Composite Nanostructures of TiO₂ and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation

Abstract

The commercialization of solar fuel devices requires the development of novel engineered photoelectrodes for water splitting applications which are based on redundant, cheap, and environmentally friendly materials. In the current study, a combination of titanium dioxide (TiO2) and zinc oxide (ZnO) onto nanotextured silicon is utilized for a composite electrode with the aim to overcome the individual shortcomings of the respective materials. The properties of conformal coverage of TiO2 and ZnO layers are designed on the atomic scale by the atomic layer deposition technique. The resulting photoanode shows not only promising stability but also nine times higher photocurrents than an equivalent photoanode with a pure TiO2 encapsulation onto the nanostructured silicon. Density functional theory calculations indicate that segregation of TiO2 at the ZnO surfaces is favorable and leads to the stabilization of the ZnO layers in water environments. In conclusion, the novel designed composite material constitutes a promising base for a stable and effective photoanode for the water oxidation reaction.

The Applications of Morphology Controlled ZnO in Catalysis

“…iii. One-dimensional ZnO nanostructures have been intensively investigated in photoelectrochemical (PEC) cells to split water and large enhancements have been achieved [74,77,79,[82][83][84]. Furthermore, ZnO nanorods have been reported in the applications of photoelectron-oxidation of ethanol and methanol [83,84]; ZnO has also been applied as an important photoelectrocatalyst component in the methanol production from CO 2 by photoelectrocatalytic reduction.…”

“…It is broadly accepted that hybrid catalysts will enhance photocatalytic properties in comparison to individual semiconductor catalysts [77,78]. For example, Sun et al found that the photo-degradation efficiency of MB over ZnO nanorod arrays (NRs) was significantly enhanced by decoration with Au (ZnO/Au composite) [187].…”

“…Thus, the high photo-degradation efficiency was probably due to the high defects concentration and the suppression of the recombination of electron-hole pairs. A semiconductor is also applied to modifiy the intrinsic semiconductor in order to improve photocatalytic properties [77,78]. Kayaci et al produced morphologically well defined poly (acrylonitrile) (PAN) nanofibrous via electronspinning, and then coated it with ZnO through an atomic layer deposition method, which served as crystal seed to grow single crystalline ZnO nanoneedles via a hydrothermal process [191].…”

Metal–Organic Framework Derived Co3O4/TiO2/Si Heterostructured Nanorod Array Photoanodes for Efficient Photoelectrochemical Water Oxidation

“…photoexcitation of semiconductor photoanode; the separation and migration of photoinduced carriers; the surface water reduction on the cathode; and water oxidation on the photoanode with photoinduced electrons/holes. [20][21][22] For instance, via constructing semiconductor heterojunction with matched band position, the separation and transportation of photoinduced carrier can be effectively enhanced (such as Bi 2 MoO 6 /Si, [23] Ag/Fe 2 O 3 , [24] NiFe-LDH/C 3 N 4[25] heterojunction). [12,13] Metal oxides (MOs), such as TiO 2 , [14] α-Fe 2 O 3 , [15] and WO 3 , [16,17] have been widely investigated as the photoanode materials for PEC water splitting, for their low-cost, environmentfriendly properties.…”

Perspective—A Brief Perspective on the Fabrication of Hierarchical Nanostructure for Solar Water Splitting Photoelectrochemical Cells

“…Likewise, the deposition process was naturally imported to make hierarchical nanostructure in terms of formation thin film structure on the metal oxide nanostructure. The deposition process was conducted by using various vacuum-based equipment such as atomic layer deposition (ALD), [40][41][42][43] chemical-vapor deposition, 21 E-beam evaporator, 44,45 pulsed laser deposition (PLD) 46,47 and sputtering 48 on the metal oxide nanostructures. By this way, a robust and dense thin film structure was accurately formed from only several nanometers to tens of nanometers onto the metal oxide nanostructure, obtained hierarchical nanostructure by controlling deposition processing conditions.…”