Aqueous electrochemical hydrogenation of nitrogen-containing organic compounds

Abstract

Hydrogenation of nitrogen-containing organic compounds (NOCs) are widely used in chemical industry, medicine and energy as an effective approach to achieving a sustainable artificial nitrogen cycle. Conventional fossil-fuel-driven thermochemical hydrogenation of high-pressure hydrogen is an energy-intensive carbon emission process. In contrast, aqueous electrochemical hydrogenation (ECH) offers a greener alternative by using water as a hydrogen source under ambient conditions, utilizing cathode potential instead of heat and hydrogen inputs. ECH of NOCs presents a potent method to convert renewable energy into value-added nitrogen-containing products under environmental conditions. However, challenges such as low conversion rates, competition from hydrogen evolution, and the complexity of the ECH process significantly impact the activity and conversion efficiency of hydrogenation catalysts, particularly reducing the selectivity for the target nitrogen-containing molecules. Investigating selective ECH can mitigate by-product and waste emissions associated with traditional chemical processes, advance green chemical technology, and expand the market for value-added nitrogen-containing organic products. This review summarizes the recent research progress on the selective ECH of representative NOCs, covering the underlying mechanisms and activity indicators related to proton activation on catalysts surface. Additionally, three strategies (structure/component optimization, interface engineering and reaction engineering) were proposed to enhance the selectivity of ECH to upgrade NOCs into nitrogen-containing organic value-added products, combined with in-situ characterization techniques for probing reaction intermediates and theoretical calculations to clarify structure-activity relationships. These approaches collectively enable the investigation and optimization of proton activation, electron transfer, and substrate hydrogenation pathways at the catalyst-electrolyte interface, aiming to upgrade NOCs into value-added products. characterization techniques for probing reaction intermediates and theoretical calculations to clarify structure-activity relationships. These approaches collectively enable the investigation and optimization of proton activation, electron transfer, and substrate hydrogenation pathways at the catalyst-electrolyte interface, ultimately aiming to upgrade NOCs into value-added products. Finally, the review discusses the challenges and future directions in designing high-efficiency ECH catalysts for organic nitrogen-containing feedstocks, with a focus on improving the application prospects of this technology in the artificial nitrogen cycle and its large-scale implementation.