The Distribution of Electrodes By the Standard Potentials

Abstract

The Distribution of Electrodes by the Standard Potentials A.I.Chernomorskii(Scientific Resources Co)e-mail: sciresources@aol.comThe distribution of electrodes (Ox/Red-pairs) by their standard potentials with the maximum number of electrodes with Eo ~ +0.5 V SHE was shown in [1,2]. The distribution was carried on the listings included ~400 ÷ 700 half-reactions [3-6]. The standard potentials for ~2000 half-reactions have been reported up to now [7,8,9]. It was arranged 1807 half-reactions including in the listing [9] in terms of their standard potentials by finding the number of half-reactions with the standard potentials in intervals 0.1÷ 0.2 V from -3.1 to +3.1 V SHE. The average value of potential was assigned to each of these intervals. Then we plotted the distribution curve (Fig.1). The distribution was carried by the use computer program. One can see from Fig.1 that the number of half-reaction increases as one approaches the center of the electrochemical series. The distribution maximum occurs at a standard potential of +0.45 V SHE (if intervals are 0.1 V) and +0.47 V SHE (if intervals are 0.14 V SHE). These potentials of the maximum are close to the Billiter potential +0.475 V SHE [10, 11].Fig. 1. The distribution law of half-reactions by their standard potentials. The intervals of finding 0.1 V. The potential of the maximums is + 0.45 V SHEThus, it follows from the distribution obtained (Fig.1) that electrode Ox/Red-pairs in this center of the electrochemical series have lower oxidation and reduction activity than the redox pairs with more positive and more negative potentials, respectively. Hence, these pairs are neither active oxidants nor active reductants. It can be suggested that their both conjugated Ox- and Red-forms would have close energy states. However, this is valid if half-reactions are analyzed as the definite chemical interactions of Ox/Red-pairs with water molecules on electrodes. Electrons neinterm with the definite non-specific electrostatic bond with Ox-forms should be formed Red → Ox + neinterm or consumed Ox + neinterm → Red in these interactions which lead to formation of the electric double layers and outer potential jumps in them on electrodes [12-14]. It takes into account that half-reactions of elements transition from metals to non-metals (for example, Eo Te2+/Te = = +0.40 V SHE; Eo Te4+/Te = +0.568 V SHE; Eo I/I - = +0.535 V SHE) are in maximum of the distribution. It can be concluded some hypothetical electrode form between metals and non-metals (characterized by the potential ~+0.47 V SHE of maximum of the distribution) with the non-specific intermediate bounded outer electrons neinterm. Such a form (neither metal nor non-metal) would not have own oxidation and reduction activity. The potential of the maximum ~+0.47 V SHE should characterize this inactive electrode form with non-specific bound outer electrons. The electron work function of non-specific bounded electrons neinterm is found to be equal 5.18-5.19 eV [12-14]. There is suggested the exponential probability e – ΔE/const of the formation of specific electron bonds in acts Ox + neinterm → Red, where ΔE is the changes of energy at the formation of specific electron bonds at accepting non-specific bound electrons neinterm. Accordingly, the probability of formation of specific electron bonds in Red-forms should exponentially decrease with the increase of energy of their formation ΔE. It is concluded, that the number of existed Red-forms (and conjugated Ox-forms) with increased ΔE should also decrease exponentially. References (1) A.I. Chernomorskii, Russ.J. Electrochemistry, 1979, 15, 1347.(2) A.I. Chernomorskii, Dokl.Akad.Nauk Uzb.SSR, 1977,10, 33-35.(3) N.E. Khomutov, in: Results of Science, Electrochemistry, 1964 (in Russian), VINITI, Moscow (1966), p.7.(4) B.P.Nicol'skii (editor), Chemist's Handbook, Second edition, Vol.3 [in Russian], Khimiya, Moscow-Leningrad (1964).(5) M Pourbaix, Atlas d’Équilibres Électrochimuque, Gathier-Villars, Paris (1963).(6) W. M. Latimer, The Oxidation States of the Elements and Their Potentials in Aqueous Solutions, Prentice-Hall, New York (1952).(7) Handbook in Electrochemistry (A.M.Sukhotin, editor), 1981 (in Russian), Khimiya, Leningrad, pp.124 - 154.(8) S.G.Bratsch, J.Phys.Chem.Data, 1989,18, 1, pp. 1-21.(9) Ya. I.Tur'yan, Redox-reactions and potentials in analytical chemistry, Khimiya, Moscow, 1989, pp.177-233.(10) J. Billiter, Z. Electrochem, 1931,37, 8/9,736-740.(11) K.J. Vetter,”Electrochemical Kinetics”(Translated into Russian),Izd.Khimiya, Moscow,1967, p.116.(12) A.I.Chernomorskii, Russ. J. Phys.Chem., 1978, 52, 757; 1981,55,474.(13) A.I Chernomorskii, Thermodynamics of electrodes, FAN, Tashkent,1993, p. 184.(14) A.I Chernomorskii, The intermediate electron bond and half-reactions, Scientific Resources, N-Y,1999. Figure 1