Investigation Of Functional Carbon Material From Oily Sludge And Its Capacitance Performance

Oily sludge is one of the major solid wastes generated in the petroleum industry.It is a complex emulsion of various petroleum hydrocarbons,water,heavy metal salts,and solid mineral particles.Due to its hazardous nature and increasing quantities,oily sludge can pose serious threats to the environment.Therefore,the effective remediation of oily sludge has became the hot spot all around the world.Despite of the traditional treatment methods are associated with some advantages and limitations,they could not utilize oily sludge harmlessly as resources.Exploring a new method of disposal of oily sludge has been urgent.Nowadays,with the ever-increasing demand for sustainability in energy and environment,developing superior,affordable and environment-friendly energy conversion and storage device has received great attention world widely.Supercapacitors,also known as electrochemical capacitors,are considered as an important supplement to traditional batteries,due to their extremely high power density,super-long cycling life and reliable safety performance.The electrode material of the commercial supercapacitors are usually carbon-based material,while the carbonaceous electrode material with high capacitance performance tends to be more expensive,which limits their wide applications.Therefore,exploring the inexpensive raw materials and manufacturing methods for carbon-based electrode materials of supercapacitor is the most important research direction in the field of supercapacitor.Considering the huge amount and abundance of hydrocarbons contents in oily sludge,it is feasible to convert it into high value-added carbonaceous materials for application in supercapacitor.However,the complex mineral content in it still remains a challenge for advanced utilization.Here,we report on a facile route to fabricate oily sludge-based hierarchical porous carbon（HPC）by using“two-steps”method of pre-carbonization and chemical activation.The smart“self-template”effect and appropriate activation effect are crucial for the rational hierarchical porous structure.The“self-template”procedure is the key point for creating the skeleton of carbon,and the KOH activation process is able to regular pore size distribution and increase specific surface area.The as-fabricated HPC possesses favorable features for electrical double-layer capacitance,such as outstanding specific surface area and excellent pore size distribution.The HPC-based electrode can deliver an admirable capacitance and energy densities,outstanding capacitance retention,cycling stability and structural stability.To further optimize the specific capacitance performance of the HPC electrode material,the preparation process was improved and the nitrogen-doped carbon materials was achieved.While retaining the high specific surface area and pore size distribution of carbon materials and maintaining characteristics of double-layer capacitance,the pseudo-capacitive effect is introduce into them successfully.The as-received N-doped porous carbon electrode material shows better capacitance performance.In addition,in order to optimize the specific capacitance and energy densities of oily sludge-based carbon materials,metal oxides-porous carbon composite material was designed and synthesized.Manganese dioxide-porous carbon electrode materials was prepared by simple redox self-assembly method for the better application of positive electrodes of supercapacitor.And iron oxide-porous carbon composite materials was fabricated by hydrothermal deposition method for the application of negative electrodes.MnO₂nano-wires and Fe₂O₃ nano-rods were uniformly loaded on the surface of the oily sludge-based HPC materials,respectively.The presence of porous carbon substrates with high specific surface area not only increase the electrical conductivity of pseudo-capacitance active material,but also improve the utilization rates of them by enlarging the reaction interfaces between pseudo-capacitance active materials and electrolyte.Thus,the composite material realizing the synergetic effect of the electrical double-layer capacitance and pseudo-capacitance.The MnO₂/HPC and Fe₂O₃/HPC composite electrode material possess excellent specific capacitance,and the MnO₂/HPC//Fe₂O₃/HPC asymmetric supercapacitor device exhibits remarkable specific capacitance and energy density.Dues to the low-cost and widely available of the raw material and the effective preparation process,the proposed method here for preparing carbonaceous electrode materials for supercapacitor by using oily sludge has significant cost advantages.Considering the environmental benefits which cannot be easily underestimated,it is reasonable to assume that the cost of the carbon-based materials could be reduced to free.Therefore,the research in this paper provides a promising avenue of large-scale fabrication of carbon-based electrode material from other hazardous industrial wastes,Which will simultaneously resolve the problems of environment pollution waste disposal and costless carbon material production.