Paper SE+EN-FrM6
Fabrication of Water-Splitting Photocatalytic Electrodes by "Particle-Transfer" Processing
Friday, November 1, 2013, 10:00 am, Room 203 C
| Session: |
Surface Engineering for Energy Conversion and Harvesting |
| Presenter: |
T. Minegishi, The University of Tokyo, Japan |
| Authors: |
T. Minegishi, The University of Tokyo, Japan
T. Yamada, The University of Tokyo, Japan
N. Nishimura, The University of Tokyo, Japan
J. Kubota, The University of Tokyo, Japan
K. Domen, The University of Tokyo, Japan
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| Correspondent: |
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We developed a process of fabricating planer electrodes from photocatalytic powder, and observed a high photo-electrocatalytic activity of LaTiO2N for H2O splitting in aqueous solutions. This technology, hereafter we call the "particle transfer (PT) method", is applicable for various kinds of photoactive semicondicting powder catalysts. We first prepare powder catalysts with a maximum grain size of a few μm. A thin layer of the powder (thickness < 0.5 mm) is spread on a planer substrate using a suspension in organic solvent. Then this layer is over-coated with a thin Nb layer and then a thick Ti layer by means of radio-frequency magnetron sputtering. The metallic Nb layer makes a good mechanical and electric contact between the grains and the Ti layer, which serves a a good electric conductor. Finally this multilayer is peeled off onto another glass substrate using an adhesive (such as epoxy resin), and a conductive electrode covered by the catalytic grains is completed. In this work we used LaTiO2N powder loaded with 5 wt% IrO2. The LaTiO2N powder was synthesized by NH3 flow gas treatment at 1223 K on La2Ti2O7 prepared by a molten salt method [1]. The purity of LaTiO2N was checked by X-ray diffraction. This material exhibits absorption of visible light shorter than 600 nm and can potentially utilize about a half of the solar energy. The cross sectional view of this electrode by EDX-aided scanning electron microscopy indicates the left-over grains of LaTiO2N mostly in firm contact with the Nb layer laminating the Ti conducting layer. The grains formed monolayer in most of places, laterally interlocking one another.
This electrode was subjected to potential-versus-current measurement in 1 M Na2SO4 solution (pH 13.5) under illumination of AM 1.5D solar simulator. The anodic photocurrent reached ~ 2 mA cm-2 at 1.0 V vs RHE, which is ~100 times higher than that on a LaTiO2N powder-coated conductive glass substrate [2]. This is attributed to the well-controlled grain-substrate contact by the Nb layer. Similar effects were observed by replacing Nb with Ta, Zr or Ti. Furthermore, the gas products (O2 from this electrode, H2 from the counter Pt electrode) was detected in two-vessel electrochemical system separated by a glass filter. From the PT LaTiO2N electrode, O2 gas bubbled out at a rate (~ 0.1 μmol cm-2 min-1) exactly matching the photo-anodic current. Evidently, the PT method makes a breakthrough in the efficiency of solar hydrogen generation in water splitting, making use of the diversity of semiconductor powder catalysts.
[1] P. A. Fuiere et al., J. Am. Ceram. Soc. 74 (1991) 2876.
[2] H. Hashiguchi et al., Bull. Chem. Soc. Jpn. 82 (2009) 401.