(558r) Electrolyte Engineering for Efficient Electrochemical Nitrate Reduction to Ammonia

Nitrates are a notorious waste product and hazardous pollutant. Traditional electrochemical water remediation approaches aim to remove nitrates by converting them into environmentally benign N₂. We have outlined and demonstrated an opportunity to electrochemically convert these waste nitrates into ammonia, a commodity product. Ammonia is traditionally made from fixed N₂ via the energy and resource intensive Haber-Bosch process, thus an appealing and supplementary alternative process could be found in electrochemical conversion of nitrates to ammonia, recycling the fixed nitrogen. We investigate electrochemical conditions (pH, nitrate concentration, applied potential) to map out the selectivity trends of nitrate reduction to ammonia at a titanium cathode. High concentrations of both protons and nitrate ions are needed to achieve high selectivity, which allows for over 75% Faradaic efficiency to ammonia in this study. Stability of the system was evaluated over time. Post-electrochemical characterization revealed titanium hydride formation at the cathode surface, which did not greatly inhibit electrochemical performance. Preliminary technoeconomic analysis indicates that it may be feasible to implement this electrochemical strategy for the production of ammonium nitrate.