The effect of defect interactions on the reduction of doped ceria.

Steffen Grieshammer

doi:10.1039/d1cp00925g

Abstract

Doped cerium oxide is known for its reduction properties that are utilized in catalytic applications as well as in thermochemical cycling to produce solar fuels. Upon reduction of the lattice, oxygen vacancies and polarons are formed leading to a highly concentrated solution of defects in which the interactions of defects cannot be neglected anymore. In this study, the effect of defect interactions on the free energy of reduction for doped ceria with composition Ce1-x-yRExZryO2-x/2-δ was investigated by large scale Metropolis Monte Carlo multi-stage sampling simulations based on first-principles calculations. The simulations allowed the prediction of the relation between oxygen partial pressure and non-stoichiometry for the highly interacting, non-ideal system. The results show that the non-ideality observed in experiments can be traced back to the interactions of defects and allow prediction of the reduction behavior for various dopant types, dopant fractions, temperatures, and non-stoichiometries.

Highlights

Cerium oxide is an essential material in various applications such as solid oxide fuel cells, industrial and automotive catalysis, and more recently the production of solar fuels.[1,2,3,4,5] One of the most prominent properties of ceria is its high oxygen storage capacity (OSC) that is utilized in catalytic reactions and the two step process to produce hydrogen from water
As the OSC and reduction behavior directly influence the efficiency of the catalytic reaction and production of solar fuels, understanding the impact of doping and defect interactions on these properties is crucial
The energy values become more negative with increasing non-stoichiometry as the amount of defects and the number of defect interactions increases

Summary

Introduction

Cerium oxide (ceria) is an essential material in various applications such as solid oxide fuel cells, industrial and automotive catalysis, and more recently the production of solar fuels.[1,2,3,4,5] One of the most prominent properties of ceria is its high oxygen storage capacity (OSC) that is utilized in catalytic reactions and the two step process to produce hydrogen from water. The effect of defect interactions on the free energy of reduction is investigated for various dopants and compositions in Ce1ÀxÀyRExZryO2Àx/2Àd using Metropolis Monte Carlo multi-stage sampling simulations based on density functional theory calculations. Internal energy Druint and free energy Dr f int contributions are negative due to the attractive interactions between the oxygen vacancies and cation defects.

Results

Conclusion