title: Significantly Enhanced Visible Light Photoelectrochemical Activity in TiO₂ Nanowire Arrays by Nitrogen Implantation.
abstract: Titanium oxide (TiO2) represents one of most widely studied materials for photoelectrochemical (PEC) water splitting but is severely limited by its poor efficiency in the visible light range. Here, we report a significant enhancement of visible light photoactivity in nitrogen-implanted TiO2 (N-TiO2) nanowire arrays. Our systematic studies show that a post-implantation thermal annealing treatment can selectively enrich the substitutional nitrogen dopants, which is essential for activating the nitrogen implanted TiO2 to achieve greatly enhanced visible light photoactivity. An incident photon to electron conversion efficiency (IPCE) of ∼10% is achieved at 450 nm in N-TiO2 without any other cocatalyst, far exceeding that in pristine TiO2 nanowires (∼0.2%). The integration of oxygen evolution reaction (OER) cocatalyst with N-TiO2 can further increase the IPCE at 450 nm to ∼17% and deliver an unprecedented overall photocurrent density of 1.9 mA/cm(2), by integrating the IPCE spectrum with standard AM 1.5G solar spectrum. Systematic photoelectrochemical and electrochemical studies demonstrated that the enhanced PEC performance can be attributed to the significantly improved visible light absorption and more efficient charge separation. Our studies demonstrate the implantation approach can be used to reliably dope TiO2 to achieve the best performed N-TiO2 photoelectrodes to date and may be extended to fundamentally modify other semiconductor materials for PEC water splitting.
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.|‡California Nanosystems Institute, University of California, Los Angeles, California 90095, United States.
authors.forename: Gongming
authors.initials: G
authors.lastname: Wang
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.|§Department of Physics, Hubei Nuclear Solid Physics Key Laboratory and Center for Ion Beam Application, Wuhan University, Wuhan 430072, People's Republic of China.
authors.forename: Xiangheng
authors.initials: X
authors.lastname: Xiao
authors.affiliation: §Department of Physics, Hubei Nuclear Solid Physics Key Laboratory and Center for Ion Beam Application, Wuhan University, Wuhan 430072, People's Republic of China.
authors.forename: Wenqing
authors.initials: W
authors.lastname: Li
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Lin
authors.affiliation: ∥Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States.
authors.forename: Zipeng
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: ⊥School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Chi
authors.initials: C
authors.lastname: Chen
authors.affiliation: ‡California Nanosystems Institute, University of California, Los Angeles, California 90095, United States.|∥Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Wang
authors.affiliation: ∥Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States.
authors.forename: Yongjia
authors.initials: Y
authors.lastname: Li
authors.affiliation: ∥Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Huang
authors.affiliation: ⊥School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
authors.forename: Ling
authors.initials: L
authors.lastname: Miao
authors.affiliation: §Department of Physics, Hubei Nuclear Solid Physics Key Laboratory and Center for Ion Beam Application, Wuhan University, Wuhan 430072, People's Republic of China.
authors.forename: Changzhong
authors.initials: C
authors.lastname: Jiang
authors.affiliation: ‡California Nanosystems Institute, University of California, Los Angeles, California 90095, United States.|∥Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States.
authors.forename: Yu
authors.initials: Y
authors.lastname: Huang
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.|‡California Nanosystems Institute, University of California, Los Angeles, California 90095, United States.
authors.forename: Xiangfeng
authors.initials: X
authors.lastname: Duan
mesh_terms: D002384:Catalysis; D055664:Electrochemical Techniques; D008027:Light; D008958:Models, Molecular; D053770:Nanowires / Q000737:chemistry* / Q000528:radiation effects*; D009584:Nitrogen / Q000737:chemistry*; D055668:Photochemical Processes; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; C009495:titanium dioxide; D014025:Titanium; D009584:Nitrogen
keywords: TiO2 nanowires; nitrogen doping; nitrogen implantation; photoelectrochemical water splitting; visible light photoactivity