Cu-doped CaFeO3 perovskite oxide as oxygen reduction catalyst in air cathode microbial fuel cells

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

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.

An Iron-Doped Calcium Titanate Cocatalyst for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is an important challenge in the development and large-scale distribution of energy conversion devices, especially low-temperature proton exchange membrane (PEM) fuel cells. In order to speed up the ORR kinetics and improve fuel cell performance, iron-doped calcium titanate (CTFO) is proposed as a cocatalyst. Fundamental physical and chemical characterizations by means of X-ray diffraction, infrared spectroscopy, and morphological and thermal analyses for the understanding of the functional features of the proposed materials were carried out. Composite catalysts containing different amounts of CTFO additive with respect to platinum (i.e., Pt:CTFO 1:0.5 and 1:1 wt:wt) were studied using a rotating disk electrode (RDE). Fuel cell tests were performed at 80 °C under 30% and 80% relative humidity. The best Pt:CTFO composite catalyst was compared to a bare Pt/C and a Pt/C:CaTiO3−δ 1:1 catalyst, revealing superior performances of the latter at high relative humidity fuel cell operation, as a combined result of an optimized electrolyte-electrode interface and improved ORR kinetics due to the inorganic additive.