Highly selective and efficient electrochemical nitrate removal via Ni-doped Cu(OH)2 nanowires promoting H* reaction

Electrochemical reduction of nitrate (NO3- ) offers a promising approach for nitrate removing from water. Development of non-noble metal electrocatalysts with high reactivity and selectivity is crucial for the electrochemical reduction of NO3- . Herein, Ni-doped Cu(OH)2 nanowires (Ni-Cu(OH)2 NW/CF) were synthesised on copper foam (CF) and utilised as a cathode, enabling efficient and selective nitrate removal with further conversion to harmless N2. The Ni-Cu(OH)2 NW/CF electrode achieved a 99.8 % NO3 --N conversion rate within 40 min, with a reaction rate 25 times higher than CF and 1.51 times than that of Cu(OH)2. It demonstrated a rapid nitrate reduction apparent rate constant (0.02072 cm- 2 min- 1) without nitrite accumulation. With the assistance of active chlorine at the anode, the electrocatalytic system effectively converted NO3 -into harmless N2, achieving a final N2 selectivity of 99.9 %. The Cu(OH)2 nanowires provided abundant active sites to enhance NO3 - adsorption and conversion, while Ni doping mainly accelerated the reduction of NO2 - intermediate by facilitating the atomic hydrogen (H*)-mediated reaction pathway on the electrode surface. This relay catalytic effect enhanced the electrode's adsorption and reduction capabilities for NO3- . Notably, the Ni-Cu(OH)2 NW/CF electrode maintained consistent performance over 10 experimental cycles. This study provides novel strategy for designing non-noble metal electrocatalysts with high selectivity and efficiency for NO3 -removal.