Current understanding of ceria surfaces for CO2 reduction in SOECs and future prospects – A review

Ceria-based materials form a very promising class of electrocatalysts for CO2 reduction in solid oxide electrolysis cells (SOECs). On the pathway towards the implementation of ceria into technological electrodes on a large scale, an in-depth atomistic understanding of the reaction mechanism over ceria surfaces is crucial in order to optimize its intrinsic electrocatalytic activity. In this review article, we offer a critical discussion of the phenomena governing the electrochemical reduction of CO2 over ceria surfaces. We focus on the steps that limit the reaction rate and on how these can be accelerated by appropriate tuning of ceria properties and defect chemistry, via the introduction of tensile or compressive isotropic strain in the lattice, the promotion of a specific surface orientation and the control of the amount of acceptor or donor dopants incorporated in the fluorite structure. Our review aims to gather and examine the evidence of the role that these levers play in altering the energy landscape of the reaction, along with their influence on the capability of ceria to suppress carbon deposition during cell operation. Ultimately, we identify the areas that need further investigation and propose new lines of work towards the performance optimization of ceria as highly efficient catalyst for CO2 reduction in SOECs. •Discussion of the electrochemical CO2 reduction mechanism on ceria surfaces.•Influence of dopants, strain and surface orientation on ceria electrocatalytic activity.•Role of dopants and surface orientation in suppressing carbon deposition on ceria.•Research directions to develop efficient ceria-based cathodes for CO2 electrolysis.