Electrochemical oxidation of nitric oxide to concentrated nitric acid with carbon-based catalysts at near-ambient conditions

Nitric oxide (NO) emissions pose significant environmental challenges that demand sustainable remediation strategies. Here we report an electrochemical approach to convert NO into salt-free, concentrated nitric acid (HNO₃) using a carbon-based catalyst at near-ambient conditions. The system achieves >90% HNO₃ Faradaic efficiency (FE) at 100 mA cm⁻² with pure NO and retains >70% FE with dilute NO (0.5 vol%). Mechanistic studies identified nitrous acid as a critical intermediate, diverging from conventional thermocatalytic nitrogen dioxide pathways. By implementing a vapour-fed strategy in a membrane electrode assembly electrolyser, we directly synthesized 32 wt% HNO₃ from NO and deionized water, achieving 86% FE at 800 mA cm⁻² without electrolyte additives or downstream purification. This work establishes an electrochemical route to valorize NO emissions to high-purity HNO₃, advancing sustainable pollution mitigation and chemical manufacturing.