Single-Molecule Confinement Induced Intrinsic Multi-Electron Redox-Activity to Enhance Supercapacitor Performance

Aggregation of polyoxometalates(POM)is largely responsible for the reduced performance of POM-based energy-storage systems.To address this challenge,here,the precise confinement of single Keggin-type POM molecule in a porous carbon(PC)of unimodal super-micropore(micro-PC)is realized.Such precise single-molecule confinement enables sufficient activity center exposure and maximum electron-transfer from micro-PC to POM,which well stabilizes the electron-accepting molecules and thoroughly activates its inherent multi-electron redox-activity.In particular,the redox-activities and electron-accepting properties of the confined POM molecule are revealed to be super-micropore pore size-dependent by experiment and spectroscopy as well as theoretical calculation.Meanwhile,the molecularly dispersed POM molecules confined steadily in the“cage”of micro-PC exhibit unprecedented large-negative-potential stability and multiple-peak redox-activity at an ultra-low loading of~11.4 wt%.As a result,the fabricated solid-state supercapacitor achieves a remarkable areal capacitance,ultrahigh energy and power density of 443 mF cm^(-2),0.12 mWh cm^(-2)and 21.1 mW cm^(-2),respectively.This work establishes a novel strategy for the precise confinement of single POM molecule,providing a versatile approach to inducing the intrinsic activity of POMs for advanced energy-storage systems.

Analysis of Residues Formed during the Liquefaction Process of Wheat Straw

Wheat straw(WS) was liquefied to analyze the reaction process of WS under the acid-catalyzed conditions. WS was liquefied almost completely in the presence of ethylene carbonate/ethylene glycol(EC/EG) blend solvents within 40min at 150 ℃. The residues with different liquefaction time were investigated by SEM, FTIR, and XRD. The residues exhibited loose structure and rough surface due to the presence of stacked irregular platelets. The FTIR results demonstrated that lignin was more easily liquefied in the presence of EC/EG blend solvents than cellulose because the bands of cellulose were stronger and the bands of lignin were much weaker during the liquefaction process of WS. Moreover, the XRD result of all residues declared that WS was gradually liquefied, dissolved and decomposed to small fragments of lower molecular weight, and condensed in part in the later stage of liquefaction.

From surface loading to precise confinement of polyoxometalates for electrochemical energy storage

Because of abundant redox activity,broad tunability,and specific atomic structure,polyoxometalates(POMs or POM)clusters have attracted burgeoning interests in electrochemical especially energy stor-age fields.Nevertheless,due to the high solubility and fully oxidized state,they often suffer from elec-trically insulation as well as chemical and electrochemical instability.Traditional noncovalent loading or covalent grafting of POMs on conductive substrates have been successfully performed to overcome this problem.However,severe shedding or agglomeration of POMs arising from weak interactions with substrates or excessive entrapment or weak destruction in conductive supports cause significantly re-duced availability and stability.To this end,precise confinement of POMs into conductive supports has been tried to improve their dispersibility and stability.Herein,recent progress of PoMs from surface loading to precise confinement in the electrochemistry energy storage field is reviewed.Firstly,we il-lustrate the typical non-confinement methods(viz.covalent and non-covalent)for supported POMs in energy storage applications.Secondly,different strategies for precise confinement of PoMs in organic and inorganic materials for related applications are also discussed.Finally,future research directions and opportunities for confined POMs,and derived ultrafine nanostructures are also proposed.This re-view seeks to point out future research directions of supported PoMs in the electrochemistry-related fields.