Preparation And Electrochemical Properties Of Plant-based Fe/N/O Co-doped Porous Carbon

The limited nature of traditional energy sources and the non-environmental characteristics of the consumption process make it difficult to meet the needs of green development.In order to solve the energy problem and the environmental problems caused by the development of new materials and to achieve green and sustainable development,people are still exploring new,stable and efficient energy storage devices.Supercapacitors have been in the focus of many energy storage devices with their fast charging and discharging modes,high-energy density and long cycle life.The electrode material is one key factor to determine the performance of supercapacitors.Biomass-derived carbon materials have been widely used as electrode materials for supercapacitors due to their abundant sources,low cost,easy processing,safety,environmental friendly and good chemical stability.Currently,there are many methods to develop porous carbon derived from biomass,mainly including template method,physical and chemical activation method,etc.Among them,although chemical activation method is easy to pore-causing,but most of the process needs to use corrosive,environmentally unfriendly activator.For this reason,the choice of safe and environmentally friendly activators for the preparation of porous carbon materials is the future trend in this field.In this paper,Fe/N/O co-doped hierarchical porous carbon with large specific surface area and well-developed pore structure was rapidly prepared by chemical activation using tissues of three different types of plants as raw materials and K₂Fe O₄ as a green activator,and successfully used in supercapacitor electrode materials.The research results include the following main parts.1.Using chestnut spiny shells as precursor,Fe/N/O co-doped hierarchical porous carbon（Fe/N/O-HPC）with interconnected pore structure and a high specific surface area of 1737.32 m²/g was conveniently prepared by chemical activation using K₂Fe O₄as activator.The electrode materials prepared from Fe/N/O-HPC exhibit excellent electrochemical performance with a high specific electric capacity of 356.2 F/g,remarkable rate performance and excellent cycling stability.In the three-electrode system,the capacitance retention rate is still as high as 96.46%after 10,000 cycles of charge and discharge at a current density of 20 A/g.The symmetrical two-electrode system assembled from Fe/N/O-HPC has an energy density of 14.59 W h/kg and 11.19W h/kg,corresponding to a power density of 650 W/kg and 6500 W/kg,respectively,and a capacitance retention of 85.88%after 10,000 charge/discharge cycles at 7.5 A/g.2.Fe/N/O co-doped three-dimensional hierarchical porous carbon was prepared by a one-step carbonization activation method using verbena as the carbon source and urea as the nitrogen source.The results show that Fe/N/O-HPC has a specific surface area of 1664.88 m²/g and a specific capacitance of 305.5 F/g.The energy density of the assembled symmetric supercapacitor reaches 13.25 W h/kg and the power density is650 W/kg.In the three-electrode system,the capacitance retention reached up to 83.01%after 10,000 cycles of charge/discharge,while in the two-electrode system（3A/g）,the capacitance retention achieved 75.44%.3.Fe/N/O co-doped three-dimensional hierarchical porous carbon was prepared by one-step direct activation carbonization using purslane as precursor and K₂Fe O₄ as activator,Fe/N/O-HPC has an obvious interconnected pore structure with a specific surface area of 1589.64 m²/g.The electrodes made from Fe/N/O-HPC exhibit good electrochemical properties:the specific electric capacity reaches 234.4 F/g at a current density of 0.5 A/g.A symmetrical supercapacitor assembled from Fe/N/O-HPC showed a capacitance retention of 71.43%after 10,000 cycles of charge and discharge at a current density of 3 A/g.Their energy density reaches 11.82 W h/kg and 8.40 W h/kg,corresponding to a power density of 325 W/kg and 3250 W/kg,respectively.The above demonstrates the good potential of the fabricated Fe/N/O-HPC in supercapacitor electrode materials.This work have provided an idea for the simple and rapid preparation of plant-based heterogeneous elements co-doped hierarchical porous carbon materials using a green activation process.