The photocathodic behavior of hierarchical ZnO/hematite hetero nanoarchitectures
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The photocathodic behavior of hierarchical ZnO/hematite hetero nanoarchitectures Debajeet K. Boraa) Laboratory for High Performance Ceramics, Empa. Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland (Received 14 December 2015; accepted 25 February 2016)
The photocathodic current density of ZnO/hematite hetero nanoarchitectures electrode has been reported in the current investigation. The electrode was obtained with a cheap and two-step hydrothermal functionalization of pristine silicon doped hematite film. The optical, structural, and morphological properties of the electrodes have been studied in detail and it is found that the ZnO functionalization of hematite changes its crystallographic properties by decreasing the Bragg peak intensity ratio for (104) planes. The morphology obtained in this case is unique in the sense that it does not cover the original hematite film and is formed in an isolated manner. Finally, employing a qualitative energy band gap model for mixed metal oxides energy levels has identified the photocathodic properties of the electrode. Here it is found that the photocathodic properties of the electrode are much higher when an electron transfer takes place from the conduction band of ZnO into the electrolyte while hole generated in ZnO is transferred back to hematite but it also degrades the structures after running photoanodic current density sweep. That points to the decrease of water oxidation behavior of hematite in conjunction with ZnO. I. INTRODUCTION
The photoelectrochemical water splitting is an alternative technique developed to meet the global oil demand crisis back in 1972 by Fujishima and Honda with TiO2 n-type semiconductor.1 Metal oxide electrodes have been widely used in this technique due to broad ranges of interesting functionalities: ability to harvest visible solar photons, stability in neutral and basic environment, environmentally friendly, and abundance in the Earth’s crust as mineral deposit. The photoelectrochemical properties of metal oxide semiconductor electrode are very significant from the perspectives of the efficiency of the electrode for solar fuel generation. We basically take two examples here: photoanodic current density and photocathodic current density. Here, the former originated due to the water oxidation reaction while the latter from water reduction reaction. In that respect, several reports are being made in the current mandate about the photoanodic current density and efficiencies of the various metal oxide photoelectrodes. But all of these electrodes reported in nanoparticulate form and structurally tunes into nanowire, nanorod, nanoflower etc. But the photoelectrochemical properties of this kind of electrode in hybrid form have not been explored widely. Hybrid here does not Contributing Editor: Heli Wang a) Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2016.107 J. Mater. Res., 2016
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