Nanoarchitecture Engineering Of Transition-Metal Oxides Toward Optical Modulation And Energy Storage Applications

The ever increasing consumption of fossil fuels leads to severe energy crisis and environmental concerns.Humans are urgently persuing new technologies to achieve efficient and clean management of energy sources.In recent years,as the representive new-type electrochemical energy-saving and energy-storage technologies,electrochromic smart window and supercapacitor are indispensable for efficient and clean management of energy sources.Transition-metal oxides are the crucial host materials to modulate light and storage charge,therefore,their comprehensive optimization plays vital role in the advancement of electrochemical energy-saving and energy-storage technologies toward practical applications.To achieve high performance transition-metal oxides in electrochemical energy and environment devices,the present thesis explores the controllable fabrication and structural optimization of TiO₂ one-dimensional core-shell nano-arrays and MnO₂ three-dimensional nano-architectures,investigates the effect of material microstructure and nano-morphology on its electrochromic optical modulation and electrochemical energy-storage properties,and realizes the efficient utilization of high-performance transition-metal oxides in electrochemical energy-saving and energy-storage devices.The front part realizes the controllable fabrication of a series of TiO₂ one-dimensional core-shell nano-arrays by low-temperature chemical process,and systematacially investigates the influence factors for electrochromic optical modulation performance by varying the composition,microstructure and morphology of shell-materials.The results indicated that TiO₂ single-crystal nanorod arrays can act as“inert template”for TiO₂–prussion blue core-shell nanorod arrays despite they are electrochemically passive in KCl electrolyte.TiO₂–prussion blue core-shell nanostructure dramatically boosts the prussion blue/electrolyte interface,resulting in comprehensive enhancement of electrochromic optical modulation properties.The further investigation demonstrates that TiO₂ single-crystal nanorod arrays exhibit inferior optical modulation effect in LiClO₄/PC electrolyte.Employing amorphous TiO₂ which has sufficient Li⁺ion storage space to modify nanorod surface via layer-by-layer method and rationally optimizing the thickness of amorphous shell could enhance the optical contrast by 139%.Moreover,the amorphous TiO₂ shell could transform into superfine nanocrystals with grain size of 5-7 nm via in situ hydrothermal crystallization,and the nanocrystals provide sufficient surface sites for Li⁺ion insertion or extraction and shorten ion diffusion paths.The as-formed hierarchical TiO₂ nanorod arrays exhibit accelerated electrochromic response speed as well as desirable optical contrast.The latter part mainly investigates the construction of MnO₂ three-dimensional nano-architectures in planar supercapacitor.A new stamp-assisted printing strategy is proposed to achieve the pattern design of Ni interdigital electrodes in an efficient and cheap solution-electrochemical method.The texture or nanotube structured Ni electrode acts as current collector to design three-dimensional nano-architectures Ni/MnO₂ electrode and the effect of electrode morphology on electrochemical energy-storage performance is analyzed in details.The results show that the textured Ni electrode could induce the formation of three dimensional porous MnO₂,which offers sufficient mass transfer channels and active surfaces.The specific capacity of planar supercapacitor reaches up to 4.15 mF cm^-22 by 40%enhancement.The further results indicated that the employment of Ni nanotube could dramatically improve electron collection efficiency and reduce the internal resistance of Ni/MnO₂ electrode;simultaneously,the Ni/MnO₂ three-dimensional nanotube architecture provide multiple channels for electrolyte infiltration and enlarge MnO₂ active surface for pseudocapacitance reactions.The specific capacity of planar supercapacitor equipped with nanotube electrode reaches up to 10.75 mF cm^-22 by 140% enhancement.