Water Photo-Electrooxidation Using Mats of TiO2 Nanorods, Surface Sensitized by a Metal–Organic Framework of Nickel and 1,2-Benzene Dicarboxylic Acid

Sheng-Mu You,Waleed M A El Rouby,Ruey-An Doong,Pierre Millet,Loïc Assaud

doi:10.3390/hydrogen2010004

Abstract

Photoanodes comprising a transparent glass substrate coated with a thin conductive film of fluorine-doped tin oxide (FTO) and a thin layer of a photoactive phase have been fabricated and tested with regard to the photo-electro-oxidation of water into molecular oxygen. The photoactive layer was made of a mat of TiO2 nanorods (TDNRs) of micrometric thickness. Individual nanorods were successfully photosensitized with nanoparticles of a metal–organic framework (MOF) of nickel and 1,2-benzene dicarboxylic acid (BDCA). Detailed microstructural information was obtained from SEM and TEM analysis. The chemical composition of the active layer was determined by XRD, XPS and FTIR analysis. Optical properties were determined by UV–Vis spectroscopy. The water photooxidation activity was evaluated by linear sweep voltammetry and the robustness was assessed by chrono-amperometry. The OER (oxygen evolution reaction) photo-activity of these photoelectrodes was found to be directly related to the amount of MOF deposited on the TiO2 nanorods, and was therefore maximized by adjusting the MOF content. The microscopic reaction mechanism which controls the photoactivity of these photoelectrodes was analyzed by photo-electrochemical impedance spectroscopy. Microscopic rate parameters are reported. These results contribute to the development and characterization of MOF-sensitized OER photoanodes.

Highlights

Water dissociation is the main route to the “hydrogen economy”, a human society in which hydrogen fuel could be produced efficiently and inexpensively from natural energy sources, without the need for fossil fuels [1]
A closer examination of the microstructure (Figure 1D) confirms the presence of the Ni-metal–organic framework (MOF) coating on the titanium dioxide nanorods (TDNRs) consists of aligned nanorods of micrometric length
A closer examination of the6m3 icrostructure (Figure 1D) confirms the presence of the Ni-MOF coating on the TDNRs mat

Summary

Introduction

Water dissociation is the main route to the “hydrogen economy”, a human society in which hydrogen fuel could be produced efficiently and inexpensively from natural energy sources, without the need for fossil fuels [1]. The principles of photoelectrolysis were discovered as early as 1839 by Becquerel, the father of the photoelectric effect [3] Another significant milestone was passed in 1973 when Fujima and Honda reported for the first time that n-TiO2 photoelectrodes operating in aqueous electrolytes could provide a significant fraction of the energy needed for direct water splitting [4]. Their photoelectrocatalytic properties can be compared on the basis of these different criteria Materials such as ZnO [9,10], CuxO [11,12], CeO2 [13,14], BiVO4 [15], WO3 [16] and TiO2based nanomaterials are still considered as good photoactive semiconductors for water splitting. The longest solar-to-hydrogen production record has been set using a TiO2 coated photocathode [21]

Methods

Results

Conclusion