The Preparation Of Inorganic Phosphate Micro-Nanomaterials And Their Application In Supercapacitors

In the context of growing energy demand and limited fossil fuel resources,advanced energy storage and conversion systems are being aggressively pursued.Among them,supercapacitors(SCs)are considered to be the first choice for high power and high energy storage devices.The design and synthesis of advanced electroactive materials with high conductivity,high capacitive activity and stability are key to the development of SCs.Transition-metal phosphate is a purely inorganic material composed of the binding of metal centers with phosphoric acid,which are prone to form a layered structure with an open framework.It possesses a good protonic conductivity and variable oxidation states of the metal species,which would enrich the redox behavior;In addition,the ligand groups in transitionmetal phosphates and phosphonates have the characteristics of flexible coordination and diverse orientations,so they are advantageous as electrodes.They are used as electrode materials for supercapacitors,and their electrochemical energy storage behavior is tested and studied.(1)NH4MⅡPO4·nH2O(M=Co,Ni,Mn,Fe,Mg,Zn)was synthesized by chemical precipitation method with several simple reagents without the participation of templates and surfactants.The crystal structure of the products was analyzed by scanning electron microscopy and X-ray diffraction.The results show that the NH4MPO4·nH2O has good crystallinity,high purity and uniform morphology and size.The six materials were used as electrode materials of SCs and applied in traditional three electrode system.The results show that NH4CoPO4·H2O exhibits higher specific capacitance and rate performance than the other five materials.(2)A series of binary,ternary,quaternary and high entropy ammonium phosphate salts(NPOs·nH2O)were synthesized by doping NH4CoPO4·H2O with other metal sources(Ni2+,Mn2+,Cu2+,Fe2+,Mg2+,Zn2+,Sr2+),which proved the universality of this method in synthesis.A series of CoxNiy-NPO·nH2O(x/y=5:0,4:1,3:2,1:1,2:3,1:4,0:5)with three-dimensional flower superstructure were synthesized by stirring at room temperature.The results show that,compared with NH4CoPO4·H2O,CoxNiy-NPO·nH2O show better specific capacitance and stability.In the three-electrode system,when the current density is 0.5 A g-1,the specific capacity of Co0.5Ni0.5-NPO·nH2O can reach 682 F g-1.More importantly,the aqueous and quasi-soild state flexible electrochemical energy storage device were assembled.The SCs showed high energy density and excellent cycle stabilities.This is because the synergistic effect of Co2+ and Ni2+ ratio contributes to the exposure of metal active sites,promotes the rapid mass transfer and electron transfer of materials,and improves the electrical conductivity of materials.(3)Using Co0.5Ni0.5-NPO·nH2O as precursor,the corresponding nitrogen-doped transition metal phosphates(X-Co0.5Ni0.5-NPO·nH2O,X=100-800℃)were obtained by controlled calcination,and their electrochemical properties were tested.The results show that A-Co0.5Ni0.5-NPO has the best electrochemical performance at 400℃,and its specific capacitance can reach 971.84 F g-1 at 0.5 A g-1.This is because under this optimal calcination condition,amorphous A-Co0.5Ni0.5-NPO has abundant active centers,porous surface and good durability,which is conducive to chemical embedding/deembedding or REDOX reaction.