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Published May 14, 2020 | Supplemental Material
Journal Article Open

Conformal SnO_x heterojunction coatings for stabilized photoelectrochemical water oxidation using arrays of silicon microcones


The efficiency of photoelectrodes towards fuel-forming reactions is strongly affected by surface-based charge recombination, charge-transfer losses, and parasitic light absorption by electrocatalysts. We report a protective tin oxide (SnO_x) layer formed by atomic-layer deposition that limits surface recombination at n-Si/SnO_x heterojunctions and produces ∼620 mV of photovoltage on planar n-Si photoanodes. The SnO_x layer can be deposited conformally on high aspect-ratio three-dimensional structures such as Si microcone arrays. Atomic-level control of the SnO_x thickness enabled highly conductive contacts to electrolytes, allowing the direct electrodeposition of NiFeOOH, CoO_x, and IrO_x electrocatalysts for photoelectrochemical water oxidation with minimal parasitic absorption losses. SnO_x-coated n-Si microcone arrays coupled to electrodeposited catalysts exhibited photocurrent densities of ∼42 mA cm⁻² and a photovoltage of ∼490 mV under 100 mW cm⁻² of simulated solar illumination. The SnO_x layer can be integrated with amorphous TiO₂ to form a protective SnO_x/TiO₂ bilayer that exhibits the beneficial properties of both materials. Photoanodes coated with SnO_x/TiO₂ exhibited a similar photovoltage to that of SnO_x-coated photoanodes, and showed >480 h of stable photocurrent for planar photoelectrodes and >140 h of stable photocurrent for n-Si microcone arrays under continuous simulated solar illumination in alkaline electrolytes.

Additional Information

© The Royal Society of Chemistry 2020. Received 29th January 2020. Accepted 19th April 2020. First published 30 Apr 2020. This work was supported through the Office of Science of the U.S. Department of Energy (DOE) under award no. DE-SC0004993 to the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, and in part by the National Science Foundation (NSF) and the Department of Energy (DOE) under NSF CA No. EEC-1041895. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of NSF or DOE. Fabrication was performed in Kavli Nanoscience Institute (KNI) at Caltech, and we thank KNI staff for their assistance during fabrication. I. M. H acknowledges a National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144469. We thank C. Garland for assistance with transmission-electron microscopy measurements. There are no conflicts to declare.

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