Multi-layered mesoporous TiO₂thin films with large pores and highly crystalline frameworks for efficient photoelectrochemical conversion

Abstract

Mesoporous thin films with various compositions are unique architectures for photoelectrochemical (PEC) solar cells. In this paper, we report the synthesis of highly ordered, multi-layered, continuous mesoporous TiO 2 thin films with uniform large pores, crystalline walls and tunable film thickness, via a ligand-assisted evaporation induced self assembly (EISA) method. A Ti(acetylacetone) precursor and a diblock copolymer PEO-b-PS are employed for the controlled assembly of the TiO 2 /template mesostructure, followed by a two-step pyrolysis that generates carbon residue as an intermediate protection layer to support the TiO 2 framework and mesostructures during the crystallization. Other transition metal ion dopants (such as Cr, Ni and Co) can be facilely incorporated into the TiO 2 frameworks by co-assembly of these metal acetylacetone precursors during the EISA process. The obtained TiO 2 thin film possesses an ordered monoclinic mesostructure distorted from a (110)-oriented primitive cubic structure, uniform and tunable large pores of 10-30 nm, a large surface area of $100 m 2 g À1 and a high crystallinity anatase wall. The film thickness can be well controlled from 150 nm to several microns to tune the absorption, with the capability of generating free-standing film morphologies. Furthermore, this designed architecture allows for effective post-deposition of other small-bandgap semiconductor nanomaterials inside the large, open and interconnecting mesopores, leading to significantly improved solar absorption and photoconversion. As a proof-of-concept, we demonstrate that the photoanodes made of 4.75 mm thick mesoporous TiO 2 film with deposited cadmium sulfide quantum dots exhibit excellent performance in PEC water splitting, with an optimized photocurrent density of 6.03 mA cm À2 and a photoconversion efficiency of 3.9%. These multi-layered mesoporous TiO 2 -based thin films can serve as a unique architecture for PEC and other solar energy conversion and utilization.

Mesoporous materials for energy conversion and storage devices

“…The stability of the dye and the durability of the cell remain problems that need to be overcome for the development of these electrodes. Alternatively, quantum dots (including carbon dots) have been demonstrated as stable sensitizers for visible-light water splitting 97,98 . For example, by using a nanocomposite 99 comprising carbon dots and C 3 N 4 , a record STH efficiency of 2% was achieved with high stability, which is close to the 5% target for commercial viability set by the US Department of Energy.…”

Visible-light driven C@TiO2 porous films: Enhanced photoelectrochemical and photoelectrocatalytic performance

“…However, a drawback, regarding commercially available TiO 2 , is that it is mainly active in the UV that accounts for less than 5% of the total solar radiation [4,5]. To improve the optical response and photocatalytic activity of TiO 2 over the entire solar spectral range, numerous efforts have been made to vary the chemical composition and structure of TiO 2 by cation or anion doping, heterojunctions and band engineering that generate donor or acceptor states in the band gap [6][7][8][9][10][11][12][13][14]. Very recently, surface modification of TiO 2 by carbonaceous species aimed at solving the above problem has been proposed and attracted much attention [15][16][17][18].…”

Templated Synthesis for Nanoarchitectured Porous Materials

“…153 Other ligands, such as acetylacetone, can be added to coordinate with the metal precursor in order to retard the hydrolysis. 154 Considering economic and environmental factors, inorganic metal salt solutions are useful precursors which, once optimized, can lead to the elaboration of ordered mesoporous metal oxides.…”