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.