Powering the Remediation of the Nitrogen Cycle: Progress and Perspectives of Electrochemical Nitrate Reduction

Abstract

Nitrate pollution in surface and ground waters has become a potent threat to ecosystem and human health. Electrochemical nitrate reduction is a promising strategy to directly convert excessive nitrates in water into environmentally benign dinitrogen gas or value-added chemicals such as ammonia under mild conditions. Once coupled with renewable electricity, it represents an eco-friendly and energy-efficient route for the recirculation of nitrogen species into the nitrogen cycle and economy. Understanding fundamental mechanisms of nitrate reduction is therefore crucial to design and develop high-performing electrocatalysts. In this review, we first discuss recent discoveries of reaction mechanisms for electrochemical nitrate reduction, focusing on the various pathways to desirable products (nitrogen and ammonia). The direct electron transfer and atom hydrogen transfer pathways are discussed in detail. We then summarize and discuss recent advances in catalytic materials spanning the material space from precious metal, nonprecious metal, and nonmetal catalysts. The existing challenges of electrochemical nitrate reduction are also highlighted. Finally, we provide the perspectives of the opportunities and outlook for the future development in electrochemical nitrate reduction.

Synthesis of core/shell nanocrystals with ordered intermetallic single-atom alloy layers for nitrate electroreduction to ammonia

“…NO 3 RR offers a promising NH 3 production route alternative to N 2 reduction because it utilizes NO 3 pollutants as the nitrogen (N)-source, circumventing the activation of the strong N≡N triple bond 29,30 . When coupled with renewable electricity, NO 3 RR represents an environmentally friendly and energy-e cient route for the recirculation of N species into the N-cycle and economy 31,32 . Our Cu/CuAu ordered SAA catalysts demonstrate high selectivity toward NH 3 from NO 3 RR with a Faradaic e ciency (FE) of 85.5% at -0.5 V vs. the reversible hydrogen electrode (RHE) and an exceedingly high yield rate of 8.47 mol h -1 g -1 at -0.6 V vs. RHE.…”

Emerging Electrochemical Processes to Decarbonize the Chemical Industry

“…Nitrate electroreduction to nitrogen proceeds following the coupling of adsorbed NO and protonated NH 2 species and then NONH 2 decomposition to N 2 . 98 Rational control of the active site for proton adsorption prevents the NH 2 from further protonation to form ammonia. The highest N 2 FE is 60–70%, demonstrated on CuPd bimetallic catalysts.…”

“…Basic conditions favor the production of nitrogen over ammonia. Nitrate electroreduction to nitrogen proceeds following the coupling of adsorbed NO and protonated NH 2 species and then NONH 2 decomposition to N 2 . Rational control of the active site for proton adsorption prevents the NH 2 from further protonation to form ammonia.…”

Research Progress on Cu-Based Catalysts for Electrochemical Nitrate Reduction Reaction to Ammonia

“…By contrast, the NO bond dissociation energy of NO 3 – is 240 kJ mol –1 , which is much smaller than that of NN. In this respect, NO 3 RR circumvents the activation of NN bond and the complex gas–liquid–solid interfacial reactions, providing a more practicable NH 3 production route . Combined with high solubility of NO 3 – , it is preferred to use water as a hydrogen source and nitrate as a nitrogen source to drive NO 3 RR, which represents a recoverable way for NH 3 production and recirculation into the nitrogen cycle. − However, there exists some problems in NO 3 RR, such as slow reaction kinetics and low product selectivity, which greatly restrict its further application.…”