Beyond Conventional Doping: Sulfur-Induced Electronic and Interfacial Dynamics for Advanced Nitrate Reduction

Electrochemical nitrate reduction reaction (NO₃ ^-RR) to ammonia (NH₃) offers a sustainable route for NH₃ synthesis and environmental remediation, yet it is hindered by sluggish kinetics due to inefficient proton-coupled electron transfer (PCET) processes and inadequate electrocatalyst design. Conventional approaches primarily focus on the bulk electronic modulation of the electrocatalyst while neglecting interfacial water dynamics. Here, we propose a dual-functional sulfur-doping strategy in Co₃O₄ (S-Co₃O₄) to simultaneously enhance bulk conductivity and optimize interfacial proton transfer. Through innovative benzene sulfonyl chloride blocking experiment, in situ spectroscopic analyses, and kinetic isotope effect studies, we reveal that sulfur doping narrows the bandgap of Co₃O₄ to enhance bulk charge transport while disrupting rigid hydrogen-bond network of water in the electric double layer; the weakly hydrogen-bonded H₂O reduces the dissociation barrier and facilitates proton supply for nitrate hydrogenation. The proposed "electronic-interfacial synergy" strategy establishes a transformative paradigm for designing electrocatalysts in PCET-driven reactions, advancing sustainable energy conversion and environmental applications.