title: Double-Layer Graphene Outperforming Monolayer as Catalyst on Silicon Photocathode for Hydrogen Production.
abstract: Photoelectrochemical cells are used to split hydrogen and oxygen from water molecules to generate chemical fuels to satisfy our ever-increasing energy demands. However, it is a major challenge to design efficient catalysts to use in the photoelectochemical process. Recently, research has focused on carbon-based catalysts, as they are nonprecious and environmentally benign. Interesting advances have also been made in controlling nanostructure interfaces and in introducing new materials as catalysts in the photoelectrochemical cell. However, these catalysts have as yet unresolved issues involving kinetics and light-transmittance. In this work, we introduce high-transmittance graphene onto a planar p-Si photocathode to produce a hydrogen evolution reaction to dramatically enhance photon-to-current efficiency. Interestingly, double-layer graphene/Si exhibits noticeably improved photon-to-current efficiency and modifies the band structure of the graphene/Si photocathode. On the basis of in-depth electrochemical and electrical analyses, the band structure of graphene/Si was shown to result in a much lower work function than Si, accelerating the electron-to-hydrogen production potential. Specifically, plasma-treated double-layer graphene exhibited the best performance and the lowest work function. We electrochemically analyzed the mechanism at work in the graphene-assisted photoelectrode. Atomistic calculations based on the density functional theory were also carried out to more fully understand our experimental observations. We believe that investigation of the underlying mechanism in this high-performance electrode is an important contribution to efforts to develop high-efficiency metal-free carbon-based catalysts for photoelectrochemical cell hydrogen production.
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Uk
authors.initials: U
authors.lastname: Sim
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 08 826, Republic of Korea.|Korea Basic Science Institute , Gwahangno, Yusung-gu, Daejeon, 305-333, Korea.
authors.forename: Joonhee
authors.initials: J
authors.lastname: Moon
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Joohee
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Junghyun
authors.initials: J
authors.lastname: An
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Hyo-Yong
authors.initials: HY
authors.lastname: Ahn
authors.affiliation: Department of Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Dong Jin
authors.initials: DJ
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Insu
authors.initials: I
authors.lastname: Jo
authors.affiliation: Korea Basic Science Institute , Gwahangno, Yusung-gu, Daejeon, 305-333, Korea.
authors.forename: Cheolho
authors.initials: C
authors.lastname: Jeon
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Seungwu
authors.initials: S
authors.lastname: Han
authors.affiliation: Department of Chemistry, Seoul National University , Seoul 08 826, Republic of Korea.|Department of Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Byung Hee
authors.initials: BH
authors.lastname: Hong
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08 826, Republic of Korea.
authors.forename: Ki Tae
authors.identifier: http://orcid.org/0000-0001-6353-8877
authors.initials: KT
authors.lastname: Nam
keywords: graphene; hydrogen evolution reaction (HER); metal free catalyst; photoelectrochemical cell; silicon