Structure - Activity Relationship of Electrodeposited Fe, Cu, and Ni on TiO2 Nanostructures for Electrocatalytic Nitrate Reduction to Ammonia

Metal deposition on the surface of TiO 2 -based electrodes can be an effective strategy to improve the electrocatalytic nitrate reduction reaction (NO 3 RR) to ammonia. In this study, the surface of TiO 2 nanostructures grown on the Ti plate substrate were modified by depositing transition metal, i.e. Fe, Cu, and Ni, which were selected for their distinct electronic properties and potential interactions with nitrate-reduction intermediates, and were deposited onto TiO 2 nanostructures grown on a Ti plate via electrodeposition to compare their effects on NO 3 RR performance. Under the identical deposition current and time, the deposited metals formed distinct morphologies, with Fe appearing sparsely dispersed, Cu producing disperse agglomerated deposits, while Ni extensively covering the TiO 2 surface. Electrocatalytic activity test revealed that the co-catalyst deposition enhanced the nitrate reduction to ammonia. Among the prepared electrodes, Cu/TiO 2 showed the most pronounced improvement over pristine TiO 2 . At the highest performance, the ammonia yield rate increased by 32-fold, from 49.4 µg h −1 cm −2 (pristine TiO 2 ) to 1616.3 µg h −1 cm −2 (Cu/TiO 2 ) while the Faradaic efficiency rose from 26.8% for TiO 2 to 80.99% for Cu/TiO 2 . Cu/TiO 2 also exhibited the highest nitrate reduction rate, with an apparent rate constant of 0.00499 min −1 , four fold faster than pristine TiO 2 (0.00104 min −1 ) for pristine TiO 2 . The enhanced performance of Cu/TiO 2 electrode can be attributed to the collective effect of the favorable surface morphology, enlarged active-site availability, and improved interfacial charge-transfer properties. This work provide an insight into surface modification of the TiO 2 -based electrode for electrocatalytic nitrate reduction to ammonia.