Alkali metal doping strategy for improved CO/CO2 conversion in reversible solid oxide cells

Reversible solid oxide cells (RSOCs) can use CO/CO2 as the energy storage medium for efficient electricity-to-gas and gas-to-electricity conversion. In this study, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) is modified by the low electronegativity alkali metal (Li or Na) doping. It is found that the alkali metal doping can effectively improve the oxygen vacancy concentration and oxygen migration capacity of LSCF, which will further enhance its CO2 reduction kinetics. At 800 °C, the chemical surface exchange coefficient (kchem) values of Li-doped and Na-doped LSCF reach 9.06 × 10−4 and 11.93 × 10−4 cm s−1, respectively, which are 13.1 % and 48.9 % higher than 8.01 × 10−4 cm s−1 of LSCF. Meanwhile, the chemical bulk diffusion coefficient (Dchem) values of Li-doped and Na-doped LSCF reach 8.86 × 10−5 and 10.73 × 10−5 cm2 s−1, respectively, which are 39.7 % and 69.2 % higher than 6.34 × 10−5 cm2 s−1 of LSCF. The electrolysis current density of the single cell with Na-doped LSCF as the fuel electrode is 1.07 A cm−2 at 800 °C/1.5 V, and the maximum power density (Pmax) can reach 207 mW cm−2 with 50%CO–50%CO2 as the fuel. When performing pure CO2 electrolysis, the single cell with Na-doped LSCF as the fuel electrode shows the best CO2 electrolysis performance with a current density of 1.81 A cm−2 at 800 °C/1.5 V, and the cell still maintains good stability after 20 h durability test with pure CO2 as the fuel. Hence, low electronegativity alkali metal Na doping can effectively improve the catalytic activity for CO/CO2 conversion. •Low electronegativity alkali metal (Li or Na) doping strategy is proposed.•LSNCF exhibits a best CO2 reduction activity.•The single cell with LSNCF reaches a Pmax of 207 mW cm−2 in RSOC mode.•The single cell with LSNCF shows a current density of 1.81 A cm−2 at 1.5 V.