Construction Of Supercapacitor Electrodes By Cobalt/Nickel-Based Compounds And Their Energy Storage Mechanism

With the deterioration of the environment and the shortage of fossil fuel resources,the growing energy demand has become one of the pressing issues for the international community.Exploring new green energy storage devices has become a hot topic of current research.In the field of energy storage,supercapacitors have attracted considerable attention for their high capacitance,long cycle life and high-power density.Capacitor electrode material is one of the important factors that directly affect the performance of supercapacitors.Therefore,exploring electrode materials with suitable application potential is the key to the development of supercapacitors.In this paper,popular biomass carbon materials,metal organic framework（MOF）derivative materials and transition metal sulfide materials were selected for the preparation of electrodes.Meanwhile,the mechanism of change inside the electrode material is simulated based on the first principle calculation,which provides theoretical support for the results of the experiment.The main work includes:（1）Supercapacitor electrodes were prepared by combining metal-organic framework derivatives as the main material and bacterial cellulose membrane（BC）as the guest material,the effects of different Zn/Co doping ratios on the electrochemical properties of the electrodes were investigated.The experimental results show that the fine mesh structure and super adsorption ability of bacterial cellulose membrane successfully avoid the cluster aggregation effect of metal-organic framework derivatives,the prepared electrode materials have large specific surface area and rich pore size structure.Finally,the best electrochemical performance(326.9 F g^-1 specific capacitance at 2 A g^-1)was obtained for the single electrode prepared at a Zn/Co ratio of 0:5.（2）The Co-MOF material was used as the substrate material and the change of electrochemical properties of the electrode was explored by controlling the Nielement doping ratio.The Co NiO/PCNFs-2 electrode prepared at a Co/Niratio of 1:1 has a high specific capacitance of 912.4 F g^-1 at a current density of 1 A g^-1,a multiplicative characteristic of more than 50%capacitance retention at 1-100 A g^-1,and an excellent cycling stability of nearly 90%capacitance retention after 6000 cycles.In addition,density function theory（DFT）calculations show that the Ni-doped electrode material has lower formation energy and OH-adsorption energy,which effectively enhance the charge transfer and energy storage during charging and discharging.（3）Mo-doped NiMoS（NMS）nanoflower electrode materials were prepared by a one-step electrodeposition method.By controlling the Modoping content combined with electrochemical analysis,it was shown that Moelement occupies an important role in the contribution of capacitive behavior.Modoping can significantly reduce the ion diffusion resistance of the material and enhance the cycling and multiplicative capability of the electrode.DFT calculations show that Modoping has an important effect on the electronic properties of NMS materials and the OH-affinity in the electrolyte.The prepared electrode can achieve a high specific capacitance of 1665.8 F g^-1and superior stability with almost no capacitance degradation for 5000 cycles due to a suitable doping ratio.The supercapacitor assembled with this electrode and activated carbon electrode can reach the highest energy density of 12.0 Wh kg^-1 at a power density of 996.9 W kg^-1.This work presents an effective method for synthesizing NMS materials and investigates theoretically and experimentally the role of Moelements in the energy storage process.