DFT+U study of CO2 reduction and CO oxidation on a reconstructed CeO2−x(110) facet

J.V Kildgaard,H.A Hansen,T Vegge

doi:10.1016/j.mtadv.2020.100111

Abstract

Catalytic oxidation of CO can remove toxic pollutants from gas emissions, whereas the reduction of CO2 can provide feedstock for fossil free products. Using density functional theory with a Hubbard U correction (DFT + U), the reduction of CO2 into CO is investigated on a reconstructed CeO2−x(110) facet at operatingsolid oxide electrolysis conditions. A reaction pathway is identified with nudged elastic band (NEB) through adsorption of CO2 as a monodentate carbonate, an intermediate CO2− and the transition state to the final adsorbed CO. The reaction barrier for CO2 reduction does not depend on the temperature, whereas the back reaction for CO oxidation decrease with temperatures. Different 4d and 5d transition metals and other suitable metals are screened as dopants to increase the activity for CO2 reduction. After the screening iridium is the most promising candidate. The same temperature dependencies are present for the Ir-doped surface as the undoped, whereas the back reaction barrier is decreased to half the undoped value. There is no evidence of destructive carbon deposition on the reconstructed CeO2−x(110) facet.

Highlights

The potential of electrolyzing CO2 to fuels and chemicals as part of a zero-emission future is promising
Fluctuating renewable energy sources are reducing in price, but the mismatch between demand and production inhibits renewable energy to completely replace fossil fuels
CO2 can be electrochemical reduced to CO in solid oxide electrolysis cells, which is one of the promising candidate for efficient conversion at elevated temperatures [3e6]

Summary

Introduction

The potential of electrolyzing CO2 to fuels and chemicals as part of a zero-emission future is promising. CO2 reduction can minimize the mismatch between production and demand and deliver carbon-neutral fuels [1,2]. CO2 can be electrochemical reduced to CO in solid oxide electrolysis cells, which is one of the promising candidate for efficient conversion at elevated temperatures [3e6]. The (110) facet of ceria can under reducing conditions at temperatures of 800 K make a reconstruction as seen experimentally [21,22]. This reconstruction is computationally observed and modeling of nanoparticles shows the degree of reconstruction can be effected by the environment [23,24]. We study how this path can be improved by doping the reconstructed surface with 4d and 5d transition metals

Computational method

CO2 and CO absorption

Doping

Conclusion