CFD modeling and simulation of benzyl alcohol oxidation coupled with hydrogen production in a continuous-flow photoelectrochemical reactor

Various conversion routes of biomass and its derivative compounds into high-value products has attracted attention from researchers recently. Among these, a solar-driven photoelectrochemical (PEC) oxidation approach of biomass alcohols to aldehydes is particularly of great interest for the potential applications because the reaction is selective and simultaneously accompanied with hydrogen production. Here, we propose a simulation of selective oxidation of benzyl alcohol into benzaldehyde coupled with hydrogen production in a 2-dimensional continuous-flow PEC reactor using COMSOL Multiphysics (5.6). In order to develop and fabricate a simple yet efficient reactor for a practical use, it is crucial to investigate the effects of operating and design parameters of the reactor on the reactions. Our studies demonstrated that the main contributions to product formation were the electrolyte flow velocity and the width of electrolyte channels. The optimized design parameter exhibited good photoelectrochemical performance with uniform potential distribution within the channels which served diffusion of neutral and charged species and electrochemical reaction. The maximum conversion of benzyl alcohol in this work was 48.25% with 100% selectivity of benzaldehyde. These findings are key for the design of the continuous-flow PEC reactor that can be applied to any series of biomass conversion reactions under mild conditions.

A Facile Surface Passivation of Hematite Photoanodes with TiO2 Overlayers for Efficient Solar Water Splitting

The surface modification of semiconductor photoelectrodes with passivation overlayers has recently attracted great attention as an effective strategy to improve the charge-separation and charge-transfer processes across semiconductor-liquid interfaces. It is usually carried out by employing the sophisticated atomic layer deposition technique, which relies on reactive and expensive metalorganic compounds and vacuum processing, both of which are significant obstacles toward large-scale applications. In this paper, a facile water-based solution method has been developed for the modification of nanostructured hematite photoanode with TiO2 overlayers using a water-soluble titanium complex (i.e., titanium bis(ammonium lactate) dihydroxide, TALH). The thus-fabricated nanostructured hematite photoanodes have been characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Photoelectrochemical measurements indicated that a nanostructured hematite photoanodes modified with a TiO2 overlayer exhibited a photocurrent response ca. 4.5 times higher (i.e., 1.2 mA cm(-2) vs RHE) than that obtained on the bare hematite photoanode (i.e., 0.27 mA cm(-2) vs RHE) measured under standard illumination conditions. Moreover, a cathodic shift of ca. 190 mV in the water oxidation onset potential was achieved. These results are discussed and explored on the basis of steady-state polarization, transient photocurrent response, open-circuit potential, intensity-modulated photocurrent spectroscopy, and impedance spectroscopy measurements. It is concluded that the TiO2 overlayer passivates the surface states and suppresses the surface electron-hole recombination, thus increasing the generated photovoltage and the band bending. The present method for the hematite electrode modification with a TiO2 overlayer is effective and simple and might find broad applications in the development of stable and high-performance photoelectrodes.

Computational modeling of self-trapped electrons in rutile TiO2

Anionic polaron migration in rutile TiO₂ is modeled by the valence bond representation in conjunction with the constrained density functional theory.

Catalytic role of TiO(2) terminal oxygen atoms in liquid-phase photocatalytic reactions: oxidation of aromatic compounds in anhydrous acetonitrile

On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen-isotope-labeled Ti(18) O2 as the photocatalyst, we demonstrate that (18) Os atoms behave as real catalytic species in the photo-oxidation of acetonitrile-dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO2 . The experimental evidence allows a terminal-oxygen indirect electron-transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence-band holes at Os species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO2 surface and their subsequent healing with oxygen atoms from either O2 or H2 O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO2 photocatalytic phenomena.