Construction Of Transition Metal Phosphide-Based Electrode Materials And Energy Storage Mechanism

The consumption of non-renewable resources such as coal and oil has gradually depleted energy,making it difficult to meet the pace of rapid human development.To this end,people have shifted their attention to the development of cleaner,more efficient and sustainable energy.Improving the energy density of hybrid supercapacitors is a hot topic in the field of electrochemical energy.The electrode material plays a decisive role in the performance of the device.Focusing on the advantages of transition metal oxides and organic metal framework porous materials,the specific surface area,conductivity and structural stability of the cathode materials were optimized.Guided by the optimal performance and centered on interface regulation,the transition metal phosphide electrode materials with high conductivity and long cycle stability were constructed by combining interface engineering,heterogeneous composite and multi-component synergistic technology,and applied to hybrid supercapacitors.The specific research work of this paper is summarized as follows:1.Amorphous nickel cobalt phosphate（Ni Co-P）ultrathin nanosheets were grown on crystalline nickel cobalt bimetallic oxide nanowires（Ni Co₂O₄）by electrodeposition to construct crystalline-amorphous CC/Ni Co₂O₄@Ni Co-P heterojunction.Theoretical calculations show that the synergistic behavior between the Ni Co-P and Ni Co₂O₄ interfaces enhances the electron transfer ability and thus improves the conductivity.The design of amorphous phosphates and crystalline bimetallic oxides with synergistic effects shows more redox reaction active sites.The amorphous material contains a large number of low-coordinated metal atoms,which promotes the interaction between electrolyte ions and active substances,and effectively alleviates the volume expansion caused during charge and discharge.The electrochemical test results show that the CC/Ni Co₂O₄@Ni Co-P electrode can reach a high specific capacity of 1254.2 C·g^-1 at 1 A·g^-1.In addition,the hybrid supercapacitor with CC/Ni Co₂O₄@Ni Co-P as positive electrode,activated carbon as negative electrode and 2 M KOH as electrolyte can provide 54.83 Wh·kg^-1 energy density at a power density of 682.53 W·kg^-1.The capacity retention is 80.2%after 10000 cycles.2.A two-dimensional porous hollow Co Ni Mn-P nanosheet array based on metal-organic framework（MOF）conversion was synthesized.Co-MOF nanosheets in situ grown on CC were etched into hollow CC/Co Ni Mn-OH nanosheet arrays by mixed solvent assisted method,and then thin-walled hollow porous ternary metal phosphides were synthesized by atmosphere phosphating method.The structure and morphology characterization results show that the obtained Co Ni Mn-P maintains the thin-walled hollow structure of the Co Ni Mn-OH nanosheet array.This structure combines the synergy between the three transition metals.The hollow structure provides a high-speed channel for electron transport,which can greatly improve the rate characteristics of the electrode material.The electrochemical test results show that the obtained CC/Co Ni Mn-P electrode has a high specific capacity of 2247 F·g^-1 at 1 A·g^-1 and excellent rate performance(90.2%,8 A·g^-1).In addition,CC/Co Ni Mn-P//AC with CC/Co Ni Mn-P as positive electrode,activated carbon as negative electrode and 2 M KOH as electrolyte can achieve a high energy density of 45.7 Wh·kg^-1 at a power density of 344.8 W·kg^-1.The capacity retention rate is 84.3%after 10000 cycles.This method provides a new idea for the preparation of multi-metal phosphide electrodes with excellent electrochemical performance.