Reverse hydrogen spillover accelerates electrocatalytic nitrate reduction to ammonia on Ru/WO3-x in acidic media

The electrocatalytic nitrate reduction reaction (NO3-RR) offers a promising route to sustainable ammonia synthesis, potentially replacing the energy-intensive Haber-Bosch process. While often studied in neutral or alkaline media, NO3-RR in acidic conditions is particularly relevant due to widespread industrial acidic nitrate wastewater, yet it remains challenging due to corrosion and dominant hydrogen evolution. To address this, we designed a corrosion-resistant Ru/WO3-x heterostructure that spatially separates proton and nitrate adsorption sites. Here, we show that a reverse hydrogen spillover effect, where the WO3-x support stores and transports protons to surface Ru active sites, dramatically enhances hydrogenation kinetics and suppresses parasitic hydrogen evolution. This catalyst achieves an ammonia Faradaic efficiency of 94.09% at a high current density of 500 mA cm−2 and a working potential of 0.026 V vs. reversible hydrogen electrode. Furthermore, we demonstrate a sulfide-nitrate “batterolyzer” with a discharge power density of 43.4 mW cm−2. This work reveals an effective proton-management strategy for efficient acidic NO3-RR, advancing its potential for coupled ammonia synthesis and wastewater treatment. Electrocatalytic nitrate reduction in acidic wastewater offers a route to produce ammonia, but faces efficiency challenges. Here, the authors report a Ru/WO3-x catalyst that uses a proton-management strategy to achieve high ammonia production and enables a device that recovers energy.