Electrocatalytic Nitrogen Oxidation for Nitric Acid Synthesis: Progress in Catalyst Design and Reaction Systems

Nitric acid is an indispensable chemical feedstock for industrial applications and the production of artificial fertilizers. Conventional production of this vital chemical is highly energy intensive and emits substantial greenhouse gases. To address these issues, the electrocatalytic nitrogen oxidation reaction (NOR) has emerged as a sustainable alternative, which directly converts atmospheric N 2 and H 2 O into NO 3 − under ambient conditions. This reaction, when coupled with renewable energy sources, offers carbon-neutral HNO 3 synthesis. However, critical challenges to developing commercially viable NOR-based systems persist, including low Faradaic efficiency, unproven reaction scalability, poor solubility of N 2 in aqueous electrolytes and NO 3 − yields that lag behind current industrial benchmarks, as well as the difficulty of elucidating catalyst-specific reaction mechanisms. This review summarizes recent progress toward addressing these hurdles. Two primary NOR pathways are discussed: electrochemical and hybrid electrochemical–chemical pathways. We also detail recent advances in NOR system design, including electrolyte optimization, innovative electrolysis systems, device modifications, and auxiliary strategies, aimed at addressing the inherent challenges in NOR implementation and commercial viability. Furthermore, this review summarizes catalysts and strategies for improving NOR performance.