Tailoring Magnéli Phase Titanium Suboxides for Electrochemical Nitrate Reduction to Ammonium

This study investigated the effect of synthesis temperature (550 to 1050 °C) on the performance of Magnéli phase titanium suboxide electrodes for electrochemical nitrate (NO3–) reduction. Different synthesis temperatures produced distinct Magnéli phases, which were characterized using X-ray diffraction and X-ray photoelectron spectroscopy. Higher temperatures increased oxygen vacancy and Ti3+ concentrations. The electrode synthesized at 850 °C consisted of a mixed Magnéli phase with predominant Ti9O17 structure and demonstrated the highest NO3– removal (∼60%) and low nitrite selectivity (∼2.8%) at −0.8 V/SHE with an 8.3 s hydraulic residence time (pH ∼8). This electrode achieved a Faradaic efficiency of 72% for ammonia production at −1.4 V/SHE with 100 mM NO3– concentration. The pseudo-first-order rate constant (172 h–1) exceeded those of other nonprecious and precious metal electrodes, attributed to the high specific surface area per volume (∼1.3 × 106 m–1) and efficient mass transfer enabled by the flow-through reactor design. Superior performance was attributed to optimized electronic properties, including band gap (1.31 eV) and flat band potential (−1.10 V/SHE), which facilitated efficient electron transfer at the electrode/electrolyte interface. These results underscore the critical role of synthesis temperature in tuning the electrochemical properties of Magnéli phase electrodes, providing insights for developing efficient, nonprecious-metal-based electrodes for nitrate remediation.