2019-Sustainable Industrial Processing Summit
SIPS2019 Volume 10: Vayenas Intl. Symp. / Physical Chemistry and its applications for sustainable development
| Editors: | Vayenas Intl. Symp. / Physical Chemistry and its applications for sustainable development Edited by: F. Kongoli, E. Aifantis, C. Cavalca, A. de Lucas Consuegra, A. Efstathiou, M. Fardis, D. Grigoriou, A. Lemonidou, S.G. Neophytides, Y. Roman, M. Stoukides, M. Sullivan, P. Vernoux, X. Verykios, I. Yentekakis |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2019 |
| Pages: | 249 pages |
| ISBN: | 978-1-989820-09-4 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Novel Method for Determining Series of Elementary Steps in Oxygen Reduction Processes Using Isotope Exchange.
Ilan Riess1;1TECHNION ISRAEL INSTITUTE OF TECHNOLOGY FACULTY OF PHYSICS, Haifa, Israel;
Type of Paper: Keynote
Id Paper: 30
Topic: 53
Abstract:
A novel method is discussed for determining series of elementary steps in the reduction process of oxygen on an oxide.[1,2] The method is based on exposure of the oxide, first to 16O2, and then to 18O2 while monitoring the rate at which 16O18O molecules are generated and evaporate into the gas stream, under short time conditions. The parameters to be changed are oxygen partial pressure, P(O2) (being the same for both isotopes) and acceptor doping level [A] of the oxide. 18O2 can be applied in the form of a pulse or a step function. The rate of 16O18O generation is shown to depend on P(O2)m1 [A] m2. Another parameter that can be determined is J0, the rate of the forward reaction in the slow step of the series which depends on P(O2)m3 [A] m4. The indices {m1,m2, m3, m4} are, in most cases, typical for a particular series of elementary steps. The series to be identified consist of fast steps ending with a relative slow one. This method is then different from the one based on the time dependence of the concentrations of 16O2, 16O18O and 18O2 in the gas phase.[3,4] The method is quite sensitive and even changing the source for electrons from the valence band to the conduction band changes the value of the exponents {m1,…,m4}.
The analysis assumes that the dependence of the concentrations of point defects (oxygen vacancies and electrons) in the outer most layer of the oxide on P(O2) and [A], is known. The method was applied so far under the conditions that the P(O2) and [A] dependence is the same as in the deep, neutral bulk. This is shown to be indeed the case under many prevailing conditions.[5] Other P(O2) and [A] dependence of the concentrations of point defects in the outer most layer of the oxide bulk are also presented.[5] Thus it is possible to determine series of elementary steps on all type of oxides which are undoped or acceptor doped.
The method is not limited to oxygen isotope exchange and can readily be extended to other isotopes e.g. 35Cl2 and 37Cl2 exchange. Exchange of H2 and D2 requires special attention due to the mass effect on the chemistry of hydrogen and we show how to cope with it.[2]
Keywords:
Electrochemistry; Heterogeneous catalysis; Solid electrolyte;References:
1. I. Riess, Solid State Ionics, 280 (2015) 51.2. I. Riess, Solid State Ionics, 302 (2017) 7.
3. K. Klier et al. J. Catal. 2 (1963) 479.
4. G.K. Boreskov, Adv. Catal. 15, (1964) 285.
5. I. Riess, Solid State Ionics, 329 (2019) 95.