Thermally Codeposited Bimetallic Copper–Cobalt Oxide Electrode for Electrocatalytic Nitrate Reduction to Ammonia

Abstract

The electrocatalytic reduction of nitrate (NO₃RR) to ammonia presents a promising avenue for both wastewater treatment and nitrogen cycle restoration while simultaneously producing valuable renewable energy carriers. Despite recent advances, the development of stable and scalable catalysts that can bridge the gap between laboratory demonstrations and practical applications remains challenging. This study reports the synthesis of bimetallic copper–cobalt oxide catalyst supported on nickel sheet (referred to as CuCo₂O₄/Ni) via thermal treatment, demonstrating exceptional NO₃RR performance. The bimetallic CuCo₂O₄/Ni catalyst, distinguished by its high surface area (10.94 mF cm⁻²) and abundant active sites, demonstrated superior catalytic activity compared to the monometallic counterparts, cobalt oxide (Co₃O₄/Ni), and copper oxide (CuO/Ni), positioning it among recently reported state-of-the-art catalytic materials. The as-prepared CuCo₂O₄/Ni achieved a remarkable ammonia (NH₃) yield rate of 2.14 mmol cm² h⁻¹ with a Faradaic efficiency (FE) of 98.2% at a low potential of −0.37 V versus reversible hydrogen electrode (RHE) with an excellent 103-h stability performance (90% retention of FE), demonstrated at high nitrate concentrations (ANSOL), a critical aspect for addressing heavily polluted industrial and wastewater streams. This study establishes a promising synthetic route for stable bimetallic catalysts with superior electrocatalytic activity, potentially advancing the field toward sustainable ammonia production at a large scale.