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Mobile proton and protonic species. A historical view of their identification and outstanding questions -The potential of vibrational spectroscopy, underused methods?

Résumé

Since the discovery of the 'wandering proton' by Beintema in 1936 in uranium phosphate hydrate (HUP)1, the attention paid to the search for solids with high proton conductivity is at first rare and then correlates with variations oil prices after the first oil crisis in 1975.2 The objective was to discover a stable solid in a range of temperature making it possible to avoid having to resort to expensive electrodes to produce fuel cells, electrolyzers and converters of CO2 into useful chemical compounds or, failing that, H-sensors.3-5 Work on the materials synthesis and measurements of conductivity are the most frequent, although often carried out under conditions that are not very representative of those required by the technical and economic constraints (temperature, high H2O pressure, current per surface unit).2 Attention to understanding the nature of protons, especially mobile ones, is much more limited, especially in recent years. At least three types of 'protons' have been identified2,6-8 but only one type, where the proton establishes covalent bond with one acceptor ion, oxygen (OH, HO-H2), nitrogen (HN-H3), or sulfur (H-SO4) is commonly considered.2-6 These species present signatures in infrared spectroscopy, which are all the more characteristic – and visible – when the X-H…Y bond is not too strong.3,6 In fact, different forms exist with a dynamic equilibrium depending on the temperature3,9, including isolated, non-covalent-bonded and gas proton10,11 and differentiating the diffusing protons from the other protons is difficult. After presenting the different proton species and their (IR/Raman/neutron) vibrational signatures and the possible contributions of structural (X-ray, neutron),12 thermal (TGA)8,12 and conductivity measurements from THz/infrared range,13 discussing the relationship between the type of species and their thermal stability, we will attempt to formulate the main questions concerning the characterization of (mobile) proton in the solid phase and the best suited techniques of study. Discriminating between surface and bulk species and conduction will be also addressed. [1]. J. Beintema, Rec. Trav. Chim. Pays- Bas, 57, 155-175 (1938) [2]. P. Colomban, Solid State Ionics, 334, 125-144 (2019) [3]. P. Colomban, Ed., Proton conductors. Solids, membranes and gels-Materials and devices, Cambridge University Press, Cambridge, United Kingdom, 1992. [4]. P. Knauth, M.L. Di Vona, Solid State Proton Conductors: Properties and Applications in Fuel Cells, Wiley, New-York, 2012. [5]. M. Marrony, Proton Conducting Ceramics, from Fundamental to Applied Research, Pan Stanford Publishing, Singapore, 2016. [6]. P. Colomban, A. Novak, J. Mol. Struct., 177, 277-308 (1988) [7]. P. Colomban, J. Tomkinson, Solid State Ionics, 97, 123-134 (1997) [8]. P. Colomban, Fuel Cells, 13, 6-18 (2013) [9]. U. Mioc, M. Davidovic, N. Tjapkin, P. Colomban, A. Novak, Solid State Ionics, 46, 103-109 (1991) [10] U. Mioc, S.K. Milonjic, D. Malovic, V. Stamenkovic, P. Colomban, M.M. Mitovic, R. Dimitrijevic, Solid State Ionics, 97, 239-246 (1997) [11] F. Fillaux, N. Leygue, R. Baddour-Hadjean, S. Parker, P. Colomban, A. Gruger, A. Régis, L.T. Yu, Chem. Phys., 216, 281-293 (1997) [12] P. Colomban, A. Slodczyck, Eur. Phys. J. Special Topics. 213, 171-193 (2012) [13]. P. Colomban, J.C. Badot, Solid State Ionics, 61, 55-62 (1993).
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hal-03964419 , version 1 (31-01-2023)

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  • HAL Id : hal-03964419 , version 1

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Philippe Colomban. Mobile proton and protonic species. A historical view of their identification and outstanding questions -The potential of vibrational spectroscopy, underused methods?. PPCC 2022, 6th International Workshop: Prospect on Protonic Ceramics Fuel Cells, Jun 2022, Dijon, France. ⟨hal-03964419⟩
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