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

The electrocatalytic nitrate reduction reaction (NO 3 RR) is an ideal NH 3 synthesis route with ease of operation, high energy efficiency, and low environmental detriment. Electrocatalytic cathodes play a dominant role in the NO 3 RR. Herein, we constructed a carbon fiber paper-supported CuO x nanoarray catalyst (CP/CuO x ) by an in situ electrochemical reconstruction method for NO 3 - -to-NH 3 conversion. A series of characterization techniques, such as X-ray diffraction (XRD) and in situ Raman spectroscopy, unveil that CP/CuO x is a polycrystalline-faceted composite copper nanocatalyst with a valence composition containing Cu 0 , Cu + and Cu 2+ . CP/CuO x shows more efficient NO 3 - -to-NH 3 conversion than CP/Cu and CP/Cu 2 O, which indicates that the coexistence of various Cu valence states could play a dominant role. CP/CuO x with a suitable Cu 2+ content obtained by adjusting the conductivity during the in situ electrochemical reconstruction process exhibited more than 90% faradaic efficiencies for the NO 3 RR in a broad range of -0.3 to -1.0 V vs. RHE, 28.65 mg cm -2 h -1 peak ammonia yield, and stable NO 3 RR efficiencies for ten cycles. These findings suggest that CP/CuO x 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 3 - -to-NH 3 conversion.