Dynamic Stability of Copper Single-Atom Catalysts under Working Conditions

Abstract

The long-term stability of single-atom catalysts is a major factor affecting their large-scale commercial application. How to evaluate the dynamic stability of single-atom catalysts under working conditions is still lacking. Here, taking a single copper atom embedded in N-doped graphene as an example, the "constant-potential hybrid-solvation dynamic model" is used to evaluate the reversible transformation between copper single atoms and clusters under realistic reaction conditions. It is revealed that the adsorption of H is a vital driving force for the leaching of the Cu single atom from the catalyst surface. The more negative the electrode potential, the stronger the adsorption of H. As a result, the competitive hydrogen evolution reaction is inhibited, and Cu−N bonds are weakened, resulting in some Cu atoms being tethered on the catalyst surface and some being dissolved in the aqueous solution. The collision of the Cu atoms in the two states forms a transient Cu cluster structure as a true catalytic active site to promote CO 2 reduction to ethanol. As the applied potential is released or switched to a positive value, hydroxyl radicals (OH • ) play a dominant role in the oxidation process of the Cu cluster, and then Cu returns to the initial atomic dispersion state by redeposition, completing the reconstruction cycle of the copper catalyst. Our work provides a fundamental understanding of the dynamic stability of Cu single-atom catalysts under working conditions at the atomic level and calls for a reassessment of the stability of currently reported single-atom catalysts considering realistic reaction conditions.

Challenges and Perspectives of Single-Atom-Based Catalysts for Electrochemical Reactions

“…The formation of highly oxidized HO–Co 1 –N 2 was revealed by DFT analysis of the electronic and geometric structural changes occurring on the Co site, with the favored dynamic H 2 O adsorption as H 2 O–(HO–Co 1 –N 2 ) . Liu and coauthors presented another original point that the formation of clusters may not be bad for the catalysts (Figure b) . They used the constant-potential hybrid-solvation dynamic model to evaluate the reversible transformation between Cu single atoms and clusters under realistic reaction conditions.…”

“…(b) Summary illustration of the mechanism of the dynamic reversible transformation of the Cu single-atom cluster catalytic structure under working conditions. Adapted with permission from ref ( 98 ). Copyright 2022 American Chemical Society.…”

Can Metal–Nitrogen–Carbon Single-Atom Catalysts Boost the Electroreduction of Carbon Monoxide?

“…32−34 Interestingly, almost all the wellprepared M−N−C SACs generate CO as the final CO 2 R product instead of formate and C1 multi-electron products, even though some of them exhibit *CO adsorption affinity close to Cu catalysts. 32−39 Note that although several Cu SACs were reported to have reactivity for producing multi-electron products, their true active species are Cu clusters and nanocrystalline materials transformed from their pristine single-Cu-atom centers during CO 2 R. 40,41 Here, an important question arises: why can Cu catalysts have the potential for achieving the further reduction of CO In this work, utilizing constant-potential density functional theory (DFT) calculations, we disclosed the origin of the inability of the M−N−C SACs for catalyzing COR and further proposed several material regulation criteria for enabling COR to form deep C1 products over the SACs. The comprehensive potential-dependent kinetic analysis revealed that the Langmuir−Hinshelwood (LH) mechanism is crucial for facilitating the hydrogenation of *CO on the Cu surface, while the pristine M−N−C SACs always fail to achieve COR due to the lack of active sites near the MN 4 centers that can place the *H species decomposed from H 2 O (a key step in the LH mechanism), given that the graphene skeleton is intrinsically inert.…”

Density Functional Theory Study of CO2 Hydrogenation on Transition-Metal-Doped Cu(211) Surfaces

“…Since the industrial revolution, the massive emission of carbon dioxide (CO 2 ) has caused a series of environmental problems and social issues. Therefore, the reduction and utilization of CO 2 have drawn great attention from scientists [ 1 , 2 , 3 ]. There are three methods for the catalytic transformation of CO 2 into value-added chemicals: thermal catalysis, electrocatalysis, and photocatalysis [ 4 , 5 , 6 ].…”