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Title: Oxidatively Stable Nanoporous Silicon Photocathodes for Photoelectrochemical Hydrogen Evolution

Stable and high-performance nanoporous 'black silicon' photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit >20 mA/cm2 photocurrent density at +0.2 V vs. reversible hydrogen electrode (RHE) for photoelectrochemical hydrogen evolution under 1 sun illumination. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers increases in oxidative environments (e.g., aqueous electrolyte) owing to a positive flat-band potential shift caused by surface oxidation. However, this beneficial oxide layer becomes a kinetic barrier to proton reduction that inhibits hydrogen production after just 24 h. To mitigate this problem, we developed a novel second Pt-assisted etch process that buries the Pt NPs deeper into the nanoporous Si surface. This second etch shifts the onset voltage positively, from +0.25 V to +0.4 V vs. RHE, and reduces the charge-transfer resistance with no performance decrease seen for at least two months.
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Conference: Presented at the 2014 U.S. Department of Energy (DOE) Hydrogen and Fuel Cells Program and Vehicle Technologies Office Annual Merit Review and Peer Evaluation Meeting, 16-20 June 2014, Washington, D. C.
Washington, D.C.: U.S. Department of Energy
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
08 HYDROGEN; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; hydrogen evolution; silicon photoelectrode; black silicon; stable