Key Takeaways & Executive Findings
- •• Defect engineering creates asymmetric active sites in carbon materials, significantly enhancing electrocatalytic activity for CO2 reduction. • The review systematically categorizes defect types, formation methods, and characterization techniques, offering a comprehensive framework for material design. • Defective carbon-based catalysts offer a low-cost, stable alternative to metal-based catalysts, with potential for scalable industrial application. • Key challenges include precise control of defect density and type, and the need for advanced in-situ characterization to correlate defects with performance.
Abstract
Electrocatalytic carbon dioxide (CO2) reduction is an important way to achieve carbon neutrality by converting CO2 into high-value-added chemicals using electric energy. Carbon-based materials are widely used in various electrochemical reactions, including electrocatalytic CO2 reduction, due to their low cost and high activity. In recent years, defect engineering has attracted wide attention by constructing asymmetric defect centers in the materials, which can optimize the physicochemical properties of the material and improve its electrocatalytic activity. This review summarizes the types, methods of formation and defect characterization techniques of defective carbon-based materials. The advantages of defect engineering and the advantages and disadvantages of various defect formation methods and characterization techniques are also evaluated. Finally, the challenges of using defective carbon-based materials in electrocatalytic CO2 reduction are investigated and opportunities for their use are discussed. It is believed that this review will provide suggestions and guidance for developing defective carbon-based materials for CO2 reduction.
1. Introduction
With the rapid development of the economy and industry, the excessive consumption of fossil fuels such as coal and petroleum has caused a shortage of resources and also resulted in the emission of large amounts of greenhouse gas carbon dioxide (CO2), which has destroyed the carbon cycle in nature and induced a series of environmental problems[1–3]. In order to reduce the concentration of CO2 in the atmosphere, there are two main strategies: (1) CO2 collection and storage; (2) CO2 conversion and utilization. However, CO2 storage faces the problem of high energy consumption and easy leakage, on the other hand, the conversion of captured CO2 into energy-rich carbon fuels and chemicals is a very efficient way[4–8]. While the C＝O in linear CO2 molecules is very stable, and the energy barrier of its conversion into the target product is high, it is difficult to achieve the reduction and conversion of CO2 molecule[9–12].
At present, a variety of techniques have been developed for the reduction and conversion of CO2, including biological catalysis, photocatalysis, thermal catalysis, and electrocatalysis[13–16]. Among these, the technique of electrochemical reduction of CO2 plays a key role in the future sustainable energy use and development. The electrochemical reduction of CO2 has the following advantages: (1) CO2 can be directly converted into high-value chemicals and liquid fuels, such as carbon monoxide, formic acid and ethanol under relatively mild reaction conditions. (2) This method can be combined with renewable energy, such as using electric energy generated by renewable sources including solar, wind and tidal as driving force. (3) The reaction process can be controlled using applied potential and electrocatalyst, so the energy consumption in the whole reaction process can be minimized, and no CO2 is produced during the reaction process. (4) The electrochemical reaction system has a compact structure with modular device, this can be applied to large-scale industrial applications. Based on the above analysis, electrochemical CO2 reduction reaction (ECRR) is one of the most promising CO2 conversion technologies and has become a hot research topic in the field of energy storage[17–24].
Among many other factors, the selection and design of catalysts play a crucial role in improving the activity and efficiency of electrocatalytic CO2 reduction. As one of the most abundant elements in nature, carbon plays a leading role in the ecological environment and human economic and social development. In the recent decades, significant progress has been made in the synthesis and application of carbon-based materials with various nanostructures[25–27]. Due to their unique characteristics, carbon materials can be used as both catalyst carrier and catalyst, thus various types of carbon materials have been widely used in energy conversion and storage as well as in catalysis[28–30]. Compared to metal-based catalysts and molecular catalysts, carbon-based catalysts (such as MOFs-derived carbon, graphene, carbon nanotubes, carbon fibers, doped carbon materials, and porous carbon materials, etc.) have great advantages, mainly reflected in the following points: (1) Low price; (2) High stability under strongly acidic or alkaline conditions; (3) S
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LU Yan-kun, CHENG Bai-xue, ZHAN Hao-yu, ZHOU Peng (2024). Defect engineering of carbon-based electrocatalysts for the CO2 reduction reaction: A review. New Carbon Materials. https://doi.org/10.1016/S1872-5805_N
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Frequently Asked Questions
What is defect engineering in carbon-based electrocatalysts?
Defect engineering involves intentionally introducing structural imperfections, such as vacancies, edges, or heteroatom dopants, into carbon materials to create asymmetric active sites that enhance their electrocatalytic activity for reactions like CO2 reduction.
Why are carbon-based materials preferred for CO2 reduction?
Carbon-based materials are low-cost, highly stable under harsh conditions, and can be tailored through doping and defect engineering to achieve high activity and selectivity for CO2 reduction, making them promising alternatives to metal-based catalysts.
What are the main challenges in using defective carbon materials for CO2 reduction?
Challenges include precise control over defect type and density, understanding the structure-activity relationship, and scaling up synthesis methods while maintaining performance and stability.
How does defect engineering improve CO2 reduction performance?
Defects create active sites with modified electronic properties, which can lower the energy barrier for CO2 activation and facilitate the formation of intermediates, thereby increasing reaction efficiency and selectivity.
What characterization techniques are used to study defects in carbon materials?
Common techniques include transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR), which help identify and quantify defects.
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