Catalytic Performance and Near-Surface X-ray Characterization of Titanium Hydride Electrodes for the Electrochemical Nitrate Reduction Reaction.

The electrochemical nitrate reduction reaction (NORR) on titanium introduces significant surface reconstruction and forms titanium hydride (TiH, 0 < x ≤ 2). With grazing-incidence X-ray diffraction (GIXRD) and X-ray absorption spectroscopy (XAS), we demonstrated near-surface TiH enrichment with increasing NORR applied potential and duration. This quantitative relationship facilitated electrochemical treatment of Ti to form TiH/Ti electrodes for use in NORR, thereby decoupling hydride formation from NORR performance. A wide range of NORR activity and selectivity on TiH/Ti electrodes between -0.4 and -1.0 V was observed and analyzed with density functional theory (DFT) calculations on TiH(111). This work underscores the importance of relating NORR performance with near-surface electrode structure to advance catalyst design and operation.