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The slow charge reactions at the semiconductor surface severely encumber the photocatalysis applications, which are elusive and complicated in a serial charge excitation-separation-reaction process. Both experimental and theoretical studies are essential in this area. Here, a classical numerical calculation of the charge reaction microkinetic is developed based on a simple consecutive charge separation and reaction model, a conservation law of photogenerated charges, and differential analysis. Several reaction conditions have been discussed to elucidate how a fast charge separation and reaction rate constant influence the apparent reaction kinetics. It is shown that a slower charge separation rate strongly limits the detection of higher-order reaction rates, and higher-order kinetics can be detected with all other processes faster than the reactions. This numerical calculation projects the possible limitations of kinetics study by transient techniques. [ABSTRACT FROM AUTHOR]

Multiple-step mechanisms have been extensively proposed in many electrocatalytic and/or photocatalytic oxygen evolution reactions. But the surface charge reaction is less studied quantitatively. More difficultly, the verification methods for new multiple-step photocatalytic reactions are rarely found, which could be one of the main reasons for the insufficient reaction mechanism study. In this work, we aim to elucidate the rate-law relationship of the multiple-charge reactions, which is derived based on the microkinetics calculation on the photophysical redox reactions using pre-equilibrium approximation and steady-state approximation. The numerical analysis demonstrates that an nth-order feature could be observed when the nth-step is a rate-determined step in a multiple-step reaction. Likely, the 4th-order charge transfer could be possibly found for oxygen evolution reaction, suggesting the analytical methods and results could further boost the fundamental studies in photocatalysts and multiple-step reactions. [ABSTRACT FROM AUTHOR]

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]