Structural Design And Mechanism Of Carbon Nanomaterials For Fast And Efficient Energy Storage And Switchable Adhesion

Supercapacitor,as an energy storage device has been widely used in small mobile devices,such as mobile phones,flat plates,smart wearable electronic devices,large power grids,vehicle and other fields due to its extremely fast charging rate and excellent cycle stability.However,the inferior energy density has always been a bottleneck restricting its popularization.In particular,with the development of electronic devices towards lightweight and miniaturization,higher requirements are put forward for the specific capacity of capacitors and their own properties.On the other hand,smart surface materials can operate in different functions under external stimulation,such as electric field,emission of light,etc.,and its large-scale research and development is likely to open up more applications and research in new field.However,no breakthrough has been made in the research of smart surface materials with both highly switchable adhesion and rapid water harvesting and reversible evaporation.In this study,molecular dynamics（MD）and density functional theory（DFT）were employed to explore the origin of design principle of heteroatom-doped graphene or graphene with oxygen functional groups as electrode in supercapacitor and smart surface.Furthermore,the effectiveness,accuracy and universality of heteroatom doping and the introduction of oxygen functional groups and theoretical prediction in capacitive enhancement and optimization of smart surface are verified through experiments,so that bottom-up design theory system for electrode material and smart surface material was established.This reflects an important research idea and thought that the theory both guides the experimental research and is tested and sublimated in experiment research.Follow this line,the main contents and results in this paper were as follows:（1）Graphene doped with p-group elements in the periodic table were used as the electrodes of pseudocapacitive supercapacitors.Moreover,after taking into account electrolyte concentration,p H value,decomposition voltage,external potential and other external conditions,their capacitive performances of different doped electrodes in acidic electrolyte（H₂SO₄）were investigated by density functional theory（DFT）.The origin of heteroatom doping,namely reducing the chemical adsorption energy barrier of electrolyte ions,was proved.The theoretical model of capacitance calculation for doping electrode was established and further the theoretical equation was derived.More significantly,the descriptorΦcorrelating the micro-doping structure and the macro-charge storage performance,was proposed to guide the experiment to screen the better electrode materials,which was in good agreement with the experiment.（2）Graphene,as a 2D carbon nanomaterial doped with p-group elements in periodic table was used as negative electrode materials in sodium ion batteries（SIB_S）and potassium ion batteries（KIB_S）based on pseudocapacitive mechanism.And the energy and power densities of electrodes with different doping structures were studied by DFT systematically in neutral electrolyte（Na₂SO₄）and alkaline electrolyte（Na OH）,respectively.Firstly,the transition from the surface-induced pseudocapacitive mechanism to metal batteries mechanism was revealed for Na and K storage in the charging process,which was in good agreement with our electrochemical experiment.The idea of suppressing the growth of Na and K dendrites in metal battery by graphene substrate was proposed and its origin resulting from lattice matching was also revealed.The"double volcano"relationship between descriptor and doping structure was established to select the best single doping electrode,and the potential of the electrode was further explored by means of double doping.Finally,the accuracy of the theoretical prediction was demonstrated by experiments.（3）The origin of charge storage of graphene oxide based all-solid-state supercapacitors and the dependence of capacitive performance on the content of water molecules intercalated in graphene oxide,the layer spacing,the saturation of oxygen-containing functional groups and the external electric field were discussed by using molecular dynamics（MD）with the first principle input.It was revealed that graphene oxide based all-solid-state supercapacitors rely on water molecular polarization to store electricity.The theoretical model of the polar molecular supercapacitors（PMSs）was put forward,the theoretical equation calculating the capacity of the capacitor was derived,and an efficient all-solid-state graphene oxide based supercapacitor was designed,the capacitive performances of which surpass the existing capacitors.Finally,our theoretical calculation was verified by the experimental results of two different types of multilayer oxygen graphene based supercapacitors.（4）We combined atomic force microscope（AFM）and molecular dynamics（MD）to explore biomimetic materials inspired by gecko foot bristle array and desert beetle’s back structure,i.e.nitrogen-doped wrinkle graphene with uneven texture（WGN）.The electric-induced switchable adhesion and the water harvesting and non-thermal effect reversible evaporation of WGNs on external stimulation,such as humidity,substrate wettability,conductivity and electric field were discussed.And combined with molecular dynamics simulation,the mechanism of the function was proved and theoretical model was established.