ARTICLE pubs.acs.org/JPCC
Thin Films of Sodium Birnessite-Type MnO2: Optical Properties, Electronic Band Structure, and Solar Photoelectrochemistry Blaise A. Pinaud, Zhebo Chen, David N. Abram, and Thomas F. Jaramillo* Department of Chemical Engineering, Stanford University, 381 North-South Axis, Stanford, California 94305, United States
bS Supporting Information ABSTRACT: Inexpensive and earth-abundant, manganese oxides (MnxOy) 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 UVvis spectroscopy. Three different electrochemical methods (illuminated open circuit potential, potential of photocurrent onset, and MottSchottky 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 (
