Integration of Nitrate Denitrification and Biomass Valorization in a Water-Splitting-Based Configuration for Concurrent Electrocatalytic Refining.

Abstract

Engineering anodic and cathodic half-reactions with more favorable thermodynamics and techno-economics in water-splitting cells for electrorefining offers a promising approach to producing green fuels and fine chemicals. Herein, we demonstrated a coelectrolysis system integrating nitrate reduction reaction (NO₃RR) and biomass oxidation reaction (BOR), where a well-designed CuNi alloy acted as the catalyst at the cathode and anode. The CuNi delivered a yield rate of 2.87 mmol h^-1 cm^-2 (8.44 mmol h^-1 mg_cat^-1) at 0 V vs RHE and a FE of 95.33% (a current density of -136 mA cm^-2) at -0.2 V vs RHE for ammonia synthesis from nitrate reduction. Mechanistic studies revealed that Cu centers rapidly converted NO₃^- to NO₂^-, while Ni sites promoted water dissociation, generating *H species for intermediate deoxygenation and hydrogenation via stepwise proton transfer. At the anode, the CuNi efficiently catalyzed the oxidative upgradation of biomass derivatives, with a Faradaic efficiency of >90% and a long-term stability over 240 h for formate production. In situ experiments demonstrate that Cu substantially enhances the dynamic transformation efficiency of the Ni^III-O active species on CuNi catalysts. The integrated NO₃RR||BOR system demonstrated an efficient and stable electrosynthesis (>120 h) of ammonia (∼3.9 mmol h^-1 cm^-2 or 11.47 mmol h^-1 mg_cat^-1) and formate (∼38.3 mmol h^-1 cm^-2 or 112.65 mmol h^-1 mg_cat^-1). This study emphasizes the design of a hybrid system for electrocatalytic refining of waste feedstocks into commodity chemicals.