Jingyan Zhu,Baolin Liu,Weibing Zhang,Jun Jiang,Xinhua Li
Single-molecule magnets in cobalt clusters is much less well known than it is in manganese(II)/(III)/(IV) clusters. To explore new types of cobalt clusters and their potential applications, a new mixed valence coordination polymer ([Co(III) 3 Co(II) 2 (mba) 6 (Hdtba) (H 2 O) 4 ] n , H 2 dtba=2,2’-dithiodibenzoic acid, H 2 mba=2-mercaptobenzoic acid) ( 1 ) is constructed by employing cobalt chloride hexahydrate and H 2 mba as starting reactants under hydrothermal conditions. Single-crystal XRD studies indicate that 1 consists of a trinuclear cobalt(III)-sulfur cluster moiety and two discrete cobalt(II) nodes, which result in the formation of a covalent three-dimensional complex network. Similarly, the cobalt(III) cluster moiety acts as a building unit in this infinite coordination polymer 1 instead of the discrete and tiara-like clusters previously reported in the literature. Magnetic studies show its slow magnetic relaxation in the absence of an applied dc field, which is characteristic behavior of single-ion magnets, caused by the individual Co(II) ions.
Rechargeable zinc-air batteries (ZABs) hold great promise for next-generation energy storage, but their practical application depends on the development of efficient bifunctional catalysts capable of catalyzing both the oxygen reduction reaction (ORR) during discharge and the oxygen evolution reaction (OER) during recharge. Herein, we propose a high-performance bifunctional oxygen electrocatalyst for ZABs, fabricated by encapsulating Co clusters into zeolite imidazole framework-8 (ZIF-8)-derived carbon via a supercritical CO 2 (scCO 2 ) fluid-assisted method. The dual-protection combining spatial confinement from porous carbon frameworks and strong Co-N coordination anchoring enables the stabilization of high-density Co clusters and preventing its aggregation. Furthermore, the scCO 2 treatment reconstructs the mesoporous structure, significantly improving mass transport and exposing more accessible active sites. Density functional theory (DFT) calculations demonstrate that the surface Co-N moieties serve as highly active centers for the ORR, whereas the metallic Co sites within the clusters predominantly drive the OER. As a result, Co@N–C exhibits a remarkably low potential gap (ΔE = 0.68 V) between ORR and OER. When applied in aqueous ZABs, the catalyst delivers an impressive specific capacity of 780 mAh g Zn −1 and a peak power density of 170 mW cm −2 , surpassing Pt/C + RuO 2 . Moreover, the solid-state ZABs assembled with this catalyst achieve a high peak power density of 87.0 mW cm −2 along with long-time cycling stability of 200 h, demonstrating great potential for flexible and portable energy storage devices.
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