Cattle Bone Based Hierarchical Porous Carbon Materials And Their Electrochemical Performance

Porous carbon materials are widely used in energy and environment fields due to high specific surface area, rich porosity, good thermal and electric conductivity, excellent chemical stability. Recent years, the growing hierarchical porous carbons(HPC), possessing three-dimensional interconnected micro-, meso-, and macropores which substantially increase the mass transfer effiency of multi-phase media, have potential applications in high-performance electrochemical material. Consequently, studying these materials is of great scientific significance and pratical value. This paper aims to develop natural biological template method for fabricating hierarchical porous carbons at low cost. In this paper, a series of hierarchical porous carbon materials were developed successfully by use of cheap and readily-available biomass based on its fine ordered lamellar nano-structure. And their application in supercapacitor electrode materials and electrocatalysts for oxygen reduction were investigated.Firstly, heteroatoms in-situ doped hierarchical porous carbons were fabricated using raw cattle bone via carbonization and activation. The reseach shows, the organic collagen in cattle bone is an important precursor for preparing functionalized carbon materials, the inorganic hydroxyapatite, served as natural hard template, facilitate the generation of three-dimensionally interconnected mesopores and macropores. The carbon mateials is successfully prepared with controllable surface area, pore structrue and surface chemistry. Hierarchical porous carbons with high content mesopores were fabricated at the activation temperature of 850 ℃, which have high specific surface area of 2520 m2 g-1, pore volume of 3.18 m3 g-1, nitrogen atomic percentage of 1.56% and oxygen of 10.2%.On this basis, the as-prepared HPCs were used for supercapacitor electrode and their electrochemical capacitance properties and device performance were explored. The results demonstrate that ultrahigh surface area offers high electric double layer capacitance. And high proportion of mesopores increase the mass transfer efficiency. Additionally, in-situ doped nitrogen- and oxygen-containing functional groups enhance the wettability of electrode material, thus increasing the utilization of micropores, and their reversible redox reaction enhances pseudo-capacitance. Therefore, the HPC displays specific capacitance of 435 F g-1, excellent rate performance and good durability. The symmetrical supercapacitors were assembled using the high-capacity HPC materials as positive and negative electrodes, which exhibits specific capacitance as high as 85.2 F g-1, and maintains 97.5% of its initial capacitance after 20000 cycles of charge/discharge. What’s more important, the device delivers gravimetric energy densities of 30.3 Wh kg-1 Lastly, the as-fabricated HPC materials were decorated by surface doping for oxygen reduction reaction (ORR). It was comfirmed that three-dimensional interlinked pore structure of HPC facilitates the highly uniform dispersion of the catalytic active sites and enhances the transfer of reaction intermediates. Iron, nitrogen co-doped HPC catalysts (Fe-N-HPC) were synthesized by pyrolyzing ferrocene, ethylene diamine in addtion of HPCs. The catalysts show good ORR activities via one-step quasi-four-electron reduction pathway. By pyrolyzing vitamin B12, cobalt, nitrogen co-doped HPC catalysts (Co-N-HPC) were prepared with specific surface area of 859 m2 g-1. The electrochemical results show, the half-wave potential (E1/2) of Co-N-HPC is 8 mV higher than that of commercial Pt/C electrode, and the kinetic current density (jk@0.8 V vs. RHE) was calculated to be 20.4 mA cm-2, which is twice that of Pt/C.Additionally, the catalyst has excellent durability and tolerance against methanol poisoning. Based on the above research, the HPCs were doped with dual transition metal atoms (FeCo-N-HPC) using vitamin B12 as cobalt source and ferrocene as iron source.And their ORR activity was further enhanced. The E1/2 of FeCo-N-HPC electrocatalyst is 23 mV higher than that of commercial Pt/C electrode, and the jk (@0.8 V) was calculated to be 51.6 mA cm-2. FeCo-N-HPC electrocatalysts also reveal excellent chemical stability. After 10000s constant-potential operation, the ORR current density for FeCo-N-HPC decrease by 10.7%, showing better stability than Pt/C(35.2%).