Electrochemical diffusion potential in the gas phase

Potentiometric based electrochemical measurement of diffusion potential at a junction between two flowing flame plasma gases is described. A flame electrochemical cell was constructed using a specially designed burner, which supports two individual flames, each fed by separate premixed methane/oxygen/nitrogen streams. The two flames were in intimate contact, creating a flowing fluid gaseous junction. By aspirating metal salt solutions into these premixed feed gases, the concentration gradient at the interface between the two flames may be controlled. A measurable electrochemical diffusion potential was formed at this junction, the magnitude of which was dependent on the concentration ratio of charged species with different mobilities. In our flame electrolyte, the dominant charged species were atomic or molecular cations and electrons, which have a difference in mobilities of approximately three orders of magnitude. A two-electrode system, in conjunction with a high impedance electrometer was used to measure the potential difference across the flame electrochemical cell. The measured potential difference was analysed using theory developed for the liquid junction potentials by the Henderson equation.