Test of a dual electrode galvanic cell in binary carbonate melt

Basicity of the (Li_0.62K_0.38)₂CO₃, the current choice of electrolyte composition for molten carbonate fuel cells (MCFC's), is defined as - log (a_M2O), where M represents an alkali metal and a_M2O is the net oxide ion activity. Net oxide ion activity is defined as the sum of the alkali oxides activities dissolved in the melt. To correlate measured cell e.m.f. values with basicity change in the (Li_0.62K_0.38)₂CO₃ melt, a dual electrode galvanic cell of the following arrangement was tested at 650 °C with P_CO2 varying above the melt: Au, A-B, CO₂, O₂ | mullite | A-B, CO₂, O₂ | ZrO₂ · Y₂O₃ | O₂, Au where A-B represents (Li_0.62K_0.38)₂CO₃. The response of the cell to P_CO2 at constant P_O2 can be explained by thermodynamic model, which states that ion transference in the mullite tube is limited to Li⁺ and/or K⁺ and the dual electrode galvanic cell voltage is a direct measure of Δa_Li2O or Δa_K2O for pure (Li_0.62K_0.38)₂CO₃ melt at constant P_O2.