# Effects of Cu Substituting Mo in Sr2Fe1.5Mo0.5O6−δ Symmetrical Electrodes for CO2 Electrolysis in Solid Oxide Electrolysis Cells

## TL;DR

This study improves CO2 electrolysis performance by substituting Cu for Mo in a perovskite material used in solid oxide electrolysis cells.

## Contribution

Cu substitution enhances electrochemical performance by increasing oxygen vacancies and reducing polarization resistance in CO2 electrolysis.

## Key findings

- Cu doping increases oxygen vacancies and lowers polarization resistance in the SFMC0.1 electrode.
- SFMC0.1 achieved a current density of 202.20 mA cm−2 at 800 °C and 1.8 V, outperforming SFM electrodes.
- Cu substitution promotes CO2 adsorption, dissociation, and oxygen ion migration, confirmed by theory calculations.

## Abstract

Solid oxide electrolysis cells (SOECs) are considered one of the most promising technologies for carbon neutralization, as they can efficiently convert CO2 into CO fuel. Sr2Fe1.5Mo0.5O6−δ (SFM) double perovskite is a potential cathode material, but its catalytic activity for CO2 reduction needs further improvement. In this study, Cu ions were introduced to partially replace Mo ions in SFM to adjust the electrochemical performance of the cathode, and the role of the Cu atom was revealed. The results show Cu substitution induced lattice expansion and restrained impurity in the electrode. The particle size of the Sr2Fe1.5Mo0.4Cu0.1O6−δ (SFMC0.1) electrode was about 500 nm, and the crystallite size obtained from the Williamson–Hall plot was 75 nm. Moreover, Cu doping increased the concentration of oxygen vacancies, creating abundant electrochemical active sites, and led to a reduction in the oxidation states of Fe and Mo ions. Compared with other electrodes, the SFMC0.1 electrode exhibited the highest current density and the lowest polarization resistance. The current density of SFMC0.1 reached 202.20 mA cm−2 at 800 °C and 1.8 V, which was 12.8% and 102.8% higher than the SFM electrodes with and without an isolation layer, respectively. Electrochemical impedance spectroscopy (EIS) analysis demonstrated that Cu doping not only promoted CO2 adsorption, dissociation and diffusion processes, but improved the charge transfer and oxygen ion migration. Theory calculations confirm that Cu doping lowered the surface and lattice oxygen vacancy formation energy of the material, thereby providing more CO2 active sites and facilitating oxygen ion transfer.