Composite fuel electrode La_0.2Sr_0.8TiO_3-δ-Ce_0.8Sm_0.2O_2-δ for electrolysis of CO₂ in an oxygen-ion conducting solid oxide electrolyser

Composite Ni-YSZ fuel electrodes are able to operate only under strongly reducing conditions for the electrolysis of CO₂ in oxygen-ion conducting solid oxide electrolysers. In an atmosphere without a flow of reducing gas (i.e., carbon monoxide), a composite fuel electrode based on redox-reversible La_0.2Sr_0.8TiO_3+δ (LSTO) provides a promising alternative. The Ti³⁺ was approximately 0.3% in the oxidized LSTO (La_0.2Sr_0.8TiO_3.1), whereas the Ti³⁺ reached approximately 8.0% in the reduced sample (La_0.2Sr_0.8TiO_3.06). The strong adsorption of atmospheric oxygen in the form of superoxide ions led to the absence of Ti³⁺ either on the surface of oxidized LSTO or the reduced sample. Reduced LSTO showed typical metallic behaviour from 50 to 700 °C in wet H₂; and the electrical conductivity of LSTO reached approximately 30 S cm^-1 at 700 °C. The dependence of [Ti³⁺] concentration in LSTO on P_O2 was correlated to the applied potentials when the electrolysis of CO₂ was performed with the LSTO composite electrode. The electrochemical reduction of La_0.2Sr_0.8TiO_3+δ was the main process but was still present up to 2 V at 700 °C during the electrolysis of CO₂; however, the electrolysis of CO₂ at the fuel electrode became dominant at high applied voltages. The current efficiency was approximately 36% for the electrolysis of CO₂ at 700 °C and a 2 V applied potential.