Improved Semiconductor Electrode for Photo-electrochemistry
Producing hydrogen from clean sources of energy has been one of the major challenges of hydrogen production. While production from fossil fuel processes has been the norm, one of the most promising clean technologies has been hydrogen production through photo-electrochemical (PEC) cells. The three main hurdles of PEC hydrogen production have been efficiency, durability, and cost of production. The U.S. Department of Energy (DOE) reports that for photo-electrochemical water splitting to be economical, solar to hydrogen efficiency must reach at least 10% for 1000+ hours.
PEC production of hydrogen works by using the sun’s energy and photo-electrodes. The sun shines on the photo-electrodes in an aqueous solution. This in turn creates an electric current which drives the water splitting processes to produce hydrogen and oxygen. The produced hydrogen can currently be used in a variety of applications including metal processing, electronics manufacturing, aerospace and others. Developing markets for hydrogen include fuel cells, transportation, and other power generation.Description
NREL scientists have developed a nanostructured semiconductor photoelectrode to improve the efficiency of PEC reactions and more specifically to maximize the efficiency of generation of H2 gas for PEC solar energy conversion. While the purpose of this process is to create H2 gas, the application could be used to make other liquid or gaseous fuels or other useful products.
The invention involves a method to fabricate a semiconductor photoelectrode having an anti-reflective (AR) surface using a nanostructured surface without any use of AR coatings. A demonstration of the invention showed improvement in the efficiency of PEC H2 production by more than 20% when applied to a silicon photocathode. Nanostructured semiconductors used in the invention have optical properties of a density graded surface that can suppress reflection well below 5% over the entire range of the solar spectrum. The semiconductors with a density-graded surface have a 1-dimensional nanostructure, such as arrays of nanopores and/or nanowires. The density-graded surface on the semiconductor is formed by a chemical etching method which involves metal catalyst and etching solution. An additional benefit of this nanoporous density-graded layer is that it provides an extremely high surface area for the photoelectrochemical reaction, thereby reducing the current density required to produce the same amount of photoelectrochemical products on a given area of semiconductor exposed to light; this reduces the overpotential needed at the photoelectrode.
Nanostructured semiconductor photoelectrodes with AR surface can reduce approximately 20% of deployment costs to achieve same H2 production from one without an AR surface.
To learn more about the process, licensing, or partnership opportunities, please contact NREL using the form below. See attached patent information for further details.Benefits
- Anti-reflective coating through etching
- Higher efficiency
- Lower production costs
- Fuel Cells
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Anti-reflective nanoporous silicon for efficient hydrogen production
Exemplary embodiments are disclosed of anti-reflective nanoporous silicon for efficient hydrogen production by photoelectrolysis of water. A nanoporous black Si is disclosed as an efficient photocathode for H.sub.2 production from water splitting half-reaction.
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