Preparation And Application Of CrO_x-based Cathode Materials For Aqueous Supercapacitors

Recently with the rapid growth of the economy,the consumption of fossil resources has risen sharply,which not only brings the problem of energy shortage to mankind,but also brings serious environmental problems.Therefore,the development of clean and renewable low-carbon energy,such as solar energy,wind energy,water energy,geothermal energy,has become a significant research project around the world.However,these new energy sources are too dependent on natural conditions such as time and place,which is difficult to widely use in daily life.Thus,it is necessary to develop an energy storage and conversion system.Presently,supercapacitors are one of the most widely used energy storage devices.And these research work mainly have made a breakthrough in the new type of positive electrode materials of aqueous supercapacitors.The main research in this paper is focused on the following three aspects of CrO_x-based electrode materials:?1?Two kinds of Cr₂O₃ nanoparticles with different sizes were synthesized by hydrothermal-calcination?H-Cr₂O₃?and solid-phase methods?S-Cr₂O₃?.The samples were treated using H-Cr₂O₃ and S-Cr₂O₃ as the positive electrode measured their electrochemical performance in 2 M KOH solution respectively.The results show that H-Cr₂O₃ electrode has a better electrochemical performance,mainly owing to the smaller particle size and a bigger specific surface area of H-Cr₂O₃ electrode material.And at a current density of 1 A g-1,the specific capacitance of the S-Cr₂O₃ electrode is only 90 F g-1,while the specific capacitance of the H-Cr₂O₃ electrode can reach 190 F g-1.Using activated carbon as the negative electrode,Cr₂O₃ nanoparticles as the positive composition,the voltage window of the capacitor is 1.25 V.H-Cr₂O₃ // AC hybrid capacitor show an energy density of 14.2 W h kg-1 at a power density of 568.16 W kg-1,higher than those for S-Cr₂O₃ // AC hybrid capacitor,with an energy density of 6.24 W h kg-1 at power density 561.29 W kg-1.?2?NiCrO_x-8 and NiCr₂O₄ were synthesized by coprecipitation and calcination at different temperatures.In the 2 M KOH solution,the electrochemical performance of the two samples were measured with Ni-grid as the counter electrode and saturated calomel electrode?SCE?as the reference electrode.The results show that the capacitance of NiCrO_x-8 electrode is 180 F g-1 at the current density is 1 A g-1,and thespecific capacitance of NiCr₂O₄ electrode can reach 380 F g-1,which mainly may be attributed to the diatomic effect of the NiCr₂O₄ electrode material and the multi-eleent oxidation reaction could provide a higher capacitance.The two electrodes show less than 5% capacitance loss after 1000 cycles between 0-0.45 vs.SCE/V at a current density of 1 A g-1.?3?NiCrO₃ electrode materials were prepared by hydrothermal-calcination?H-NiCrO₃?and solid-phase methods?S-NiCrO₃?.The electrochemical performance of the two materials were tested in a 2 M KOH solution.The results show that H-NiCrO₃ electrode exhibitd a better electrochemical performance between 0-0.45 vs.SCE/V.The specific capacitance of the H-NiCrO₃ electrode is 600 F g-1 at the current density of 2 A g-1,and the specific capacitance of the S-NiCrO₃ electrode is only 391 F g-1,even when the current density increases to 10 A g-1,the specific capacitance of the H-NiCrO₃ electrode can reach 377 F g-1.This is mainly that the particles of the H-NiCrO₃ electrode material are smaller relating to a larger surface area,more conducive to the occurrence of redox reaction.Both of those electrodes present an excellent cycling performance with almost no capacity loss after 8000 cycles at the current density of 5 A g-1.