Synthesis Of Nanoporous Metal Oxide Electrode Materials And Their Capacitive Storage Properties

The aggravation of climate change and the depletion of fossil energy promote the development and utilization of sustainable clean energy.At the same time,it is urgent to develop energy storage devices with high energy densities and high power densities.Supercapacitors are important energy storage devices,as they show higher power density,longer cycle life,and lower sustention cost compared with lithium-ion batteries.However,the low energy density of supercapacitors significantly restricts their applications in some burgeoning fields.In this paper,from the perspective of electrode material,suitable electrode materials are firstly selected to improve their specific capacitances;then,from the viewpoint of supercapacitor structure,flexible micro-supercapacitors with planar interdigital structure are designed to optimize their electrochemical performances.The main results and conclusions are as follows:Fe₂O₃,a kind of ideal electrode material,possesses high theoretical specific capacitance(3625 F·g^-1),good chemical stability,abundant reserve,and low price.Porous hollow Fe₂O₃ microboxes are synthesized using Prussian blue as a precursor,and their composition,structure,formation mechanism and electrochemical properties are studied.The specific capacitance of Fe₂O₃ electrode is 380 F·g^-1 at a current density of 0.1 A·g^-1 in1 mol·L^-1 Na₂SO₃ electrolyte,and the capacitance retention is 55%?10,000 cycles?.The actual specific capacitance of Fe₂O₃ is much lower than its theoretical specific capacitance,and the cycling stability is poor,owing to the low conductivity(?10^-14 S·cm^-1)and obvious volume change of Fe₂O₃ in the intercalation/de-intercalation process.To solve the problems of Fe₂O₃,highly conductive Ag nanoclusters are introduced onto the surface of Fe₂O₃ microboxes.The composition,structure,formation mechanism and electrochemical properties of the Fe₂O₃@Ag are investigated.The specific capacitance of Fe₂O₃@Ag electrode is 701 F·g^-1 at a current density of 0.1 A·g^-1 in 1 mol·L^-1 Na₂SO₃electrolyte,and the capacitance retention is 72%?10,000 cycles?.Compared with Fe₂O₃electrode,the specific capacitance and retention rate of Fe₂O₃@Ag electrode are obviously improved.After the introduction of Ag nanoclusters,the equivalent series resistance decreases from 1.52??Fe₂O₃ electrode?to 1.28??Fe₂O₃@Ag electrode?,and the charge transfer resistance reduces from 92.04?to 22.60?,which mean that the electron transport and ion diffusion in charge/discharge process are enhanced.Moreover,introducing Ag nanoclusters could enhance structural stability of the electrode,resulting in an improved cycling performance.Finally,the asymmetric supercapacitor based on Fe₂O₃@Ag and activated carbon shows a specific capacitance of 123 F·g^-1,whose maximum energy density and power density could be 41.8 W·h·kg^-1 and 16 kW·kg^-1,respectively,which proving that Fe₂O₃@Ag is a promising anode material for supercapacitors.Three-dimensional interdigital electrodes are prepared by physical deposition and electrochemical deposition,and their electrochemical properties are studied.Au collectors with Interdigital structure are firstly prepared by magnetron sputtering on polyimide substrates,then three-dimensional Ni frameworks are deposited on Au collectors by electrodeposition using polystyrene microspheres as templates.MnO₂ positive electrodes and MoO_x negative electrodes are deposited on Ni frameworks,respectively.The MnO₂electrode shows a three-dimensional structure and a specific capacitance of 101.7 mF·cm^-2,while the MoOx electrode is rod-like structure with a specific capacitance of 28.16 mF·cm^-2 at a scan rate of 1 mV·s^-1 in 5 mol·L^-1 LiCl electrolyte.