Photooxidation Products of Ethanol During Photoelectrochemical Operation Using a Nanocrystalline Titania Anode and a Two
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Photooxidation Products of Ethanol During Photoelectrochemical Operation Using a Nanocrystalline Titania Anode and a Two Compartment Chemically Biased Cell Maria Antoniadou Æ Dimitris I. Kondarides Æ Panagiotis Lianos
Received: 20 October 2008 / Accepted: 7 January 2009 / Published online: 4 February 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Production of hydrogen and/or electricity by photocatalytic treatment of aqueous ethanol solutions has been investigated in a two compartment chemically biased photoelectrochemical cell, employing commercial nanocrystalline Titania as photoanode and Pt as cathode. Results show that hydrogen is produced during photooxidation of ethanol by cathode reduction and by means of a flow of external electric current. The performance of the cell decreased after several hours of operation, most possibly due to the formation of hydrocarbons of higher molecular weight. This is contrary to simple photocatalytic ethanol oxidation where complete mineralization of alcohol is observed. Keywords Titanium dioxide Ethanol photooxidation Photoelectrochemical cell Photooxidation intermediates Hydrogen production
1 Introduction Photocatalytic decomposition of aqueous solutions of organic substances under anaerobic conditions can lead to production of hydrogen. The process can be simply described as follows: a semiconductor photocatalyst is excited by absorption of photons generating electron–hole pairs. Holes oxidize organic substrates liberating hydrogen M. Antoniadou P. Lianos (&) Engineering Science Department, University of Patras, 26500 Patras, Greece e-mail: [email protected] D. I. Kondarides Department of Chemical Engineering, University of Patras, 26500 Patras, Greece
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ions, among other oxidation products. Hydrogen ions are in turn reduced by excited electrons, producing hydrogen molecules. This simple and straight forward process has to compete with electron–hole recombination. To suppress recombination, several techniques have been devised, most popular among them being the so-called photocatalytic (PC) process [1–13] and the photoelectrochemical (PEC) process [14–16]. In the PC case, noble metal nanoparticles are deposited on the nanostructured semiconductor. The metal nanoparticles act as electron traps, which impede recombination and facilitate transfer of electrons to reduce hydrogen ions, thereby decreasing the overpotential for H2 evolution. In the PEC case, the nanocrystalline semiconductor is deposited on an electrode, which acts as the anode. The cathode is made of a high work function metal; typically Pt. Excited electrons are channeled through an external circuit to the cathode. Hydrogen ions are then reduced at the cathode producing molecular hydrogen. In the present work, photocatalytic oxidation of ethanol has been studied by employing the PEC operation. Both PC and PEC process lead to the same result, that is, oxidation of the target substance and production of hydrogen. PC process is more efficient, since it operates at the nanoscale, where one
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