title: Metal-Free Carbon-Based Nanomaterial Coatings Protect Silicon Photoanodes in Solar Water-Splitting.
abstract: The decreasing cost of silicon-based photovoltaics has enabled significant increases in solar electricity generation worldwide. Silicon photoanodes could also play an important role in the cost-effective generation of solar fuels, but the most successful methods of photoelectrode passivation and performance enhancement rely on a combination of precious metals and sophisticated processing methods that offset the economic arguments for silicon. Here we show that metal-free carbon-based nanomaterial coatings deposited from solution can protect silicon photoanodes carrying out the oxygen evolution reaction in a range of working environments. Purified semiconducting carbon nanotubes (CNTs) act as a hole extraction layer, and a graphene (Gr) capping layer both protects the CNT film and acts as a hole exchange layer with the electrolyte. The performance of semiconducting CNTs is found to be superior to that of metallic or unsorted CNTs in this context. Furthermore, the insertion of graphene oxide (GO) between the n-Si and CNTs reduces the overpotential relative to photoanodes with CNTs deposited on hydrogen-passivated silicon. The composite photoanode structure of n-Si/GO/CNT/Gr shows promising performance for oxygen evolution and excellent potential for improvement by optimizing the catalytic properties and stability of the graphene protective layer.
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: KunHo
authors.initials: K
authors.lastname: Yoon
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Jae-Hyeok
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Joohoon
authors.initials: J
authors.lastname: Kang
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Junmo
authors.initials: J
authors.lastname: Kang
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Moody
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hersam
authors.affiliation: Department of Materials Science and Engineering, ‡Department of Chemistry, §Department of Medicine, and ∥Department of Electrical Engineering and Computer Science, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Lincoln J
authors.initials: LJ
authors.lastname: Lauhon
keywords: Carbon nanotube; graphene; graphene oxide; photoanode; solar fuel; water-splitting