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Article

Extracting Turnover Frequencies of Electron Transfer in Heterogeneous Catalysis: A Study of IrO2-TiO2 Anatase for Water Oxidation Using Ce4+ Cations

1
Surface Science and Advanced Characterizations Department, SABIC-CRD at KAUST, Thuwal 23955, Saudi Arabia
2
Department of Chemistry, University College London, London WC1H 0AJ, UK
*
Author to whom correspondence should be addressed.
Academic Editors: Stanisław Wacławek, Dionysios (Dion) D. Dionysiou, Andrzej Kudelski and Jochen A. Lauterbach
Catalysts 2021, 11(9), 1030; https://doi.org/10.3390/catal11091030
Received: 4 August 2021 / Revised: 16 August 2021 / Accepted: 23 August 2021 / Published: 26 August 2021
Within the context of electron transfer during the catalytic water oxidation reaction, the Ir-based system is among the most active. The reaction, mimicking photosynthesis II, requires the use of an electron acceptor such the Ce4+ cation. This complex reaction, involving adsorbed water at the interface of the metal cation and Ce4+, has mostly been studied in homogenous systems. To address the ambiguity regarding the gradual transformation of a homogenous system into a heterogeneous one, we prepared and studied a heterogeneous catalyst system composed of IrO2, with a mean particle size ranging from about 5 Å to 10 Å, dispersed on a TiO2 anatase support, with the objective of probing into the different parameters of the reaction, as well as the compositional changes and rates. The system was stable for many of the runs that were conducted (five consecutive runs with 0.18 M of Ce4+ showed the same reaction rate with TON > 56,000) and, equally importantly, was stable without induction periods. Extraction of the reaction rates from the set of catalysts, with an attempt to normalize them with respect to Ir loading and, therefore, to obtain turnover frequencies (TOF), was conducted. While, within reasonable deviations, the TOF numbers extracted from TPR and XPS Ir4f were close, those extracted from the particle shape (HR-STEM) were considerably larger. The difference indicates that bulk Ir atoms contribute to the electron transfer reaction, which may indicate that the reaction rate is dominated by the reorganization energy between the redox couples involved. Therefore, the normalization of reaction rates with surface atoms may lead to an overestimation of the site activity. View Full-Text
Keywords: oxygen evolution reaction; OER; Ce4+/Ce3+; IrO2/TiO2; water oxidation; scanning transmission electron microscopy (STEM); X-ray photoelectron spectroscopy (XPS Ir4f); metal clusters; iridium dispersion; turnover frequency (TOF) oxygen evolution reaction; OER; Ce4+/Ce3+; IrO2/TiO2; water oxidation; scanning transmission electron microscopy (STEM); X-ray photoelectron spectroscopy (XPS Ir4f); metal clusters; iridium dispersion; turnover frequency (TOF)
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MDPI and ACS Style

Alrushaid, M.; Nadeem, M.A.; Wahab, K.A.; Idriss, H. Extracting Turnover Frequencies of Electron Transfer in Heterogeneous Catalysis: A Study of IrO2-TiO2 Anatase for Water Oxidation Using Ce4+ Cations. Catalysts 2021, 11, 1030. https://doi.org/10.3390/catal11091030

AMA Style

Alrushaid M, Nadeem MA, Wahab KA, Idriss H. Extracting Turnover Frequencies of Electron Transfer in Heterogeneous Catalysis: A Study of IrO2-TiO2 Anatase for Water Oxidation Using Ce4+ Cations. Catalysts. 2021; 11(9):1030. https://doi.org/10.3390/catal11091030

Chicago/Turabian Style

Alrushaid, Mogbel, Muhammad A. Nadeem, Khaja A. Wahab, and Hicham Idriss. 2021. "Extracting Turnover Frequencies of Electron Transfer in Heterogeneous Catalysis: A Study of IrO2-TiO2 Anatase for Water Oxidation Using Ce4+ Cations" Catalysts 11, no. 9: 1030. https://doi.org/10.3390/catal11091030

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