Nickel-facilitated in-situ surface reconstruction on spinel Co₃O₄ for enhanced electrochemical nitrate reduction to ammonia

Transition metal oxides have shown efficient catalytic performance for electrochemical nitrate reduction reaction (e-NO₃RR). However, the surface evolution on catalyst remains elusive. Deciphering the dynamic evolution of electrocatalyst is pivotal for unveiling the catalytic origin and maximizing catalytic performance. Here, we report that incorporating nickel into Co₃O₄ can improve the electrocatalytic performance for e-NO₃RR to ammonia. Co₂NiO₄ shows excellent e-NO₃RR performance with a maximum Faraday efficiency of 94.9 % and NH₃ yield of 20 mg h⁻¹ cm⁻² at −1.0 V. Importantly, the reconstructed cobalt-nickel hydroxides (Co_yNi_1−y(OH)₂) on the surface of Co_3−xNi_xO₄ is the active phase. DFT calculations confirm that Co_yNi_1−y(OH)₂ facilitates the formation of *NOH intermediate and suppresses HER. Our findings reveal that Ni-incorporation not only promotes the surface reconstruction, but also tunes the electronic structure of catalyst to improve the adsorption of intermediates and reduce the energy barrier. Our work may present a novel strategy to design electrocatalysts for e-NO₃RR. © 2023 Elsevier B.V.