Continuous and sustainable electrosynthesis of free hydroxylamine enabled by a self-regenerative catalyst system

Direct electrosynthesis of hydroxylamine (NH2OH) from nitrate offers a promising alternative for upgrading nitrogenous product in chemical industry. However, catalyst aging, especially in acidic media, remains a critical challenge due to the irreversible surface reconstruction under cathodic potentials, which limits long-term catalytic activity. Here, we develop an eco-efficient regenerative catalyst system that overcomes this durability bottleneck through a dynamic in situ catalyst self-repair strategy. By adding trace Bi3+ in solution, active metallic Bi nanofractals form on demand during electrolysis, delivering a 91.0% Faradaic efficiency for electrochemical HNO3-to-NH2OH conversion. Periodically switching to open-circuit potential fully resets the aged catalyst back into its ionic state without extra energy inputs. Leveraging this reversible Bi3+/Bi redox cycle, we demonstrate a continuous operation of HNO3-to-NH2OH conversion for 30 days, with a consistent product selectivity of over 90% and current density of ~ 0.4 A cm-2. This potential-driven regenerative strategy provides an efficient approach for sustainable synthesis of fine chemicals.