Study On The Preparation Of Transition Metal Phosphides And The Performance Of Supercapacitors

Supercapacitors had received extensive attention due to their high power density,long cycle life,fast charge and discharge,et al.Electrode materials play a vital role in the performance of supercapacitors.Among them,transition metal phosphides(TMPs)with metallic characteristics were recognized as promising electrode materials due to their high specific capacitance and good conductivity.Compared with single-metal phosphides,studies had shown that bimetallic phosphides had higher conductivity and better electrochemical performance.In this paper,based on the above ideas,two-component transition metal phosphides with a special morphology was prepared by a simple method,and the electrochemical properties of the materials were studied.Firstly,the NiMnP directly grown on the NF substrate was prepared by a simple hydrothermal method and low temperature phosphating,and then the optimal manganese element doping ratio was explored.On the one hand,the substitution of Mn made the electrode material have more active sites.On the other hand,the substitution of Mn was beneficial to the rapid progress of the Faraday redox reaction.In addition,the self-supporting structure can significantly increase the charge transfer rate and contribute to the improvement of electrochemical performance.The obtained NiMnP-NF electrode had a specific capacitance of1630.0 F g^-1 when the current density was 1 A g^-1,and had an excellent cycle stability(88.7%capacity retention rate after 10,000 cycles at a current density of 5 A g^-1).Simultaneously,the assembled NiMnP-NF//AC asymmetric supercapacitor(ASC)had an energy density of 69 W h kg^-1 at a power density of 750 W kg^-1.What's more,85.2%of the capacity was maintained after10,000 cycles at a current density of 5 A g^-1.Solvothermal and low-temperature phosphating methods were used to prepare NiCoP/C electrodes with a hollow structure,and the influence of Co doping on electrode performance was explored.The unique structure of the hollow spherical NiCoP/C electrode material lead to the better electrochemical performance.Electrochemical tests showed that the NiCoP/C electrode had a specific capacitance of 1550.4 F g^-1 at a current density of 1 A g^-1.At the same time,the capacity loss was only 6.7%at a current density of 5 A g^-1 for 10,000 cycles.In addition,the ASC device composed of NiCoP/C and activated carbon had an energy density of53.7 W h kg^-1 at a power density of 750 W kg^-1.What's more,under the current density of 5 A g^-1,the capacity loss after 10,000 cycles was only 7.2%.By combining the experimental ideas of the previous two chapters,the NiCoP/rGO-NF electrode material which was directly grown on the NF and covered with graphene was designed and prepared.The NiCoP/rGO-NF electrode material had a specific capacitance of2137.8 F g^-1 at 1 A g^-1,and a capacity retention rate of 86.5%(10,000 cycles at a current density of 5 A g^-1).In addition,the ASC equipment had an energy density of 54.25 W h kg^-1 when the power density was 750 W kg^-1.At a current density of 5 A g^-1,the capacity retention rate after10,000 cycles is 87.3%,indicating that the prepared NiCoP/rGO-NF has the potential as an excellent electrode material for supercapacitors.