title: Hydrogen-treated TiO2 nanowire arrays for photoelectrochemical water splitting.
abstract: We report the first demonstration of hydrogen treatment as a simple and effective strategy to fundamentally improve the performance of TiO(2) nanowires for photoelectrochemical (PEC) water splitting. Hydrogen-treated rutile TiO(2) (H:TiO(2)) nanowires were prepared by annealing the pristine TiO(2) nanowires in hydrogen atmosphere at various temperatures in a range of 200-550 °C. In comparison to pristine TiO(2) nanowires, H:TiO(2) samples show substantially enhanced photocurrent in the entire potential window. More importantly, H:TiO(2) samples have exceptionally low photocurrent saturation potentials of -0.6 V vs Ag/AgCl (0.4 V vs RHE), indicating very efficient charge separation and transportation. The optimized H:TiO(2) nanowire sample yields a photocurrent density of ∼1.97 mA/cm(2) at -0.6 V vs Ag/AgCl, in 1 M NaOH solution under the illumination of simulated solar light (100 mW/cm(2) from 150 W xenon lamp coupled with an AM 1.5G filter). This photocurrent density corresponds to a solar-to-hydrogen (STH) efficiency of ∼1.63%. After eliminating the discrepancy between the irradiance of the xenon lamp and solar light, by integrating the incident-photon-to-current-conversion efficiency (IPCE) spectrum of the H:TiO(2) nanowire sample with a standard AM 1.5G solar spectrum, the STH efficiency is calculated to be ∼1.1%, which is the best value for a TiO(2) photoanode. IPCE analyses confirm the photocurrent enhancement is mainly due to the improved photoactivity of TiO(2) in the UV region. Hydrogen treatment increases the donor density of TiO(2) nanowires by 3 orders of magnitudes, via creating a high density of oxygen vacancies that serve as electron donors. Similar enhancements in photocurrent were also observed in anatase H:TiO(2) nanotubes. The capability of making highly photoactive H:TiO(2) nanowires and nanotubes opens up new opportunities in various areas, including PEC water splitting, dye-sensitized solar cells, and photocatalysis.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064 United States.
authors.forename: Gongming
authors.initials: G
authors.lastname: Wang
authors.forename: Hanyu
authors.initials: H
authors.lastname: Wang
authors.forename: Yichuan
authors.initials: Y
authors.lastname: Ling
authors.forename: Yuechao
authors.initials: Y
authors.lastname: Tang
authors.forename: Xunyu
authors.initials: X
authors.lastname: Yang
authors.forename: Robert C
authors.initials: RC
authors.lastname: Fitzmorris
authors.forename: Changchun
authors.initials: C
authors.lastname: Wang
authors.forename: Jin Z
authors.initials: JZ
authors.lastname: Zhang
authors.forename: Yat
authors.initials: Y
authors.lastname: Li
mesh_terms: D004563:Electrochemistry / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry*; D036103:Nanotechnology; D053770:Nanowires / Q000737:chemistry*; D010316:Particle Size; D055668:Photochemical Processes / Q000528:radiation effects*; D012834:Silver / Q000737:chemistry; D018030:Silver Compounds / Q000737:chemistry; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D018030:Silver Compounds; D014867:Water; C009495:titanium dioxide; D012834:Silver; D006859:Hydrogen; D014025:Titanium; C037548:silver chloride