Photochargeable Semiconductors: in “Dark Photocatalysis” and Beyond

Abstract

Photochargeable semiconductors enable energy harvesting and storage in a single material. Charges separated upon absorption of photons can accumulate in highly energetic trap states if morphology, size, and chemical composition are appropriately chosen. For example, electrons can survive for several hours if hole scavengers are used to prevent their recombination with photogenerated holes, and their negative charge is balanced by positive counter‐ions. The first database of charge‐storing semiconductors is recently released, containing information from more than 50 publications within the past 40 years. Now, the database has been updated with more than 90 entries from the latest works on the topic. These materials have been largely utilized in the context of “dark photocatalysis”, that is, redox reactions enabled by photocharged semiconductors long after cessation of light irradiation. Nevertheless, a variety of further potential applications have not received enough visibility, including memory storage, steel anti‐corrosion, sensors, and micromotors. In this review, the key figures of merit of photocharged semiconductors and the empirical relationships found between them is highlighted. After showing the latest advances in dark photocatalysis, it is discussed how other application fields may benefit from these materials. For each area, promising research directions based on the findings from the database are recommended.

Cyclic time-separated redox reaction using accumulated electrons in titanium(iv) oxide in a two-phase system

“…To obtain reduction products with high selectivity, hole scavengers, such as alcohols, are often used to prevent back reaction and recombination. Interest has recently been shown in a new type of photocatalytic reaction called "dark photocatalysis" 12,13 or "round-the-clock photocatalysis", 14 though some reactions based on a similar phenomenon, such as a metal corrosion system, 15 reductive energy storage systems, 16 the reduction of toxic metal ions and nitrogen oxide ions, 17,18 and the hydrogenation of carbonyl compounds 19,20 using metal oxide photocatalysts, have already been reported. The advantage of catalysis is that redox reactions can be driven even in the dark using the reducing/oxidizing energy stored under photoirradiation.…”

Bimetallic CoNi-metal–organic framework@molybdenum disulfide core–shell Z-scheme heterojunctions with broad-spectrum response toward optimized photocatalytic performance

“…In recent times, the accelerated progress of society and industry has resulted in the fast depletion of finite resources, concomitant with the emergence of environmental contamination (such as the difficult degradation of toxic substances, the release of industrial waste and global warming), which seriously affects and threatens the survival and development of human beings. 1–3 Solar energy, as a rich, low-cost, pollution-free renewable energy, has attracted people's attention, and photocatalysis, as an emerging green technology, has the potential to deal with today's environmental and energy problems, such as water decomposition to produce hydrogen 4,5 and removal of toxic and harmful substances from water. 6,7 While addressing pollutants in the environment, clean energy can also be created from solar energy.…”

Photodoping-based broadband photochromism of semiconductor nanocrystals under air operated by a supramolecular gel

“…The unique characteristics of photodoping have also been applied to various fields other than photochromism, including photocatalysis 9–12 and solar energy storage. 13 However, in general, photodoping occurs only under inert atmospheres because the accumulated electrons react with oxygen, posing large impediments to its wide applications.…”