title: Efficient solar water-splitting using a nanocrystalline CoO photocatalyst.
abstract: The generation of hydrogen from water using sunlight could potentially form the basis of a clean and renewable source of energy. Various water-splitting methods have been investigated previously, but the use of photocatalysts to split water into stoichiometric amounts of H2 and O2 (overall water splitting) without the use of external bias or sacrificial reagents is of particular interest because of its simplicity and potential low cost of operation. However, despite progress in the past decade, semiconductor water-splitting photocatalysts (such as (Ga1-xZnx)(N1-xOx)) do not exhibit good activity beyond 440 nm (refs 1,2,9) and water-splitting devices that can harvest visible light typically have a low solar-to-hydrogen efﬁciency of around 0.1%. Here we show that cobalt(II) oxide (CoO) nanoparticles can carry out overall water splitting with a solar-to-hydrogen efficiency of around 5%. The photocatalysts were synthesized from non-active CoO micropowders using two distinct methods (femtosecond laser ablation and mechanical ball milling), and the CoO nanoparticles that result can decompose pure water under visible-light irradiation without any co-catalysts or sacrificial reagents. Using electrochemical impedance spectroscopy, we show that the high photocatalytic activity of the nanoparticles arises from a significant shift in the position of the band edge of the material.
authors: Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA.
authors: Longb
authors: L
authors: Liao
authors: 1] Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA [2] College of Electronics & Information Engineering, Sichuan University, Chengdu 610064, China.
authors: Qiuhui
authors: Q
authors: Zhang
authors: Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA.
authors: Zhihua
authors: Z
authors: Su
authors: Materials Engineering Program, University of Houston, Houston, Texas 77204, USA.
authors: Zhongzheng
authors: Z
authors: Zhao
authors: Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA.
authors: Yanan
authors: Y
authors: Wang
authors: Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA.
authors: Yang
authors: Y
authors: Li
authors: Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA.
authors: Xiaoxiang
authors: X
authors: Lu
authors: Carl Zeiss Microscopy, LLC, One Zeiss Drive, Thornwood, New York 10594, USA.
authors: Dongguang
authors: D
authors: Wei
authors: College of Electronics & Information Engineering, Sichuan University, Chengdu 610064, China.
authors: Guoying
authors: G
authors: Feng
authors: Ingram School of Engineering, and Materials Science, Engineering and Commercialization, Texas State University, San Marcos, TX 78666, USA.
authors: Qingkai
authors: Q
authors: Yu
authors: Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
authors: Xiaojun
authors: X
authors: Cai
authors: Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Jimin
authors: J
authors: Zhao
authors: Department of Physics, University of Houston, Houston, Texas 77204, USA.
authors: Zhifeng
authors: Z
authors: Ren
authors: Department of Physics, Sam Houston State University, Huntsville, Texas 77341, USA.
authors: Hui
authors: H
authors: Fang
authors: College of Engineering Technology, University of Houston, Houston, Texas 77204, USA.
authors: Francisco
authors: F
authors: Robles-Hernandez
authors: Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
authors: Steven
authors: S
authors: Baldelli
authors: 1] Department of Electrical & Computer Engineering, University of Houston, Houston, Texas 77204, USA [2] Materials Engineering Program, University of Houston, Houston, Texas 77204, USA [3] Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
authors: Jiming
authors: J
authors: Bao