Conductivity-mediated in situ electrochemical reconstruction of CuOx for nitrate reduction to ammonia

Electrocatalytic nitrate reduction reaction (NO3RR) is an ideal NH3 synthesis route with ease of operation, high energy efficiency, and low environmental detriment. The electrocatalytic cathodes play a dominant role in NO3RR. Herein, we constructed a carbon fiber paper-supported CuOx nanoarray catalyst (CP/CuOx) by an in situ electrochemical reconstruction method for NO3−-to-NH3 conversion. XRD, in situ Raman, and XPS characterizations unveil the CP/CuOx is a polycrystalline-faceted composite copper nanocatalyst with a valence composition containing Cu0, Cu+ and Cu2+. The CP/CuOx shows more efficient NO3−-to-NH3 conversion than CP/Cu and CP/Cu2O, which indicates the coexistence of various Cu valence states could play a dominant role. The CP/CuOx with suitable Cu2+ content that obtained by adjusting the conductivity during the in situ electrochemical reconstruction process exhibited more than 90% of Faradaic efficiencies for NO3RR in the broad range of -0.3 to -1.0 V vs. RHE, 28.65 mg cm-2 h-1 of peak ammonia yield, and stable NO3RR efficiencies for ten cycles. These findings suggest that the CP/CuOx 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 NO3−-to-NH3 conversion.