Highly Stable Water Splitting on Oxynitride TaON Photoanode System Under Visible Light Irradiation

Catalysis Research Center, Hokkaido University, North 21, West 10, Sapporo 001-0021, Japan.
Journal of the American Chemical Society (Impact Factor: 12.11). 04/2012; 134(16):6968-71. DOI: 10.1021/ja302059g
Source: PubMed


Highly stable photoelectrochemical water splitting is demonstrated for the first time on a tantalum oxynitride (TaON) photoanode under visible light irradiation. Highly dispersed CoO(x) nanoparticles on the TaON photoanode efficiently scavenge photogenerated holes and effectively suppress self-oxidative deactivation of the TaON surface, resulting in a stable photocurrent. The use of highly dispersed CoO(x) cocatalyst on TaON together with phosphate solutions significantly increased the photocurrent due to the formation of a cobalt/phosphate phase. This enabled us to stably split water into H(2) and O(2) under visible light irradiation at a relatively low applied bias (0.6 V vs Pt counter electrode).

Download full-text


Available from: Ryu Abe, Oct 09, 2014
77 Reads
  • Source
    • "This sustainable method of hydrogen production needs to integrate solar light absorber and water electrolyser into a single photoelectrode [2]. Since the pioneering report of photo water-splitting using TiO 2 by Fujishima and Honda in 1972 [3], many semiconductors, such as bismuth vanadate (BiVO 4 ), hematile (-Fe 2 O 3 ), tantalum oxynitride (TaON) and tantalum nitride (Ta 3 N 5 ) etc., have been developed and show high efficiencies in photo-induced water cleavage [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]. Due to its chemical stability, high photo catalytic activity, earth abundance , low cost and nontoxicity, TiO 2 still is the most promising photo-catalyst to split water into hydrogen and oxygen. "
    [Show abstract] [Hide abstract]
    ABSTRACT: TiO2 nanotube arrays were prepared by a modified two-step anodization, and the effects of annealing temperature and cooling manners on the photoelectrochemical water-splitting performance of TiO2 nanotube arrays were investigated. The results showed that higher annealing temperature and faster cooling rate resulted in higher solar conversion efficiency. TiO2 nanotube arrays annealed at 650 degrees C with oil quenching showed maximum solar conversion efficiency of 1.75% under simulated solar illumination. This superior photoelectrochemical water-splitting performance was attributed to high crystallinity by elevated annealing temperature, pure anatase phase and thin barrier layer due to oil quenching, as well as the carbon doping during anodization in organic electrolyte.
    Applied Surface Science 09/2014; 313:633-639. DOI:10.1016/j.apsusc.2014.06.035 · 2.71 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Photoelectrochemical water splitting is one of many approaches being studied to harvest sunlight and produce renewable H2. Tantalum nitride (Ta3N5) is a promising photoanode candidate as its band edges straddle the water redox potentials and it absorbs a large portion of the solar spectrum. However, reported photocurrents for this material remain far from the theoretical maximum. Previous results indicate Ta3N5 may be hindered by charge transport limitations attributed to poor bulk charge transport, charge transport across grain boundaries, and/or charge transfer across the interface at the back contact. The primary goal of this work was to study these mechanisms, especially bulk hole and electron transport, to determine which processes limit device efficiency. Crystalline thin films (60–780 nm) of Ta3N5 (Eg = 2.1 eV) on Ta foils were synthesized by oxidation of Ta metal in air at 550 °C and subsequent nitridation in NH3 at 900 °C. Scanning electron microscopy revealed that thermal stresses and differences in the density of the phases resulted in the formation of porous, textured films with high surface area. Films were characterized by their photon absorption, crystal grain size, and electrochemically active surface area. Trends in photoactivity as a function of film thickness under broadband illumination as well as in the incident photon-to-current efficiency revealed that minority charge carrier (hole) and majority carrier (electron) transport both play important roles in dictating photoconversion efficiency in Ta3N5 films.
    The Journal of Physical Chemistry C 07/2012; 116(30):15918–15924. DOI:10.1021/jp3041742 · 4.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel, highly efficient, and stable water oxidation catalyst was prepared by a pH-controlled adsorption of Co(II) on ∼10 nm diameter silica nanoparticles. A lower limit of ∼300 s(-1) per cobalt atom for the catalyst turnover frequency in oxygen evolution was estimated, which attests to a very high catalytic activity. Electron microscopy revealed that cobalt is adsorbed on the SiO(2) nanoparticle surfaces as small (1-2 nm) clusters of Co(OH)(2). This catalyst is optically transparent over the entire UV-vis range and is thus suitable for mechanistic investigations by time-resolved spectroscopic techniques.
    Journal of the American Chemical Society 08/2012; 134(35):14275-8. DOI:10.1021/ja304030y · 12.11 Impact Factor
Show more