Boosting Electrochemical Denitrification and Resource Recovery in Low-Concentration Nitrate via Proton Transfer Adjustment

Electroreduction of nitrate (eNO₃RR) to ammonia (NH₃) in low-concentration nitrate (NO₃^-) is of great significance for actual wastewater purification and nitrogen resource recovery. However, the competing hydrogen evolution reaction (HER) inevitably constrained nitrate hydrogenation and aggravated energy consumption in the low NO₃^- content media. This study introduces a hydrophobic electrode interface to inhibit active hydrogen (H*) generation and facilitate the direct proton transfer from H₂O to NO₃^-, thereby minimizing HER selectivity and enhancing NH₃ conversion. Consequently, the iodine-modified Mxene (TCTI) electrode consistently performed with high NH₃ selectivity (∼90%) and low-energy consumption in various low-concentration nitrate environments (NO₃^--N: 10-80 mg L^-1). The H₂O-mediated proton-coupled electron transfer (PCET) in the TCTI electrode was validated by in situ characterization and theoretical calculations. Furthermore, a cross-flow electrofiltration system (CFE) incorporating TCTI was designed to synchronously eliminate NO₃^- and recycle NH₃, ultimately achieving high purity NH₄Cl recovery with economically feasible operating costs. Our research provides novel insights into the efficient electrochemical denitrification and resource recovery of wastewater containing low-concentration nitrate.