Identification of Active Sites for CO₂ Reduction on Graphene‐Supported Single‐Atom Catalysts

Abstract

Transition metal-and nitrogen-codoped graphene (referred to as MÀ NÀ G, where M is a transition metal) has emerged as an important type of single-atom catalysts with high selectivities and activities for electrochemical CO 2 reduction (CO 2 R) to CO. However, despite extensive previous studies on the catalytic origin, the active site in MÀ NÀ G catalysts remains puzzling. In this study, density functional theory calculations and computational hydrogen electrode model is used to investigate CO 2 R reaction energies on ZnÀ NÀ G, which exhibits outstanding catalytic performance, and to examine kinetic barriers of reduction reactions by using the climbing image nudged elastic band method. We find that single Zn atoms binding to N and C atoms in divacancy sites of graphene cannot serve as active sites to enable CO production, owing to *OCHO formation (* denotes an adsorbate) at an initial protonation process. This contradicts the widely accepted CO 2 R mechanism whereby single metal atoms are considered catalytic sites. In contrast, the C atom that is the nearest neighbor of the single Zn atom (C NN ) is found to be highly active and the Zn atom plays a role as an enhancer of the catalytic activity of the C NN . Detailed analysis of the CO 2 R pathway to CO on the C NN site reveals that *COOH is favorably formed at an initial electrochemical step, and every reaction step becomes downhill in energy at small applied potentials of about À 0.3 V with respect to reversible hydrogen electrode. Electronic structure analysis is also used to elucidate the origin of the CO 2 R activity of the C NN site.

Optimizing the Electrocatalytic Selectivity of Carbon Dioxide Reduction Reaction by Regulating the Electronic Structure of Single‐Atom M‐N‐C Materials

“…Kang et al combined DFT calculations and experimental investigation to study the catalytic ability of Zn-NG catalyst with Zn-N 3 sites for CO 2 RR. [163] Because *OCHO adsorbent was produced in the process of pronation, the single-atom Zn coordinated with N and C in the Zn-NG catalyst cannot be used as the active site for CO generation, which was inconsistent with many studies. They found that the real active sites were C atoms bonded by Zn atoms, which had high activity.…”

Synthesis and Characterization of a Highly Reactive and Robust Chlorine‐Bound Ni Single‐Atom‐Catalyst for the Continuous Flow Ring‐Opening Reaction of Epoxides

“…The N 1s spectrum was deconvoluted into three major peaks indicating pyridinic, Ni−N, and pyrrolic N contents. The pyridinic and pyrrolic nitrogen served as the coordinating sites for Ni 2+ , [43,44] and the binding energy at 399.4 eV was ascribed to the coordination of Ni to nitrogen (Figure 3a). [45] The Ni 2 p spectrum indicated two dominant peaks at 854.3 and 871.9 eV for Ni 2 p 3/2 and Ni 2 p 1/2 , respectively (Figure 3b), which were attributed to the Ni 2+ state of nitrogen‐coordinated Ni, [46] whereas Ni 2 p spectrum for Ni/C catalyst were deconvoluted in Ni 0 , and Ni 2+ states (Figure S10).…”

Computational Design of Single‐atom Modified Ti‐MOFs for Photocatalytic CO2 Reduction to C1 Chemicals

“…[25] In the past few years, single-atom catalysts (SACs) have attracted extensive attention in the field of catalysis due to their near-unity atom efficiency thus minimizing the use of precious metals. [26][27][28] In particular, single-atom modified MOFs have been studied as catalysts for CO 2 reduction reactions. [15,29,30] Notably, photoactive organic or metal-organic complexes are used as ligands to construct single-atom MOFs, which can produce photocatalytically active MOFs with isolated catalytic sites.…”

“…Therefore, the development of reusable heterogeneous photocatalysts for CO 2 reduction is imminent [25] . In the past few years, single‐atom catalysts (SACs) have attracted extensive attention in the field of catalysis due to their near‐unity atom efficiency thus minimizing the use of precious metals [26–28] . In particular, single‐atom modified MOFs have been studied as catalysts for CO 2 reduction reactions [15,29, 30] .…”