Evaluating Copper-Modified Carbon Composite Nanofiber Electrodes for Electrocatalytic Nitrate Reduction

The increasing urgency to address nitrate (NO₃ ^-) pollution in water sources has intensified research on electrochemical nitrate reduction, a process capable of transforming NO₃ ^- into valuable ammonia (NH₃) by using renewable electricity. Copper (Cu) catalysts can reduce NO₃ ^-, but their activity and selectivity toward NH₃ can vary based on their structure, reaction environment, and support material. This study examines the efficacy of Cu-modified carbon nanofiber (CNF) supports, tailored through electrospinning, in enhancing the electrocatalytic reduction of NO₃ ^- to NH₃. Three variants of CNF supports were synthesized: pristine CNFs, CNFs integrated with carbon nanotubes (CNF/CNTs), and CNFs embedded with titanium dioxide nanoparticles (CNF/TiO₂). Each electrode's physical and electrochemical properties were analyzed before and after Cu electrodeposition. Notably, the CNF/TiO₂/Cu composites demonstrated a selectivity exceeding 40% for the conversion of NO₃ ^- to NH₃ at neutral pHsignificantly outperforming the CNF/CNT/Cu (<5%) and CNF/Cu (20%) configurations when deposited with equivalent amounts of Cu. The CNF/TiO₂/Cu electrode also exhibited consistent and stable performance over the extended experimental duration (|<i>Q</i>| = 70 C), maintaining NH₃ selectivity rates of over 50%. Tafel analysis and operando Raman spectroscopy suggest that TiO₂ plays an active role in hydrogenating nitrogenous reduction products for enhanced selectivity. This research highlights the importance of electrode-catalyst selection in electrochemical NO₃ ^- reduction and identifies TiO₂-containing electrodes as promising solutions in this domain.