Three Dimensional Nanoarchitectures By Atomic Layer Deposition For Energy Related Applications

Atomic layer deposition (ALD) is a cyclic, multi-step thin film chemical vapor deposition process based on sequential self-limiting surface reactions. It has been widely applied for synthesizing various three dimensional (3D) nanoscale morphologies. Recently, based on ALD process, a surface-reaction-limited pulsed chemical vapor deposition (SPCVD) technique was developed for 3D hierarchical branched nanowire (NW) architecture with super high surface area density and good electronic transport properties. This new ALD-based nanomanufacturing technique demonstrated great potential to conduct large-area and low-cost fabrication of high-density 3D nanomaterials for energy harvesting and storage applications, such as photoelectrochemical (PEC) water splitting, solar cells, batteries and supercapacitors. In this dissertation, a series of experimental work is presented regarding fundamental understandings and rational controls of the SPCVD process in branched nanorod (NR) synthesis, as well as the application potentials of 3D branched nanowire architectures. First, the composition control ability of SPCVD was studied on nitrogen-doped TiO2 NRs to overcome the intrinsically visible light absorption constrains of metal oxide semiconductors. Second, to further improve the porosity and surface area while maintain good redox reaction kinetics, several 3D cellulose nanofibers (CNFs) templated fibrous TiO2 nanoarchitectures were synthesized. By integrating the strong capillary property of CNF film, the capillary PEC and capillary photocatalytic systems were developed by performing water redox reactions outside of the body of electrolyte with enhanced reaction kinetics and higher efficiency. At last, SPCVD was applied to the growth of high-density vanadium oxide (VOx) NR branches on Si NW backbones. Such a 3D hierarchical VOx/Si NW structure exhibited enhanced performance as a supercapacitor. These achievements open a new avenue of ALD for large-area, low-cost, and green fabrication of materials, which would be used in solar energy conversion and electrical energy storage.