Abstract
A promising strategy to mitigate both energy shortage and global warming is the conversion of CO2 into chemicals that can be used as fuels (chemical fuels) by utilizing renewable energy sources. Up to date, solar-driven CO2 reduction has been achieved with photochemical (PC) and photoelectrochemical (PEC) systems or electrochemical cells combined with a photovoltaic system (PV-EC). This study is intended to compare and highlight the state-of-the-art PEC systems for CO2 reduction and show the limitation factors that still hinder their widespread utilization. The review starts with a description of semiconducting photocatalyst properties and fundamental understanding of PEC CO2 reduction process. Then, the most significant performance metrics used for evaluation of PEC systems are explained in details. In addition, recent progress in PEC CO2 reduction systems is summarized and classified in different categories according to the chemical product. Different strategies such as doping, combination of two or more semiconductors, synthesis of nanostructured materials, passivation layers and co-catalysts that enhance light absorption, chemical stability, charge transfer and reduce ohmic losses and overpotentials of photoactive materials are reviewed. Besides the improvement of photocatalysts, research progress on the front of PEC reactor design, combined with the development of advanced modelling tools and characterization techniques are expected to bring PEC CO2 reduction a step closer to commercialization.
Highlights
Human civilization heavily relies on non-renewable hydrocarbon fuel sources such as crude oil, coal and natural gas for energy supply
It has been proven that the global increase of CO2 levels in the atmosphere is the major contributor to global warming [3]
The increasing research interest in the field of sunlight-assisted CO2 reduction to several chemicals or fuels has driven the development of several methods. These methods can be categorized into three groups: photochemical reduction by photocatalysts (PC), electrochemical reduction by an electrolyzer supplied with electrical energy by a typical photovoltaic cell (PV-EC) [19,23] and photoelectrochemical reduction by semiconducting photoelectrodes (PEC)
Summary
Human civilization heavily relies on non-renewable hydrocarbon fuel sources such as crude oil, coal and natural gas for energy supply. The increasing research interest in the field of sunlight-assisted CO2 reduction to several chemicals or fuels has driven the development of several methods These methods can be categorized into three groups: photochemical reduction by photocatalysts (PC), electrochemical reduction by an electrolyzer supplied with electrical energy by a typical photovoltaic cell (PV-EC) [19,23] and photoelectrochemical reduction by semiconducting photoelectrodes (PEC). There are several cases where PV-EC and PV-PEC approaches have been used for water splitting and hydrogen production, there is limited research reported using this type of systems for CO2 transformation into chemical fuels These systems have achieved very high efficiencies, but the expensive metal electrodes combined with the cost of the peripherals (cables, wires, converters etc.) are significant drawbacks for the commercialization of this technology. A significant part of the review is intended to demonstrate a lot of examples of the recent literature emphasizing the challenges of this field and showing the large variety of possible chemical products
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