Abstract
The massive emission of greenhouse gas carbon dioxide (CO2) has attracted great attention due to its impact on global warming. Researchers have been working on this project for a long time and found that photocatalytic CO2 reduction has shown great potential in developing cost-effective clean energy resources. However, the efficiency of CO2 photo-reduction is low because of limited light absorption efficiency, undesired charge recombination, and high CO2 activation barrier in thermodynamics and kinetics. In this Perspective, we concentrate on recent advanced strategies to improve CO2 photo-reduction and illustrate the mechanism of CO2 activation and we intend to find the most plausible strategy on solving the problems listed. The mainstream approaches for boosting CO2 photo-reduction efficiency lie in (1) tuning the bandgap of the photocatalysts by incorporating heteroatoms in a photosensitizer causing enhanced light absorption; (2) constructing heterojunctions resulting in effective charge separation; and (3) introducing surface defects, basic sites, and functional groups, as well as increasing the surface area of catalysts contributing to enhanced CO2 adsorption and activation. Moreover, this Perspective will conclude with brief perspectives and recommendations regarding the promising research of converting CO2 into valuable fuels.
Highlights
CO2 emission has been rapidly growing, which caused the greenhouse effect and global warming nowadays
The electrons are captured by active sites on the surface where their adjacent absorbed CO2 molecule would be reduced if the conduction band (CB) potential of the semiconductor is more negative than the normal hydrogen electrode (NHE) of CO2
We comprehensively summarize the recent findings of enhanced CO2 photo-reduction efficiency from the parts including improvement of light absorption and effective charge separation as well as the enhancement of CO2 adsorption and activation
Summary
CO2 emission has been rapidly growing, which caused the greenhouse effect and global warming nowadays. (I) Usually, the most accepted mechanism is the CO2 reduction via selective generation of the CO2− intermediate formed with −1.9 V negative potential vs NHE in theory.30 This step is the rate-limiting step since an enormous reorganizational energy needs from the linear molecule of CO2 to the radical anion of bent CO2−.6. It is important to preserve a fair number of protons in solution and enriched electron density around the exposed sites of photo-catalysts in the PCET mechanism As a result, both thermodynamics and kinetics limitations increase the difficulties in converting CO2 into fuels. We comprehensively summarize the recent findings of enhanced CO2 photo-reduction efficiency from the parts including improvement of light absorption and effective charge separation as well as the enhancement of CO2 adsorption and activation. We hope that this review can provide comprehensive discussions about CO2 photoreduction and help people optimize their own reaction system for CO2 reduction
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