Evaluating the Catalytic Efficiency of Paired, Single-Atom Catalysts for the Oxygen Reduction Reaction

Metal-Organic Framework-Based Catalysts with Single Metal Sites

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Impact of electron transfer of atomic metals on adjacent graphyne layers on electrochemical water splitting

Efficient electrocatalysts are needed for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), while the influence of electron transfer from the adjacent layer of multilayered electrocatalysts on their catalytic performance is usually neglected. Here, we used the single cobalt atom trapped graphyne catalyst (Co@GY) to study the feasibility of modulating its water-splitting catalytic activity through interfacial electron transfer. A series of Co@GY/transition-metal doped graphyne double-layered structures (Co@GY/GY and Co@GY/TM@GY, TM = Mn, Fe, Co, Ni, Cu) are systematically evaluated for water splitting via theoretical computations. The electronic structure analyses of different stacking cases revealed that the atomic metals on the adjacent TM@GY layer remarkably tune the electronic structures of the Co atom in the Co@GY layer. A strong linear correlation between ΔG_H* and the d band center of the Co atom was found, suggesting that the HER activity on the Co atom can be tailored by adjusting the TM on the adjacent TM@GY layer with different d-electron occupations. The volcano-type trend of OER catalytic performance is obtained to show the best Co@GY/Ni@GY catalyst for the OER with an over-potential of 0.38 V, indicating that higher catalytic performance arises from moderate interfacial electron transfer. These results arouse a re-thinking of the intrinsic activity origins of single-atom catalysts (SACs) and offer a new strategy for the structure designing of SACs.

Single-Atom Catalysts in Catalytic Biomedicine

The intrinsic deficiencies of nanoparticle-initiated catalysis for biomedical applications promote the fast development of alternative versatile theranostic modalities. The catalytic performance and selectivity are the critical issues that are challenging to be augmented and optimized in biological conditions. Single-atom catalysts (SACs) featuring atomically dispersed single metal atoms have emerged as one of the most explored catalysts in biomedicine recently due to their preeminent catalytic activity and superior selectivity distinct from their nanosized counterparts. Herein, an overview of the pivotal significance of SACs and some underlying critical issues that need to be addressed is provided, with a specific focus on their versatile biomedical applications. Their fabrication strategies, surface engineering, and structural characterizations are discussed briefly. In particular, the catalytic performance of SACs in triggering some representative catalytic reactions for providing the fundamentals of biomedical use is discussed. A sequence of representative paradigms is summarized on the successful construction of SACs for varied biomedical applications (e.g., cancer treatment, wound disinfection, biosensing, and oxidative-stress cytoprotection) with an emphasis on uncovering the intrinsic catalytic mechanisms and understanding the underlying structure-performance relationships. Finally, opportunities and challenges faced in the future development of SACs-triggered catalysis for biomedical use are discussed and outlooked.

Enhancing the oxygen reduction reaction with three-dimensional graphene hollow nanosphere supported single-atomic cobalt catalyst

Three-dimensional graphene hollow nanospheres supported single-atomic cobalt catalyst shows superior electrocatalytic activity, long-term stability, and excellent methanol tolerance for the oxygen reduction reaction in alkaline media.