The mechanism of concentric HfO2/Co3O4/TiO2 nanotubes investigated by intensity modulated photocurrent spectroscopy (IMPS) and electrochemical impedance spectroscopy (EIS) for photoelectrochemical activity
| Autor: | Gaetano Granozzi, Xiaochen Huai, Ran Lu, Yu Zhao, Yunhan Ling, Leonardo Girardi, Shang Gao, Zhengjun Zhang, Gian Andrea Rizzi |
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| Rok vydání: | 2019 |
| Předmět: |
Materials science
Passivation IMPS Analytical chemistry 02 engineering and technology 010402 general chemistry 01 natural sciences Capacitance NTs Co Depletion region TiO General Materials Science Electrical and Electronic Engineering Spectroscopy Photocurrent EIS Renewable Energy Sustainability and the Environment business.industry HfO 021001 nanoscience & nanotechnology 0104 chemical sciences Dielectric spectroscopy Semiconductor Equivalent circuit 3 O 4 2 0210 nano-technology business |
| Zdroj: | Nano Energy. 65:104020 |
| ISSN: | 2211-2855 |
| Popis: | In this work, we describe the preparation and photoelectrochemical (PEC) properties of concentric HfO2/Co3O4/TiO2 nanotubes (NTs). From a methodological point of view, we demonstrated, for the first time, that intensity modulated photocurrent spectroscopy (IMPS) and electrochemical impedance spectroscopy (EIS) efficiently complement and can be highly valuable to optimize PEC water-splitting devices. We verified that the CSC and CH values (the capacitance of space charge region and Helmholtz layer, derived from a phenomenological equivalent circuits model, ECM) are of similar magnitude and that the CH can be affected by applied bias, the nature of the catalytic material and the passivation layer. The calculated CH/(CH + CSC) are in agreement with the high frequency intercept (HFI) derived by the IMPS experimental data. The charge transfer efficiencies (ղtr) were obtained from the IMPS and ECM data: the ղtr values for HfO2/Co3O4/TiO2-NTs increased to 80.4% (0 V vs Ag/AgCl) compared to those in Co3O4/TiO2-NTs (56.9%,0 V vs Ag/AgCl) and in TiO2-NT (25.6%, 0 V vs Ag/AgCl). We proved that the excellent PEC properties of HfO2/Co3O4/TiO2-NTs are due to i) the band alignment between small bad gap of Co3O4 and TiO2 semiconductors, ii) increased hole transfer efficiency ղtr caused by excellent catalytic properties of Co3O4 and iii) the passivation effect on surface defects of a HfO2 layer with appropriate thickness. |
| Databáze: | OpenAIRE |
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