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

Abstract

The electrochemical nitrate reduction reaction (NO 3 RR) on titanium introduces significant surface reconstruction and forms titanium hydride (TiH x , 0 < x ≤ 2). With ex situ grazing-incidence X-ray diffraction (GIXRD) and X-ray absorption spectroscopy (XAS), we demonstrated near-surface TiH 2 enrichment with increasing NO 3 RR applied potential and duration. This quantitative relationship facilitated electrochemical treatment of Ti to form TiH 2 /Ti electrodes for use in NO 3 RR, thereby decoupling hydride formation from NO 3 RR performance. A wide range of NO 3 RR activity and selectivity on TiH 2 /Ti electrodes between −0.4 and −1.0 V RHE was observed and analyzed with density functional theory (DFT) calculations on TiH 2 (111). This work underscores the importance of relating NO 3 RR performance with near-surface electrode structure to advance catalyst design and operation.

Recent advances in nanostructured heterogeneous catalysts for N-cycle electrocatalysis

“…We recommend some works once more. According to Tarpeh's group [468], the near surface of an unaltered Ti foil electrode (99.7%, 0.127 mm) changes into a composite consisting of various phases such as α-Ti, TiOx (0 < x ≤ 2), and TiHx after NO3RR. Simultaneously, the formation of crystalline titanium nitride is ruled out.…”

Role of Electronic Structure on Nitrate Reduction to Ammonium: A Periodic Journey

“…Lines are to guide the eye. Ti is excluded from (a) due to uncertainties in the work function , and surface termination (e.g., oxidation state or the presence of hydrides) , but is included in Figure S20 for reference. (c) Selectivity to nitrite at –0.4 and –0.5 V RHE against the calculated reaction free energy for nitrite reduction to nitric oxide.…”

“…High work function metals also have more anodic potentials of zero charge, providing nominally negatively charged surfaces that electrostatically attract protons. In contrast, low work function Ti has the strongest H chemisorption energy, providing H*-saturated surfaces that impede nitrate adsorption and/or hydrogen-bond-formation kinetics (i.e., PCET or hydrogenation). ,, The dependence of the nitrate rate order on Δ G H* – Δ G NO 3 – * (discussed in Section ) may provide additional context for understanding the relationship between NO 3 RR FE and work function as a future direction for the field. Differences in NO 3 RR FE are expected to be more pronounced for lower nitrate concentrations typical of, e.g., groundwater (∼1.5 mM). ,,,, …”

“…Here, we discuss the relationship between nitric oxide adsorption and dissociation energies and TM electronic structure by DFT. We limit our discussion to elements in the metallic state under the NO 3 RR conditions considered here, with consideration of Ti (uncertain surface oxidation state) 38,39 in the Supporting Information (Table S3).…”

“…To better understand the exceptional ammonium selectivity of Co, we consider the calculated reaction free energies of nitrite reduction to nitric oxide and its further dissociation (Figure 7c,d). Selectivity to nitrite nominally decreases as Δ(G NO* − 29,48 and surface termination (e.g., oxidation state or the presence of hydrides) 38,39 but is included in Figure S20 G NOd 2 − * ) decreases (Figure 7c). However, while nitrite reduction is more favorable on Ni than Co, Ni demonstrates a poorer ammonium selectivity than Co.…”