Determining Na+ transport number in Na2Si2O5 glass with Na concentration cell

Solid-state fast-ion conductors are a core class of functional materials for solid-state electrochemical cells such as batteries, sensors and fuel cells. The Na2Si2O5 glass has recently been reported as a potential intermediate-temperature Na+-conductor, but a direct evidence of its pure Na+ conduction is still lacking. We here show that the Na+ transport number of the Na2Si2O5 glass can be determined by the ratio of the measured open-circuit voltage to the theoretical Nernst potential of a Na-concentration cell. The Na-concentration cell is consisted of a Na2Si2O5 glass electrolyte and two two-phase reference electrodes of defined Na-chemical potentials, Na2ZrO3 + ZrO2 and NaAlO2 + Al2O3. The result explicitly suggests that the Na2Si2O5 glass is a pure Na+ conductor at <400 °C.