The effect of transition-metal addition on the non-equilibrium E.M.F.-type gas sensor

In this study, we made single chamber gas sensor which had two SnO₂ electrodes pasted onto either side of zirconia electrolyte. Transition metal (TM) was added in one of two SnO₂ electrodes to induce and thus confirm the catalytic effect of transition-metal. Since 1 mol% TM-doped SnO₂ showed the negligible change in microstructure, the effect of microstructure change could be ignored. The Co addition increased the e.m.f. of working electrode (TM-added SnO₂) in air, implying the enhanced oxygen adsorption. The addition of TM to SnO₂ was also effective in changing the e.m.f. values in H₂ balanced by air. Fe and Ni addition exhibited decreased e.m.f. in H₂ from that in air. Thus, Fe and Ni addition improved the catalytic activity for H₂ oxidation. Cu addition slightly improved the catalytic activity for CO oxidation. The results show that Co is expected to be a good additive for the cathode of solid-oxide-fuel-cell (SOFC) at low temperature. On the other hand, Fe, Cu, or Ni is good additives for anode.