Ultrathin Silicon Oxide Film‐Induced Enhancement of Charge Separation and Transport of Nanostructured Titanium(IV) Oxide Photoelectrode

Abstract

The development of nanostructured semiconductor electrodes represented by a mesoporous TiO2 nanocrystalline (mp‐TiO2) film is currently bringing great progresses in photoelectrochemical (PEC) devices for solar‐to‐electricity and solar‐to‐chemical conversion. Two serious losses can occur in PEC devices: 1) recombination between the conduction band (CB) electrons and valence band (VB) holes in the bulk and at the surface and 2) back reaction or electron trapping by oxidant in the electrolyte solution during transport to the electron‐collecting electrode. Thus, the major challenge in common with the nanostructured semiconductor photoanodes is to achieve efficient charge separation and electron transport. In this study, an ultrathin SiOx layer was formed on both the external and the internal surface of mp‐TiO2 using an original chemisorption‐calcination technique employing 1,3,5,7‐tetramethyltetrasiloxane as a starting material. The SiOx surface modification of the mp‐TiO2 photoanode drastically prolongs the mean lifetime of CB‐electrons in TiO2 because of enhanced charge separation and electron transport by the negative charge applied in aqueous electrolyte solution. We have demonstrated that the performance of a one‐compartment H2O2‐photofuel cell using mp‐TiO2 as the photoanode is greatly boosted by the surface modification with the SiOx layer. We anticipate that this methodology is widely applicable to nanostructured metal oxide semiconductor electrodes, contributing to the improvement in the performance of PEC devices.

Optical Hot Spot Generation by the Plasmonic Coupling of Au Nanoparticles in the Nanospaces of Mesoporous Titanium(IV) Oxide

“…TMCTS is chemisorbed on various metal oxides such as TiO 2 to form a monolayer containing residual Si-H groups with a high density. − Scheme shows the strategy for forming Au NPs on TiO 2 . In this study, a glass plate with a fluorine-doped SnO 2 film was used as the substrate for the mp-TiO 2 film.…”

“…On the other hand, a mesoporous TiO 2 nanocrsytalline (mp-TiO 2 ) film and the analogs with a large surface area have been used as a base electrode for photoelectrochemical devices . Also, we previously showed by means of various characterization techniques that the 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) monolayer and silicon oxide ultrathin layer can be formed on mp-TiO 2 using a chemisorption–calcination (CC) method. − …”

Hydrogen peroxide photo-fuel cells

“…The performances of one-compartment H 2 O 2 -PFC with the structure of SiO x ( N )/mp-TiO 2 (photoanode) | deaerated aqueous solution of 0.1 M NaClO 4 containing 0.1 M H 2 O 2 (pH3) | PB (cathode) were assessed under UV-light irradiation by using UV-LED as a light source (365 nm, I 365 = 31.2 mW cm −2 nm −1 ). 26 The mp-TiO 2 photoanode cell provided a J sc of 0.71 mA cm −2 and a V cell of 0.62 V. Interestingly, the surface modification of mp-TiO 2 with SiO x ( N = 1) drastically increases J sc to 1.2 mA cm −2 and V cell to 0.70 V, whereas the J sc decreases at N ≥ 2. To clarify the origin, the photopotential decay after interrupting irradiation was measured for two-electrode photoelectrochemical (PEC) cells with the structure of SiO x ( N = 0 and 1)/mp-TiO 2 (photoanode) | deaerated aqueous electrolyte solution of 0.1 M NaClO 4 containing 0.1 M H 2 O 2 (pH 3) | GC (cathode).…”

“…25 The film thickness (l SiO ). 26 The mp-TiO 2 photoanode cell provided a J sc of 0.71 mA cm −2 and a V cell of 0.62 V. Interestingly, the surface modification of mp-TiO 2 with SiO x (N = 1) drastically increases J sc to 1.2 mA cm −2 and V cell to 0.70 V, whereas the J sc decreases at N ≥ 2. To clarify the origin, the photopotential decay after…”

Platinum and Iridium Oxide Co-modified TiO2 Nanotubes Array Based Photoelectrochemical Sensors for Glutathione

“…In addition, the unique one-dimensional However, the application of TiO2 in PEC detection is limited by its wide band gap and fast recombination of photogenerated charges, which can lower the photoenergy conversion efficiency and sensitivity of PEC sensors. A typical method to solve these problems is modification the TiO2 photoelectrode with noble metals [22][23][24] or metal oxides [25,26]. The presence of noble metal results in the formation of a Schottky barrier at the metal-semiconductor interface, which can reduce the recombination of photogenerated charges and promote the separation of photogenerated charge carriers [27][28][29].…”