Atomic-level partial replacement of Co in cubic Co3O4 with Cu for effective and stable nitrate electroreduction

Abstract

Electroreduction of nitrate (NO₃⁻) into ammonia (NH₃) has been regarded as a promising strategy to mitigate environmental pollution and obtain value-added product. However, this process is mainly limited by the adsorption and activation of NO₃⁻. How to optimize the binding energy of *NO₃ intermediate on electrode interface for facilitating the conversion of NO₃⁻ into NH₃ is of great importance. Here, we report an effective and stable electrode of Cu_0.75Co_2.25O₄ nanowire arrays grown on nickel foam (Cu_0.75Co_2.25O₄ NAs@NF), where Cu partially replaces Co in Co₃O₄ at the atomic level with unchanged cubic structure. Compared with that of Co₃O₄ NAs@NF, Cu_0.75Co_2.25O₄ NAs@NF exhibits high catalytic activity, selectivity, and stability, which enables a completed removal of 50 mg l^-1 NO₃⁻ in just 50 min. Computational and theoretical analysis confirms that the tri-coordination Co mononuclear site is the active center of Cu_0.75Co_2.25O₄ NAs@NF for NO₃⁻ electroreduction. The reason for such high activity is that the introduction of Cu can cause the d-band center upshift of tri-coordination Co mononuclear site, enhancing the adsorption and activation of NO₃⁻, and lowering the reaction barrier. Notably, Cu_0.75Co_2.25O₄ NAs@NF is a promising electrocatalyst that can work in a wide range of initial NO₃⁻ concentration and solution pH.