Water splitting cycles

Non-electrolytic sources of hydrogen have also been studied. The chemical problem is how to transfer the correct amount of free energy to a water molecule in order to decompose it. In the last few years about I0(X)0 such thermochemical water-splitting cycles have been identified, most of them with the help of computers, though it is significant that the most promising ones were discovered first by the intuition of chemists. 

Norman, J.H. et al., Thermochemical water-splitting cycle, bench-scale investigations and process engineering, GA-A 16713,1982. 

Kubo, S. et al., Corrosion test on structural materials for iodine-sulfur thermochemical water splitting cycle, in Proc. 2nd Topical Conf. on Fuel Cell Tech., AIChE 2003 Spring National Meeting, New Orleans, March 30-April 3, 2003. 

The sulfur-iodine thermochemical water-splitting cycle (S-1 cycle) developed for hydrogen production from water is fundamentally based on the following three chemical reactions (Wang, 2007) ... 

Norman JH, Mysels KJ, Sharp R, Williamson D (1982) Studies of the sulfur-iodine thermochemical water-splitting cycle. Int J Hydrogen Energy 7 545-556... 

By H20/D20 exchange a deuterium modulation could also be detected in the So state by ESEEM spectroscopy449,470 indicating that substrate water might already be bound at the beginning of the water splitting cycle. 

UV irradiation of low-valent cations (e.g. V2+, Cr2+, Fe2+) in acidic aqueous solution leads to photooxidation of the metal and evolution of H2.110 This reaction, described by equation (47), is thought to involve the formation of the oxidized metal and an electron in the primary photochemical act. Immediate scavenging of the photoelectrons by protons yields hydrogen atoms which then combine to produce H2. Some interest has been shown in this type of system as a component of a photochemical water-splitting cycle.110 111... 

O Keefe, D.R., et al. (1982), Preliminary Results from Bench-scale Testing of Sulphur-iodine Thermochemical Water-splitting Cycle , Int. J. Hydrogen Energy, 7 (5), 381-92. 

Buckingham, R., et al. (2009), Influence of HTR Core Inlet and Outlet Temperatures on Hydrogen Generation Efficiency Using the Sulphur-iodine Water-splitting Cycle , these proceedings. 

Norman, J.H., et al. (1982), Thermochemical Water-splitting Cycle, Bench-scale Investigations and Process Engineering. Final Report for the Period February 1977 through December 31, 1981, GA-A16713 report, May. 

Influence of HTR core inlet and outlet temperatures on hydrogen generation efficiency using the sulphur-iodine water-splitting cycle... 

Hilier W, Wydrzynski T. lsO-water exchange in photosystem II Substrate binding and intermediates of the water splitting cycle. Coord Chem Rev 2008 252 306-17. 

These studies also indicate an overall efficiency (ratio of higher heating value of hydrogen output to the nuclear heat input) in the range of 40 to 43%, which is comparable to that presently estimated for the most promising thermochemical water splitting cycles. 

From a thermodynamic point of view, many water-splitting cycles are possible and have been proposed chemical feasibility, thermal efficiency and engineering and cost considerations have gradually enacted a selection mechanism and only few cycles are actively being studied today. 

Complete operation of the CLCD confirmed the feasibility of of the GA water-splitting cycle and provided the laboratory personnel with information useful for the detailed construction and operation of the Bench Scale Unit. 

The sulfur-iodine thermo chemical water-splitting cycle continues to represent a promising approach to the production of hydrogen utilizing an entirely thermal energy source. Another significant step toward its viability has been taken by the successful closure of the cycle in this laboratory demonstration. 

Norman, J. H. Mysels, K. J. O Keefe, D. R. Stowell, S. A. Williamson, D. G., "Chemical Studies on the General Atomic Sulfur-Iodine Thermochemical Water-Splitting Cycle," paper presented at the Second World Hydrogen Energy Conference, Zurich, Switzerland, August 1978. 

A. Weidenkaff, A. Reller, A. Wokaun, and A. Steinfeld, Thermogravimetric analysis of the ZnO/Zn water splitting cycle, Thermochim. Acta, 359 69-75 (2000). 

N.B., Hydrogen (and oxygen) production by the met Hanoi-water splitting cycle,... 

Kubo, S. et al.. Corrosion Test on Strnctnral Materials for Iodine-Sulfur Thermochemical Water-Splitting Cycle, paper presented at the Proceedings of the 2nd Topical Conference on Fuel Cell Technology, AlChE 2003 Spring National Meeting, 2003. 

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