Premixed hydrogen/oxygen flame doped with ionisable alkali metals was considered as a dilute electrolyte. Two identical premixed flames which were in physical contact, served as a two compartment flame electrolyte cell. Five different electrochemical cells were studied, each containing a different combination of three alkali metals, Li, K and Cs. Pairs of boron doped diamond (BDD) and platinum electrodes were used to measure the overall zero current cell potential. The total potential measured across the cell was shown to be the sum of the mixed potential, dependent on the identity of ionised species present in the flame, and the diffusion potential originating at the junction between the two flames. Classical kinetic molecular theory and electrochemical theory of mixed potentials have been applied to account for the potential difference measured across these gas phase electrochemical cells. The relative merits of both models are discussed in the context of the experimental results obtained.

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