Direct electroconversion of air to nitric acid under mild conditions

Nitric acid (HNO 3 ) synthesis is an important industrial process but typically requires multiple energy-intensive steps, including the synthesis and subsequent oxidation of ammonia. Here we report the direct conversion of air to HNO 3 under ambient conditions through a hydroxyl radical (OH ­· )-mediated hetero-homogeneous electrochemical route. The conversion proceeds at a reductive potential of 0 V versus the reversible hydrogen electrode at the cathode and can achieve a Faradaic efficiency of 25.37% with over 99% HNO 3 selectivity. Experimental and theoretical investigations reveal that OH · produced from Fe 2+ -induced dissociation of in situ generated H 2 O 2 can efficiently activate N 2 . This delivers a high HNO 3 productivity of \(141.83\,\upmu{\mathrm{mol}}\,{\mathrm{h}}^{-1}\,{\mathrm{g}}_{\mathrm{Fe}}^{-1}\) , which is 225 times that of directly using H 2 O 2 as the oxidant. This process opens an energy-efficient and green route for the direct conversion of air to HNO 3 under mild conditions.