Lightly Fluorinated Graphene as a Protective Layer for n-Type Si(111) Photoanodes in Aqueous Electrolytes.
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.
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Adam C
AC
Nielander
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Annelise C
AC
Thompson
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Christopher W
CW
Roske
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Jacqueline A
JA
Maslyn
Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States.
Yufeng
Y
Hao
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Noah T
NT
Plymale
Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States.
James
J
Hone
Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Nathan S
NS
Lewis
2D materials; Photoelectrochemistry; anticorrosion; graphene; solar energy conversion