Material strategies in the electrochemical nitrate reduction reaction to ammonia production

Abstract

Artificial nitrogen fixation causes excess nitrate (NO₃⁻) production due to an unbalanced nitrogen cycle. Recently, the electrocatalytic nitrate reduction reaction (NO₃RR) used to produce value-added chemicals such as ammonia (NH₃) has attracted attention as a promising technology for energy and environmental reasons; however, the design of the catalytic material used in this reaction is yet to be fully understood for the production of NH₃. Herein, the fundamentals of the NO₃RR are introduced to understand the thermodynamics and kinetics of the NO₃RR using heterogeneous electrocatalysts, and the analytical methods are explained to provide a precise evaluation of the NO₃RR performance. The recent strategies used to design efficient and selective electrocatalysts have been reviewed, including the effects of facets, heterogeneous interfaces, alloying, strain, oxygen vacancies in metal oxides, single atom catalysts, and bio-inspired structures. The critical factors determining the NO₃RR activity and selectivity are highlighted in terms of the nitrate adsorption, intermediate nitrite conversion, chemical environment, and intermediate species adsorption upon modifying the electronic and chemical states of the catalyst surface. The NO₃RR is potentially applied for the electrochemical synthesis of nitrogen-containing chemicals.