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

Electrocatalytic nitrate (NO3 -) reduction offers a sustainable route for simultaneous NO3 - remediation and ammonia (NH3) production, yet its efficiency is limited by the competing hydrogen evolution reaction (HER) and the imbalance between NO3 - activation and hydrogen supply. Herein, Co-Cu bimetallic sulfide nanoflowers were synthesized via a one-step hydrothermal method and optimized for NO3 - to NH3 conversion. The Co0.9Cu0.1S nanoflowers, assembled from two-dimensional nanosheets, delivered 97.83% ± 1.71% nitrate conversion, nearly complete NH4 +-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 NO3 - activation and electronically modulates Co sites, while Co facilitates reactive hydrogen generation and utilization. This synergy enables on-demand hydrogen supply, directing hydrogen toward NO3 - hydrogenation rather than HER. pH-dependent tests further identify a neutral electrolyte as favorable for balancing proton supply and competitive HER.