Cobalt–Copper Nanoparticles on Three-Dimensional Substrate for Efficient Ammonia Synthesis via Electrocatalytic Nitrate Reduction

Abstract

Ammonia (NH3) is a valuable chemical for fertilizer production and for use as an effective hydrogen carrier. Electrocatalytic nitrate reduction has recently received great attention as an alternative for NH3 synthesis due to its kinetically favorable reaction. However, this promising strategy suffers from low Faradaic efficiency (FE) at large current density (>100 mA cm–2) and low nitrate concentrations because of the competing hydrogen evolution reaction. Herein, we report a catalyst consisting of earth-abundant cobalt–copper (Co1–xCux) nanoparticles supported on a three-dimensional substrate for efficient and selective NH3 synthesis via electrocatalytic nitrate reduction. Typically, the optimized Co0.5Cu0.5 catalyst performs at a high NH3 Faradaic efficiency (FE) of over 95% at −0.03 V with NH3 partial current density of ∼176 mA cm–2 at 50 mM nitrate, which is 7.3- and 1.7-fold higher than that of pure Co and Cu counterparts. Importantly, replacing Co with Cu enables the tuning of onset potential on Co catalyst maintaining high selectivity toward NH3. A stability test over 12 cycles confirmed the long-term operation of this catalyst. This work offers a facile strategy for tuning the catalyst’s elemental composition to attain a desired electrocatalytic activity.