Electrolyte‐Engineered Photoelectrochemical Ammonia Oxidation Enabling Sustainable Hydrogen Production via Catalyst Regeneration

Abstract Ammonia oxidation reaction (AOR) offers a promising carbon‐free hydrogen production pathway under ambient conditions, yet practical implementation faces critical challenges from catalyst deactivation and competing side reactions in aqueous systems. We present an electrolyte‐engineered approach to photoelectrochemical (PEC) AOR that enables both enhanced hydrogen production and reversible catalyst regeneration. By employing a non‐aqueous acetonitrile electrolyte at the BiVO 4 photoanode, we suppress competing oxygen evolution and NO x poisoning, achieving a 6.9‐fold higher hydrogen yield than aqueous systems. Spectroscopic and electrochemical analyses reveal that catalyst deactivation in water is not permanent but dynamically reversible upon re‐exposure to nonaqueous environment, emphasizing the solvent‐governed interfacial behavior. This electrolyte‐engineering approach proves broadly applicable across metal oxide photoanodes (BiVO 4 , WO 3 , α‐Fe 2 O 3 ), establishing a universal design principle for PEC AOR systems. Our findings redefine the role of electrolyte composition in governing interfacial pathways and provide a practical framework for developing high‐efficiency ammonia‐to‐hydrogen conversion platforms with enhanced durability and flexibility.