Preparation of TiO2-reduced graphene oxide nanocomposites by hydrothermal method for hydrogen production from water splitting

Poster, Andreia Morais, 048
Publication date: 31st March 2013

 

Nowadays, there are many studies focusing on the development of photocatalyst materials that can work towards efficient conversion of solar energy in the form of molecular fuels such as H₂ (obtained from the photoelectrolysis of water) [1]. Among the materials, TiO₂ has been considered as one of the most promising because of its exceptional optical and electronic properties, non-toxicity, low cost, easy availability andhigh chemical stability [2]. The photocatalytic properties of TiO₂ have been widely studied since the first report of water splitting by TiO₂ from Fujishima and Honda [3]. Although TiO₂ is the most widely studied material for photoelectrochemical (PEC) water splitting, its practical use as a water splitting photocatalyst is limited due to the high energy of the band gap transition (3.2 eV for anatase TiO₂).This limits the absorption of TiO₂ to the UV region, which corresponds to only approximately 4% of incident solar energy.Furthermore, the slow charge carrier diffusion in a conventional TiO₂ photoelectrode increases the probability for charge recombination. A promising alternative to improve the electronic transport is the incorporation of reduced graphene oxide (rGO) into nanocrystalline TiO₂ films. Thus, these materials can be used to enhance charge carrier mobility and to act as an electron collector in the photoelectrode [4].

In this work, we characterized the graphite oxide (GO) samples obtained by the Hummers method [5]. Herein, we also report the synthesis of TiO₂-rGO nanocomposites by a one step hydrothermal process, employing titanium isopropoxide and GO as starting materials. The TiO₂-rGO nanocomposites were characterized by X-Ray diffraction, Raman spectroscopy and thermogravimetric analysis. The morphological properties of the nanocomposites were analyzed by Field Emission Scanning Electron Microscopy (FEG-SEM) and Transmission Electron Microscopy (TEM), as shown in Figure 1a and 1b, respectively. In the photoelectrochemical studies, the J-V curves (Figure 1c) showed that the film based on TiO₂-rGO (0.1 wt%) exhibited an increase in current density compared to TiO₂ film. Besides, transient absorption spectroscopy (TAS) also indicated an increase in lifetime of TiO₂ photoholes and a decrease of photoelectrons, consistent with reports of enhanced charge separation from rGO. In this case, we propose that the rGO introduced an alternative electrical conduction pathway which facilitated rapid electron transport in the film, resulting in an increase in photocurrent.

 

We acknowledge support from FAPESP, CAPES, CNPq, Inmetro, LNNano.

Figura 1. (a) FEG-SEM and (b) TEM images obtained for the TiO2-rGO nanocomposite. (c) J-V curves for the TiO2 porous films in the absence of or containing different amounts (in weight) of rGO, under illumination of 100 mW cm-2. Supporting electrolyte: H2SO4 (0.5 mol L-1). Active cell area: 1.0 cm2.
[1] Cowan, A. J., Tang, J. W., Leng, W. H., Durrant, J. R., Klug, D. R. Water splitting by nanocrystalline TiO2 in a complete photoelectrochemical cell exhibits efficiencies limited by charge recombination. Journal of Physical Chemistry C, 2010, 114, 4208-4214. [2] Shah, M. S. A. S., Park, A. R., Zhang, K., Park, J. H., Yoo, P. J. Green synthesis of biphasic TiO2-reduced graphene oxide nanocomposites with highly enhanced photocatalytic activity. ACS Applied Materials & Interfaces, 2012, 4, 3893-3901. [3] Fujishima, A. and K. Honda. Electrochemical photolysis of water at a semiconductor electrode. Nature, 1972, 238, 37-38. [4] Lightcap, I. V., Goodwin, K., Matsumura, M., Kamat, P. V. To what extent do graphene scaffolds improve the photovoltaic and photocatalytic response of TiO2 nanostructured films? Journal of Physical Chemistry Letters. 1, 2222-2227 (2010)

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