On-Demand Hydrogen Supply Over Co–Cu Bimetallic Sulfide Nanoflowers for Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate (NO 3 − ) reduction offers a sustainable route for simultaneous NO 3 − remediation and ammonia (NH 3 ) production, yet its efficiency is limited by the competing hydrogen evolution reaction (HER) and the imbalance between NO 3 − activation and hydrogen supply. Herein, Co–Cu bimetallic sulfide nanoflowers were synthesized via a one-step hydrothermal method and optimized for NO 3 − to NH 3 conversion. The Co 0.9 Cu 0.1 S nanoflowers, assembled from two-dimensional nanosheets, delivered 97.83% ± 1.71% nitrate conversion, nearly complete NH 4 + -N selectivity, and a Faradaic efficiency of 98.52% ± 0.83% at −0.75 V vs. RHE. Systematic Co/Cu-ratio studies, electrochemical kinetics, Bode analysis, hydrogen adsorption/desorption behavior, and XPS results reveal that Cu promotes NO 3 − activation and electronically modulates Co sites, while Co facilitates reactive hydrogen generation and utilization. This synergy enables on-demand hydrogen supply, directing hydrogen toward NO 3 − hydrogenation rather than HER. pH-dependent tests further identify a neutral electrolyte as favorable for balancing proton supply and competitive HER. Graphical Co–Cu bimetallic sulfide nanoflowers enable efficient nitrate-to-ammonia conversion through on-demand hydrogen supply. Cu sites promote nitrate activation, while Co sites regulate reactive hydrogen generation and consumption, thereby enhancing ammonia selectivity and suppressing competitive hydrogen evolution.