Abstract
Electrocatalytic CO2 reduction (ECR) is an attractive approach to convert atmospheric CO2 to value-added chemicals and fuels. However, this process is still hindered by sluggish CO2 reaction kinetics and the lack of efficient electrocatalysts. Therefore, new strategies for electrocatalyst design should be developed to solve these problems. Two-dimensional (2D) materials possess great potential in ECR because of their unique electronic and structural properties, excellent electrical conductivity, high atomic utilization and high specific surface area. In this review, we summarize the recent progress on 2D electrocatalysts applied in ECR. We first give a brief description of ECR fundamentals and then discuss in detail the development of different types of 2D electrocatalysts for ECR, including metal, graphene-based materials, transition metal dichalcogenides (TMDs), metal–organic frameworks (MOFs), metal oxide nanosheets and 2D materials incorporated with single atoms as single-atom catalysts (SACs). Metals, such as Ag, Cu, Au, Pt and Pd, graphene-based materials, metal-doped nitric carbide, TMDs and MOFs can mostly only produce CO with a Faradic efficiencies (FE) of 80~90%. Particularly, SACs can exhibit FEs of CO higher than 90%. Metal oxides and graphene-based materials can produce HCOOH, but the FEs are generally lower than that of CO. Only Cu-based materials can produce high carbon products such as C2H4 but they have low product selectivity. It was proposed that the design and synthesis of novel 2D materials for ECR should be based on thorough understanding of the reaction mechanism through combined theoretical prediction with experimental study, especially in situ characterization techniques. The gap between laboratory synthesis and large-scale production of 2D materials also needs to be closed for commercial applications.
Highlights
CO2 is the main component of greenhouse gases which lead to environmental concerns, and its concentration has increased from approximately 280 ppm in the early 1800s to 410 ppm today [1,2,3]
We first give a brief description of Electrocatalytic CO2 reduction (ECR) fundamentals and discuss in detail the development of different types of 2D electrocatalysts for ECR, including metal, graphene-based materials, transition metal dichalcogenides (TMDs), metal– organic frameworks (MOFs), metal oxide nanosheets and 2D materials incorporated with single atoms as single-atom catalysts (SACs)
An effective electrocatalyst is the key to the potential deployment of commercial ECR processes
Summary
CO2 is the main component of greenhouse gases which lead to environmental concerns, and its concentration has increased from approximately 280 ppm in the early 1800s to 410 ppm today [1,2,3]. The effects of precursors and preparation environments on the structure of single-atom catalysts (SACs) were discussed They compared the intrinsic activity of different metal centers and methods for enhancing ECR efficiency [52]. Zhang et al reviewed recent advances on materials development for CO2 conversion by thermocatalysis, photocatalysis and photothermocatalysis, highlighting the reaction pathways and mechanism on C=O bond activation and intermediate formation [54]. Electrocatalysts can effectively reduce activation energy, accelerate reactions or increase desired product selectivity in ECR. It should dissociate water in solution to promote proton–electron transfer because the proton-assisted multiple-electron transfer can be beneficial for CO2 activation. As mentioned above, the interaction between intermediates and electrocatalysts plays a crucial role in forming final products, demonstrating the importance of electrocatalysts
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