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RESEARCH PAPERS

Hydrogen From Solar Via Light-Assisted High-Temperature Water Splitting Cycles

[+] Author and Article Information
A. T-Raissi1

Florida Solar Energy Center, University of Central Florida, 1679 Clearlake Road, Cocoa, Fl 32922-5703ali@fsec.ucf.edu

N. Muradov, C. Huang, O. Adebiyi

Florida Solar Energy Center, University of Central Florida, 1679 Clearlake Road, Cocoa, Fl 32922-5703

1

Corresponding author.

J. Sol. Energy Eng 129(2), 184-189 (Apr 19, 2006) (6 pages) doi:10.1115/1.2710493 History: Received July 11, 2005; Revised April 19, 2006

Hydrogen production from solar-driven thermochemical water splitting cycles (TCWSCs) provides an approach that is energy efficient and environmentally attractive. Of particular interest are TCWSCs that utilize both thermal (i.e., high temperature) and light (i.e., quantum) components of the solar resource, boosting the overall solar-to-hydrogen conversion efficiency compared to those with heat-only energy input. We have analyzed two solar-driven TCWSCs: (1) carbon dioxide (CO2)/carbon monoxide cycle; and (2) sulfur dioxide (SO2)/sulfuric acid cycle. The first cycle is based on the premise that CO2 becomes susceptible to near-ultraviolet and even visible radiation at high temperatures (greater than 1300K). The second cycle is a modification of the well-known Westinghouse hybrid cycle, wherein the electrochemical step is replaced by a photocatalytic step. At the Florida Solar Energy Center (FSEC), a novel hybrid photo-thermochemical sulfur-ammonia (S–A) cycle has been developed. The main reaction (unique to FSEC’s S–A cycle) is the light-induced photocatalytic production of hydrogen and ammonium sulfate from an aqueous ammonium sulfite solution. Ammonium sulfate product is processed to generate oxygen and recover ammonia and SO2 that are then recycled and reacted with water to regenerate the ammonium sulfite. Experimental data for verification of the concept are provided.

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Figures

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Figure 3

A simplified block diagram of FSEC’s solar-powered sulfur-ammonia (S–A) cycle: (1) solar photocatalytic reactor; (2) gas-–liquid separator, (3) NH3 recovery unit; (4) sulfuric acid decomposition reactor; (5) mixer; (6) absorber; and (7) solar dish concentrating system. Red solid and dotted arrows denote photon and heat transfer, respectively.

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Figure 4

Experimental setup for the production of hydrogen via photochemical oxidation of ammonium sulfite aqueous solution

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Figure 5

Photoreactor for the photochemical H2 production

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Figure 6

Hydrogen production from aqueous ammonium sulfite solution (0.5M) with suspended photocatalyst subjected to visible light

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Figure 1

Thermodynamics of CO2 and H2O dissociation reactions

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Figure 2

Energy and mass flow diagram for the FSEC’s sulfur-ammonia (S-A) cycle (19)

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