title: Vertically oriented Ti-Fe-O nanotube array films: toward a useful material architecture for solar spectrum water photoelectrolysis.
abstract: In an effort to obtain a material architecture suitable for high-efficiency visible spectrum water photoelectrolysis, herein we report on the fabrication and visible spectrum (380-650 nm) photoelectrochemical properties of self-aligned, vertically oriented Ti-Fe-O nanotube array films. Ti-Fe metal films of variable composition, iron content ranging from 69% to 3.5%, co-sputtered onto FTO-coated glass are anodized in an ethylene glycol + NH4F electrolyte. The resulting amorphous samples are annealed in oxygen at 500 degrees C, resulting in nanotubes composed of a mixed Ti-Fe-O oxide. Some of the iron goes into the titanium lattice substituting titanium ions, and the rest either forms alpha-Fe2O3 crystallites or remains in the amorphous state. Depending upon the Fe content, the band gap of the resulting films ranges from about 380 to 570 nm. The Ti-Fe oxide nanotube array films are utilized in solar spectrum water photoelectrolysis, demonstrating 2 mA/cm2 under AM 1.5 illumination with a sustained, time-energy normalized hydrogen evolution rate by water splitting of 7.1 mL/W.hr in a 1 M KOH solution with a platinum counter electrode under an applied bias of 0.7 V. The surface morphology, structure, elemental analysis, optical, and photoelectrochemical properties of the Ti-Fe oxide nanotube array films are considered.
authors.affiliation: Department of Electrical Engineering and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Gopal K
authors.initials: GK
authors.lastname: Mor
authors.forename: Haripriya E
authors.initials: HE
authors.lastname: Prakasam
authors.forename: Oomman K
authors.initials: OK
authors.lastname: Varghese
authors.forename: Karthik
authors.initials: K
authors.lastname: Shankar
authors.forename: Craig A
authors.initials: CA
authors.lastname: Grimes
mesh_terms: D003460:Crystallization / Q000379:methods; D004572:Electrolysis / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008567:Membranes, Artificial; D008968:Molecular Conformation; D036103:Nanotechnology / Q000379:methods*; D043942:Nanotubes / Q000737:chemistry* / Q000648:ultrastructure; D010100:Oxygen / Q000737:chemistry; D010316:Particle Size; D010777:Photochemistry / Q000379:methods*; D012993:Solar Energy; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D046911:Macromolecular Substances; D008567:Membranes, Artificial; D014867:Water; D006859:Hydrogen; D014025:Titanium; D007501:Iron; D010100:Oxygen