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

Abstract

The electrochemical nitrate reduction reaction (NO₃RR) on titanium introduces significant surface reconstruction and forms titanium hydride (TiH_x, 0 < x ≤ 2). With <i>ex situ</i> grazing-incidence X-ray diffraction (GIXRD) and X-ray absorption spectroscopy (XAS), we demonstrated near-surface TiH₂ enrichment with increasing NO₃RR applied potential and duration. This quantitative relationship facilitated electrochemical treatment of Ti to form TiH₂/Ti electrodes for use in NO₃RR, thereby decoupling hydride formation from NO₃RR performance. A wide range of NO₃RR activity and selectivity on TiH₂/Ti electrodes between -0.4 and -1.0 V_RHE was observed and analyzed with density functional theory (DFT) calculations on TiH₂(111). This work underscores the importance of relating NO₃RR performance with near-surface electrode structure to advance catalyst design and operation.