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Free keywords:
hydrogen storage; organic synthesis; photocatalysis; photocharging; photodoping; semiconductors; solar batteries
Abstract:
Photocharging or photodoping is a process in which electrons are accumulated in a semiconductor upon bandgap excitation followed by quenching of the photogenerated holes by reductants. In semiconductors with excess of electrons, negative charge is compensated by cations, of which the most ubiquitous is H+. Photocharging of semiconductors has been studied since 1980s both from a fundamental perspective and application—as source of electrons and protons for reduction of organic compounds in the dark, solar-to-electric energy conversion, and recently also in the design of autonomous microswimmers. In this review, experimental data collected over 40 years of research are summarized and quantified. Maximum specific concentration of electrons stored in 1 g of a semiconductor, maximum average number of electrons stored per semiconductor particle, initial rate of photocharging, and initial rate of discharging are calculated for six classes of semiconductor materials, Ti-, Zn-, Cd-, In-, W-based and graphitic carbon nitrides. Dependence of these parameters on material specific surface area, particle volume, and other properties is analyzed and trends are derived. A public database of photocharged materials is created to facilitate design of high-performing materials with photocharging function, their application as rechargeable reductants in organic synthesis and development of devices.
