Lewis acid-triggered hydroxyl spillover enables selective urea electrooxidation to nitrite with concurrent energy-saving hydrogen production

Nitrite (NO₂^⁻) is a high-value chemical pivotal to agriculture and pharmaceuticals, yet its conventional via the Ostwald process is energy-intensive and polluting. Electrochemical urea oxidation reaction (UOR) offers a sustainable NO₂^⁻ synthesis pathway with concurrent energy-saving hydrogen (H₂) production, but suffers from non-selective N₂/CO₂ pathways. Here, we report Cr³⁺ Lewis acid sites in Ni₃S₂ that act as hydroxyl (OH^⁻) pumps, dynamically spilling OH^⁻ to adjacent Ni sites via a Lewis acid-base interaction. This triggers a urea-to-NO₂^⁻ pathway, achieving a NO₂^⁻ yield of 120.98 mg h^-1 cm^-2 (600 mA cm^-2). The OH^⁻ spillover accelerates C-N cleavage while suppressing N-N coupling, enabling energy-saving H₂ production (3.7 kWh m^-3 at 500 mA cm^-2) and Zn-urea-air batteries (charging potential 288 mV lower than Zn-air). Techno-economic analysis reveals $1,210.5 per ton of urea processed at 400 mA cm^-2. This work establishes OH^⁻ spillover as a universal design principle for selective electrocatalysis.