Research progress on graphene-based electrocatalytic materials for carbon dioxide reduction

Abstract

Electrochemical reduction of carbon dioxide (CO2) to produce fuels and high-value chemicals is an effective strategy to mitigate global warming and address energy and environmental challenges. Due to the stable molecular structure of CO2, designing highly selective, energy-efficient, and low-cost electrocatalysts is crucial. Graphene and its derivatives, with their unique and excellent physical, mechanical, and electrical properties, and relatively low cost, are competitive for CO2 electroreduction. Moreover, the surface of graphene-based materials can be modified through various methods, including doping, defect engineering, constructing composite structures, and coating shapes. This review first summarizes the fundamental concepts, evaluation criteria, and catalytic principles and processes of electrochemical CO2 reduction. Then, it briefly introduces the preparation methods of graphene-based catalysts and summarizes recent research progress according to the categories of catalytic sites. Finally, future directions for CO2 electroreduction technology are discussed and prospected.

1. Introduction

The progress of human society and the development of industrial economy have led to increased energy consumption. Due to the over-exploitation and use of traditional fossil fuels such as coal, oil, and natural gas, the concentration of carbon dioxide (CO2) in the atmosphere has significantly increased [1]. Excessive CO2 emissions have caused serious problems in many fields of environment and climate, such as ocean acidification and sea level rise [2–4]. As a cheap and easily available carbon resource, CO2 has broad application prospects in converting it into fuels or high-value chemicals through biochemical, photocatalytic, and electrocatalytic methods [5]. Traditional technical routes for CO2 utilization usually require harsh conditions such as high temperature and high pressure, which implies many problems in safety, efficiency, energy saving, and environmental protection [6]. Therefore, new materials and technologies for CO2 conversion and utilization have great practical significance and social benefits for ecological environment protection and sustainable utilization of resources [7–9]. Electrocatalytic CO2 reduction reaction (CO2RR) is regarded as an important method to solve the above problems due to its mild conditions, controllable process, low energy consumption, and easy scalability [10]. Meanwhile, as renewable energy technologies (including solar, tidal, wind, and geothermal energy) become more mature and cost-effective, the task of storing electricity from intermittent renewable sources is increasingly heavy [11–13]. From the strategic perspective of resource utilization and energy development, using low-grade renewable electricity to efficiently convert CO2 into high-value chemicals or fuels can not only "turn waste into treasure" and reduce CO2 emissions, but also reduce human dependence on fossil fuels, achieving a transition from a "fossil fuel economy" to a sustainable "CO2 economy", thereby realizing efficient clean energy utilization [14–16].

Electrocatalytic CO2RR can be conducted under mild conditions to produce different products, such as C1 (CO, CH4, CH3OH, HCOOH/formate, etc.), C2 (C2H6, C2H4, C2H6O, CH3COOH, etc.), and C3 (C3H6, C3H8O, CH3COCH3, etc.) [17–19]. However, electrochemical CO2 reduction technology faces a series of problems and challenges. First, CO2 has a stable thermodynamic molecular structure, and the dissociation of its C=O double bond requires overcoming a relatively high energy barrier [20]. Second, during the electrochemical reduction of CO2, multi-proton coupled and electron transfer processes usually generate a large number of intermediates, leading to low product selectivity. Finally, in aqueous electrolytes, the inevitable hydrogen evolution side reaction also reduces the selectivity of CO2RR [21]. Therefore, in-depth exploration of the reaction mechanism of CO2 reduction, and rational design and construction of highly active electrocatalysts with low cost, high selectivity, and good stability are the keys to solving these problems.