Photocatalysts Based on Organic Semiconductors with Tunable Energy Levels for Solar Fuel Applications

Abstract

development of sustainable energy sources. [1] Among these, solar energy has the greatest potential, with more solar energy irradiating the surface of the Earth in one hour than human society consumes in one year. [2] However, the intermittency of solar energy limits its utility. In order for solar energy to provide power on a scale commensurate with that currently generated from fossil fuels, it must be stored and supplied to users on demand. [3] On short timescales (seconds to days) this is possible to achieve using batteries, which can store electricity generated from solar photovoltaics. [4,5] However, the expensive materials required and their relatively high rates of self-discharge make batteries unsuitable for seasonal energy storage. [6,7] Storing solar energy in the chemical bonds of a fuel, which can be stored indefinitely at low cost, transported, and converted to electrical or heat energy on demand is therefore highly desirable. Solar fuels such as H 2 , CH 3 OH, and CH 4 can be generated from abundant and renewable feedstocks such as water and CO 2 using semiconductor photocatalysts. The vast majority of research to date has focused on photocatalysts fabricated from wide bandgap semiconductors such as TiO 2 , [8] SrTiO 3 , [9] and carbon nitride (CN). [10-14] Photocatalysts based on some of these semiconductors have achieved operational stabilities exceeding 1000 h and maximum external quantum efficiencies (EQEs) of over 50% for overall water splitting. [9,15-18] However, their wide and difficult to tune bandgaps mean that photocatalysts fabricated from these semiconductors are almost exclusively active at UV wavelengths, which carry <5% of solar energy. [19] This fundamentally limits their efficiency below what is required for many practical solar fuels applications. For example, an estimated solar-to-hydrogen efficiency (η STH) of 5-10% would be required to photocatalytically produce H 2 at a cost that meets the U.S. Department of Energy's target of $2-4 kg −1 , which is difficult or impossible to achieve with the aforementioned wide bandgap semiconductors. [20] This has stimulated interest in developing novel photocatalysts based on semiconductors with narrower bandgaps that are able to absorb a greater proportion of the solar spectrum and can therefore achieve higher maximum theoretical solar energy conversion efficiencies. [18] Among these, non-CN organic semiconductors have recently gained prominence due to the Earth abundance of their constituent elements, and their high extinction coefficients and The photocatalytic synthesis of solar fuels such as hydrogen and methane from water and carbon dioxide is a promising strategy to store abundant solar energy in order to overcome its intermittency. Although this approach has been studied for decades using inorganic semiconductor photocatalysts, organic semiconductors have only recently gained notable attention. The tunable energy levels of organic semiconductors can enable the design of photocatalysts with optimized solar light utilization. However,...

Boosting the Photocatalytic Hydrogen Evolution Activity for D–π–A Conjugated Microporous Polymers by Statistical Copolymerization

“…[ 33 ] The high photocatalytic activity of PyDOBT‐1 can be ascribed to not only the advantages of BTDO but also the pyrene unit, which features with strong electron‐donating ability, high coplanarity, and extended π‐electron delocalization. [ 26,31,36,40 ] In order to get in‐depth insight into the influence of chemical structure and the monomer compositions on the photocatalytic activity, we constructed here a series of D–π–A CMP photocatalysts using statistical copolymerization by insetting a “π‐bridge” of benzene between the pyrene donor and BTDO acceptor units. The influence of chemical structure and particularly the monomer compositions on the photocatalytic activity of the resulting D–π–A copolymers was systematically investigated by tuning the feed ratio of donor to acceptor.…”

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Selective CO2‐to‐CH4 Photoconversion in Aqueous Solutions Catalyzed by Atomically Dispersed Copper Sites Anchored on Ultrathin Graphdiyne Oxide Nanosheets

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