H2O2-mediated electrosynthesis of nitrate from air

Abstract

Renewable electricity-driven electrochemical nitrogen oxidation is a promising alternative to traditional Haber–Bosch and Ostwald processes to directly synthesize nitrate from nitrogen. However, its efficiency is hindered by strong competition from the oxygen evolution reaction in aqueous environments, along with a deficiency in standardized testing protocols. Here we present an efficient approach for nitrogen oxidation, substituting the oxygen evolution reaction with hydroxyl radicals (·OH) generated through hydrogen peroxide decomposition to serve as an active oxygen source. Electrochemical tests demonstrate that the nitrogen oxidation, facilitated by ·OH, can achieve a Faradaic efficiency of 25.6% and a nitrate yield of 8.3 nmol s−1 cm−2. Furthermore, we employed in situ electrochemical mass spectrometry, gas-phase infrared and electron paramagnetic resonance spectroscopy to establish a comprehensive set of benchmarks to confirm the authenticity of nitrogen activation and to examine the reaction mechanism mediated by ·OH. Techno-economic analysis underscores the promising feasibility and sustainable economic value of the presented method. Renewable electricity-driven nitrogen oxidation is a green alternative to Haber–Bosch and Ostwald processes, but it is challenging to effectively steer oxygen intermediates towards the nitrogen oxidation reaction pathway. Now, to mitigate competing oxygen evolution and improve nitrogen oxidation efficiency, the use of hydroxyl radicals as the nitrogen oxidant is proposed.