Sn基电催化剂还原CO2制备甲酸的研究进展

Progress on Sn-based catalysts for electrochemical conversion of CO2 to formic acid

关键词:  气候变化  CO₂电催化还原  Sn基电催化剂  甲酸

摘要:

工业革命以来，大气中CO₂浓度的增加导致全球气候变化和海平面上升，严重威胁人类的生存环境。电催化CO₂还原是实现碳循环的一条有前景的途径，其中产物甲酸是重要的高值化学品。近年来， 各种电催化剂被用于CO₂电化学还原反应 （CO₂RR） 的研究，并在提高法拉第效率和降低反应过电位等关键性能上取得了一些进展。Sn基催化剂具有低成本、环境友好、甲酸选择性高等优点，最有可能在 CO₂RR领域大规模应用。文章重点总结Sn基电催化剂的研究进展，包括单质Sn催化剂、Sn基合金催化剂、Sn基氧化物以及Sn基硫化物的研究现状，其次简要介绍催化剂失活的原因以及影响稳定性的因素。 最后，提出Sn基催化剂电还原CO₂制甲酸的主要挑战和未来研究方向。

Abstract:

Background, aim, and scope The increasing concentration of CO₂ in the atmosphere since the industrial revolution has led to global climate change and sea level rise, which is seriously threatening the living environment of human beings. Electrocatalytic CO₂ reduction is a promising approach to carbon cycling in which formic acid is an important high-value chemical product. In recent years, various electrocatalysts have been used for CO₂ electrochemical reduction (CO₂RR), and some progress has been made in improving the Faradaic efficiency and reducing the reaction overpotential. Sn-based catalysts have the advantages of low cost, environmental friendliness and high formic acid selectivity, and are most likely to be used in the field of CO₂ R on a large scale. Therefore, this review focuses on the research progress of Sn-based electrocatalysts, including elemental Sn catalysts, Sn-based alloy catalysts, Sn-based oxides and Sn-based sulfides, and then briefly introduces the cause of catalyst deactivation and primary factors affecting the stability of the catalysts. In addition, the main challenges and further research direction of electrochemical reduction of CO2 to formic acid by Sn-based catalyst are also presented. Materials and methods A total of 72 articles were retrieved from the Web of Science (WOS) database prior to November 18, 2022, using the search query TS= (Electrocatalytic *AND Sn). Four main types of Sn-based electrocatalysts for CO₂ reduction were identified and summarized, including monometallic Sn, bimetallic Sn, Sn-based oxides and Sn-based sulfides. Results Sn-based materials are appropriate for electrocatalytic CO₂ reduction due to their environment friendliness, non-toxicity, and low cost. Through appropriate modification, these materials can achieve high faradaic efficiency for formic acid production, making them promising candidates for large-scale industrial applications. Discussion For each type of Sn electrocatalysts, including metallic Sn, bimetallic Sn alloys, Sn oxides and Sn sulfides, the common strategies like metal or non-metal doping, defect engineering, crystal facet engineering, and nanostructuring are generally employed. These approaches aim to increase the electrochemical active surface area or create new active sites for CO₂ adsorption and conversion. Furthermore, in situ Raman or infrared spectroscopy coupled with electrochemical measurements is frequently employed to trace the intermediate species. Based on these experimental insights, the reaction pathways can be established with the assistance of density functional theory calculations, thereby providing a rational guideline for designing efficient and selective electrocatalysts for CO₂ reduction. Conclusions For Sn-based catalysts, defect engineering, doping, and composite construction are effective ways to enhance the catalyst activity. Furthermore, alloying Sn with metals such as In, Cu, Pd, Bi and Au have been widely adopted to further improve performance. Nevertheless, several challenges still must be overcome to enable the widespread practical and commercial application of Sn-based catalysts in CO2RR. Specifically, achieving industrial relevance requires a current density >120 mA/cm² , a Faraday efficiency >95% and formic acid concentration >30% by weight, all while maintaining long-term stability under economically viable electrode costs. Recommendations and perspectives (1) The size of the Sn-based catalysts can be reduced by tuning the synthesis method, thereby exposing more active sites and increasing the electrochemical active surface area. For example, decreasing the thickness of the catalyst to atomic scale can improve its current density. (2) Coating carbon, such as amino-group modified carbon, onto the catalyst surface can not only significantly improve the conductivity of the catalyst and accelerate the charge transfer rate, but also modulate the electronic structure of the Sn-based catalyst, thereby enhancing the adsorption capacity of CO2 and reaction intermediates. (3) Doping with heteroatoms is another effective approach for improving the current density of Sn-based catalysts. The introduced dopants can create defects or oxygen vacancies to a certain extent, thereby regulating the adsorption energy of intermediates, and increasing the charge density of the active sites. (4) It is also crucial to gain a deep understanding of the mechanism of electrochemical CO₂ reduction on Sn-based catalysts. Advanced in situ characterization techniques, such as in situ infrared and Raman spectroscopy can be utilized for this purpose. Furthermore, advanced theoretical calculations can be employed to reveal the reaction mechanisms and the structure-activity relationships of the catalysts. Based on the related mechanisms and principles, guided by theoretical calculations, high-performance catalysts can be screened and designed, thereby significantly reducing the time and energy costs associated with troublesome catalyst preparation.