measuring photoelectrochemical properties of Metal-Oxide-Semiconductor nanoStructures with high spatial resolution

Daniel Esposito, Alec Talin, Thomas Moffat


            Using sunlight to produce H2 from the electrolysis of water is a promising approach to harvesting and storing solar energy.  One such solar-to-hydrogen conversion pathway is through the use of photoelectrochemical cells (PECs), electrochemical devices containing at least one semiconducting photoelectrode that is capable of absorbing light and using it to drive the electrolysis of water.  However, presently demonstrated PECs suffer from a combination of low solar-to-hydrogen conversion efficiency and poor stability of the photoelectrode.  In order to overcome these deficiencies, new materials and photoelectrode architectures are needed. 

In this work, we investigate an alternative photoelectrode design based on ordered metal-oxide-semiconductor (MOS) structures.  This design consists of uniformly spaced metal nanostructures situated on the surface of oxide-covered semiconductors.  The thin oxide layer serves the role of protecting the underlying semiconductor layer while the metallic structures collect minority charge carriers and catalyze the hydrogen evolution reaction (HER).  Although this design has shown great promise, a better understanding of nano- and micro-scale charge transfer phenomena in MOS structures is needed to further increase solar to hydrogen conversion efficiency.  As a means to achieve this goal, this research focuses on using nano/micro-scale in situ measurement techniques to evaluate the performance of well-defined MOS structures.  Central to this effort are photoelectrochemical microscopy (PEM) and scanning electrochemical microscopy (SECM), complimentary techniques that can be used to map catalytic activity and quantum efficiency with high spatial resolution.  In this poster, we illustrate the usefulness of these techniques for evaluating photoelectrode performance and optimizing MOS structures for stable and efficient water splitting.  As a platform for this work, we have studied p-Si photocathodes capped with a uniform SiO2 overlayer and patterned with uniform metallic Pt structures.