Elucidating the Role of B-Site Cations toward CO₂ Reduction in Perovskite-Based Solid Oxide Electrolysis Cells

Abstract

Solid oxide electrolysis cells (SOECs) are promising systems for the selective electrochemical conversion of CO2, or mixed streams of CO2 and H2O, into high energy products, such as CO and H2. These products can be converted to fuels and chemicals using existing technologies. Although promising, state-of-the-art SOEC Ni-based cathode electrocatalysts are affected by poor redox stability leading to limited long-term performance. Due to their favorable redox properties, mixed ionic-electronic conducting (MIEC) oxides are promising alternatives to minimize these adverse effects. However, the electrochemical activities of MIECs are inferior to the Ni-based cathode electrocatalysts. Thus, improvement of the electrochemical performance of MIEC-based SOEC electrocatalysts is needed and requires an understanding of the factors that govern their activity. Herein, we investigate the effect of the B-site cations of LaBO3 perovskites on their electrochemical activity toward the reduction of CO2 in SOECs. We correlate changes in the B-site composition to the nature of adsorbed species and active sites on the oxide surfaces by integrating in situ CO2 Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) studies with density functional theory (DFT)-based calculations. These studies provide insights critical toward devising ways to improve the performance of MIEC-based SOEC cathodes for the electroreduction of CO2.

Electrochemical Reduction of CO2 using Solid Oxide Electrolysis Cells: Insights into Catalysis by Nonstoichiometric Mixed Metal Oxides

“…Simple perovskites (ABO 3 ) are the most commonly investigated nonstoichiometric mixed ionic and electronic conducting oxides for electrochemical CO 2 reduction. ,,− It is well established that the B-site transition-metal cations in these oxides are responsible for the catalytic activity and electron transfer. − B-site cations are highly hybridized with the surrounding oxygen anions in BO 6 octahedra . Due to B-site hybridization with lattice oxygen, oxygen vacancies interact with the B-site to promote the adsorption and activation of CO 2 on the surface.…”

“…A natural question would be whether there is an influence on the reported results if one would use the same bulk structure as what is reported experimentally. In the studies that we discuss in the next subsection regarding CO 2 activation, the cubic unit cell was used in all but one study …”

“…Only a few of the studies related to CO 2 electrochemical reduction on perovskites delve deep into the mechanism utilizing transition state theory and determination of kinetic barriers. ,, In general, theoretical studies concerning the mechanism have focused mainly on the effects of oxygen vacancies ,, on the activation of CO 2 on the surface, with some investigations also probing the effect of supported heterogeneous nanoparticles on the oxide. ,,− Although there have been many studies on perovskite surfaces regarding the oxygen evolution and reduction reactions, we restrict ourselves to the studies that involved the activation of CO 2 in the next subsection.…”

“…In the cases where multiple possible configurations were present within the DFT-based model, the intensities of the IR peaks were averaged, and overall peaks were established. Reproduced with permission from ref . Copyright 2022 IOP Publishing.…”

“…The atoms are marked as follows: La in green, Co in dark blue, surface O in red, O from CO 2 in purple, and C from CO 2 in black. Reproduced with permission from ref . Copyright 2022 IOP Publishing.…”