Intrinsic Regularity of Catalytic Cobalt Chalcogenides in Lithium-Sulfur Battery: Theoretical Study Delivers New Insights.

Cobalt chalcogenides CoX2 (X=S, Se, Te) render great performance of lithium-sulfur batteries based on catalytic capacity to alleviate shuttle effect. Given that S/Se/Te belong to the same main group, the outstanding cycling stability delivered by CoTe2 aroused the curiosity about the uniqueness of CoTe2 and intrinsic laws of cobalt chalcogenide. Herein, comprehensive theoretical study delivers new insights into the intrinsic laws of CoX2 : the relative vertical distance of two X atomic layers (rather than atom electronegativity) mainly controls adsorption; CoX2 mainly regulates the charging process (rather than discharging process) thus contributes to great cycling stability. On this basis, the advantages of CoTe2 are three-fold: moderate polysulfide adsorption, facile ion transport capacity, and surprisingly great promotion of charging process. It is hope the results will facilitate the development of cobalt chalcogenides, especially tellurides as catalytic material in lithium sulfur batteries.

Unravelling intrinsic descriptors based on a two-stage activity regulation of bimetallic 2D c-MOFs for CO2RR.

The bimetallic 2D conductive MOFs of M1Pc-M2-O, possessing dual metal sites to realize flexible molecular-level structural modification, are brilliant catalysts for electrochemical CO2 reduction. However, the bimetallic centers bring about the complex regulatory mechanism of catalytic activity and obscure principles for catalyst design. Herein, systematical theoretical investigation unravels intrinsic descriptors to design favorable M1Pc-M2-O catalysts based on the discovered coarse-fine two-stage activity regulation mechanism. The reaction site controls the M-COOH distance of the key intermediate and therefore affects the reaction kinetics for the first stage of coarse regulation. The other metal site influents the d-band center of the reaction site and thus constitutes the second stage of fine regulation. The coarse and fine regulation are related to the valence electrons (V), electronegativity (E), and bond length (LM-N/O) between the metal and coordination atoms. The intrinsic descriptor ϕ = (4 × VM1 × (EM1 + EN/O)/EN/O + VM2 × (EM2 + EN/O)/EN/O) × LM1-N/O (with a coefficient ratio of 4 : 1) was eventually established and correlated well with the reported experiments. On this basis, the favorable catalysts CoPc-Zn-O and CoPc-Co-O were located. The research results could contribute to the diversity of bimetallic 2D c-MOFs in CO2RR.