Vanadium as Auxiliary for Fe-V Dual-Atom Electrocatalyst in Lithium-Sulfur Batteries: "3D in 2D" Morphology Inducer and Coordination Structure Regulator.

The undesirable shuttling behavior, the sluggish redox kinetics of liquid-solid transformation, and the large energy barrier for decomposition of Li2S have been the recognized problems impeding the practical application of lithium-sulfur batteries. Herein, inspired by the spectacular catalytic activity of the Fe/V center in bioenzyme for nitrogen/sulfur fixation, we design an integrated electrocatalyst comprising N-bridged Fe-V dual-atom active sites (Fe/V-N7) dispersed on ingenious "3D in 2D" carbon nanosheets (denoted as DAC), in which vanadium induces the laminar structure and regulates the coordination configuration of active centers simultaneously, realizing the redistribution of the 3d-orbital electrons of Fe centers. The high coupling/conjunction between Fe/V 3d electrons and S 2p electrons shows strong affinity and enhanced reactivity of DAC-Li2Sn (1 ≤ n ≤ 8) systems. Thus, DAC presents strengthened chemisorption ability toward polysulfides and significantly boosts bidirectional sulfur redox reaction kinetics, which have been evidenced theoretically and experimentally. Besides, the well-designed "3D in 2D" morphology of DAC enables uniform sulfur distribution, facilitated electron transfer, and abundant active sites exposure. Therefore, the assembled Li-S cells present outstanding cycling stability (637.3 mAh g-1 after 1000 cycles at 1 C) and high rate capability (711 mAh g-1 at 4 C) under high sulfur content (70 wt %).

Understanding structure-performance relationships of CoOx/CeO2 catalysts for NO catalytic oxidation: Facet tailoring and bimetallic interface designing.

Crystalline structure and bimetallic interaction of metal oxides are essential factors to determine the catalytic activity. Herein, three different CoOx/CeO2 catalysts, employing CeO2 nanorods (predominately exposed {110 facet), CeO2 nanopolyhedra ({111} facet) and CeO2 nanocubes ({100} facet) as the supports, are successfully prepared for investigating the effect of exposed crystal facets and bimetallic interface interaction on NO oxidation. In comparison with the {111} and {100} facets, the exposed crystal facet {110} exists the best superiority to anchor and stabilize Co species. Moreover, ultra-small CoOx clusters composed of strong Co-O coordination shells with minor Co-O-Ce interaction are formed and uniformly dispersed on the CeO2 nanorods. Structural characterizations reveal that the active exposed crystal facet {110} and the strong bimetallic interface interaction in CoOx/CeO2-nanorods (R-CC) result in more structural defect, endowing it with abundant oxygen vacancies, excellent reducibility and strong adsorption capacity. The DRIFTs spectra further indicate that the exposed crystal facet {110} has a significant promoting effect on the strength of nitrates compared with {111} and {100} facets. The bimetallic interface interaction not only significantly facilitates the formation of nitrate species at lower temperature, but also effectively suppresses the generation of sulfate and lower the sulphation rate. Therefore, R-CC catalyst exhibits the maximum NO oxidation activity with the conversion of 86.4 % at 300 °C and still sustains its high activity under cyclic condition or 50 ppm SO2. The provided crystalline structure and interaction-enhanced strategy sheds light on the design of high-activity NO oxidation catalysts.