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J. Electrochem. Sci. Technol > Volume 2(4); 2011 > Article
Journal of Electrochemical Science and Technology 2011;2(4):187-192.
DOI: https://doi.org/10.5229/JECST.2011.2.4.187   
Photoelectrochemical Water Oxidation Using ZnO Nanorods Coupled with Cobalt-Based Catalysts
Tae-Hwa Jeon, Sung-Kyu Choi, Hye-Won Jeong, Seung-Do Kim, Hyun-Woong Park
Department of Energy Science, Kyungpook National University;Department of Physics, Kyungpook National University;School of Energy Engineering, Kyungpook National University;Deptartment of Environmental Science and Biotechnology, Hallym University;School of Energy Engineering, Kyungpook National University;
Abstract
Photoelectrochemical performances of ZnO electrodes are enhanced by coupling with cobalt-based catalyst (CoPi) in phosphate electrolyte (pH 7). For this study, hexagonal pillar-shaped ZnO nanorods are grown on ZnO electrodes through a chemical bath deposition, onto which CoPi is deposited with different photodeposition times (10-30 min). A scanning electron microscopic study indicates that CoPi deposition does not induce any change of ZnO morphology and an energy-dispersive X-ray spectroscopic analysis shows that inorganic phosphate ions (Pi) exist on ZnO surface. Bare ZnO electrodes generate the current of ca. $0.36mA/cm^2$ at a bias potential of 0.5 V vs. SCE, whereas ZnO/CoPi (deposited for 10 min) has ca. 50%-enhanced current ($0.54mW/cm^2$) under irradiation of AM 1.5G-light ($400mW/cm^2$). The excess loading of CoPi on ZnO results in decrease of photocurrents as compared to bare ZnO likely due to limited electrolyte access to ZnO and/or CoPi-mediated recombination of photogenerated charge carriers. The primary role of CoPi is speculated to trap the photogenerated holes and thereby oxidize water into molecular oxygen via an intervalency cycle among Co(II), Co(III), and Co(IV).
Key Words: Artificial photosynthesis, Solar hydrogen, Electrocatalyst, Water splitting, Semiconductors


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