However, the shuttle effect triggered by the dissolution of long-chain polysulfides (Li 2 S x , 4 ≤ x ≤ 8) results in severe active sulfur loss and fast capacity decay, which severely hinders the commercial application of these batteries. [4,6] Fundamentally, these problems are a result of the slow and complex sulfur reduction reaction (SRR), i.e., the sluggish kinetic transformation of soluble lithium polysulfides (LiPSs) to insoluble Li 2 S 2 /Li 2 S (discharge products). [7,8] Therefore, exploring effective strategies to accelerate the conversion of LiPSs from the liquid to the solid state is essential to boost the practical energy density and lifespan of lithium-sulfur batteries. [9,10] Considerable efforts have been devoted to addressing the aforementioned problems, typically by using sulfides, nitrides, phosphides as host materials to trap the LiPSs in the sulfur cathode. [11][12][13][14] However, these physical or electrostatic confinement/trapping methods fail to entirely avoid the dissolution and accumulation of LiPSs in the electrolyte. [8] A catalytic approach has therefore been proposed as a more proactive solution to cure the shuttle effect by accelerating the conversion of the liquid-phase long-chain LiPSs into final solid-phase discharge products. [15,16] Like the oxygen Seeking an electrochemical catalyst to accelerate the liquid-to-solid conversion of soluble lithium polysulfides to insoluble products is crucial to inhibit the shuttle effect in lithium-sulfur (Li-S) batteries and thus increase their practical energy density. Mn-based mullite (SmMn 2 O 5 ) is used as a model catalyst for the sulfur redox reaction to show how the design rules involving lattice matching and 3d-orbital selection improve catalyst performance. Theoretical simulation shows that the positions of Mn and O active sites on the (001) surface are a good match with those of Li and S atoms in polysulfides, resulting in their tight anchoring to each other. Fundamentally, dz 2 and dx 2 −y 2 around the Fermi level are found to be crucial for strongly coupling with the p-orbitals of the polysulfides and thus decreasing the redox overpotential. Following the theoretical calculation, SmMn 2 O 5 catalyst is synthesized and used as an interlayer in a Li-S battery. The resulted battery has a high cycling stability over 1500 cycles at 0.5 C and more promisingly a high areal capacity of 7.5 mAh cm −2 is achieved with a sulfur loading of ≈5.6 mg cm −2 under the condition of a low electrolyte/sulfur (E/S) value ≈4.6 µL mg −1 .

Revealing the catalytic oxidation mechanism of volatile organic compounds (VOCs) is insightful for the development of efficient catalysts. However, because of the complicated interactions and a large number of intermediate species during the reactions, the analysis of the entire reaction mechanism (including the activation modes of reactant molecules and the rate-limiting step) remains a great challenge. Herein, the YMn2O5 mullite catalyst was proposed to demonstrate how to distinguish the deep oxidation difference among C3–C4 alkanes and olefins via combining experiments and theoretical calculations. The YMn2O5 catalyst prepared via the hydrothermal method displayed a superior catalytic behavior with a low T90 temperature (C3H8 at 250 °C; C3H6, C4H10, and C4H8 less than 200 °C) (1000 ppm of C3–C4 and 10% O2 balanced with He, WHSV = 30 000 mL/g·h). The catalytic activity remained the same after continuous reaction for 100 h at 275 °C for each reactant. Overall, the YMn2O5 mullite catalyst exhibits excellent durability with no activity declines for 400 h. Combined with TPD, DRIFTS, XPS, and DFT analysis, surface oxygen species were found to be active for the oxidation. Owing to the difference of the HOMO induced partial charge distributions between alkanes and alkenes, the dehydrogenation of the end-site C–H of propane is the first step prior to the crucial conversion of acrylate over surface labile oxygen in an octahedral ligand unit. For propene oxidation, the CC double bond is preferentially attacked by two surface oxygen atoms belonging to the octahedral and pyramid ligand units with the crucial step of acetate decomposition. These findings provide insights into the oxide catalyst design toward the complicated VOCs oxidation from a fundamental point of view.

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A high theoretical limit of supercapacitance of MXene Ti3C2 is predicted based on rigid band approximation (RBA).