Substrate Strain Engineering of Single-Atomic Sn-N4 Sites Embedded in Various Carbon Matrixes for Bifunctional Oxygen Electrocatalysis

Single-Atom Doped Fullerene (MN4-C54) as Bifunctional Catalysts for the Oxygen Reduction and Oxygen Evolution Reactions

Development of high-performance oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts is crucial to realizing the electrolytic water cycle. C60 is an ideal substrate material for single atom catalysts (SACs) due to its unique electron-withdrawing properties and spherical structure. In this work, we screened for a novel single-atom catalyst based on C60, which anchored transition metal atoms in the C60 molecule by coordination with N atoms. Through first-principles calculations, we evaluated the stability and activity of MN4-C54 (M = Fe, Co, Ni, Cu, Rh, Ru, Pd, Ag, Pt, Ir, Au). The results indicate that CuN4-C54, which is based only on earth-abundant elements, exhibited low overpotentials of 0.46 and 0.47 V for the OER and ORR, respectively, and was considered a promising bifunctional catalyst, showing better performance than the noble-metal ones. In addition, according to the linear relationship of intermediates, we established volcano plots to describe the activity trends of the OER and ORR on MN4-C54. Finally, d-band center and crystal orbital Hamiltonian populations methods were used to explain the catalytic origin. Suitable d-band centers lead to moderate adsorption strength, further leading to good catalytic performances.

Curved Structure Regulated Single Metal Sites for Advanced Electrocatalytic Reactions

Curved surface with defined local electronic structures and regulated surface microenvironments is significant for advanced catalytic engineering. Since single-atom catalysts are highly efficient and active, they have attracted much attention in recent years. The curvature carrier has a significant effect on the electronic structure regulation of single-atom sites, which effectively promote the catalytic efficiency. Here, the effect of the curvature structure with exposed metal atoms for catalysis is comprehensively summarized. First, the substrates with curvature features are reviewed. Second, the applications of single-atom catalysts containing curvature in a variety of different electrocatalytic reactions are discussed in depth. The impact of curvature effects in catalytic reactions is further analyzed. Finally, prospects and suggestions for their application and future development are presented. This review paves the way for the construction of high curvature-containing surface carriers, which is of great significance for single-atom catalysts development.

p-d Orbital Hybridization Induced by Asymmetrical FeSn Dual Atom Sites Promotes the Oxygen Reduction Reaction

With more flexible active sites and intermetal interaction, dual-atom catalysts (DACs) have emerged as a new frontier in various electrocatalytic reactions. Constructing a typical p-d orbital hybridization between p-block and d-block metal atoms may bring new avenues for manipulating the electronic properties and thus boosting the electrocatalytic activities. Herein, we report a distinctive heteronuclear dual-metal atom catalyst with asymmetrical FeSn dual atom sites embedded on a two-dimensional C2N nanosheet (FeSn-C2N), which displays excellent oxygen reduction reaction (ORR) performance with a half-wave potential of 0.914 V in an alkaline electrolyte. Theoretical calculations further unveil the powerful p-d orbital hybridization between p-block stannum and d-block ferrum in FeSn dual atom sites, which triggers electron delocalization and lowers the energy barrier of *OH protonation, consequently enhancing the ORR activity. In addition, the FeSn-C2N-based Zn-air battery provides a high maximum power density (265.5 mW cm-2) and a high specific capacity (754.6 mA h g-1). Consequently, this work validates the immense potential of p-d orbital hybridization along dual-metal atom catalysts and provides new perception into the logical design of heteronuclear DACs.

Unraveling the Impact of Curvature on Electrocatalytic Performance of Carbon Materials: A State-of-the-Art Review

Curvature of carbon materials has gained significant attention as catalysts due to their distinctive properties and potential applications. This review comprehensively summarizes how the bending of carbon materials can improve electrocatalytic performance, with special attention to the applications of various bent carbon materials (such as carbon nanotubes, graphene, and fullerene) in electrocatalysts and a large number of related density functional theory (DFT) theoretical calculations. Extensive mechanism research has provided a wealth of evidence indicating that the curvature of carbon materials has a profound impact on catalytic activity. This improvement in catalytic performance by curved carbon materials is attributed to factors like a larger active surface area, modulation of electronic structure, and better dispersal of catalytic active sites. A comprehensive understanding and utilization of these effects enable the design of highly efficient carbon-based catalysts for applications in energy conversion, environmental remediation, and chemical synthesis.

