Hematite-based photoelectrochemical water splitting supported by inverse opal structures of graphene.

By coupling α-Fe2O3 with a 3D graphene inverse opal (3D-GIO) conducting electrode, the short diffusion length of carriers and low absorption coefficient in α-Fe2O3 for photoelectrochemical applications were successfully addressed. GIO was directly grown on FTO substrate under low temperature conditions, removing the need for a graphene transfer process. α-Fe2O3 nanoparticles (NPs) were hydrothermally deposited on the surface of GIO, creating α-Fe2O3/GIO. The photocurrent density of α-Fe2O3/GIO in water splitting reactions reached 1.62 mA/cm(2) at 1.5 V vs RHE, which is 1.4 times greater than that of optimized α-Fe2O3. The EIS and IPCE data confirm reduced electron-hole recombination and fast electron transfer processes due to the short distance between active materials and the conducting electrode in the α-Fe2O3/GIO system. Our result may pave the way for designing devices in advanced energy conversion applications as well as a high efficiency hematite-based PEC system.

Highly ordered freestanding titanium oxide nanotube arrays using Si-containing block copolymer lithography and atomic layer deposition.

Highly ordered freestanding TiO(2) nanotube arrays with atomic layer control of wall thickness were fabricated using an organic-inorganic hybrid nanoporous template and atomic layer deposition (ALD). The hybrid nanoporous template with a high-aspect-ratio cylindrical nanopore array can be readily fabricated by pattern transfer from a thin silicon-containing block copolymer film into a thick cross-linked organic polymer layer. The template exhibited excellent thermal stability and thus allowed the high-temperature ALD process to conformally deposit TiO(2) thin films on the inner surface of cylindrical nanopores. The ultrafine thickness tunability of the ALD process made it possible to develop TiO(2) nanotubes with various wall thicknesses. After the template was removed using a dry etch followed by calcination, vertically aligned and highly crystalline anatase TiO(2) nanotube arrays were produced without collapse or bundling. We also fabricated the highly uniform freestanding arrays of multi-component nanotubes composed of TiO(2)/Al(2)O(3)/TiO(2) nanolaminate and Ti-Al-O mixed-phase films with precisely controlled thickness and composition.