Abstract
Photocatalysis combined with membrane technology could offer an enormous potential for power generation in a renewable and sustainable way. Herein, we describe the one-step hydrogen and oxygen evolution through a photocatalytic membrane reactor. Experimental tests were carried out by means of a two-compartment cell in which a modified Nafion membrane separated the oxygen and hydrogen evolution semi-cells, while iron ions permeating through the membrane acted as a redox mediator. Nanosized Au/TiO2 and Au/CeO2 were employed as suspended photocatalysts for hydrogen and oxygen generation, respectively. The influence of initial Fe3+ ion concentration, ranging from 5 to 20 mM, was investigated, and the best results in terms of hydrogen and oxygen evolution were registered by working with 5 mM Fe3+. The positive effect of gold on the overall water splitting was confirmed by comparing the photocatalytic results obtained with the modified/unmodified titania and ceria. Au-loading played a key role for controlling the photocatalytic activity, and the optimal percentage for hydrogen and oxygen generation was 0.25 wt%. Under irradiation with visible light, hydrogen and oxygen were produced in stoichiometric amounts. The crucial role of the couple Fe3+/Fe2+ and of the membrane on the performance of the overall photocatalytic system was found.
Highlights
Photocatalytic water splitting to generate hydrogen from solar light is a process that can play an important role for the future development of clean and renewable energies alternative to fossil fuels [1,2,3,4,5,6,7,8]
We reported that gold nanoparticles supported on titania (Au/TiO2) represent a suitable photocatalyst for the generation of hydrogen with visible light using methanol and ethylenediaminetetraacetic acid (EDTA) as sacrificial electron donors [14]
We studied the overall photocatalytic water splitting using Au nanoparticles as a sensitizer of TiO2 and CeO2 semiconductors irradiated with visible light in combination, a Nafion film as a membrane separating two cells, and ferric sulfate as the electrolyte
Summary
Photocatalytic water splitting to generate hydrogen from solar light is a process that can play an important role for the future development of clean and renewable energies alternative to fossil fuels [1,2,3,4,5,6,7,8]. Considering the above precedents and the visible-light photocatalytic activity for independent hydrogen and oxygen generation using Au/TiO2 or Au/CeO2, respectively, in the presence of an appropriate sacrificial agent, it occurs that these two photocatalysts could work in a system to perform the simultaneous generation of hydrogen and oxygen in the absence of sacrificial agents using a Z-scheme [25,26,27,28] In this Z-scheme methodology, hydrogen and oxygen are generated photocatalytically in different cells that are irradiated and separated by a membrane [5,29,30,31,32,33,34]. We studied the overall photocatalytic water splitting using Au nanoparticles as a sensitizer of TiO2 and CeO2 semiconductors irradiated with visible light in combination, a Nafion film as a membrane separating two cells, and ferric sulfate as the electrolyte. The photocatalytic activity of the pairs (Au/TiO2 and Au/CeO2) for the photocatalytic water splitting through a Z-scheme under visible light was demonstrated
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