Ultrasound-Assisted Preparation and Performance Regulation of Electrocatalytic Materials

With the advancement of scientific research, the introduction of external physical methods not only adds extra freedom to the design of electro-catalytical processes for green technologies but also effectively improves the reactivity of materials. Physical methods can adjust the intrinsic activity of materials and modulate the local environment at the solid-liquid interface. In particular, this approach holds great promise in the field of electrocatalysis. Among them, the ultrasonic waves have shown reasonable control over the preparation of materials and the electrocatalytic process. However, the research on coupling ultrasonic waves and electrocatalysis is still early. The understanding of their mechanisms needs to be more comprehensive and deep enough. Firstly, this article extensively discusses the adhibition of the ultrasonic-assisted preparation of metal-based catalysts and their catalytic performance as electrocatalysts. The obtained metal-based catalysts exhibit improved electrocatalytic performances due to their high surface area and more exposed active sites. Additionally, this article also points out some urgent unresolved issues in the synthesis of materials using ultrasonic waves and the regulation of electrocatalytic performance. Lastly, the challenges and opportunities in this field are discussed, providing new insights for improving the catalytic performance of transition metal-based electrocatalysts.

Realizing a high OER activity in new single-atom catalysts formed by introducing TMNx (x = 3 and 4) units into carbon nanotubes using high-throughput calculations

Exploring highly efficient electrocatalysts for the oxygen evolution reaction (OER) is of great significance for hydrogen production through water splitting. By means of high-throughput density functional theory (DFT) calculations, we investigated the OER catalytic activity of a series of one-dimensional carbon nanotube (CNT)-based systems containing TMN4 or TMN3 functional units. Through the screening of 3d/4d/5d transition metals (TMs) from Group IVB to Group VIII, eight newly obtained TMNx@CNT (x = 3 and 4) systems were found to exhibit excellent OER activity, with very low overpotentials in the range 0.29-0.51 V, where the Co, Rh, Ir, Ti, Fe, and Ru atoms could be used as active sites. It was found that under the framework of TMN3@CNTs, the pre-adsorption of some species from water dissociation on the relevant TM sites (TM = Ti, Fe, and Ru) could lead to a high OER catalytic activity, which was different from the general situation where OER reactions directly occur on the clean surfaces of the remaining systems with Co/Rh/Ir metal centers. Moreover, the catalytic mechanisms were analyzed in detail. This work can be conducive to obtaining low-cost and high-performance OER single-atom electrocatalysts based on excellent CNT nanomaterials.

d- and p-Block single-atom catalysts supported by BN nanocages toward electrochemical reactions of N2 and O2

Electrocatalysis is involved in many energy storage and conversion devices, triggering research and development of electrocatalysts, particularly single-atom catalysts (SACs). The introduction of the strain effect to enhance the performance of SACs has drawn ever-increasing research attention, which can tailor the local atomic and electronic structure of active sites. Herein, via high throughput calculations, we have explored the effects of strain on the catalytic performance of SACs with MN4 configuration for electrochemical reactions of N2 and O2 by incorporating d- and p-block single metal atoms into BN nanocages (BNNCs). The calculations demonstrate that Os@BNNC exhibits the highest catalytic activity for the nitrogen reduction reaction (NRR) with a limiting potential of -0.29 V. Co@BNNC can serve as an excellent bifunctional SAC for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), with overpotentials of 0.32 and 0.37 V, respectively. In particular, Sn@BNNC with a p-block metal as the active center is a competitive SAC for the ORR with an overpotential of 0.64 V. More interestingly, the NRR and ORR performances of SACs supported by BNNCs have a close correlation with the structural and electronic properties of adsorbed N2 and O2 molecules, which proves that controlling the adsorption energy of N2 and O2 molecules is crucial to improving the catalytic activity of BNNC. The current investigation opens up an avenue for designing SACs embedded in nanocages possessing intrinsically curved surfaces for electrochemical reactions.