Design And Electrochemical Performance Research Of Ruthenium-Carbon Core-Shell Structural Materials

Supercapacitors were widely used for high-power energy devices of renewable energy systems and miniature portable devices due to their advantages of fast charging and discharging speed,high power density and long cycle life.The improved performance of electrode materials could effectively increase the energy density of supercapacitors.Carbon materials were currently the most commonly used electrode materials due to their large specific surface area,good electrical conductivity and stable mechanical properties.However,the limited electric double layer capacitance of carbon materials was difficult to meet the increasing energy demand.The specific capacitive performance of the material could be improved by designing the interface layer structural or by compounding with other pseudocapacitive materials with high specific capacitance.In this paper,resorcinol-formaldehyde（RF）resin was used as carbon source and tetraethyl orthosilicate（TEOS）was as templates,and the influencing factors of the synthesis of hollow carbon microspheres were systematically investigated.Subsequently,the efficient strategy of compounding ruthenium oxide（RuO₂）with carbon microspheres was further studied,and an electrode material with a ruthenium carbon layer covering the ruthenium oxide core was obtained.The results showed that the energy storage performance of the electrode material was significantly improved.The hollow structure of the electrode material was rich in effective surface area that could be accessible to shorten the electron diffusion distance and increase the energy storage capacity of the material.Hollow carbon microspheres（HCs）were synthesized by the modified St（?）ber method and hard template method.Meanwhile,the effects of formaldehyde/resorcinol（F/R）ratio,RF concentration,TEOS concentration and reaction time of hydrolytic polycondensation,and the type of silane alkoxy on the morphological and dimensions of the synthesized HCs were investigated in detail during the synthesis process.By optimizing the experimental conditions,the particle size of the as-prepared hollow carbon microspheres could be tuned in the range of200 nm to 500 nm.The structures and properties of HCs synthesized by changing the reaction time of TEOS hydrolysis and polycondensation were further studied.The results indicated that the hollow carbon microspheres（HCs-20）with the 20 min reaction time had the large specific surface area,high degree of graphitization,and the fast ion diffusion rate due to the difference in the degree of hydrolysis and polycondensation of TEOS and the occurrence of the polycondensation reaction of RF resin.And it exhibited excellent capacitance performance.HCs-20 exhibited a specific capacitance of 260.3 F·g^-1 at a current density of 0.5 A·g^-1 and the retention rate of the specific capacitance of the material was 98.4%after 2000 cycles at 10 A·g^-1.RuO₂ had excellent pseudocapacitive properties,high proton conductivity and wide voltage window.And it was an ideal electrode material for supercapacitors.We composited it with carbon materials to construct a novel hollow core-shell structure electrode material with hard template method and co-assembly strategy.The material used RuO₂ as the core and hierarchical porous carbon layer loaded with Ru nanoparticles as the outer shell.The results indicated that the Ru particles were uniformly assembled in the carbon layer,which not only improved the electronic conductivity but also provided more active centers to enhance the pseudocapacitance.The RuO₂ core further enhanced the material’s energy storage capacity.Excellent energy storage performance(318.5 F·g^-1 at 0.5 A·g^-1),rate capability（64.4%）and cycling stability（92.3%retention after 5000 cycles）were obtained with the Ru loading being0.92 wt%.It could be attributed to the wider pore size distribution in the micropores which increased the diffusion rate of electrons.Besides,the symmetric supercapacitor device based on RuO₂@Ru/HCs material successfully lighted up a small LED lamp,illustrating the value of RuO₂@Ru/HCs material in practical application.