Reduction of ${\text{CO}}_2$ to CO in presence of ${\text{H}}_2$ on strontium doped lanthanum manganite cathode in solid oxide electrolysis cell

Electrochemical performance of ${\text{La}}_{0.8}{\text{Sr}}_{0.2}{\text{MnO}}_{3-\delta }$ (LSM) for ${\text{CO}}_2$ reduction in solid oxide cell is studied by performing impedance spectroscopy measurement and current-voltage characterizations for varying ratio of ${\text{CO}}_2/{\text{H}}_2$. Ohmic resistance $\left({\text{R}}_{\Omega }\right)$ is observed to be slightly increased from 2.59 to $2.70\Omega {\text{ cm}}^2$, however; the cathode polarization resistance $\left({\text{R}}_2\right)$ decreased significantly from 16.20 to 4.70 $\Omega {\text{ cm}}^2$ as the ${\text{H}}_2$ percentage increased from 8 to 82%, respectively. As the ${\text{H}}_2$ content increased in feed gas, the improved polarization resistance indicated an enhanced activity of LSM for ${\text{CO}}_2$ reduction reaction. Furthermore, the cathode polarization resistance for ${\text{CO}}_2/{\text{H}}_2$ of 92/08, is observed to be decreased from 16.20 $\Omega {\text{ cm}}^2$ (OCV 0.89 V) to 1.90 $\Omega {\text{ cm}}^2$ (2.0 V) as the applied potential increased in the electrolysis mode of operation. A maximum conversion of ${\text{CO}}_2$ of 6.0% with 55% of faradaic efficiency for the production of CO is achieved for ${\text{CO}}_2/{\text{H}}_2$ ratio of 38/62, which is supported by improved current-voltage polarization, i.e.,  an increase in reduction current from $-0.28$ to $-0.32{\text{ A cm}}^{-2}$ (at 2.5 V) as the ${\text{CO}}_2/{\text{H}}_2$ ratio decreased from 92/08 to 38/62 respectively. These results demonstrate LSM as an active electrocatalyst to reduce ${\text{CO}}_2$, which could further be improved by increasing the ${\text{H}}_2$ concentration in the feed composition to the cathode.

Graphical Abstract

Synopsis: Solid oxide cell is fabricated with strontium doped lanthanum manganite electrodes and yttria stabilized zirconia electrolyte. Electrochemical performance in terms of impedance spectroscopy and current-voltage characteristics of the cell are reported for the reduction of carbon dioxide into carbon monoxide in presence of hydrogen with varying ratio of ${\text{CO}}_2/{\text{H}}_2$. .