Solid-state Chemical Synthesis And Electrochemical Properties Of Manganese Oxides Nanomaterials

With the rapid development of social science and technology,people's demand for electronic products is increasing.Therefore,it is particularly important to develop sustainable energy storage and conversion devices.Due to its abundant reserves,low price and multiple oxidation states,the transition metal manganese oxide usually exhibits good electrochemical properties,which has attracted extensive attention from researchers.In the development of sustainable energy storage and conversion technology,it has become an ideal substitute for precious metal electrochemical materials.In this paper,two-dimensional electrochemical material with controllable morphology based on manganese oxides was prepared by using a simple solid-state chemical reaction and adding different surfactants,and its electrochemical properties were further improved by compositing with other non-metallic and metallic elements.The specific research work is as follows:?1?Taking cheap manganese acetate and oxalic acid as raw materials,the precursor was firstly synthesized by a simple solid-state chemical method,and then MnO nanoparticles were synthesized by heat treatment.The particle size of MnO nanoparticles could be changed by adjusting the calcination temperature,and the MnO nanoparticles had good electrocatalytic oxygen reduction performance?ORR?.?2?Using polyethylene glycol 400 as carbon source and melamine as nitrogen source,the recombination of nitrogen doped carbon with MnO nanoparticles was studied.Uniform MnO/C-N nanosheets were obtained by adjusting the ratio of reactant,the heat-treating temperature and the heating program.The doping of nitrogen and carbon can transform the morphology of MnO nanomaterials from nanoparticles to nanosheets,and improve the electrocatalytic activity of ORR.?3?Transition metal Ni was composed into MnO/C-N nanosheets by adjusting the solid-state synthetic conditions.The rod-like Ni-MnO/C-N electrocatalytic materials were obtained.Ni-MnO/C-N electrocatalytic materials exhibit better catalytic performance of oxygen reduction than commercial Pt/C due to the interaction between Ni and MnO,whcih have a relatively positive initiation?0.98 V vs.RHE?,a half-wave potential?0.81 V vs.RHE?and a large limiting current density(6.39 mA cm^-2).The electrocatalytic reaction were finished following four-electron transfer process.?4??-MnO₂ and?-MnO₂ nanoparticles were prepared by solid-state chemical reaction using different manganese salts as raw materials.Since the specific surface area of the former is larger than that of the latter,the capacitance of?-MnO₂nanoparticles as the active material of electrochemical supercapacitors is larger,and the specific capacitance is 179.6 F·g^-1 at the current density of 1 A·g^-1.?5?In the reaction system of solid state synthesis of?-MnO₂,different surfactants were added to achieve the morphological transformation of?-MnO₂ nanoparticles into two-dimensional piece-like?-MnO₂ nanomaterials.The addition of the surfactant polyethylene glycol 4000 could successfully produce three-dimensional flower-like?-MnO₂ materials composed of two-dimensional ultra-thin nanomaterials.Compared with?-MnO₂ nanoparticles,flower-like?-MnO₂ has more abundant microcellular structure,which is conducive to the rapid transmission of ions and electrons in the electrolyte,and shows better electrochemical energy storage performance,with a specific capacitance of 195.9 F·g^-1 at the current density of 1 A·g^-1.