Thin Films of Sodium Birnessite-Type MnO2: Optical Properties, Electronic Band Structure, and Solar Photoelectrochemistry

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• 作者：Blaise A. Pinaud ; Zhebo Chen ; David N. Abram ; Thomas F. Jaramillo
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：June 16, 2011
• 年：2011
• 卷：115
• 期：23
• 页码：11830-11838
• 全文大小：971K
• 年卷期：v.115,no.23(June 16, 2011)
• ISSN：1932-7455

文摘

Inexpensive and earth-abundant, manganese oxides (Mn_xO_y) have attracted considerable attention for catalysis, but fewer efforts have focused on their semiconducting properties. In this study, crystalline Na birnessite-type MnO₂ thin films were investigated for their surface and bulk chemistry in the context of hydrogen production by photoelectrochemical water splitting. Thin films were synthesized by electrodeposition onto fluorine-doped tin oxide (FTO) substrates, imaged by scanning electron microscopy (SEM), and characterized by X-ray diffraction (XRD) as well as X-ray photoelectron spectroscopy (XPS) and UV鈥搗is spectroscopy. Three different electrochemical methods (illuminated open circuit potential, potential of photocurrent onset, and Mott鈥揝chottky plots) were used to probe the flat-band potential required to construct a band diagram for the material. Photostability, conductivity, and band structure are discussed as potential causes of the low external quantum efficiency (<1%) for the birnessite-type MnO₂ photoanode. The position of the conduction band well below the hydrogen evolution potential likely mitigates this material鈥檚 potential use in a single absorber configuration, but its chemical, optical, and electronic characteristics as shown in this work may be well-suited for a photoanode in a tandem device.