10 - Interfacial electrochemistry

Summary

In this chapter we shall discuss both the theoretical and experimental aspects of the following types of interfaces:

1. (a) metal/polymer electrolyte, e.g. Li/PEO–LiCF₃SO₃ or Pt/PEO–LiCF₃SO₃;

2. (b) metal/crystalline ionically conducting solid, e.g. Ag/Ag₄RbI₅ or C/Ag₄RbI₅;

3. (c) aqueous salt solution/polymer electrolyte, e.g. AsPh₄Cl-H₂O/ AsPh₄BPh₄–PVC or KCl–H₂O/AsPh₄BPh₄–PVC;

4. (d) polymer electrolyte/electronically and ionically conducting solid, e.g. PEO-LiCF₃SO₃/Li_xV₆O₁₃;

5. (e) solid electrolyte/solid electrolyte, e.g. Ag₄RbI₅/Ag-β-Al₂O₃.

We shall not attempt to review exhaustively the literature on interfacial electrochemistry in solid state systems. Instead we shall indicate the appropriate theoretical models for different situations. Most of the models and the related equations were developed some time ago in relation to the electrochemistry of aqueous systems. However, we will not assume a knowledge of these models on the part of the reader. It is important to realise that a direct transposition of models from one situation to another is fraught with difficulty, particularly since in aqueous electrochemistry a supporting electrolyte is generally present.

It is convenient for the purposes of this chapter initially to make a number of simplifying assumptions about the nature of the electrolytes under discussion. For example, Ag₄RbI₅ will be assumed to be an ionic conductor with negligible electronic conductivity and with only the silver ion mobile. Likewise Na-β-Al₂O₃ will be assumed to be a substance in which the only mobile charge is Na⁺.