Reduction of $$\hbox {CO}_{2}$$ CO 2 to CO in presence of $$\hbox {H}_{2}$$ H 2 on strontium doped lanthanum manganite cathode in solid oxide electrolysis cell

Abstract

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