Characterization of Hematite Thin Films for Photoelectrochemical Water Splitting in a Dual Photoelectrode Device

Both nanorod and pyrolysis thin films have pure hematite structure and both show direct and indirect bandgap transitions. The nanorod film shows a direct bandgap of 2.14 eV and an indirect one of 2.04 eV. The pyrolysis film gives a direct bandgap of 2.15 eV and an indirect one of 2.08 eV. The pyrolysis film shows much higher incident photon-to-current efficiency (IPCE) values, whereas the nanorod film has a wider absorption edge. Based on the IPCE measurements, bandgaps of 1.94 and 2.00 eV were estimated for the nanorod and pyrolysis films, respectively. Photocurrent onsets in 1 M NaOH were -0.44 V for the nanorod film and -0.14 V for the pyrolysis film. The nanorod film has a linear (photocurrent)(0.5)-light intensity relationship, meaning a high charge carriers' recombination. The linear photocurrent-light intensity relationship with pyrolysis film indicates a fast charge-transfer process. Adopting pyrolysis film in the dual photoelectrode assembly resulted in zero short-circuit photocurrent due to the mismatch of the conduction band minimum of the pyrolysis film with the valence band maximum of p-GaInP2. Combining the advantages of the two should form an efficient electrode for photoelectrochemical water splitting with efficient charge transfer and a large surface area. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3489940] All rights reserved.