Ag-Ni(OH)2/Cu Heterostructure for Tandem Electrocatalytic Nitrate Reduction to Ammonia Coupled with 5-Hydroxymethylfurfural Electrooxidation

Electrochemical reduction of nitrate ions to NH₃ provides a sustainable route for both NH₃ synthesis and wastewater treatment, but it remains challenging. Here we report a Ag-Ni(OH)₂/Cu NW heterostructure that exhibits a high NH₃ Faraday efficiency of 97.3% with an NH₃ yield rate of 4.01 mg h^-1 cm^-2 at -0.1 V vs RHE. Theoretical studies reveal that the excellent performance of Ag-Ni(OH)₂/Cu NW results from the multisite synergy via a cascade electrocatalysis, in which Ag and Ni(OH)₂ species promote NO₃^- reduction to NO₂^- and H₂O dissociation to generate *H, respectively, and Ni(OH)₂/Cu interface accelerates NO₂^- reduction to NH₃. Meanwhile, using Ag-Ni(OH)₂/Cu NW as both the anode and cathode, a two-electrode system integrating the nitrate reduction reaction with the 5-hydroxymethylfurfural oxidation reaction achieves 98.1% NH₃ Faraday efficiency with a 3.17 mg h^-1 cm^-2 NH₃ yield rate and 99.7% 2,5-furandicarboxylic acid selectivity with 99.2% 5-hydroxymethylfurfural conversion.