Unveiling the role of Ru nanoclusters in Ru-CuOx nanowires for electrochemical nitrate reduction to ammonia

Electrochemical nitrate reduction reaction (NO3RR) is a sustainable strategy to treat wastewater and produce ammonia. However, it is still a challenge to prepare electrocatalysts with high activity and selectivity. Herein, the CuOx nanowires supported Ru nanoclusters (Ru-CuOx) were fabricated via a three-step procedure for efficient nitrate conversion and highly selective ammonia generation. The prepared Ru-CuOx shows a high ammonia yield rate of 2286.5 μg h−1 cm−2 at −0.7 V vs. RHE and Faradaic efficiency (FE) of 80.1 % at −0.4 V vs. RHE. Additionally, the nitrate conversion rate exceeds 90 % at the potential range from −0.2 to −0.7 V vs. RHE, and the ammonia selectivity can reach 97.7 % at −0.7 V vs. RHE in 100 mg L−1 NaNO3 solution. The systematic characterizations clarify that the introduction of Ru not only regulates the electronic structure of CuOx and accelerates the reconstruction of CuOx to Cu but also promotes H2O dissociation to generate active hydrogen. Moreover, in-situ Raman spectroscopy reveals that the formed Ru-Cu is considered the actual active species during the NO3RR. Density functional theory (DFT) calculations further prove that the obtained Ru-Cu facilitates the adsorption of nitrate and lowers the Gibbs free energy of the rate-determining step, thus improving the NO3RR performance.