Solar-driven electrochemical nitrate reduction to ammonia catalyzed by nickel cobalt oxide-palladium heterojunction

Abstract

Ammonia is an important chemical raw feedstock, and electrochemical nitrate reduction to ammonia (NO3RR) in a neutral system offers a sustainable, distributed route for abandoned nitrate handling and ammonia production. However, the sluggish kinetics of H2O dissociation, nitrite accumulation, and catalyst deactivation are an obstacle to the rapid development of NO3RR. Here, an efficiently organized heterostructure nickel cobalt oxide-palladium (NCO-Pd) electrocatalyst has been efficiently fabricated for NO3RR. The porous NCO nanosheet grown on carbon cloth could largely expedite the electrochemical mass transfer process, where the Pd could regulate the electronic structure of catalysis sites and inhibit the undesirable byproducts. Density functional theory results indicate that the heterostructure construction could effectively suppress the hydrogen evolution reaction and reduce the energy barrier of NO3RR. Operando Fourier transform infrared spectroscopy has been implemented to recognize the reaction intermediates and potential pathway. Finally, NCO-Pd shows excellent NO3RR property with an ammonia selectivity of 96.2% and Faradaic efficiency of 91.2 % in 0.1 M Na2SO4 neutral electrolyte. In order to better couple with current chemical technology, the synthesized catalyst has been assembled into a flow electrolyzer. Furthermore, solar cell integration with this flow electrolyzer could stably run for as long as eight hours, displaying a hopeful application prospect for ammonia production by solar-driven.