(490a) Electrolyte Engineering for Efficient Electrochemical Nitrate Reduction to Value-Added Products | AIChE

(490a) Electrolyte Engineering for Efficient Electrochemical Nitrate Reduction to Value-Added Products


Nielander, A., Stanford University
Jaramillo, T., Stanford University
McEnaney, J. M., Stanford University
Nitrate contamination of bodies of water is both a human health concern and disrupts fragile aquatic ecosystems. Such contamination is largely attributed to the application of nitrate-based fertilizers to crops, upon which excess nitrates become incorporated into agricultural runoff. Such nitrate-based fertilizers are produced via the Ostwald process, which requires temperatures up to 900 ËšC and emits more N2O globally than any other industrial process. Furthermore, the process most commonly uses Haber-Bosch ammonia, which is additionally cost- and energy-intensive to produce and is responsible for 1% of global CO2 emissions. While many studies have focused on electrochemical reduction of nitrates to environmentally-benign N2, direct electrochemical conversion of nitrates to ammonia could close this gap in the nitrogen cycle and recycle expensive pollutants (NO3-), to form value-added products.

To this end, a titanium-based cathode was used to electrochemically reduce NO3- to ammonia. Applied potential, electrolyte pH, and nitrate concentration were varied to map selectivity toward ammonia under a variety of electrode/electrolyte conditions. Selectivity varied depending on proton and nitrate anion concentration, with a maximum Faradaic efficiency (FE) toward NH3 of 82% occurring at a pH of 1 and 0.4 M NO3- under an applied potential of -1 V vs RHE and current density of -22 mA/cm2. Additionally, the cathode was stable over 8 hours while demonstrating a FE toward ammonia greater than 50%. Analysis of the cathode during and after operation suggests that titanium hydride (TiHx) may play an important role in the reduction to NH3. We have recently expanded our efforts to develop new electrochemical syntheses involving such environmental pollutants (NO3-), with an aim toward more sustainable resource cycling strategies that can be coupled to renewable sources of electricity.