Lightly Fluorinated Graphene as a Protective Layer for n-Type Si(111) Photoanodes in Aqueous Electrolytes

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• 作者：Adam C. Nielander ; Annelise C. Thompson ; Christopher W. Roske ; Jacqueline A. Maslyn ; Yufeng Hao ; Noah T. Plymale ; James Hone ; Nathan S. Lewis
• 刊名：Nano Letters
• 出版年：2016
• 出版时间：July 13, 2016
• 年：2016
• 卷：16
• 期：7
• 页码：4082-4086
• 全文大小：305K
• 年卷期：0
• ISSN：1530-6992

文摘

The behavior of n-Si(111) photoanodes covered by monolayer sheets of fluorinated graphene (F–Gr) was investigated under a range of chemical and electrochemical conditions. The electrochemical behavior of n-Si/F–Gr and np⁺-Si/F–Gr photoanodes was compared to hydride-terminated n-Si (n-Si−H) and np⁺-Si−H electrodes in contact with aqueous Fe(CN)₆^3-/4- and Br₂/HBr electrolytes as well as in contact with a series of outer-sphere, one-electron redox couples in nonaqueous electrolytes. Illuminated n-Si/F–Gr and np⁺-Si/F–Gr electrodes in contact with an aqueous K₃(Fe(CN)₆/K₄(Fe(CN)₆ solutions exhibited stable short-circuit photocurrent densities of ∼10 mA cm^–2 for 100,000 s (>24 h), in comparison to bare Si electrodes, which yielded nearly a complete photocurrent decay over ∼100 s. X-ray photoelectron spectra collected before and after exposure to aqueous anodic conditions showed that oxide formation at the Si surface was significantly inhibited for Si electrodes coated with F–Gr relative to bare Si electrodes exposed to the same conditions. The variation of the open-circuit potential for n-Si/F–Gr in contact with a series of nonaqueous electrolytes of varying reduction potential indicated that the n-Si/F–Gr did not form a buried junction with respect to the solution contact. Further, illuminated n-Si/F−Gr electrodes in contact with Br₂/HBr(aq) were significantly more electrochemically stable than n-Si−H electrodes, and n-Si/F−Gr electrodes coupled to a Pt catalyst exhibited ideal regenerative cell efficiencies of up to 5% for the oxidation of Br^– to Br₂.