Student Abstracts: Chemistry at NREL

Increasing Efficiency in Photoelectrochemical Hydrogen Production. SCOTT WARREN (Whitman College, Walla Walla, WA 99362) JOHN TURNER (National Renewable Energy Laboratory, Golden, CO 89401) .
Photoelectrochemical hydrogen production promises to be a renewable, clean, and efficient way of storing the sun's energy for use in hydrogen-powered fuel cells. We use p-type Ga.51In.49P semiconductor (henceforth as GaInP2) to absorb solar energy and produce a photocurrent. When the semiconductor is immersed in water, the photocurrent can break down water into hydrogen and oxygen. However, before the GaInP2 can produce hydrogen and oxygen, the conduction band and the Fermi level of the semiconductor must overlap the water redox potentials. In an unmodified system, the conduction band and Fermi level of GaInP2 do not overlap the water redox potentials. When light shines on the semiconductor, electrons build up on the surface, shifting the bandedges and Fermi level further away from overlap of the water redox potentials. We report on surface treatments with metallated porphyrins and transition metals that suppress bandedge migration and allow bandedge overlap to occur. Coating ruthenium octaethylporphyrin carbonyl (RuOEP CO) on the GaInP2 surface shifted bandedges in the positive direction by 270 mV on average, allowing the bandedges to frequently overlap the water redox potentials. Coating the GaInP2 surface with RuCl3 catalyzed charge transfer from the semiconductor to the water, lessening bandedge migration under light irradiation. Future work will focus on the long-term surface stability of these new treatments and quantitative applications of porphyrins.