Achieving high selectivity for nitrate electrochemical reduction to ammonia over MOF-supported RuxOy clusters

Abstract

Nitrate (NO₃⁻) electroreduction to ammonia (NH₄⁺) is a sustainable alternative strategy for NH₄⁺ synthesis, and it can be used to solve the water pollution problem by simultaneously turning waste into high-value ammonia. However, the conversion of NO₃⁻ into NH₄⁺ involves multi-electron transfer reactions that could generate a series of nitrogen oxyanions and hydrogen as undesired byproducts. The design of efficient catalysts to selectively transform NO₃⁻ into NH₄⁺ is, therefore, highly needed. In this work, we report Ru_xO_y clusters stabilized on nickel metal–organic frameworks (RuNi-MOFs) and evaluate their electrocatalytic NO₃⁻ reduction performance. The catalyst exhibits nearly 100% NH₄⁺ selectivity with an NH₄⁺–N yield rate of up to 274 μg h⁻¹ mg_cat.⁻¹ at −1.7 V vs. Ag/AgCl, and a maximal NH₄⁺ faradaic efficiency (FE) of ∼73% at −1.2 V vs. Ag/AgCl. The theoretical calculations show that the NO₂⁻ intermediate is easily further reduced to NH₄⁺, and could maintain nearly 100% NH₄⁺ selectivity. This novel strategy will provide a new idea for green ammonia synthesis.