No abstract

The nature and characteristics of the overpotential in cells of the type normalAr‐O2,H2‐H2O,normalorCO‐CO2/ZrO2‐normalCaO/O2 were determined from 700° to 1100°C over a wide range of oxygen pressures. Porous Pt black electrodes were deposited on impervious ZrO2+10 normalm/normalo false(normalmole per centfalse)normalCaO tubes. Almost pure resistance polarization is observed when normalAr‐O2 or H2‐H2O mixtures are present at the anode. However, for normalAr‐O2 mixtures dilute in O2 at the cathode, diffusion overpotential readily appears and limiting currents are eventually reached. Limiting currents, proportional to PO2 , are controlled by the diffusion of gaseous oxygen in the pores of the Pt electrode. Based on the present results and adsorption data, a mechanism is proposed for the cathode reaction. For CO‐CO2 mixtures, transition overpotential associated with the reaction CO2+2e⇄CO+O−− is observed. The transition factor is about 0.5 and exchange current densities are in the vicinity of 1 mA/cm2. Equations relating exchange current density to PCO , PCO2 , and the amount of CO adsorbed on the electrolyte are derived and compared with the experimental results. It is concluded that either gaseous or adsorbed CO and gaseous CO2 are directly involved in the electrochemical step of the reaction.

A “closed system” solid electrolyte electrochemical cell has been designed to investigate the thermodynamic properties of metal oxides. The measurements with this cell are free of mixed potentials arising from nonequilibrium oxygen pressure conditions in the electrode compartments. The oxide systems investigated include normalNi‐normalNiO , normalPb‐PbOfalse(S,Lfalse) , normalCu‐Cu2O , Cu2O‐normalCuO , normalFe‐FexO , FeyO‐Fe3O4 , Fe3O4‐Fe2O3 , normalMnO‐Mn3O4 , and Mn3O4‐Mn2O4 .

SEMICONDUCTOR-ELECTROLYTE CIRCUITNi is determined by kinetic expressions such asThe first term of the right-hand side is the rate of hole capture by the unfilled interface states giving rise to the filled state; the second term is the rate of electron capture by these filled states; the third term is the rate of a second hole capture by the filled states, e.g., the second step in a corrosion process; and the fourth term is the rate of electron capture from a reducing species in the electrolyte with concentration, Cr.