Activating Single-Atom Ni Site via First-Shell Si Modulation Boosts Oxygen Reduction Reaction

Covalent organic frameworks derived Single-Atom cobalt catalysts for boosting oxygen reduction reaction in rechargeable Zn-Air batteries

The design and development of high-performance and long-life Pt-free catalysts for the oxygen reduction reaction (ORR) is of great important with respect to metal-air batteries and fuel cells. Herein, a new low-cost covalent organic frameworks (COFs)-derived CoNC single-atoms catalyst (SAC) is fabricated and compared with the engineered nanoparticle (NP) counterpart for ORR activity. The ORR performance of the SAC catalyst (CoSA@NC) surpasses the NP counterpart (CoNP-NC) under the same operation condition. CoSA@NC also achieves improved long-term durability and better methanol tolerance compared with the Pt/C. The zinc-air battery assembled by the CoSA@NC cathode delivers a higher power density and energy density than that of commercial Pt/C catalyst. Molecular dynamics (MD) is performed to explain the spontaneous evolution from clusters to single-atom metal configuration and density functional theory (DFT) calculations find that CoSA@NC possesses lower d-band center, resulting in weaker interaction between the surface and the O-containing intermediates. Consequently, the reductive desorption of OH*, the rate-determine step, is further accelerated.

Ni clusters immobilized on oxygen-rich siloxene nanosheets for efficient electrocatalytic oxygen reduction toward H2O2 synthesis

Hydrogen peroxide (H2O2) electrosynthesis via the two-electron oxygen reduction reaction (2e- ORR) represents a green alternative to the energy-intensive anthraquinone process. However, the practical application of this method is limited by the lack of cost-effective and high-performance electrocatalysts. Reported here is a hybrid catalyst composed of nickel (Ni) clusters immobilized onto the surface of two-dimensional siloxene nanosheets (Ni/siloxene), which exhibits excellent efficiency and selectivity in electrocatalytic oxygen reduction to H2O2 in an alkaline medium, demonstrating a standard 2e- pathway with >95% H2O2 selectivity across a wide potential range. Experimental results disclose that the high performance of Ni/siloxene can be traced to a synergy of the Ni clusters and the oxygen-rich surface of siloxene. Density functional theory (DFT) calculations further reveal a weakened interaction between Ni/siloxene and *OOH and the consequently reduced energy barrier for the *OOH protonation toward H2O2 desorption, thus leading to a high 2e- ORR reactivity and selectivity. This work provides a valuable and practical guidance for designing high-performance 2e- ORR electrocatalysts based on the rational engineering of the metal-support interaction.

Structural and compositional analysis of MOF-derived carbon nanomaterials for the oxygen reduction reaction

The development of low-cost and efficient cathode catalysts is crucial for the advancement of fuel cells, as the oxygen reduction reaction (ORR) on the cathode is constrained by expensive commercial Pt/C catalysts and a significant energy barrier. Metal-organic frameworks (MOFs) are considered excellent precursors for synthesizing carbon nanomaterials due to their simple synthesis, rich structure and composition. MOF-derived carbon nanomaterials (MDCNM) inherit the morphology of their precursors at low dimensional scales, providing abundant edge defects, larger specific surface area, and excellent electron transport paths. Furthermore, the rich composition of MOFs enables the carbon nanomaterials derived from them to exhibit various physicochemical properties, including stronger electron gaining ability, oxygen affinity, and a higher degree of graphitization, resulting in excellent ORR activity. However, a more detailed analysis is necessary to understand the advantages and mechanisms of MDCNM in the field of the ORR. This review classifies and summarizes the structure and different chemical compositions of MDCNM in low dimensions, and provides an in-depth analysis of the reasons for their improved ORR activity. Additionally, the recent practical applications of MDCNM as cathode material in fuel cells are introduced and analyzed in detail, with a focus on the enhanced electrochemical performance.

Review of Carbon Support Coordination Environments for Single Metal Atom Electrocatalysts (SACS)

This topical review focuses on the distinct role of carbon support coordination environment of single-atom catalysts (SACs) for electrocatalysis. The article begins with an overview of atomic coordination configurations in SACs, including a discussion of the advanced characterization techniques and simulation used for understanding the active sites. A summary of key electrocatalysis applications is then provided. These processes are oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2 RR). The review then shifts to modulation of the metal atom-carbon coordination environments, focusing on nitrogen and other non-metal coordination through modulation at the first coordination shell and modulation in the second and higher coordination shells. Representative case studies are provided, starting with the classic four-nitrogen-coordinated single metal atom (MN4 ) based SACs. Bimetallic coordination models including homo-paired and hetero-paired active sites are also discussed, being categorized as emerging approaches. The theme of the discussions is the correlation between synthesis methods for selective doping, the carbon structure-electron configuration changes associated with the doping, the analytical techniques used to ascertain these changes, and the resultant electrocatalysis performance. Critical unanswered questions as well as promising underexplored research directions are identified.