Self-supported copper-cobalt oxide hybrid electrode for bifunctionally electrocatalytic nitrate reduction and methanol oxidation reactions.

Electrochemical nitrate reduction reaction (NO3RR) to ammonia (NH3) is a sustainable approach to upcycle nitrate (NO3-) pollutant, the further pairing of cathodic NO3RR with anodic methanol oxidation reaction (MOR) enables coproduction of NH3 and formate chemicals by electrolysis at enhanced energy efficiency. Bifunctional catalytic electrode for both reactions is crucial for achieving such a target. In view of the strong NO3- adsorption ability of copper (Cu) and the high active hydrogen adsorption ability of cobalt (Co) based compound, the catalyst composed of Cu and Co elements facilitates the deoxidation and complete hydrogenation of NO3- into NH3. In addition, the Cu- and Co-containing material is also possible catalyst or precatalyst for MOR. Herein, a self-supported Cu-cobalt oxide (CoO) hybrid onto nickel foam substrate, denoted as Cu-CoO/NF electrode, was fabricated by electrodeposition at negative potential. Due to the relaying effect of Cu and CoO components during NO3RR, the Cu-CoO/NF achieved a decent faradaic efficiency (FE) of 84 ± 4 % and an NH3 yield of 0.40 ± 0.02 mmol h-1 cm-2 at a high operation potential of -0.1 V. Moreover, the Cu-CoO/NF demonstrated high MOR property for formate production at significantly reduced potential (over 0.2 V) compared to the oxygen evolution reaction. The NO3RR-MOR coelectrolyser enabled coproduction of NH3 and formate at reduced energy consumption. This work provides a promising paradigm for pairwise production of valuable chemicals via rational design of catalytic electrode and construction of coelectrolysis system.