Conductivity-mediated electrochemical reconstruction of CuO for nitrate reduction to ammonia.

The electrocatalytic nitrate reduction reaction (NORR) is an ideal NH synthesis route with ease of operation, high energy efficiency, and low environmental detriment. Electrocatalytic cathodes play a dominant role in the NORR. Herein, we constructed a carbon fiber paper-supported CuO nanoarray catalyst (CP/CuO) by an electrochemical reconstruction method for NO-to-NH conversion. A series of characterization techniques, such as X-ray diffraction (XRD) and Raman spectroscopy, unveil that CP/CuO is a polycrystalline-faceted composite copper nanocatalyst with a valence composition containing Cu, Cu and Cu. CP/CuO shows more efficient NO-to-NH conversion than CP/Cu and CP/CuO, which indicates that the coexistence of various Cu valence states could play a dominant role. CP/CuO with a suitable Cu content obtained by adjusting the conductivity during the electrochemical reconstruction process exhibited more than 90% faradaic efficiencies for the NORR in a broad range of -0.3 to -1.0 V RHE, 28.65 mg cm h peak ammonia yield, and stable NORR efficiencies for ten cycles. These findings suggest that CP/CuO with suitable copper valence states obtained by fine-tuning the conductivity of the electrochemical reconstruction may provide a competitive cathode catalyst for achieving excellent activity and selectivity of NO-to-NH conversion.