liquid-liquid interface. The synthesis temperature and nominal oxide loading were optimized, and the resulting catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). Their interfacial HER activity was examined by gas chromatography, four-electrode electrochemical polarization, and in situ UV-visible absorption spectroscopy monitoring of DMFc oxidation to DMFc+. A nominal loading of 7.5 wt% gave the best activity for both hybrids. Compared with the catalyst-free reaction, WC/NiOx and WC/CoOx increased the apparent reaction rate by approximately 89- and 70-fold, respectively, whereas pristine WC gave a 33-fold enhancement. The superior activity of WC/NiOx is attributed to the cooperative role of the conductive WC scaffold, oxide-derived catalytic sites, and more accessible NiOx-containing domains. These results demonstrate that WC/NiOx and WC/CoOx are promising earth-abundant hybrid catalysts for interfacial HER and provide design guidelines for Pt-free oxide-carbide systems.