Sucrose-Assisted Solution Combustion Synthesis of Doped Strontium Ferrate Perovskite-Type Electrocatalysts: Primary Role of the Secondary Fuel

Abstract

The methodologies and experimental conditions used for the synthesis of cathode materials for electrochemical devices strongly influence their electrocatalytic performance. In particular, solution combustion synthesis is a convenient and versatile methodology allowing a fine-tuning of the properties of the material. In this work, we used for the first time a sucrose assisted-solution combustion synthesis for the preparation of Cerium and Cobalt-doped SrFeO3–δ electrocatalysts and we investigated the effect of polyethylene glycol (PEG) addition as a secondary fuel on their structural, microstructural, redox and electrochemical properties. The perovskite-type powders were characterized by X-ray diffraction coupled with Rietveld refinement, scanning, and high-resolution transmission electron microscopies, thermogravimetric analysis, nitrogen adsorption measurements, and temperature-programmed reduction. Electrical conductivity and overpotential measurements were performed after the deposition of the powders onto a Gd-doped ceria electrolyte pellet. Stable high-valence B-site cations were detected in the powders prepared from sucrose-PEG fuel mixtures, although a substantial improvement of the conductivity and a decrease of the overpotential values were obtained only with high molecular weight PEG. The superior electrochemical performance obtained using PEG with high molecular weight has been ascribed to a faster interaction of the powder with the oxygen gas phase favored by the nanometer-sized crystalline domains.

Clarifying the Role of the Reducers-to-Oxidizers Ratio in the Solution Combustion Synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Oxygen Electrocatalysts

“…Therefore, it is possible to trace the oxidation states of the elements that have reducible species, i.e., iron and cobalt, whose oxidation state will gradually decrease from the initial value toward the metallic state. Figure 5a-d As expected, the profile's shapes are very similar for all the samples (Figure 5a-d) and resemble the H2-TPR profiles reported in the literature for other iron and cobalt containing perovskite-type compounds [23,64]. In detail, there is a peak in the range 400-600 °C (peak B), with a shoulder in the range 200-400 °C (peak A), and further hydrogen consumption in the range 700-1000 °C, which does not arrive at completeness.…”

“…Therefore, the reduction of some Co 3+ to Co 2+ species already occurred at low temperature (peak A), followed by the stepwise process Co 3+ to Co 2+ to Co 0 , which continues under peak B. Indeed, postulating that, upon reduction of some Co 4+ species (part of the peak A), all the cobalt species involved in peak B are Co 3+ , the theoretical hydrogen consumption required for the reduction of Co 3+ to Co 2+ to Co 0 corresponds As expected, the profile's shapes are very similar for all the samples (Figure 5a-d) and resemble the H 2 -TPR profiles reported in the literature for other iron and cobalt containing perovskite-type compounds [23,64]. In detail, there is a peak in the range 400-600 • C (peak B), with a shoulder in the range 200-400 • C (peak A), and further hydrogen consumption in the range 700-1000 • C, which does not arrive at completeness.…”

“…In detail, there is a peak in the range 400-600 °C (peak B), with a shoulder in the range 200-400 °C (peak A), and further hydrogen consumption in the range 700-1000 °C, which does not arrive at completeness. According to the literature, peaks A and B are mainly related to the reduction of cobalt species, whereas the smaller peaks at temperatures higher than 700 °C are related to the iron reduction [23,64,65]. Peak A is ascribable to the reduction of cobalt ions in high oxidation state, like Co +4 and Fe +4 (200-300 °C) and to the reduction of Co 3+ in a surrounding which is different from the perovskite oxygens octahedra of the cubic structure (300-450 °C) [23].…”

Favoring Product Desorption by a Tailored Electronic Environment of Oxygen Vacancies in SrTiO3 via Cr Doping for Enhanced and Selective Electrocatalytic CO2 to CO Conversion

“…61 Furthermore, TGA/DTA analysis of the samples under a N 2 atmosphere (Figure S8) also confirms the presence of higher O vac in Cr-doped than in pristine STO. According to the literature reports, 62,63 three different regions or types of weight losses may occur on metal oxide surfaces, viz., weight loss before 100 °C (associated with the physiosorbed water molecule), followed by weight loss between 100 and 350 °C (attributed to the chemisorbed water molecule at the O vac due to the presence of α-oxygen, namely, mobile oxygen, that is directly related to O vac ) and a third weight loss after 350 °C (ascribed to the release of lattice oxygen). In our case, weight loss in the range of 100−350 °C for Cr-STO 5 is approximately 2.1 times higher than that for STO, indicating relatively more O vac in Cr-STO 5 than in the pristine STO.…”

Sr0.85Ce0.15Fe0.67Co0.33-xCuxO3 perovskite oxides: effect of B-site copper codoping on the physicochemical, catalytic and antibacterial properties upon UV or thermal activation

“…Other materials were developed by adding cobalt at B-site beyond the A-site Ce substitution. The oxides were a series of Sr 0.85 Ce 0.15 Fe 0.67 Co 0.33 O 3-δ , which were prepared by SCS using mixtures of sucrose and polyethylene glycol with different molecular weights (PEG1000 and PEG 20000) as combustion fuels (Tummino et al, 2020). The materials were tested as cathodes for Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFC), namely, operating between 500 °C-800 °C (Shi et al, 2016).…”