Self-Recycled electron donor resists disfavored oxidation reconstruction of Cu^(I)-based electrocatalyst for nitrate removal by charge compensation

The overuse of nitrate has led to the accumulation in natural water, being a globe issue in environment and human health. Electrochemical NO₃⁻ reduction reaction (eNO₃RR) to ammonia occurs under ambient condition with low energy consumption and the yield of value-added product, being promising for NO₃⁻ removal. Cu^(I)-based eNO₃RR catalysts suffer from unavoidable oxidation reconstruction to Cu^(II), reducing the performance of NO₃⁻ removal. In this work, we demonstrate charge compensation strategy to resist oxidation reconstruction of Cu^(I)-based eNO₃RR catalysts by introducing self-recycled electron donor. Taking Ti^(III)-modified Cu₂O/Cu as the proof-of-concept model, electron donor Ti^(III) can donate electron to Cu^(II) to regenerate Cu^(I), meanwhile the expended Ti^(III) can be recycled from the generated Ti^(IV) via intervalence charge transfer (IVCT). Benefiting from those, Ti-Cu₂O/Cu-10 exhibits significantly improved activity and durability for NO₃⁻ removal compared to Cu₂O/Cu. The percentage of NO₃⁻ removal keeps at ∼95.0 % with the initial concentration of 60 mg•L⁻¹ NO₃⁻-N at -0.9 V vs. RHE in 15 consecutive cycling tests (corresponding to 30 h). This work presents a feasible strategy to resist oxidation reconstruction of Cu^(I)-based eNO₃RR catalysts, making NO₃⁻ removal more effective, more durable, and more sustainable.