Hierarchically Porous Calcium-containing Manganese Dioxide Nanorod Bundles with Superior Photoelectrochemical Activity

Authors

  • Dr. Yan-Gu Lin,

    Corresponding author
    1. National Synchrotron Radiation Research Center, Hsinchu 30076 (Taiwan)
    • Yan-Gu Lin, National Synchrotron Radiation Research Center, Hsinchu 30076 (Taiwan)===

      Li-Chyong Chen, Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617 (Taiwan)===

      Yu-Kuei Hsu, Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien 97401 (Taiwan)===

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  • Ying-Chu Chen,

    1. Karlsruhe Institute of Technology, Institut für Anorganische Chemie, Engesserstraße 15,D-76131 Karlsruhe (Germany)
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  • Dr. Jeffrey T. Miller,

    1. Chemical Sciences and Engineering Division, Argonne National Laboratory, IL 60439 (USA)
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  • Dr. Li-Chyong Chen,

    Corresponding author
    1. Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617 (Taiwan)
    • Yan-Gu Lin, National Synchrotron Radiation Research Center, Hsinchu 30076 (Taiwan)===

      Li-Chyong Chen, Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617 (Taiwan)===

      Yu-Kuei Hsu, Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien 97401 (Taiwan)===

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  • Dr. Kuei-Hsien Chen,

    1. Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617 (Taiwan)
    2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617 (Taiwan)
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  • Prof. Yu-Kuei Hsu

    Corresponding author
    1. Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien 97401 (Taiwan)
    • Yan-Gu Lin, National Synchrotron Radiation Research Center, Hsinchu 30076 (Taiwan)===

      Li-Chyong Chen, Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617 (Taiwan)===

      Yu-Kuei Hsu, Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien 97401 (Taiwan)===

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Abstract

Bioinspired by the composition of the oxygen evolving complex and the fundamental role of calcium for catalysis, we have synthesized calcium–manganese oxides as promising photoelectrodes. We report the first demonstration of hierarchically porous Ca-containing MnO2 nanorod (NR) bundles as visible-light-sensitive photofunctional nanoelectrodes to fundamentally improve the performance of MnO2 for photoelectrochemical hydrogen generation. A substantial amount of Ca (up to 7.8 atom %) can be in situ incorporated into the MnO2 lattice by a simple electroplating technique because of the exceptionally small feature sizes of several nanorods. The maximum photocurrent could be successfully achieved as high as 0.42 mA cm−2, which is the best value for a MnO2 photoanode to date. Significantly, Ca-containing MnO2 photoanodes illustrated striking photoelectrochemical activity in response to visible light with a high incident photon-to-current conversion efficiency of 7 % at a monochromatic wavelength of 450 nm. The improvement in photoactivity of photoelectrochemical response may be attributed to the enhanced visible-light absorption, increased charge-carrier densities, and large contact area with electrolyte owing to the synergistic effects of Ca incorporation and specific mesopore networks, thus contributing to photocatalysis. The new design of constructing highly photoactive Ca-containing MnO2 nanorod bundles sheds light on developing high-efficiency photoelectrodes for solar hydrogen generation.

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