Iodine speciation studies on Bunsen reaction of SeI cycle using spectroscopic techniques Deepak Tyagi, Salil Varma*, K. Bhattacharya, D. Jain, A.K. Tripathi, C.G.S. Pillai, S.R. Bharadwaj Chemistry Division, Bhabha Atomic Research Centre, 400085 Mumbai, India article info Article history: Received 9 March 2011 Received in revised form 27 April 2011 Accepted 29 April 2011 Available online 12 June 2011 Keywords: HIx Raman spectroscopy UVevisible spectroscopy Speciation abstract Bunsen reaction is an important step of sulfureiodine cycle for hydrogen production from thermochemical splitting of water. Polyiodide species generated during the separation process need to be identified for complete understanding of the mechanism involved. Speciation of these polyiodide species formed during Bunsen reaction can lead to better understanding of kinetics of the process. HIx species formed have been analyzed using UVevisible and Raman spectroscopic techniques. Peak corresponding to HI 3 species have been ascertained and their conversion to higher HI 5 , HI 7 .. species has been observed. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Fossil fuel resources of earth will not be able to meet the energy needs of future generations, which leads to investi- gation of many alternate energy sources. Among these hydrogen seems to be an attractive energy carrier if it can be produced in a clean and cost effective manner. Hydrogen is future fuel to bring out shift from carbon based energy sources to more energy efficient and environmentally clean systems [1,2]. The development of newer technologies based on fuel cells and other techniques require production of hydrogen on large scale and in an economically viable manner. The two processes which seems to be most prom- ising for massive hydrogen production are electrolysis [3,4] and thermochemical cycles [5e7]. In thermochemical cycles heat can be directly used so they have potential of better efficiency than alkaline electrolysis. Various thermochemical cycles like sulfureiodine cycle [7], copper chlorine cycle [8,9] are explored for their capability to fulfill the future hydrogen demand. Sulfureiodine cycle is based on integration of following three reactions in a loop: I 2 ðIÞþ SO 2 ðgÞþ 2H 2 OðIÞ/2HIðaq:Þþ H 2 SO 4 ðaq:Þ (1) 2HIðgÞ/I 2 ðgÞþ H 2 ðgÞ (2) H 2 SO 4 ðgÞ/SO 2 ðgÞþ H 2 OðgÞþ 0:5O 2 ðgÞ (3) First reaction is known as the Bunsen reaction, which forms an important step of sulfureiodine cycle for thermochemical splitting of water. This reaction is carried out in liquid water media with a large excess of iodine. Excess iodine is added to avoid side reactions between iodine and sulfur compounds; also excess iodine facilitates segregation of the two product acids into two corresponding liquid phases [10e13]. These phases are sulfuric acid phase (about 50 wt% H 2 SO 4 ) in which HI * Corresponding author. Tel.: þ91 22 25592282; fax: þ91 22 25505151. E-mail address: svarma@barc.gov.in (S. Varma). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 3621 e3625 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.04.221