A H2S sensor-based on Na-β-alumina as solid electrolyte and Na2S as auxiliary electrode

A solid-state sensor for H2S was evaluated using (single phase) Na-beta-alumina as solid electrolyte and Na2S as auxiliary electrode, These auxiliary electrodes are used to convert the sulphur chemical potential difference across the electrolyte to an equivalent sodium chemical potential difference, Tests of the electrochemical cell. (Pt/(H2S + H-2 + Ar)/Na2S//Na-beta-alumina//Na2S/(H2S + H-2 + Ar)/Pt) revealed that the H2S concentration variations were followed by the experimental E.M.F. values according to the Nernst law, Nevertheless, a drift of the. E.M.F. was observed. Therefore, it was not possible to obtain reproducible E.M.F. values, However, after two weeks the drift disappears and reproducible E.M.F. values were measured. The drift can be explained by the fact that the Na2O activity of the beta-alumina is changing during the test, due to the reaction of the H2S gas with beta-alumina. This reaction also introduces a second phase, alpha-alumina, at the interface of the beta-alumina and this can explain the fact that the sensor becomes stable after two weeks. From this study, it can be concluded that the E.M.F. drift can be minimised by using a double phase solid electrolyte instead of a single phase solid electrolyte. (C) 1997 Elsevier Science S.A.