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

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 RuxOy 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 mu g h(-1) mg(cat.)(-1) at -1.7 V vs. Ag/AgCl, and a maximal NH4+ faradaic efficiency (FE) of similar to 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.

Automated summary

Nitrate electroreduction to ammonia is a sustainable alternative strategy for ammonia synthesis and water pollution control. The design of efficient catalysts for selective conversion of nitrate to ammonia is highly needed. In this work, RuxOy clusters stabilized on nickel metal-organic frameworks are reported as catalysts with nearly 100% ammonia selectivity and high yield rates. The theoretical calculations show the potential of this novel strategy for green ammonia synthesis.