Catalytic Potential of Post-Transition Metal Doped Graphene-Based Single-Atom Catalysts for the CO2 Electroreduction Reaction

The activity origin of two-dimensional MN4-contained periodical macrocyclic structures towards electro-catalytic hydrogen evolution

The two-dimensional MN4-contained periodical macrocyclic structures (2D MN4/PMCs) have been extensively explored as single atom catalysts through both experimental and theoretical approaches. However, there still lacks deep understanding on the effect of the outer coordination environment in determining the catalytic activity of the inner MN4 center. Combining the density functional theory (DFT) calculations and machine learning (ML) algorithm, we computationally unraveled the origin of electro-catalytic activity of five kinds of 2D MN4/PMCs towards hydrogen evolution reaction (HER). With hydrogen adsorption free energy (ΔGH*) as the indicator for HER catalytic activity, the IrPpor and RhPPpz are screened out as superior HER electrocatalysts based on the DFT calculations. Furthermore, ML studies generated the universal descriptor Φ that highly depends on charge assigned on the metal center (q) and the d-band center of central metal (εd), which is reversely proportional to ΔGH*. The dependence of q and εd on the structural parameters of MN4/PMCs is further unraveled, demonstrating how the outer framework determines catalytic activity of 2D MN4/PMCs.

The Significance of the 'Insignificant': Non-covalent Interactions in CO2 Reduction Reactions with 3C-TM (TM=Sc-Zn) Single-Atom Catalysts

With energy shortages and excessive CO2 emissions driving climate change, converting CO2 into high-value-added products offers a promising solution for carbon recycling. We investigate CO2 reduction reactions (CO2RR) catalyzed by 10 single-atom catalysts (SACs), incorporating weak non-covalent interactions, specifically lone pair-π and H-π interactions. The SACs, consisting of transition metals coordinated by three carbon atoms in a defective graphene substrate (3C-TM, TM=Sc-Zn), leverage these interactions to influence the energy fluctuations of intermediates and the limiting potentials of CO2RR, without altering the overall reaction pathway. Our findings show that SACs based on early transition metals (Sc, Ti, V, Cr) can serve as catalysts for C1 products, including HCOOH, HCHO, CH3OH, and CH4, while those based on Fe and Co are suitable for CO formation. Driving force analysis helps bridge theoretical results with experimental observations and propose a modified approach for assessing hydrogen evolution reactions (HER) competition. SACs based on Ni and Cu exhibit moderate HER tolerance, while early transition metals excel in selective CO2 reduction. We also identify a linear scaling relationship between the free energies of *COOH and *CO. This study offers valuable insights for future experimental studies and large-scale computational screenings.

Composite interfaces of g-C3N4 fragments loaded on a Cu substrate for CO2 reduction

Designing an electrocatalyst with high efficiency and product selectivity is always crucial for an electrocatalytic CO2 reduction reaction (CO2RR). Inspired by the great progress of two-dimensional (2D) nanomaterials growing on Cu surfaces and their promising CO2RR catalytic efficiencies at their interfaces, the unique performance of Cu-based 2D materials as high-efficiency and low-cost CO2RR electrocatalysts has attracted extensive attention. Herein, based on density functional theory (DFT) calculations, we proposed a composite structure of graphitic carbon nitride (g-C3N4) fragments loaded on a Cu surface to explore the CO2RR catalytic property of the interface between g-C3N4 and the Cu surface. Three composite interfaces of C3N4/Cu(111), C3N4/Cu(110) and C3N4/Cu(100) have been studied by considering the reaction sites of vertex nitrogen atoms, edge nitrogen atoms and the nearby Cu atoms. It was found that the C3N4/Cu interfaces where nitrogen atoms contact the Cu substrate present competitive CO2RR activity. Among them, C3N4/Cu(111)-N3 exhibited a better activity for CH3OH production, with a low overpotential of 0.38 V. For HCOOH and CH4 production, C3N4/Cu(111)-Cu and C3N4/Cu(100)-N1 have overpotentials of 0.26 V and 0.44 V. The electronic analysis indicates the electron transfer from the Cu substrate to the g-C3N4 fragment and mainly accumulates on the nitrogen atoms of the interface. Such charge accumulation can activate the adsorbed CO bond of CO2 and lead to lower energetic barriers of CO2RR. DFT calculations indicate that the boundary nitrogen sites reduced the energy barrier of *CHO, which is crucial for CO2RR, compared with that of the pristine Cu surface. Our study explores a new Cu-based electrocatalyst and indicates that the C3N4/Cu interface can enhance the activities and selectivity of CO2RR and open a new strategy to design high-efficiency electrocatalysts for CO2RR.

Recent Advances in Electrochemical, Photochemical, and Photoelectrochemical Reduction of CO2 to C2+ Products

Environmental problems such as global warming are one of the most prominent global challenges. Researchers are investigating various methods for decreasing CO₂ emissions. The CO₂ reduction reaction via electrochemical, photochemical, and photoelectrochemical processes has been a popular research topic because the energy it requires can be sourced from renewable sources. The CO₂ reduction reaction converts stable CO₂ molecules into useful products such as CO, CH₄ , C₂ H₄ , and C₂ H₅ OH. To obtain economic benefits from these products, it is important to convert them into hydrocarbons above C₂ . Numerous investigations have demonstrated the uniqueness of the CC coupling reaction of Cu-based catalysts for the conversion of CO₂ into useful hydrocarbons above C₂ for electrocatalysis. Herein, the principle of semiconductors for photocatalysis is briefly introduced, followed by a description of the obstacles for C₂₊ production. This review presents an overview of the mechanism of hydrocarbon formation above C₂ , along with advances in the improvement, direction, and comprehension of the CO₂ reduction reaction via electrochemical, photochemical, and photoelectrochemical processes.