Effect of Oxygen Content on the Photoelectrochemical Activity of Crystallographically Preferred Oriented Porous Ta₃N₅ Nanotubes

Abstract

Crystallographically preferred oriented porous Ta 3 N 5 nanotubes (NTs) were synthesized by thermal nitridation of vertically oriented, thick-walled Ta 2 O 5 NTs, strongly adhered to the substrate. The adherence on the substrate and the wall thickness of the Ta 2 O 5 NTs were finetuned by anodization, thereby helping to preserve their tubular morphology for nitridation at higher temperatures. Samples were studied by scanning electron microscopy, high-resolution electron microscopy, X-ray diffraction, Rietveld refinements, ultraviolet−visible spectrophotometry, X-ray photoelectron spectroscopy, photoluminescence spectra, and electrochemical techniques. Oxygen content in the structure of porous Ta 3 N 5 NTs strongly influenced their photoelectrochemical activity. Structural analyses revealed that the nitridation temperature has crystallographically controlled the preferential orientation along the (110) direction, reduced the oxygen content in the crystalline structure and the tubular matrix, and increased the grain size. The preferred oriented porous Ta 3 N 5 NTs optimized by the nitridation temperature presented an enhanced photocurrent of 7.4 mA cm −2 at 1.23 V vs RHE under AM 1.5 (1 Sun) illumination. Hydrogen production was evaluated by gas chromatography, resulting in 32.8 μmol of H 2 in 1 h from the pristine porous Ta 3 N 5 NTs. Electrochemical impedance spectroscopy has shown an effect of nitridation temperature on the interfacial charge transport resistance at the semiconductor−liquid interface; however, the flat band of Ta 3 N 5 NTs remained unchanged.

Photoelectrode for water splitting: Materials, fabrication and characterization

“…For the steady-state PL, researchers usually hold the point that the lower the PL intensity is, the less the recombination centres will exist [102,103]. It is widely used to characterize the defect state in Ta 3 N 5 as demonstrated in Fig.…”

“…It is widely used to characterize the defect state in Ta 3 N 5 as demonstrated in Fig. 13a, where Khan et al [103] attributed the lower PL intensity at higher temperature to the suppressed oxygen defect states. However, this is partially correct only when the recombination occurs via recombination centres rather than from the band-to-band recombination.…”

Evolution of TiO2 Nanotubular Morphology Obtained in Ethylene Glycol/Glycerol Mixture and its Photoelectrochemical Performance

“…These electrodes were thermally treated at 450 °C which contributes to avoid organic contamination. Prior to each measurement, the photoanodes were cleaned by 3 successive cyclic voltammetry scans, applying potentials from 1 V to -1 V vs Ag/AgCl with a scan rate of 50 mV/s 43,44,45 . Prior to Electrochemical impedance spectroscopy (EIS) measurements, 3 successive CV runs were carried out.…”

“…of illumination. Since even 10 sec illumination is enough for the open circuit potential (V oc ) stability; however, we followed experimental protocol of giving more time to stabilize the V oc under illumination before performing the EIS experiments 43,44,45 Figure 1 shows the current transient (I-t) curve obtained during the maximum time period of the anodization process. At the beginning of the anodization process, up to ~5 minutes, the anodizing current density increases abruptly to a value of ca.…”

Pristine Ta3N5 Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

“…On the other hand, in the presence of the redox couple of [Fe(CN) 6 ] 3À/4À the pristine Ta 3 N 5 photoelectrodes have presented improveda nd stable PEC activity even under lower applied potential. [33][34][35][36] Furthermore, for other devices such as those based on hematite the [Fe(CN) 6 ] 3À/4À has been found to be an efficient sacrificiala gent. [18] Now,t he question remains as to why pristine Ta 3 N 5 photoelectrodes requireh igh external biasing for water oxidation and why as acrificial agent dramatically improves its PEC activity even at lower externalb iasing.…”