Cu₂O-Cu@Titanium Surface with Synergistic Performance for Nitrate-to-Ammonia Electrochemical Reduction

Transition metals, such as titanium (Ti) and copper (Cu) along with their respective metal oxides (TiO₂, Cu₂O, and CuO), have been widely studied as electrocatalysts for nitrate electrochemical reduction with important outcomes in the fields of denitrification and ammonia generation. Based on this, this work conducted an evaluation of a composite electrode that integrates materials with different intrinsic activities (i.e., Cu and Cu₂O for higher activity for nitrate conversion; Ti for higher faradaic efficiency to ammonia) looking for potential synergistic effects in the direction of ammonia generation. The specific performance of single-metal and composite electrodes has shown a strong dependence on pH and nitrate concentration conditions. Faradaic efficiency to ammonia of 92% and productivities of 0.28 mmol_NH ·cm^-2·h^-1 at 0.5 V vs reversible hydrogen electrode (RHE) values are achieved, demonstrating the implicit potential of this approach in comparison to direct N₂RR with values in the order of μmol_NH ·h^-1·cm^-2. Finally, the electrochemical rate constants (k) for Ti, Cu, and Cu₂O-Cu/Ti disk electrodes were determined by the Koutecky-Levich analysis with a rotating disk electrode (RDE) in 3.02 × 10^-6, 3.88 × 10^-4, and 4.77 × 10^-4 cm·s^-1 demonstrating an apparent synergistic effect for selective NiRR to ammonia with a Cu₂O-Cu/Ti electrode.