Dynamically forming Cu3Mo2O9/Cu heterojunction for efficient nitrate reduction in Zn-nitrate batteries

Abstract

The sustainable production of ammonia (NH3) via electrochemical nitrate reduction reaction (NO3-RR) presents a dual solution for environmental remediation and renewable energy storage. However, this process is hindered by the sluggish kinetics of sequential deoxygenation and hydrogenation steps, particularly under alkaline conditions where proton scarcity exacerbates competing hydrogen evolution reaction (HER). In this work, a heterostructured Cu3Mo2O9/Cu is purposely designed that can be reductively formed during the NO3-RR to incorporate the advantages of dual-function active sites in the processes of water dissociation and nitrate reduction. Experimental and theoretical results indicate that the in-situ generated Cu3Mo2O9 can drive efficient water dissociation to supply protons (H⁺), while the metallic Cu enhances nitrate adsorption and facilitates the subsequent deoxygenation. The Cu3Mo2O9/Cu catalyst achieves an excellent NH3 Faradaic efficiency (FE) of 97.5% at -0.5 V vs. RHE with an NH3 yield rate of 19.3 mg h-1 mgcat-1 in 0.05 M KNO3. This performance is among the highest under neutral/alkaline H-cell conditions. The Cu3Mo2O9/Cu based Zn-nitrate battery delivers a peak power density of 20.24 mW cm-2 and maintains an FENH3 of 93.8% at 60 mA cm-2. This work not only elucidates the dynamic synergy of heterostructured catalysts for multi-step reactions but also establishes a general framework for coupling catalytic nitrate conversion with energy storage applications.