Title

Electrochemical Studies of Solar Thermal, Decoupled, Electrolysis Processes for Hydrogen Production

Document Type

Poster Presentation

Celebration Date

Spring 4-24-2013

Abstract

We present the latest experimental findings of our concept for a solar thermal electrolytic process for the production of hydrogen from water within the context of our previous work. In our process, a metal oxide is reduced in air with concentrated solar energy. The reduced metal oxide then serves as an anode or solute for the production of hydrogen in aqueous acidic or basic solution. During the electrolysis of water at 1 bar, hydrogen evolves at the cathode while the reduced metal oxide returns to its original oxidation state, thus closing the hydrogen production cycle. The potential required is substantially less than the theoretical 1.23 V necessary when hydrogen and oxygen evolve at 1 bar and 298 K in the absence of the metal oxide. Ideal sunlight-to-hydrogen thermal efficiencies were established for three metal oxide systems: Fe2O3–Fe3O4, Co3O4–CoO, and Mn2O3-Mn3O4. The ideal efficiencies include radiation heat loss from the solar thermal step and are as high as or higher than corresponding ideal values reported in the literature. Our experimental study for the iron oxide system confirmed that the electrolytic oxidation and thermal reduction steps of the metal oxide occur in a laboratory scale environment. Unfortunately, some of the Fe3+ product for the magnetite system stays in solution when the electrolysis is done in a strong acid. The research described here begins to establish the fraction of metal oxide remaining in solution and how best to increase the amount in a solid phase by controlling: 1) the electrolyte’s pH; 2) the electrolyte’s temperature; and 3) the degree to which the electrolyte is saturated with Fe3+.

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