Preparation And Electrochemical Properties Of Core-shell Nanoreactors And Their Derivatives

Materials with core-shell nanostructures are of great interest because of their new chemical,biological or catalytic activity and unique morphological features.At present,the reasonable optimization of structure and composition is exceedingly important for enhancing the electrochemical performance of core-shell nanoreactor.In this paper,sandwich core-shell structure ZIF-67@SiO2 are synthesized through controlling the growth of Co-zeolite imidazole framework(ZIF-67)crystal with the hydrolysis of tetraethoxysilane.The ZIF-67 crystals can provide a cobalt metal source and serve as a template for silica growth.On the basis of synthesis of ZIF-67@SiO2,a series of core-shell structureal nanoreactors with regular morphology and uniform distribution were prepared by facile calcination and hydrothermal method,including yolk-shell strcutured Co3O4@SiO2,CoP@SiO2 of and hollow core-shell structured Co3(OH)4Si2O5.Then the electrochemical supercapacitor and oxygen evolution catalytic performance of the core-shell structured samples were investigated.Specifically including the following three parts:1.Using a simple room temperature stirring method,Co(NO3)2·6H2O and tetraethoxysilane were poured into an aqueous solution in which 2-methylimidazole(2-MeIm)was dissolved to prepare ZIF-67@SiO2 with a dodecahedral structure,then calcined ZIF-67@SiO2 under different temperatures(350?,500?,600?,800?)to synthesize yolk-shell structured Co3O4@SiO2 nanoreactor(CS1,CS2,CS3,CS4),successfully encapsulated metal oxide nanoparticles(Co3O4)into the protective shell(SiO2).Under the same conditions,The supercapacitor performance of Co3O4@SiO2 obtained with temperature as the only variable were investigated.It can be concluded from the testing results that the product(CS2)calcined at 500? displayed better supercapacitor performance.2.Using a simple hydrothermal method,the above-mentioned Co3O4@SiO2(CS1,CS2,CS3,CS4)calcined at different temperatureso as a precursor was dissolved in deionized water,and the hollow dodecahedron structure with nanosheets,Co3O4@SiO2(CSH1,CSH2,CSH3,CSH4)was obtained,through reacting at 180? for 24 hours.The supercapacitor performance of CSH series derivatives were tested,and the results showed that CSH series derivatives exhibited better superelectrical properties than CS series precursors.The specific capacitance of CSH2 can reach 1648 F g-1 at 0.5 A g-1,significantly higher than other substances in the same series.3.Using a simple calcination method,Co3O4@SiO2(CS2)as a precursor,and NaH2PO2 with different mass(100 mg,200 mg,500 mg)was pyrolyzed at 350? in N2 atmosphere,the released PH3 reacted with the Co3O4 core in the precursor to synthesize the CoP@SiO2 nanoreactor(CP 1,CP2,CP3).The electrocatalytic performance of the precursors and reactants with different phosphating degrees were tested and the results showed that the OER performance of the phosphating products was significantly superior to the precursors.Among them,CP3 with deep phosphating degree exhibited the best electrocatalytic activity,the overpotential was 280 mV at the current density of 10 mA cm-2,the Tafel value was 89 mV dec-1,and it still maintain good catalytic activity through 1000 CV cycles.