Guan Z, Chen D, Chueh W C. Analyzing the dependence of oxygen incorporation current density on overpotential and oxygen partial pressure in mixed conducting oxide electrodes[J]. Physical Chemistry Chemical Physics, 2017, 19(34): 23414-23424.

ABSTRACT

The oxygen incorporation reaction, which involves the transformation of an oxygen gas molecule to twolattice oxygen ions in a mixed ionic and electronic conducting solid, is a ubiquitous and fundamentalreaction in solid-state electrochemistry. To understand the reaction pathway and to identify the rate-determining  step,  near-equilibrium  measurements  have  been  employed  to  quantify  the  exchangecoefficients as a function of oxygen partial pressure and temperature. However, because the exchangecoefficient contains contributions from both forward and reverse reaction rate constants and depends onboth  oxygen partial pressure  and  oxygen  fugacity in the  solid,  unique and  definitive mechanisticassessment has been challenging. In this work, we derive a current density equation as a function of bothoxygen partial pressure and overpotential, and consider both near and far from equilibrium limits. Ratherthan considering specific reaction pathways, we generalize the multi-step oxygen incorporation reactioninto the rate-determining step, preceding and following quasi-equilibrium steps, and consider the numberof oxygen ions and electrons involved in each. By evaluating the dependence of current density onoxygen partial pressure and overpotential separately, one obtains the reaction orders for oxygen gasmolecules and for solid-state species in the electrode. We simulated the oxygen incorporation currentdensity-overpotential curves for praseodymium-doped ceria for various candidate rate-determining steps.This work highlights a promising method for studying the exchange kinetics far away from equilibrium