Improving a Sulfur-Tolerant Ruddlesden–Popper Catalyst by Fluorine Doping for CO<sub>2</sub> Electrolysis Reaction
Seongmin Park, Hyunsu Han, Wongeun Yoon, Junil Choi, Yoongon Kim, Hwan Kim, Won Bae Kim
Abstract
We report a highly improved cathode catalyst by doping fluorine anions in oxygen sites of a Ruddlesden–Popper material for CO2 electrolysis to produce CO in solid oxide electrolysis cells (SOECs). The obtained fluorine-doped catalyst of La0.9Sr0.8Co0.4Mn0.6O3.9−δF0.1 (R.P.LSCoMnF) exhibited the higher electrochemical performance of 499 mA/cm2 at 1.3 V and 850 °C with the smaller polarization resistance of 0.853 Ω·cm2 than those of the undoped catalyst of La0.9Sr0.8Co0.4Mn0.6O4−δ (R.P.LSCoMn). Moreover, a high faradaic efficiency of 98.6% and a CO production rate of 135 μmol/cm2·min were achieved for CO2 electrolysis reaction in the single cell with the R.P.LSCoMnF cathode catalyst. These enhanced performances are mainly attributed to the improved properties of surface exchange of oxygen and bulk oxygen diffusion by fluorine doping. More importantly, a negligible sign of performance degradation was observed from the galvanostatic test under CO2 gas streams containing H2S gas, and its structure was maintained even after exposure to 100 ppm H2S in an N2 gas stream at 850 °C for 10 h, suggesting that R.P.LSCoMnF is highly robust against poisonous sulfur species. Therefore, this newly developed fluorine-doped Ruddlesden–Popper catalyst could be a promising cathode for the electrolysis of sulfur-containing CO2 gas stream, which is emitted from steel-making blast furnaces or power plants.