Tannic Acid-Assisted Nickel-Modified Self-Supported Copper Nanowire Electrodes for Sustainable Electrocatalytic Nitrate-to-Ammonia Conversion.

Electrocatalytic nitrate reduction to ammonia offers a sustainable route for nitrate pollution control and nitrogen resource recovery. Herein, a self-supported copper nanowire electrode is fabricated on copper foam through in situ oxidative etching and reduction, followed by tannic acid-assisted nickel modification to obtain Ni-TA/Cu NW. The interconnected copper nanowire framework increases the accessible active area, while tannic acid introduces oxygen-containing coordination sites that regulate the surface microenvironment and promote metal species dispersion. Structural characterizations confirm that Ni-related species and tannic acid-derived functional groups are introduced on the Cu nanowire surface without destroying the conductive framework. The Ni-TA/Cu NW electrode exhibits excellent nitrate-to-ammonia performance in neutral electrolyte, achieving an ammonia yield rate of 5.7360 mg h-1 cm-2 at -0.64 V versus RHE and a Faradaic efficiency of 98.16% at -0.54 V versus RHE. It also suppresses nitrite accumulation and maintains stable performance during cycling tests. This work provides an effective interface-engineering strategy for copper-based self-supported electrodes toward sustainable nitrate conversion.