Electrochemical Method for Synthesis of a ZnFe2O4/TiO2 Composite Nanotube Array Modified Electrode with Enhanced Photoelectrochemical Activity

An electrode with intimate and well‐aligned ZnFe₂O₄/TiO₂ composite nanotube arrays is prepared via electrochemical anodization of pure titanium foil in fluorine‐containing ethylene glycol, followed by a novel cathodic electrodeposition method. The deposition of ZnFe₂O₄ is promoted in the self‐aligned, vertically oriented TiO₂ nanotube arrays but minimized at the tube entrances. Thus, pore clogging is prevented. Environmental scanning electron microscopy, energy‐dispersive X‐ray spectra, high‐resolution transmission electron microscopy, X‐ray diffraction patterns, and X‐ray photoelectron spectroscopy indicate that the as‐prepared samples are highly ordered and vertically aligned TiO₂ nanotube arrays with ZnFe₂O₄ nanoparticles loading. The TiO₂ nanotubes are anatase with the preferential orientation of <101> plane. Enhanced absorption in both UV and visible light regions is observed for the composite nanotube arrays. The current–voltage curve of ZnFe₂O₄‐loaded TiO₂ nanotube arrays reveals a rectifying behavior. The enhanced separation of photoinduced electrons and holes is demonstrated by surface photovoltage and photocurrent measurements. Meanwhile, the photoelectrochemical investigations verify that the ZnFe₂O₄/TiO₂ composite nanotube array modified electrode has a more effective photoconversion capability than the aligned TiO₂ nanotube arrays alone. In addition, the photoelectrocatalytic ability of the novel electrode is found enhanced in the degradation of 4‐chlorophenol.     

Multistep hydrothermal route for nanocoral architecture of anatase TiO2: synthesis and characterization of dye‐sensitized solar cell performance

Multistep hydrothermal (MSH) process is employed for growth of TiO₂ nanocorals onto the conducting fluorine‐doped tin oxide‐coated glass substrates. The surface morphological features and physical properties of TiO₂ films were investigated by field emission scanning electron microscopy, high resolution transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, room temperature photoluminescence spectroscopy and X‐ray photoelectron spectroscopy. The surface morphology revealed the formation of TiO₂ corals having nanosized (30–40 nm) polyps. The photoelectrochemical properties of the TiO₂ nanocoral electrodes were investigated in 0.1 M NaOH electrolyte under ultraviolet illumination. The results presented in this study highlight two major findings: (i) tuning the photoelectrochemical response and photoconversion efficiency via controlled thickness of TiO₂ nanocorals by MSH route and (ii) the substantial increase in short‐circuit photocurrent (J_sc) because of the improved charge transport through TiO₂ nanocorals prepared via MSH process. Copyright © 2012 John Wiley & Sons, Ltd.     

Reduced Graphene Oxide as a Catalyst Binder: Greatly Enhanced Photoelectrochemical Stability of Cu(In,Ga)Se2 Photocathode for Solar Water Splitting

The photoelectrochemical (PEC) properties of a Cu(In,Ga)Se₂ (CIGS) photocathode covered with reduced graphene oxide (rGO) as a catalyst binder for solar‐driven hydrogen evolution are reported. Chemically reduced rGO with various concentrations is deposited as an adhesive interlayer between CIGS/CdS and Pt. PEC characteristics of the CIGS/CdS/rGO/Pt are improved compared to the photocathode without rGO due to enhancement of charge transfer via efficient lateral distribution of photogenerated electrons by conductive rGO to the Pt. More importantly, the introduction of rGO to the CIGS photocathode significantly enhances the PEC stability; in the absence of rGO, a rapid loss of PEC stability is observed in 2.5 h, while the optimal rGO increases the PEC stability of the CIGS photocathode for more than 7 h. Chemical and structural characterizations show that the loss of the Pt catalyst is one of the main reasons for the lack of long‐term PEC stability; the introduction of rGO, which acts as a binder to the Pt catalysts by providing anchoring sites in the rGO, results in complete conservation of the Pt and hence much enhanced stability. Multiple functionality of rGO as an adhesive interlayer, an efficient charge transport layer, a diffusion barrier, and protection layer is demonstrated.