title: Nano-Photoelectrochemical Cell Arrays with Spatially Isolated Oxidation and Reduction Channels.
abstract: Photoelectrochemical conversion of solar energy is explored for many diverse applications but suffers from poor efficiencies due to limited solar absorption, inadequate charge carrier separation, redox half-reactions occurring in close proximity, and/or long ion diffusion lengths. We have taken a drastically different approach to the design of photoelectrochemical cells (PECs) to spatially isolate reaction sites at the nanoscale to different materials and flow channels, suppressing carrier recombination and back-reaction of intermediates while shortening ion diffusion paths and, importantly, avoiding mixed product generation. We developed massively parallel nano-PECs composed of an array of open-ended carbon nanotubes (CNTs) with photoanodic reactions occurring on the outer walls, uniformly coated with titanium dioxide (TiO2), and photocathodic reactions occurring on the inner walls, decorated with platinum (Pt). We verified the redox reaction isolation by demonstrating selective photodeposition of manganese oxide on the outside and silver on the inside of the TiO2/CNT/Pt nanotubes. Further, the nano-PECs exhibit improved solar absorption and efficient charge transfer of photogenerated carriers to their respective redox sites, leading to a 1.8% photon-to-current conversion efficiency (a current density of 4.2 mA/cm2) under white-light irradiation. The design principles demonstrated can be readily adapted to myriads of photocatalysts for cost-effective solar utilization.
authors.affiliation: Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213-3890, United States.
authors.forename: Hang-Ah
authors.initials: HA
authors.lastname: Park
authors.affiliation: Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213-3890, United States.
authors.forename: Siyuan
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213-3890, United States.
authors.forename: Youngseok
authors.initials: Y
authors.lastname: Oh
authors.affiliation: Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213-3890, United States.
authors.forename: Paul A
authors.identifier: 0000-0001-7106-0017
authors.initials: PA
authors.lastname: Salvador
authors.affiliation: Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213-3890, United States.
authors.forename: Gregory S
authors.identifier: 0000-0002-9671-3034
authors.initials: GS
authors.lastname: Rohrer
authors.affiliation: Department of Materials Science and Engineering, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213-3890, United States.
authors.forename: Mohammad F
authors.identifier: 0000-0001-9253-3709
authors.initials: MF
authors.lastname: Islam
keywords: TiO2; carbon nanotubes; photocatalyst; photoelectrochemical cell; water splitting