I would like to propose for starters to divide the set of subjects onto two groups according to remarks in “Introduction” about preferably my personal interest (items ”a” and “b”) and evidently common interest (items “c” and “d”). Of course such division has enough relative character, but, by my opinion, it seems suitable.
Yu. M. Baikov, E. I. Nikulin, B. T. Melekh, L. G. Baikova
The family of complex materials such as crystalline hydrates and solid eutectics, on the base of hydroxides of alkaline metals (Na, K, Rb, Cs) has been studied thoroughly from the general physico-chemical point of view. However, the high proton conductivity of the members of this family has been revealed on for the last few years. Correspondingly there was no information on the electrochemical activity of heterostructures “alkaline proton | electron conductor”. In our opinion the crucial reason for this objectionable approach of world ionic community to whole alkaline-hydroxide-family was due to dramatic history of arising and then falling of interest in individual alkaline hydroxides. The key aim of the paper is to present our results of the development of solid and molten hydroxide materials which are good proton conductors at intermediate / room temperatures (450 < T < 250K) and low-humidity or even anhydrous conditions, as well as are electrochemically active in MEA with Ti, TiFe, Sn and Si. The main experimental results and informal discussions on necessary further progress in fundamental understanding of the underlying proton conduction mechanisms are collected now on website http://www.solidionic.com.
Yu.M.Baikov, B.T.Melekh, V.A.Klimov, E.I.Nikulin, L.G.Baikova
Ioffe Physical Technical Institute of RAS, Saint-Petersburg, 194021 Russian Federation, baikov.solid@mail.ioffe.ru
Fig.1 Simple model electrochemical cell. The details: glass tube as a case; metallic Sn and graphite as electrodes; solid electrolyte obtained after cooling the melt of 61w % of KOH and 39 w % H2O.Lighting head of match for scaling.
Sn(-)|KOH·2H2O| C(+)
The semiconductor-protonic heterojunction in the heterostructure ‘C(+)|KOH·2H2O|Si(-)’ could be considered as the opportunity of the matching of small-sized electronic devices with batteries studied here.
Compound compositions NaOH, KOH, H2O of lower melting points showed high proton conductivity at 300-450 K1,2. They are eutectics KOH\KOH·H2O (372.5K), KOH\NaOH(448K), and KOH·H2O (419K) and NaOH·H2O (338K).
The pioneering investigation of the electrochemical activity of certain ionic heterostructures with solid electrolyte KOH·2H2O (Tmelt=315 K) is due to basic and applied interest in. The special study of different chemical elements of IV group (C, Si, Sn, Pb) as electrodes of electrochemical cells in contact with hydroxide superproton conductor as electrolyte has been performed.
Table 1.
EMF (1,2 – 1,3 V) and exchange currents (~0,1-1 mA/cm2) of ‘C | KOH·2H2O | TiFe’ and ‘C | KOH·2H2O | Sn’ are adequate to work as low-power sources for electronic devices. Therefore they could be factually batteries without any catalysts and noble metals, i.e. from cheap materials.
The metal-proton heterojunction Sn(-)|KOH·2H2O has been studied firstly. It is characterized by exchange current at 290 K (1 mA/cm2, a polish surface).
References
1. Yu.M.Baikov,SolidStateIonics 181 (2010) 545
2 Yu.M.Baikov, J.Power Sources 193 (2009) 371
The support of Programm of Presidium of RAS “Quantum Physics of Condensed Matter” .
Abstract—The self-diffusion coefficients of ions of the three chemical elements forming lithium hydroxide have been determined by the crystal–crystal and crystal–gas isotope exchange method in the temperature range 500–720 K. Crystal samples with different isotope compositions have been grown by the Bridgman method from melts. The melting temperature is 743 ± 2 K. Original methods have been developed for high-precision measurements of the isotope ratios of all the three elements, i.e., lithium (6Li/7Li), hydrogen (H/D), and oxygen (16O/18O), and their changes after diffusion annealing with the use of the same sample. The self-diffusion coefficients of lithium and hydrogen ions differ but by a factor of no more than 3–5; however, their magnitudes exceeds those for oxygen by several orders of magnitude. In particular, at 670 K, they are equal to 6.0·10-9 , 3.2·10–9, and 2.0·10–12 cm2 s–1 for hydrogen, lithium, and oxygen, respectively. In the range 680–720 K, the self-diffusion coefficients of hydrogen and lithium increase sharply with increasing temperature to approximately 10–6 cm2 s–1. A probable mechanism of migration of protons and lithium ions in LiOH and the role played in this process by the oxygen ions with a lower mobility have been discussed.
DOI: 10.1134/S1063783410100070
Correction of the equation (5) in
Self-Diffusion of Lithium, Hydrogen, and Oxygen Ions in Crystalline Lithium Hydroxide 2010 Vol. 52, No.10, 2044-2057 (the correction elated to third member in (5) on P.2054)
Исправление формулы (5) в статье
ФТТ 2010 Том 52 вып 10 на стр 1917
Full article in English is here
Self of Lithium, Hydrogen, and Oxygen Ions in Crystalline Lithium Hydroxide.PDF
Full article in Russian is here
Самодиффузия ионов лития, водорода и кислорода в кристаллическом гидроксиде лития.PDF
1. Why is it necessary to discuss both general and particular properties of protonics?
The external similarity of processes of electric charge transfer by protons in sometimes extremely different materials seems rather strange because of significant discrepancy of other macroscopic properties of such materials. It is clearly even if to read chapter titles of brilliant survey of proton-conducting compounds published sixteen years ago by K.D.Kreuer [1]. He has divided them into four families: water-containing systems (WCS), oxo-acids and their salts (OAS), high-temperature proton conductors (HTPC) and organic/inorganic systems. Solid hydroxides of alkali metals were not included in this classification though they have became a subject of interest in the field of ionic conductors after successful application of KOH·0.5H2O as a molten electrolyte of fuel cells in the spacecraft. However, in the ensuing ~25 years (1980 – 2005) the number of publications dealing with investigation of the ionic conductivity of alkali metal hydroxides in solid state has hardly risen over two dozens (see [2 - 5] and references therein). This should be attributed primarily to the pessimistic conclusions inferred from assessment of the potential application of these compounds, which were based on their low conductivity and formation of noticeable amounts of impurities due to the interaction with the ambient medium [5].
2. Similarity and discrepancy in individual and complex alkaline hydroxides.
3. Special notes on electrochemical activity of new hydroxide protonics.
4. Similarity and discrepancy of complex hydroxides and oxo-acidic salts.
Full article in English is here:
SIMILARITY and DISCREPANCY of INORGANIC SOLID PROTONIC CONDUCTORS: HYDROXIDES and OXO ACID SALTS