Effect of different hole scavengers on the photoelectrochemical properties and photocatalytic hydrogen evolution performance of pristine and Pt-decorated TiO2 nanotubes

Abstract

TiO2 nanotubes have been investigated in photoelectrochemistry and photocatalysis for more than a decade. However, up to now, a systematic investigation of different hole scavengers is still lacking. Here we investigate the effect of the most relevant sacrificial hole scavengers on the photoelectrochemical properties and photocatalytic H2 evolution performance of pristine and Pt-decorated anodic TiO2 nanotubes. We examine methanol, isopropanol, ethylene glycol, EDTA-Na2, as well as Na2SO3, and find that the incident photocurrent conversion efficiency (IPCE) of the TiO2 nanotubes in 0.1 M Na2SO4 electrolytes increases by 1.8-3.1 times, depending on the used hole scavenger. The efficiency increases in the sequence Na2SO3 < isopropanol < MeOH < ethylene glycol < EDTA-Na2. In presence of any hole scavenger, for nanotubes in the length-range of 2-10 µm, the photocurrent spectra and the ICPE magnitude are independent of the tube length. The photocurrent onset potential (optical flatband potential) is significantly affected by the different type of scavengers, in line with their red-ox potential. Under open circuit conditions (photocatalytic conditions), organic hole scavengers lead to a 10.0-28.8 times higher H2 production by TiO2 nanotubes than the scavenger-free case, with a sequence MeOH > i-PrOH > EDTA-Na2 > EG, while a detrimental effect of Na2SO3 is observed. These results are compared to results obtained for TiO2 particles, and discussed in terms of various concepts in the literature.

One‐step synthesis of a WO3‐CuS nanosheet heterojunction with enhanced photocatalytic performance for methylene blue degradation and Cr(VI) reduction

“…However, the addition of MeOH resulted in a violent suppression of the photocatalytic activity. It was reported in previous studies that MeOH can scavenge both h + and •OH . In the trapping experiments herein, the kinetic rate constant of MB removal in the existence of Na 2 C 2 O 4 was 0.0202 min −1 , which is 62% of the value without this •OH scavenger.…”

Photoelectrochemical properties of “increasingly dark” TiO2 nanotube arrays

“…On the other hand, for the 400-1h and 500-1h samples ηtrans does not exceed 95% even at 1 V. Evidently, introduction of defects into TiO2 lattice affects the competition between the recombination and the charge transfer to the electrolyte. Apparently, increased recombination rates in the hydrogenated TNTAs lead to the anodic shift of the corresponding jss saturation potentials, and thus, it can be expected that higher jss values would be generated by these samples at potentials above 1 V. previous work [33], in the present work the potential was changed stepwise from -0.5 to 1 V in order to avoid the formation of stable peroxide surface states under illumination at anodic bias [34], which could cause a significant reduction current at cathodic bias [35]. The determined Efb values are summarized in Table 1.…”

SrTiO3/Bi4Ti3O12 Nanoheterostructural Platelets Synthesized by Topotactic Epitaxy as Effective Noble-Metal-Free Photocatalysts for pH-Neutral Hydrogen Evolution

“…Here, the holes at VB/Bi 4 Ti 3 O 12 were consumed by the hole-scavenger methanol. 54 PL spectroscopy with an excitation wavelength of 320 nm was used to evaluate the separation efficiencies of the photo-excited charge carriers in the studied photocatalyst platelets ( Figure 7 ). The Bi 4 Ti 3 O 12 platelets show strong PL emission peaks at approximately 415 and 450 nm, which is in line with the reported PL spectra of Bi 4 Ti 3 O 12 .…”