Preparation And Storage Properties Of Carbon Nano Research Bacterial Cellulose Fiber Material

Super capacitors, also called electrochemical super capacitor,is a new type of energy storage unit between electrochemical batteries and traditional capacitors.Super capacitors have some advantages such as high power density, long cycle life and high safety performance. In the past two decades, super capacitors have been widespread concerned by scientists from various countries. Super capacitors have been successfully applied in many aspects such as memory backup power supply system, electric power toys, communication instruments, electric vehicles, railways,and even spacecraft power system. But it is not mature enough for super capacitors applying in commercial field because of their relatively poor performance, for example, specific capacitance and high-power discharge stability. It is significant to improve the electrochemical performance and discharging performance, therefore, it is still a significant research subject.The capacitor consists of two parts in a super capacitor, namely the surface electric double layer capacitance and bulk pseudocapacitance. In the paper, bacterial cellulose(BC) produced by fermented coconut water was used as precursor. Based on the method of temperature programmed thermal carbonization under a nitrogen atmosphere, a series of bacterial cellulose nano carbon fibers(BCNCF) were prepared,which were provided as the the structural components of the surface on electric double layer capacitors. At the same time, Keggin-type heteropolyacid salt Cs4PW11O39Fe(III)(H2O)(PW11Fe) were used as the components of the pseudocapacitance, and PW11Fe/BCCNF composite materials were prepared by hydrothermal method. These materials were characterized by some processes such as XRD 、 Raman 、 SEM 、 TEM 、 BET and elemental analysis. Then charging and discharging performance, capacitance and cycling stability of these materials were examined and studied by some electrochemical methods such as cyclic voltammetry and timing power. The results showed that after bacterial cellulosecarbonization, the obtained nanometer carbon fiber materials were mainly mesoporous structure, and specific surface area is 756.82 m2g-1,specific capacitance is 289 Fg-1.After 5000charge-discharge cycles, the capacitance value remains above 80% of the initial value.However, the pore structure, the specificsurface area, the degree of graphitization,charge and discharge performance and cycling stability of these materials are closelyrelated to the carbonization temperature. High carbonization temperature(900°C) is conducive to the formation and stability of the pore structure, high specific surface area and charge-discharge cycling stability can be obtained, but the degree of graphitization is relatively high, which is not conducive to storage of electricity and the specific capacitance is relatively low. The degree of graphitization of low carbonization temperature(700°C) is relatively low, specific capacitance is relatively high, but the relatively surface is low, pore structure is unstable, and the charge-discharge cycling stability is relatively poor. For another, specific capacitance relates to the thickness of the bacterial cellulose precursor, for example, if the thickness of bacterial cellulose carbon nanofibers were respectively 0.4 cm, 0.3 cm,and 0.2 cm, specific capacitances were 289Fg- 1, 177Fg- 1and 169 Fg- 1. When loaded PW11 Fe on the 0.3 cm-thick bacterial cellulose carbon nano fibers by hydrothermal method, the specific capacitance of the PW11Fe/BCCNF composite materials was 215.3 Fg-1, which was obvious higher than 177 Fg-1. And after 5000 cycles, the loss of the capacitance value was merely 17%, which means they have preferable cycling stability.