An experimental investigation to improve the hydrogen production by water photoelectrolysis when cyanin-chloride is used as sensibilizer Federico Rossi, Andrea Nicolini ⇑ University of Perugia, Department of Industrial Engineering, Via G. Duranti 67, 06125 Perugia, Italy article info Article history: Received 5 July 2011 Received in revised form 20 October 2011 Accepted 13 November 2011 Available online 10 December 2011 Keywords: Hydrogen Electrolysis Photolysis Sensibilizer Catalyst abstract This paper deals with an experimental investigation to improve the hydrogen production by water photoelectrolysis. An experimental facility was built: it is mainly constituted by a solar simulator, the photoelectrolytic cell, the electric power supply system and a recirculating and gas sampling hydraulic circuit. Titanium dioxide was chosen as catalyst because of its good photocatalytic efficiency and its high stability to pH variations in watery solutions. Cyanin chloride was tested as sensibilizer: it is a flavonoid, an organic dye, which gives to the watery solution better solar radiation absorption performances. The catalyst and the sensibilizer were deposited on the cathode surface. A sacrificial reducing agent, ethylene- diaminetetraacetic acid (EDTA), was also introduced in the solution to reduce the sensibilizer and restore the original conditions. Different radiation power and electrolytic pH conditions were tested in order to verify the proposed arrangements. Results showed a growing in the hydrogen production by the pro- posed photoelectrolytic arrangements with respect to the performance of a simple electrolysis. Thus, the obtained results showed that this technology has good possibilities of improvement and interesting perspective of future development. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Electrolysis is used for over 80 years as commercial technique to produce hydrogen by water splitting [1]. Electrolytic hydrogen pro- duction demands the employment of electric power. Therefore, the production of great amounts of hydrogen is economic only in those countries where electricity can be generated at low costs, for exam- ple by hydroelectric plants or the solar source. Furthermore, the so- lar radiation may be also used to increase the hydrogen production by the photolysis process [2]. This paper deals with the develop- ment of a system for hydrogen production from water by catalytic photoelectrolysis. Photoelectrolysis is a technique for water split- ting which is supplied by solar radiation and electric energy. Solar radiation and electric energy are converted into chemical energy; solar radiation conversion is obtained by the support of a semicon- ductor which helps the photon absorption. This technology may have many benefits but the following technical and scientific limits have still to be overcome before its commercialization: high costs, low efficiency of the photolytic process, the complexity of imple- menting photoelectrolytic systems and hydrogen recovery sys- tems, the short life-time. Many investigations were performed in the past years about the photocatalytic phenomena or the catalyst employment for solar cell implementations. In particular, the first important investigation dealing with the photoelectrochemical hydrogen production was made by Fujishima and Honda which studied the employment of TiO 2 as catalyst [3]. Researches on semi- conductor photocatalysis continued in the following years: many review papers can be found in the scientific literature, but they are mainly related to the semiconductor photocatalytic water/air purification: only a small amount of them are related to photocat- alytic hydrogen production [3–5]. However, TiO 2 was shown to be a good catalyst for water splitting by photocatalysis also because of its relatively low cost and its good corrosion resistance properties [6]. A problem is given by TiO 2 high ‘‘band-gap energy’’ (approxi- mately 3.2 eV in its anatase form) [7]: it is able to absorb solar en- ergy only in the ultraviolet wavelength range (not in the visible wavelength range). Thus, the hydrogen production efficiency may be about 1–2% that is lower than a 10% commercial target. In order to obtain better results by this technology, TiO 2 band-gap charac- teristics and absorption properties have to be modified. A known approach involves the dye photosensitization of the catalyst. This approach, even if theoretically possible for water photoelectrolysis, is characterized by practical problems: most of the investigated sensibilizers would be too unstable [8,9]. However, some dyes hav- ing redox property and visible light sensitivity can be used in solar cells as well as photocatalytic systems [10,11]. Different dyes and reducing agents were analyzed and tested in photoelectrochemical cells. Dhanalakshmi carried out an investigation to study the effect of using [Ru(dcpy) 2 (dpq)] 2+ as dye sensibilizer on TiO 2 photocata- lytic hydrogen production from water: an enhanced hydrogen production rate was shown [12]. Gurunathan investigated the 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.11.034 ⇑ Corresponding author. Tel.: +39 0755853714; fax: +39 0755853697. E-mail addresses: frossi@unipg.it (F. Rossi), nicolini.unipg@ciriaf.it (A. Nicolini). Applied Energy 97 (2012) 763–770 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy