Preparation Of Manganese Dioxide Supercapacitor Material By Hydrogen Bubble Template Method

Renewable energies,such as tidal energy,wind energy,and solar energy,are greatly affec ted by environmental factors and require the use of energy storage devices to improve transpo rtation efficiency.Supercapacitors with fast chargingdischarging velocity,long cycle life and e nvironmental friendliness are ideal devices for energy storage.MnO₂ is one of the well know supercapacitor electrode materials since it has high theoretical specific capacity and low price.However,due to the poor conductivity,MnO₂ usually display a specific capacitance much lo wer than the theoretical value,especially when high loading amount is required.Meantime,th e specific capacitance retention rate decreases rapidly with the increase of chargedischarge vel ocity.Therefore,this work intend to new MnO₂ with large capacity,low impedance and high s pecific capacitance through two-step deposition.This work first fabricated a series of NiCu alloy templates with hierarchical porous struct ure by hydrogen bubble template depostion.The influence of deposition solutions and deposit ion parameters on the composition,morphology and specific surface area of NiCu alloy templ ates were studied.The results showed that in a solution containing 0.2 M Ni SO₄+0.0075 M C u SO₄+1.2 M（NH₄）₂SO₄+0.3 M Na₃C₆H₅O₇+0.4 M H₃BO₃,the Ni₉₅Cu₅ template with high el ectrochemical stability can be prepared under a cathode deposition current density of-2 A/cm² for 90 s.The as-deposited Ni₉₅Cu₅ template had a three-dimensional interconnected mi croporous structure,the pore wall was composed of a large number of Ni₉₅Cu₅ dendrites,and t here were a large number of sub-micron pores between the dendrites,resulting in a high speci fic electrochemical active area of 6234 cm₂ g^-1.Secondly,MnO₂ was deposited on the porous Ni₉₅Cu₅ template by anodic oxidation to pr epare a three-dimensional porous Ni₉₅Cu₅-MnO₂ supercapacitor with large capacity,low impe dance and high specific capacitance.The effects of anodizing voltage,template thickness,and deposition parameters on the structure,morphology and electrochemical performance of Ni₉₅Cu₅-MnO₂ were studied.The results showed that when the anodic oxidation voltage was 1.8 V vs.SCE and the deposition time is 600 s,the Ni₉₅Cu₅-MnO₂ composite material prepared in t he 0.1 M Mn（CH₃COOH）₂·4H₂O+0.1 M Na₂SO₄ deposition solution has the best super elect ric performance.Tts specific area capacitance is 0.503 F cm^-2 at a scan rate of 5 mv/s,and the specificarea capacitance reached 0.328 F cm^-2 at a current density of 1 m A cm^-2.Finally,the performance of Ni₉₅Cu₅-MnO₂ supercapacitors was further optimized by pro moting the transport flux of Mn²⁺in porous Ni₉₅Cu₅.The effects of electro-obsorption,diffusi on time and convection on the deposition of MnO₂ in the hierarchical porous structure were st udied.The results showed that the cyclic method of anodic oxidation-electro-adsorption-anod ization could promote the diffusion of Mn²⁺in porous Ni₉₅Cu₅ and improve the uniformity of the Ni₉₅Cu₅-MnO₂ supercapacitors.The specific area was improved to 0.71 F cm^-2 at a current density of 1 m A cm^-2.However,Mn²⁺in the solution has side reactions on the counter electro de.By Introducing stirring between the anodic oxidation process,a Ni₉₅Cu₅-MnO₂ supercapa citor with improved uniformity could also be obtained,and its area specific capacitance reach ed 0.254 F cm^-2 at a current density of 1 m A cm^-2.