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Effects of bubbles on the electrochemical behavior of hydrogen-evolving Si microwire arrays oriented against gravity

Kempler, Paul A. and Coridan, Robert H. and Lewis, Nathan S. (2020) Effects of bubbles on the electrochemical behavior of hydrogen-evolving Si microwire arrays oriented against gravity. Energy and Environmental Science, 13 (6). pp. 1808-1817. ISSN 1754-5692. doi:10.1039/d0ee00356e.

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The size-distribution, coverage, electrochemical impedance, and mass-transport properties of H₂ gas-bubble films were measured for both planar and microwire-array platinized n⁺-Si cathodes performing the hydrogen-evolution reaction in 0.50 M H₂SO₄ (aq). Inverted, planar n⁺-Si/Ti/Pt cathodes produced large, stationary bubbles which contributed to substantial increases in ohmic potential drops. In contrast, regardless of orientation, microwire array n⁺-Si/Ti/Pt cathodes exhibited a smaller layer of bubbles on the surface, and the formation of bubbles did not substantially increase the steady-state overpotential for H₂ (g) production. Experiments using an electroactive tracer species indicated that even when oriented against gravity, bubbles enhanced mass transport at the electrode surface. Microconvection due to growing and coalescing bubbles dominated effects due to macroconvection of gliding bubbles on Si microwire array cathodes. Electrodes that maintained a large number of small bubbles on the surface simultaneously exhibited low concentrations of dissolved hydrogen and small ohmic potential drops, thus exhibiting the lowest steady-state overpotentials. The results indicate that microstructured electrodes can operate acceptably for unassisted solar-driven water splitting in the absence of external convection and can function regardless of the orientation of the electrode with respect to the gravitational force vector.

Item Type:Article
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Kempler, Paul A.0000-0003-3909-1790
Coridan, Robert H.0000-0003-1916-4446
Lewis, Nathan S.0000-0001-5245-0538
Additional Information:© 2020 The Royal Society of Chemistry. Submitted 03 Feb 2020; Accepted 08 Apr 2020; First published 08 Apr 2020. 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 No. DE-SC0004993. High-speed microscopy experiments were supported by the National Science Foundation under Grant No. 1732096 (R. H. C.). Fabrication of the Si microwire arrays was performed in the Kavli Nanoscience Institute (KNI) at Caltech, and we thank the KNI staff for their assistance during fabrication. We thank K. M. P. and B. S. B. for helpful discussions on experimental design. Author contributions: Conceptualization, P. A. K., and N. S. L.; Methodology, P. A. K., Investigation, P. A. K. and R. H. C.; Writing—Original Draft, P. A. K. and N. S. L.; Writing—Review & Editing, N. S. L., P. A. K., R. H. C.; Funding Acquisition, N. S. L. and R. H. C.; Supervision, N. S. L. The authors declare no competing interests.
Group:JCAP, Kavli Nanoscience Institute
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
Issue or Number:6
Record Number:CaltechAUTHORS:20200519-103638391
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Official Citation:Effects of bubbles on the electrochemical behavior of hydrogen-evolving Si microwire arrays oriented against gravity. Energy Environ. Sci., 2020, 13, 1808-1817; doi: 10.1039/d0ee00356e
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103312
Deposited By: Tony Diaz
Deposited On:19 May 2020 17:44
Last Modified:16 Nov 2021 18:20

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