Identifying the Role of the Cationic Geometric Configuration in Spinel Catalysts for Polysulfide Conversion in Sodium–Sulfur Batteries

Abstract

An AB 2 X 4 spinel structure, with tetrahedral A and octahedral B sites, is a paradigmatic class of catalysts with several possible geometric configurations and numerous applications, including polysulfide conversion in metal−sulfur batteries. Nonetheless, the influence of the geometric configuration and composition on the mechanisms of catalysis and the precise manner in which spinel catalysts facilitate the conversion of polysulfides remain unknown. To enable controlled exposure of single active configurations, herein, Co td 2+ and Co oh 3+ in Co 3 O 4 catalysts for sodium polysulfide conversion are in large part replaced by Fe td 2+ and Fe oh 3+ , respectively, generating FeCo 2 O 4 and CoFe 2 O 4. Through an examination of electrochemical activation energies, the characterization of symmetric cells, and theoretical calculations, we determine that Co oh 3+ serves as the active site for the breaking of S−S bonds, while Co td 2+ functions as the active site for the formation of S−Na bonds. The current study underlines the subtle relationship between activity and geometric configurations of spinel catalysts, providing unique insights for the rational development of improved catalysts by optimizing their atomic geometric configuration.

Tuning the d-Band Center of Co3O4 via Octahedral and Tetrahedral Codoping for Oxygen Evolution Reaction

“…Compared with Co 3 O 4 , the shift of the Co 2+ and Co 3+ peaks to higher binding energy in M-Co 3 O 4 (M = Al, Ga, Fe, Ni, and In) indicates that both Co 2+ and Co 3+ in them were affected by the introduction of heteroatoms and the electronic structure is changed. To visualize the occupation sites of doping atoms, the ratios of the peak area of Co 3+ to Co 2+ are sorted out and shown in Figures b, S10, S11 and Tables S5, S6. For M-Co 3 O 4 (M = Al and Ga), the Co 3+ /Co 2+ value shows a decline with the increase of doping.…”

Controllable Regulation of the Oxygen Redox Process in Lithium–Oxygen Batteries by High-Configuration-Entropy Spinel with an Asymmetric Octahedral Structure

“…Thus, we generally calculated the characteristic surface of the catalyst rather than the bulk structure, and the (311) surface is used in this work. In the process of surface system calculation, some hanging bonds will form on the surface of the material, which will cause much higher electronic activity and narrowing or even disappearance of its internal band gap. − In the vicinity of EF, the electron density of HEOS is obviously higher than that of Co 3 O 4 and MEOS, which means the highest conductivity of HEOS among the three materials. Figure c shows the projected density of states (PDOS) of Co 3d and O 2p in different materials, where the center positions of Co d and O p bands are calculated by integrating each PDOS at EF.…”

Expediting Ethylbenzene Oxidation via a Bimetallic Cobalt–Manganese Spinel Structure with a Modulated Electronic Environment

“…Catalysts play an important role in the modern chemical industry, ranging from chemical synthesis, environmental remediation, and energy conversion and storage. − Compared with the homogeneous catalytic systems, the merit of facile separation and reutilization has pushed scientists and engineers to explore advanced heterogeneous catalytic systems. , Notably, appropriate catalysts that are able to combine the features of high activity/selectivity/stability/recyclability, easy handling, cost-effectiveness, and environmentally friendly nature should act as privileged candidates in diverse catalytic applications. According to these assessment criteria, spinel metal oxides with multiple cations and synergistic effects stand out as promising catalysts in many catalytic fields. − Recent explorations have shown that new opportunities may become feasible when proper cations and preparation methods are selected to achieve a remarkably boosted reaction performance. For example, Wang et al developed spinel oxide composites (ACo 2 O 4 /NCNTs, A = Mn, Co, Ni, Cu, Zn) for oxygen electrocatalysis.…”