CoWO4 nanoparticles with dual active sites for highly efficient ammonia synthesis†

The electrochemical reduction reaction of NO₃⁻ (NO₃RR) represents a promising green technology for ammonia (NH₃) synthesis. Among various electrocatalysts, Co-based materials have demonstrated considerable potential for the NO₃RR. However, the NH₃ production efficiency of Co-based materials is still limited due to challenges in the competitive hydrogen evolution reaction (HER) and hydrogenating oxynitride intermediates (*NO_x). In this study, tungsten (W) and cobalt (Co) elements are co-incorporated to form cobalt tungstate (CoWO₄) nanoparticles with dual active sites of Co²⁺ and W⁶⁺, which are applied to optimize the hydrogenation of NO_x and decrease the HER, thereby achieving a highly efficient NO₃RR to NH₃. Theoretical calculations indicate that the Co sites in CoWO₄ facilitate the adsorption and hydrogenation of *NO_x intermediates, while W sites suppress the competitive HER. These dual active sites work synergistically to enhance NH₃ production from the NO₃RR. Inspired by these calculations, CoWO₄ nanoparticles are synthesized using a simple ion precipitation method, with sizes ranging from 10 to 30 nm. Electrochemical performance tests demonstrate that CoWO₄ nanoparticles exhibit a high faradaic efficiency of 97.8 ± 1.5% and an NH₃ yield of 13.2 mg h⁻¹ cm⁻². In situ Fourier transform infrared spectroscopy characterizes the enhanced adsorption and hydrogenation behaviors of *NO_x as well as a minimized HER on CoWO₄, which contributes to the high efficiency and selectivity to NH₃. This work introduces CoWO₄ nanoparticles as an electrocatalytic material with dual active sites, contributing to the design of electrocatalysts for NH₃ synthesis.