Preparation And Electrochemical Performance Investigations Of Heavy Oil-Based Carbon Materials For Energy Storage

Currently,clean and efficient utilization of energy has become one of the world’s development strategies.It is urgent to research and develop the energy storage system,and carbon material is considered to be a significant alternative in composing the energy conversion and storage system due to its advantages of abundant raw materials,excellent electrical conductivity,and stable chemical properties.Carbon materials can be obtained from the heavy oil bitumen as it has high content of carbon,abundant raw materials,and low price.Therefore,this paper aims to investigate the fabrication of porous carbon material via the chemical activation method and template preparation while utilizing the heavy oil bitumen as a carbon source.Moreover,the prepared porous carbon material is used as a skeleton for the nano flake and nano linear combination of manganese dioxide to grow on its surface through the hydrothermal method to generate the composites.The electrochemical properties of as-grown carbon materials and composites are further evaluated by the electrochemical performance experiments.（1）Using the heavy oil bitumen as a carbon source and the KOH as an activator,the high-temperature alkali etched bitumen was formed and then used to prepare cellular porous carbon materials.Under the conditions of mass ratio of heavy oil bitumen to KOH of 1:3,activation temperature of 800℃,activation time of 2 h,the average pore size of HPC-3 sample was approximately 1.91 nm,the total pore volume was 0.99cm³/g,and the specific surface area was up to 2075 m²/g.Under the condition of 1 A/g current density,the HPC-3 sample had the highest specific capacity of 260.8 F/g,and the specific capacity loss of the HPC-3 sample was only 5%after completing 5000charge and discharge tests.In conclusion,heavy oil asphalt is an excellent king of carbon source,and electrode materials with high specific capacity and long life cycle could be prepared by the one-step activation method.（2）Using the heavy oil asphalt as a carbon source,and the KOH as an activator,nano ferric oxide,and zinc oxide as templates to accurately control the pore structure,porous carbon materials with high mesoporous ratio were prepared.The effects of dosage and particle size of template on mesoporous ratio and energy storage performance of carbon materials were investigated systematically.When the mass ratio of asphalt to ferric oxide was 1:0.08（Fe/HPC-3）and the mass ratio of asphalt to zinc oxide was 1:0.25（Zn/HPC-3）,the porous carbon had the largest mesoporous ratio.The mass-specific capacities of Fe/HPC-3 and Zn/HPC-3 were 309.6 F/g and 365.7 F/g,respectively,under current density of 1 A/g.Compared with the porous carbon materials prepared without templating agent,the specific capacity of porous carbon materials was increased by 18.7%and 42.2%,respectively,which provides a preparation method of porous carbon materials with a high capacity for the preparation of heavy oil asphalt supercapacitor.（3）Using the prepared porous carbon HPC-3 as a carbon source,C/Mn O₂composites were produced by the hydrothermal reaction with KMn O₄ and Mn SO₄.By adjusting the mass ratio of KMn O₄,Mn SO₄ and HPC-3,the structure and loading capacity of Mn O₂ in the composites were precisely controlled to optimize the electrochemical properties of the composites.When the mass of KMn O₄,Mn SO₄,and HPC-3 was 36.34 mg,58.30 mg and 50.00 mg,respectively,the Mn O₂ in the composites was in state of nano-lamellar and nano-linear,while C/Mn O₂-2 still retained the porous structure of HPC-3.The manganese dioxide composite with state of nano-lamellar and nano-linear on the surface of porous carbon materials greatly improved the pseudo capacitance of porous carbon materials.Under the current density of 1 A/g,the C/Mn O₂-2 sample had the highest specific capacity of 396.5 F/g,which was 52.0%higher than that of the HPC-3 porous carbon.In the asymmetric system,the energy density of C/Mn O₂-2 was 19.0 Wh/kg when power density was 772.1 W/kg.The results demonstrated that the heavy oil asphalt-based porous carbon composites with manganese dioxide had excellent electrochemical performance.