Core–shell heterojunction engineering of Co3O4/NiFe LDH nanosheets as bifunctional electrocatalysts for efficient reduction of nitrite to ammonia

An electrocatalytic NO₂⁻ reduction reaction (NO₂⁻RR) has cast new light on renewable NH₃ synthesis and treatment of NO₂⁻-contaminated aquatic ecosystems. Numerous studies have been devoted to developing NO₂⁻RR  electrocatalysts with superior selectivity. However, few efforts have  focused on constructing bifunctional catalysts promoting the NO₂⁻RR  and the oxygen evolution reaction (OER) simultaneously, which is  significant to reduce the energy consumption and cost of  electrocatalytic ammonia production. Herein, we demonstrate the  core–shell heterostructures of NiFe LDH nanoarrays attached to Co₃O₄ nanosheets on Ni foam, which exhibit an excellent NO₂⁻RR performance (yield: 4.27 mg h⁻¹ cm⁻², FE: 96.53% at −0.5 V) and a remarkable OER performance (η₁₀₀: 270 mV) as well as decent stability. Furthermore, a two-electrode electrolyzer assembled with Co₃O₄/NiFe LDH heterostructures only requires 1.55 V to reach 10 mA cm⁻², approaching that of the ammonia production system assembled with a noble-metal-based catalyst. The decent NO₂⁻RR  and OER properties benefit from the optimized electronic structure due  to the heterojunction formation and the increased electrochemically  active area owing to the core–shell structure construction. This effort  offers new insights into achieving high-efficiency and low-cost  electrocatalytic ammonia production.