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For artificial photosynthesis, the lower photon conversion efficiencies of the photogenerated charges hinder the practical application in solar energy harvesting. The challenges are commonly ascribed to the sluggish surface redox reactions and significant surface charge recombination. Although there are several transient techniques applied for monitoring the surface charges evolution, how the experimental spectroscopy data is interpreted still involves ambiguous explanations on the complicated reactions. Here, we firstly developed a parallel 1st–nth order reaction model, which could be applied to quantitatively analyze the surface charge reactions. The microkinetic calculations were carried out by varying the reaction order, rate constants as well as the contribution of the competitive ones. Interestingly, the simplified reaction model can successfully demonstrate the charges react rate changes, which can be further applied in mechanism study complementary with those experimental methods. [ABSTRACT FROM AUTHOR]

FePO 4 (FP) particles with a mesoporous structure amalgamated by nanoscale primary crystals were controllably prepared using an ultrasound-intensified turbulence T-junction microreactor (UTISR). The use of this type of reaction system can effectively enhance the micro-mixing and remarkably improve the mass transfer and chemical reaction rates. Consequently, the synergistic effects of the impinging streams and ultrasonic irradiation on the formation of mesoporous structure of FP nanoparticles have been systematically investigated through experimental validation and CFD simulation. The results revealed that the FP particles with a mesoporous structure can be well synthesised by precisely controlling the operation parameters by applying ultrasound irradiation with the input power in the range of 0–900 W and the impinging stream volumetric flow rate in the range of 17.15–257.22 mL·min−1. The findings obtained from the experimental observation and CFD modelling has clearly indicated that there exists a strong correlation between the particle size, morphology, and the local turbulence shear. The application of ultrasonic irradiation can effectively intensify the local turbulence shear in the reactor even at low Reynolds number based on the impinging stream diameter (Re < 2000), leading to an effective reduction in the particle size (from 273.48 to 56.1 nm) and an increase in the specific surface area (from 21.97 to 114.97 m2·g−1) of FP samples. The FP irregularly-shaped particles prepared by UTISR exhibited a mesoporous structure with a particle size of 56.10 nm, a specific surface area of 114.97 m2·g−1 and a total pore adsorption volume of 0.570 cm3·g−1 when the volumetric flow rate and ultrasound power are 85.74 mL·min−1 and 600 W, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhanced photoelectrochemical water oxidation on Bi 2 WO 6 photoanodes by heterojunction and facet-engineering. • The heterojunction of WO 3 /Bi 2 WO 6 improved charge separation and transfer. • Crystalline {2 0 0} and {1 3 1} orientations on WO 3 /Bi 2 WO 6 and Bi 2 WO 6 films, respectively. • A 1st-order and a 2nd-order charge reaction kinetics were discovered on {2 0 0} and {1 3 1} facets, respectively. Charge separation and transfer kinetics play a significant role in photocatalytic water oxidation, which is sensitive to the crystal facets. Herein, the bismuth tungstate (Bi 2 WO 6) films were used as a model photoanode to investigate how the photogenerated charges react on {1 3 1} and {2 0 0} facets under constantly applied bias in a photoelectrochemical (PEC) cell. On the WO 3 electron transport layer, the Bi 2 WO 6 films have a {2 0 0} orientation while possessing a {1 3 1} orientation on the fluorine-doped tin oxide substrate. It is discovered that {2 0 0} facets on the WO 3 /Bi 2 WO 6 heterojunction display a low overpotential of PEC water oxidation, showing a 1st-order reaction behavior and faster charge transfer rate constant. Differently, water oxidation on the {1 3 1} facet on Bi 2 WO 6 displays a 2nd-order reaction behavior. Further, density functional theory calculations were applied to demonstrate how the rate-determining step and the major formed intermediate correlate with the charge accumulation and reaction orders. The findings of this work shed fundamental light on how to rationally design and precisely modulate surface charge density and reaction kinetics for efficient (photo)electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhanced photoelectrochemical water oxidation on anatase TiO 2 nanotubes photoanodes. • Ultrafast charge separation and parallel charge consumption on TiO 2 films. • Increased doping level and negative shift of flat-band potential on TiO 2 nanotube photoanodes. • A 1st-order and a 2nd-order charge reaction kinetics were discovered on TiO 2 nanotube photoanodes. • A parallel reaction model was established coincided with the reaction order transition. Artificial photosynthesis relies on the photoreactions between the chemical molecules and photogenerated charges. The oxygen evolution reactions are regarded as the most difficult procedure, because they are multiple-step reactions with multiple charges transfer. Notwithstanding the extensive study on photoelectrochemical and photochemical water oxidation, understanding how the surface charge reacts with the chemical molecules is limited, especially the reaction kinetics of the surface charges. We prepared anatase TiO 2 nanotubes array and dense polycrystalline TiO 2 films on Ti substrates, where the photocurrent increased about 4–4.5 times on nanotubes compared with the dense films. Moreover, the surface charge reaction rate and the accumulated charge densities were analyzed by transient surface photovoltage and transient photocurrent techniques. It was found a 2nd-order charge reaction behavior could be found when the charge density was high, differently, a 1st-order charge reaction could be observed when the charge density was low. The nanotubes structures would in situ grow from the Ti substrates, which simultaneously enhanced charge separation and transfer kinetics to improve the PEC performance. [ABSTRACT FROM AUTHOR]

• A CFD model providing reasonable predictions of FePO4 synthesis in a CSIR is proposed. • Revealing effects of turbulent intensification on the performance of the CSIR. • Revealing the mechanism controlling the synthesis performance in a CSIR. LiFePO 4 particles has been widely recognised as a promising positive electrode material for rechargeable lithium-ion batteries due to its excellent properties. Confined impinging jet reactor was recently proposed to replace the stirring reactor for synthesising LiFePO 4 nanoparticles. It has been recognised that the use of impinging jet reactor can provide higher mixing intensity and shorter residence time for the reaction so as to improve the synthesis efficiency. The present work conducts CFD simulations to gain a better understanding of the mechanism of LiFePO 4 synthesis in an impinging jet reactor, focusing on the effects of local turbulent kinetic energy and turbulence dissipation rate distributions in the impinging core region on the mixing of two reactant streams and reaction kinetics. Compared with the experimental results, it is revealed that larger turbulent kinetic energy in the impinging centre region can effectively promote the mixing of reactant streams but the reaction completeness will be reduced due to shortening of reaction time if a large turbulence dissipation rate occurs in the impinging core region. It is also indicated from the simulations that the reaction completeness of LiFePO 4 synthesis significantly depends on the turbulent mixing and turbulent kinetic energy distribution but less on reaction kinetics. [ABSTRACT FROM AUTHOR]