A dual-carrier adsorbate-modulated surface conductance model better captures the thermal dependence of conductance in Ti
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A dual‑carrier adsorbate‑modulated surface conductance model better captures the thermal dependence of conductance in TiO2 and MoO3 powders than an inter‑grain hopping model Karl Sohlberg1 Received: 15 June 2020 / Accepted: 4 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Non-Arrhenius thermal dependence of surface conductance has previously been observed in the transition-metal oxides T iO2 and M oO3. Through the application of thermochemical modeling, kinetic modeling, and analysis of equivalent resistance networks, it is shown that a dual-charge-carrier model in which the adsorbate surface coverage is modulated by bi-Langmuir adsorption is better able to capture the thermal dependence of surface conductance in these materials than a model based on the hypothesis that conductance is governed by bottlenecks to charge hopping between grains. Adsorption energies predicted by the dual-charge-carrier model are in agreement with estimates of the same from published first-principles calculations. Particle-size dependence of the conductance likely arises from the increasing importance of surface processes to charge transport with decreasing particle size, not from an increase in the number of inter-particle contacts. Keywords Titania · Molybdena · Catalytic metal oxides · Surface conductance · Modeling
Introduction The surface conductance of metal oxides in the presence of gas adsorption is of wide importance. For example, if gas adsorption on a material produces a change in the surface conductance, the material may potentially be used as the sensing component Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1114 4-020-01833-5) contains supplementary material, which is available to authorized users. * Karl Sohlberg [email protected] 1
Department of Chemistry, and Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA
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Reaction Kinetics, Mechanisms and Catalysis
of a gas detector. Such sensors have been used to detect humidity, combustibles, toxins and oxygen [1, 2]. In addition, surface conductance is a valuable tool to investigate the catalytic behavior of oxide materials because adsorption/desorption of gases is frequently accompanied by charge transfer, which plays a central role in governing catalytic activity [3]. In practice, surface conductance often serves as a proxy measurement for catalytic activity. Although the measurement of surface conductance is a macroscopic technique, its magnitude depends on the atomic-scale structures present on the surface of a material. Mathematical models that connect atomic-scale surface structure to surface conductance therefore provide a way to understand the surface structure of heterogeneous catalytic materials under realistic operating conditions [4, 5]. In particular, the thermal dependence of surface conductance contains information about the prevalence of surface-adsorbed species [6]. Strikingly non-Arrhenius thermal dependen
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