Three-Dimensional High-Density Hierarchical Nanowire Architecture for High-Performance Photoelectrochemical Electrodes

Abstract

Three-dimensional (3D) nanowire (NW) networks are promising for designing high-performance photoelectrochemical (PEC) electrodes owing to their long optical path for efficient light absorption, high-quality one-dimensional conducting channels for rapid electron-hole separation and charge transportation, as well as high surface areas for fast interfacial charge transfer and electrochemical reactions. By growing titanium dioxide (TiO(2)) nanorods (NRs) uniformly on dense Si NW array backbones, we demonstrated a novel three-dimensional high-density heterogeneous NW architecture that could enhance photoelectrochemical efficiency. A 3D NW architecture consisting of 20 μm long wet-etched Si NWs and dense TiO(2) NRs yielded a photoelectrochemical efficiency of 2.1%, which is three times higher than that of TiO(2) film-Si NWs having a core-shell structure. This result suggests that the 3D NW architecture is superior to straight NW arrays for PEC electrode design. The efficiency could be further improved by optimizing the number of overcoating cycles and the length/density of NW backbones. By implementing these 3D NW networks into electrode design, one may be able to advantageously impact PEC and photovoltaic device performance.

One-Dimensional Core/Shell Structured TiO2/ZnO Heterojunction for Improved Photoelectrochemical Performance

“…To date, a variety of inorganic heterojunction architectures have been developed to enhance the efficiency of photoelectrochemical water splitting cell. [22][23][24][25][26][27][28][29][30] In our study, we adapted this long-established strategy to enhance the photocatalytic activity of hydrothermally grown TiO 2 nanorod array. As a coupling material, we chose ZnO because its conduction band-edge is positioned at more negative potential in comparison with that of TiO 2 , thus being suitable for building the type-II band alignment (Scheme 1).…”

Branched nanostructures for photoelectrochemical water splitting

“…Shi et al demonstrated that the novel 3-D high-density heterogeneous NW architecture of Si/TiO 2 could enhance PEC efficiency. 29 A 3-D NW architecture consisting of 20 μm long wet-etched Si NWs and dense TiO 2 NRs yielded a PEC efficiency of 2·1%, which was three times higher than that of Si NWs/TiO 2 core-shell film ( Figure 16). The author also proved that the efficiency could be further improved by optimising the number of overcoating cycles and the length/density of NW backbones.…”

“…Branched nanostructures for photoelectrochemical water splitting Mao reported by the same group 29 showed high hydrogen production efficiency, they require high biasing potential to drive water splitting. In this regard, the branched CuO/ZnO NWs may be more promising because they are photoactive at low biasing potentials.…”

“…9,10 To simultaneously enhance the chemical stability of Si NWs, TiO 2 was chosen by Shi and co-workers as a corrosion-resistive material to interface with electrolyte other than a functional PEC photoelectrode component. 29 First, vertical Si NW arrays were prepared by selectively etching a heavily doped n-type Si substrate. Then high-density TiO 2 NR branches were uniformly grown around the dense Si NW array backbones by way of a surface-reactionlimited pulsed CVD process (Figure 15).…”

Effect of Hydrogen Treatment on Anatase TiO2Nanotube Arrays for Photoelectrochemical Water Splitting

“…8 Accordingly, one-dimensional (1-D) nanostructures such as nanowires, nanotubes, and nanorods are advantageous over planar geometries because these structures permit considerable light absorption depths, enhanced charge separation by providing high electrode/ electrolyte interface areas, and a reduction in the charge carrier transport distance to the electrolyte, which increases quantum efficiency. 9 In addition, some dopants such as nitrogen (N), carbon (C), and hydrogen (H) serve as electron donors to contribute to light absorption in the visible region and increase the electrical conductivity of the film. 10 In particular, the valence band edge of nonmetal (N, C)-incorporated TiO 2 is upshifted by forming impurity states above the valence band or hybridizing with O 2p states to extend the absorption spectrum toward the visible light region.…”