Redox Polyoxometalates Utilized For The Construction Adhesive Soft Materials

Polyoxometalates(POMs)is a kind of inorganic molecular clusters formed by condensation of simple metal oxides.One molecule cluster of polyoxometalates can contain 6 to 368 metal ions,which is highly monodisperse and the size can be precisely tunable from angstroms to 10 nanometers.The unique structures and physicochemical properties of POMs are unmatched by other compounds.Nowdays,POMs have been widely used in many fields,such as catalysis,detection,senser and so on.In particular,they can undergo reversible redox reactions without changing their own structure.So,they are an excellent class of electronic storage materials and often used as an electrode active material for supercapacitors.However,with the development of the needs the flexible devices have received more and more attention.The development of flexible supercapacitors based on POMs is a new growth trend.In this paper,we have proposed a flexible supercapacitor based on POMs,which has excellent adhesion,flexible processing performance and electrochemical activity.This paper mainly introduces how to prepare supramolecular adhesive soft materials containing POMs,and use the oxidation reduction property of POMs to construct flexible supercapacitors.The specific research contents are as follows:Firstly,based on the construction of POMs and like-dopamine molecules,we prepared organic/inorganic hybrid supramolecular water-based adhesives in aqueous solution by one-step Co-assembly method.The systematic study shows that the strong oxidizability of the POMs can oxidize the like-dopamine molecules to the corresponding oligomers.At the same time,the polyvalent surface charge of POMs and the oligomers cross-linked and assembled to form a continuous three-dimensional network structure,leading to the formation of adhesives.We systematically investigated the effect of the oxidation ability of POMs on the cross-linking assembly.It was found that POMs containing Mo and V could oxidize like-dopamine molecules to form adhesives rapidly,while POMs with low oxidation ability could not oxidize like-dopamine molecules to form adhesives.The results of tensile shear test showed that the adhesives have good dry/wet state bonding properties and can be applied to a variety of solid substrates.The rheological test results showed that the adhesive have certain mechanical strength.However,pyrocatechol is easily oxidized to quinone structure,which leads to the weakening or even loss of this kind of adhesive.Secondly,in order to improve the stability of the adhesive and develop the ability of POMs to store electrons,we used aromatic amino acids and POMs as building blocks to prepare a conductive adhesive which can be used in the coating materials of supercapacitor electrodes by solid-phase grinding and water-phase assembly under the condition of carbon doping.FT-IR showed that the topological structure of POMs remained complete before and after assembly.Raman and XRD test results showed that the structure of graphite microchip is complete.The tensile shear test results showed that the adhesive had good bonding strength above and below water.The rheological test results showed that the adhesive have good mechanical properties.The conductivity of the adhesive was tested by four probes.We used the conductive adhesive as the electrode coating of supercapacitor,and measured the capacitive performance of adhesive of the adhesive by three electrodes methods using electrochemical workstation.The test results showed that the adhesive have excellent electrical storage capacity.Then we successfully assembled a solid-state super capacitor with carbon paper as electrode and tested its electrochemical performance.We use commercial power equipment to charge it for 10 seconds.After disconnecting the external power supply,the capacitor can successfully charged the electronic timer for several minutes.In addition,due to the excellent adhesion and mechanical properties of the adhesive,we coated the conductive adhesive on the flexible and stretchable rubber substrate,and prepared a flexible and stretchable electrodeless supercapacitor(wave shape)by structural design.In summary,a series of supramolecular water-based adhesives have been successfully prepared by covalent or noncovalent cross-linking assembly,using POMs,like-dopamine and aromatic amino acids as building units in this paper.Moreover,the mechanical properties of this kind of adhesives can be regulated by the hydroxyl numbers of small like-dopamine molecules and the charge number of POMs.We found that the more the charge number of POMs and the hydroxyl numbers of small like-dopamine molecules,the better the adhesive performance.In addition,we dominate the adhesive good conductive function by doping conductive carbon materials.We use the ability of reversible electronic gain and loss of POMs and the adhesive property to obtain the flexible electrode coating material,and successfully prepare an electrode independent flexible supercapacitor.