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MSD - Materials Sciences Division

High Current Density Nanostructured Photocathodes

A team of MSD researchers within the Joint Center for Artificial Photosynthesis led by Joel Ager and Ali Javey has shown that nanostructured InP can be a high performance photocathode for the conversion of sunlight into hydrogen. The combination of high efficiency and stability demonstrated in this system is a significant step towards the realization of artificial photosynthesis.

Artificial photosynthesis aims to convert sunlight directly into a chemical fuel, as plants do. One approach is to split water into hydrogen and oxygen. In such a system, protons in aqueous solution are converted to gas phase H2 by a electron current at the semiconductor photocathode. Achieving high efficiency involves balancing high surface areas which are beneficial for the chemical catalysis with the need for efficient charge creation and transport in the semiconductor.

To explore this trade-off, the JCAP researchers used single crystal InP as it is known to generate large photocurrents for H2 production in planar form. After modifying the surface with a novel nanotexturing process, high H2 generation rates were achieved but only for a limited period of time due to degradation of the high surface area structure. However, they discovered that applying a few nanometer thick oxide coating by atomic layer deposition produced near-complete stabilization of the surface with little or no loss in performance. Optimized systems produced nearly a 15% solar to hydrogen conversion efficiency. Future work is aimed at replacing the single crystal InP with less expensive alternatives.

This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

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Lee, M. H., Takei, K., Zhang, J., Kapadia, R., Zheng, M., Chen, Y.-Z., Nah, J., Matthews, T. S., Chueh, Y.-L., Ager, J. W. and Javey, A. (2012), p-Type InP Nanopillar Photocathodes for Efficient Solar-Driven Hydrogen Production. Angew. Chem. Int. Ed.. doi: 10.1002/anie.201203174