Dual–Spillover Mediated Highly Efficient Electrocatalytic Nitrate Reduction to Ammonia Over Co–Doped Sr ₂ CuWO ₆ Double Perovskite

ABSTRACT Electrocatalytic nitrate reduction reaction (NO ₃ RR) provides a green route to concurrently mitigate nitrate pollution and address the unsustainability of Haber–Bosch ammonia (NH ₃ ) synthesis. However, the development of high–performance NO ₃ RR catalysts is plagued by inappropriate active site spacing, insufficient functional synergy, and sluggish multi–proton–coupled multi–electron transfer kinetics. Herein, we design Co–doped Sr ₂ CuWO ₆ double perovskite catalysts to optimize active site spacing and construct functionally complementary active sites for efficient NO ₃ RR. Experimental and theoretical results reveal a synergistic dual–spillover mechanism: the dominant NO ₃ ⁻ adsorption and initial activation (NO ₃ ⁻ →NO ₂ ⁻ ) on Cu sites are promoted by active hydrogen ( ^* H) from water dissociation on Co sites via hydrogen spillover, whereas the generated ^* NO ₂ intermediates from Cu sites diffuse to Co sites via intermediate spillover for further hydrogenation to NH ₃ due to the enhanced ^* NO ₂ adsorption on Co sites. As expected, the optimal Sr ₂ Cu _0.7 Co _0.3 WO ₆ achieves an exceptional NH ₃ yield rate of 47.2 mg h ^{− 1} mg _cat ⁻¹ with a Faradaic efficiency (FE) of 93 % at −0.7 V (vs. RHE). This work establishes a rational cation doping strategy for constructing functionally complementary active sites in double perovskites, shedding light on the structure–activity relationship and guiding the design of advanced NO ₃ RR catalysts for sustainable NH ₃ synthesis and nitrate remediation.