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 (CoyNi1−y(OH)2) on the surface of Co3−xNixO4 is the active phase. DFT calculations confirm that CoyNi1−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.