Investigating Water Splitting with CaFe2O4 Photocathodes by Electrochemical Impedance Spectroscopy

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Title: Investigating Water Splitting with CaFe2O4 Photocathodes by Electrochemical Impedance Spectroscopy
Authors: Díez García, María Isabel | Gómez, Roberto
Research Group/s: Grupo de Fotoquímica y Electroquímica de Semiconductores (GFES)
Center, Department or Service: Universidad de Alicante. Departamento de Química Física | Universidad de Alicante. Instituto Universitario de Electroquímica
Keywords: CaFe2O4 | P-type | Oxide | Photocathode | Water splitting | Hydrogen | Electrochemical impedance spectroscopy | Kinetic model
Knowledge Area: Química Física
Issue Date: 28-Jul-2016
Publisher: American Chemical Society
Citation: ACS Applied Materials & Interfaces. 2016, 8(33): 21387-21397. doi:10.1021/acsami.6b07465
Abstract: Artificial photosynthesis constitutes one of the most promising alternatives for harvesting solar energy in the form of fuels, such as hydrogen. Among the different devices that could be developed to achieve efficient water photosplitting, tandem photoelectrochemical cells show more flexibility and offer high theoretical conversion efficiency. The development of these cells depends on finding efficient and stable photoanodes and, particularly, photocathodes, which requires having reliable information on the mechanism of charge transfer at the semiconductor/solution interface. In this context, this work deals with the preparation of thin film calcium ferrite electrodes and their photoelectrochemical characterization for hydrogen generation by means of electrochemical impedance spectroscopy (EIS). A fully theoretical model that includes elementary steps for electron transfer to the electrolyte and surface recombination with photogenerated holes is presented. The model also takes into account the complexity of the semiconductor/solution interface by including the capacitances of the space charge region, the surface states and the Helmholtz layer (as a constant phase element). After illustrating the predicted Nyquist plots in a general manner, the experimental results for calcium ferrite electrodes at different applied potentials and under different illumination intensities are fitted to the model. The excellent agreement between the model and the experimental results is illustrated by the simultaneous fit of both Nyquist and Bode plots. The concordance between both theory and experiments allows us to conclude that a direct transfer of electrons from the conduction band to water prevails for hydrogen photogeneration on calcium ferrite electrodes and that most of the carrier recombination occurs in the material bulk. In more general vein, this study illustrates how the use of EIS may provide important clues about the behavior of photoelectrodes and the main strategies for their improvement.
Sponsor: The authors gratefully acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness through projects MAT2012-37676 and MAT2015-71727-R both cofinanced by FEDER funds.
ISSN: 1944-8244 (Print) | 1944-8252 (Online)
DOI: 10.1021/acsami.6b07465
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2016 American Chemical Society
Peer Review: si
Publisher version:
Appears in Collections:INV - GFES - Artículos de Revistas

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