Sustainable future energy scenarios require significant efficiency improvements in both electricity generation and storage. High-temperature solid oxide cells, and in particular carbon dioxide electrolysers, afford chemical storage of available electricity that can both stabilize and extend the utilization of renewables. Here we present a double doping strategy to facilitate CO₂ reduction at perovskite titanate cathode surfaces, promoting adsorption/activation by making use of redox active dopants such as Mn linked to oxygen vacancies and dopants such as Ni that afford metal nanoparticle exsolution. Combined experimental characterization and first-principle calculations reveal that the adsorbed and activated CO₂ adopts an intermediate chemical state between a carbon dioxide molecule and a carbonate ion. The dual doping strategy provides optimal performance with no degradation being observed after 100 h of high-temperature operation and 10 redox cycles, suggesting a reliable cathode material for CO₂ electrolysis.

Self-doped SrTiO_3−δ was prepared through a carbon-free one-step combustion method followed by a series of heat treatments in Ar at temperatures ranging from 1200 to 1400 °C. X-Ray Photoelectron Spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) and High-Resolution TEM confirm the presence of Ti³⁺ in samples with oxygen vacancy accommodated in perovskite by forming Ruddlesden–Popper crystallographic shears. The UV-vis spectra and electronic structure calculations show that the oxygen vacancy and Ti³⁺ together induce an in-gap band to enhance the visible light absorption. Pulsed Adsorption of CO₂ and Temperature Programmed Desorption (TPD) experiments show that the higher oxygen deficiency tends to improve the chemical adsorption of CO₂ on the surface as well as in the bulk of SrTiO_3−δ, especially the accommodation of CO₂ molecule in the oxygen vacancy. It is the synergetic effect of visible light absorption and chemical adsorption of CO₂ that improves the artificial photosynthesis to generate hydrocarbon fuels from CO₂/H₂O under visible light irradiation. We also demonstrated that the incorporation of oxygen from CO₂/H₂O into the oxygen vacancy of SrTiO_3−δ leads to the absence of oxygen evolution which therefore results in the oxidation of SrTiO_3−δ (Ti³⁺ → Ti⁴⁺).

Electrochemical reforming of CH ₄ /CO ₂ is demonstrated in a solid oxide electrolyser.

Synthetic fuels produced from CO₂/H₂O are an attractive alternative energy carrier. Here we demonstrate a novel strategy to electrochemically convert CO₂/H₂O into hydrocarbon in a single step in an oxygen-ion conducting solid oxide electrolyser. Methane was directly synthesized in an efficient electrolyser with configuration of (anode) (La_0.8Sr_0.2)_0.95MnO_3−δ/YSZ/La_0.2Sr_0.8TiO_3+δ (cathode) by combining coelectrolysis of CO₂/H₂O and in situ Fischer–Tropsch-type synthesis. We demonstrate a high Faradaic yield of CO/H₂ and lower methane yield, which shows that the limit on conversion efficiency comes from the heterogeneous catalysis process. Electrochemical results also show that the electrochemical reduction of La_0.2Sr_0.8TiO_3+δ cathode is the main process at low electrical voltages while the coelectrolysis is the main process at high voltages.

Remarkable chemical adsorption of CO₂ has been achieved in titanate with significant concentration of oxygen vacancies towards the efficient direct CO₂ electrolysis in solid oxide electrolysers.