Fabrication Of 3D Si-based Micro/nano-arrays For Specific Applications In Micro Energy Systems

Clean and efficient energy storage/producing techniques,such as lithium ion batteries(LIBs)and proton exchange membrane fuel cells(PEMFCs)are attracting much attention due to the shortage of fossil fuels and serious environmental issues.On the other hand,with the rapid development of micro-electro-mechanical system(MEMS)and nanotechnology the increasing demand for compatible micro energy systems is being driven by the shrinking dimensions of electronic appliances.Si,as the mostly used material in microelectronic devices,also presents great potential as an anode material in micro LIBs because of its highest theoretical capacity for the Li+ storage,and a qualified candidate for constructing micro PEMFCs given its feasible integration with other micro/nano electronic devices.However,further investigations are still needed to regulatethe Si-based composite configurations and components in LIBs and improve the performances of Si-based micro fuel cells.So,in this thesis,focusing on the above-mentioned two significant issuesdetailed experimental and theoretical works have been performed withthe results presented as follows:1.The effect of core-shell structure on the energy storage properties of three-dimensional(3D)Si-based nano composite anode in micro LIBs.The Si-Ge core-shell structures in variant configurations,named as Si-Ge nanorods(NRs)and Si-airbag-Ge NRs,were fabricated on wafer scale Si substrates through a Si-compatible procedure.It has been demonstrated by electrochemical characterizations that the contact Si-Ge composite electrodes have better lithium storage abilities than those of non-contact electrodes,resulting from the protection of Si surface and the inhibition of volume expansion by the Ge shell.The first principles calculations also verified the smaller forces on the Si layers covered by Ge layers.However,the electrochemical properties of the Si-based composite electrodes are still preferred to be enhanced by the introduction of other novel composite materials,which would facilitate the Li+ diffusion.2.The fabrication of ZIF-8/TiN/Ti/Si NRs as efficient anodes in micro LIBs.The increased electrochemical properties,100 times higher in capacity than that of only Si NR,was demonstrated in the multilayerd electrode with zeolite imidazolate framework-8(ZIF-8)cooperating in TiN/Ti/Si NRs.Based on the 1H nuclear magnetic resonance(NMR),first principle calculations and electrochemical impedance spectroscopy(EIS)characterizations,the interaction between Li+ and ZIF-8,the favorable diffusivity of Li in ZIF-8,and the boosted electron/Li+ transfer caused by the multilayer coating are proposed to result in the enhanced energy storage ability.Furthermore,metal-organic segments(MOSs)are fabricated onto the Si NRs homogeneously by an optimized solution growth method,which helped to improve the electrochemical properties of the Si-based composite NR electrode dramatically without the introduction of conducting interlayers.Meanwhile,the growth mechanism of MOSs has been investigated by transmission electron microscope(TEM)and time of flight mass spectrometer(TOF-MS),which provides a general strategy for the growth of MOSs-based composite materials.3.The construction of integrated Si-based micro PEMFCs.The PEMFCs consist of Si-based flow fields,the carbon black as gas diffusion layer(GDL),and the Pt/C catalyst layer.The dot-type flow fields for fluids transfer were fabricated by Si-compatible processes,and further optimized by the introduction of conducting layer and dicing procedure.Furthermore,the carbon black and Pt/C catalysts with precisely controlled recipes were deposited onto the Si-based flow fields in sequence,which successfully replaced the traditional gas diffusion layer(GDL)and avoided hot-press processing.As a result,a record-high(with measured size>0.2 cm2)peak power of 354 mW/cm2 was accomplished in this Si-based μPEMFC.In summary,3D Si-based micro/nano arrays were fabricated by Si-compatible technologies,with the applications in the micro energy storage/producing systems well demonstrated.This work provides promisingly applicable strategies for the integration and development of 3D Si-based energy systems.