Next Article in Journal
Startup Sustainability Forecasting with Artificial Intelligence
Previous Article in Journal
Beyond Thymol and Carvacrol: Characterizing the Phenolic Profiles and Antioxidant Capacity of Portuguese Oregano and Thyme for Food Applications
Previous Article in Special Issue
Analytical Estimation of Hydrogen Storage Capacity in Depleted Gas Reservoirs: A Comprehensive Material Balance Approach
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Applied Sciences
Volume 14
Issue 19
10.3390/app14198923
applsci-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Sintering Aids Strategies for Improving LSGM and LSF Materials for Symmetrical Solid Oxide Fuel Cell

by
Egor Gorgeev
1,2,
Ekaterina Antonova
1,3 and
Denis Osinkin
1,4,*
1
Kinetics Laboratory, Institute of High-Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences, Yekaterinburg 620066, Russia
2
Scientific Laboratory of Electrochemical Devices and Materials, Institute of Hydrogen Energy, Ural Federal University, Yekaterinburg 620002, Russia
3
Department of Life Safety, Institute of Fundamental Education, Ural Federal University, Yekaterinburg 620002, Russia
4
Department of Environmental Economics, Graduate School of Economics and Management, Ural Federal University, Yekaterinburg 620002, Russia
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(19), 8923; https://doi.org/10.3390/app14198923
Submission received: 5 September 2024 / Revised: 27 September 2024 / Accepted: 1 October 2024 / Published: 3 October 2024
(This article belongs to the Special Issue Production, Storage and Utilization of Hydrogen Energy)
Browse Figures
Versions Notes

Abstract

:

Featured Application

The findings of the research study have implications for the development of high-temperature electrochemical devices based on solid electrolytes with symmetrical electrodes.

Abstract

R&D in the area of high-temperature symmetrical electrochemical devices is needed to meet the challenges of hydrogen energy. In the present study, the effect of Fe2O3 and CuO sintering aids on the electrochemical properties of the highly conductive solid electrolyte La0.8Sr0.2Ga0.8Mg0.2O3−δ and La0.6Sr0.4FeO3−δ electrodes for symmetrical solid oxide fuel cells was investigated. It is shown that the use of sintering aids leads to an improvement in grain boundary conductivity and allows us to reduce the sintering temperature to obtain a dense electrolyte with the same level of conductivity. It is shown for the first time that the nature of the sintering aids and the sintering temperature affect the La0.6Sr0.4FeO3−δ electrode activity differently depending on the gas environment (air or hydrogen). On the basis of the analysis of the impedance spectra by the distribution of relaxation times, assumptions were made about the nature of the rate-determining steps of hydrogen oxidation and oxygen reduction. It is shown that the nature of the rate-determining steps can change depending on the electrode sintering temperature. It was found that among the studied electrodes, La0.6Sr0.4FeO3−δ with 3 wt.% Fe2O3 sintered at 1050 °C is optimal in terms of activity in oxidizing and reducing atmospheres.

1. Introduction

State-of-the-art high-temperature electrochemical devices have high potential for utilization due to their diverse applications, including power generation in fuel cells [1,2,3], electrolysis and gas utilization [4,5,6], purification and production of high-purity gases [7,8,9], gas analysis and detection [10,11,12], conversion of various gases, such as ammonia or hydrocarbons [13,14,15], etc. In most cases, the functional materials utilized in the primary components of such devices, including the electrolyte, cathode, and anode, are complex oxides that exhibit high stability at elevated temperatures and a variety of essential electrical, electrochemical, and functional properties [16,17,18,19,20,21,22,23]. It is often difficult to achieve properties such as high electrolyte density and an optimal electrode/electrolyte interface, even at elevated temperatures. This is due to a number of factors, including evaporation, phase decomposition, chemical interaction, thermal expansion mismatch, segregation, and so forth [24,25,26]. In this context, an effective strategy for enhancing the functional properties of the electrolyte and electrodes is the incorporation of sintering aids.
Sintering aids are typically binary compounds, such as fluorides [27,28,29], although they are more commonly oxides, which are introduced into the base material prior to the heat treatment. Sintering aids possess low melting points or form low-temperature intermediate phases or eutectic mixtures with the base material, thus improving material properties at low sintering temperatures [30,31,32]. In the case of solid electrolytes, the incorporation of sintering aids results in an enhancement of the density of the material or in the reduction in the temperature required for the formation of dense electrolytes. In [33], Hagy et al. note the positive effect of ZnO sintering aids on the properties of BaCe0.2Zr0.7Y0.1O3−δ electrolytes. The use of the Bi2O3–CuO sintering aid allowed Zeng et al. to obtain dense (Ni0.2Cu0.2Zn0.6O)1.03(Fe2O3)0.97 ceramic at a low temperature [34]. Many studies have shown the positive effect of Fe2O3 as a sintering aid on the properties of Gd0.1Ce0.9O1.95 [35,36], Gd0.2Ce0.8O2−δ [37], GdSmZr2O7 [38] and Sr2Fe1.5Mo0.5O6-δ [39]. In [40], the effect of CuO, ZnO, Al2O3, NiO, Fe2O3, Co3O4 and MoO3 on the properties of the La0.9Sr0.1ScO3−δ electrolyte was investigated. The findings revealed that the incorporation of Co3O4 resulted in the most optimal outcome. The investigation of the solid proton-conducting electrolyte BaSn0.8Y0.2O3−δ with the CuO sintering aid was performed by Starostina et al. in [41].
In the case of electrode materials, the utilization of sintering aids makes it possible to increase electrode conductivity and improve electrode adhesion to the electrolyte. In [42], it was demonstrated that the incorporation of the Bi0.75Y0.25O2−δ + CuO aid markedly influences the conductivity and electrochemical activity of LaNi0.6Fe0.4O3−δ electrodes. In [43], it was shown that the introduction of 1–3 wt.% CuO into the cathode material based on lanthanum nickelate increases its electrical conductivity by 2–3 times. The positive effect of copper oxide on the properties of electrode materials was also noted in [44].
Among the various high-temperature electrochemical devices, it is noteworthy to mention the so-called symmetrical electrochemical cells [45,46,47], which consist of a highly conductive supporting electrolyte and a cathode and anode of the same chemical composition. In such cells, electrolytes with high conductivity, based on lanthanum gallate, are typically utilized as the supporting substrate. Additionally, complex oxides based on alkaline earth metal ferrites, which demonstrate stability in oxidizing and reducing atmospheres, are employed as electrodes [48,49,50,51,52,53,54].
In [55,56], a comprehensive study was carried out to elucidate the impact of sintering aids, including barium, bismuth, aluminum, calcium, silicon, zinc, vanadium, lithium, boron, copper, nickel, cobalt, iron and manganese oxides, on the sintering ability, phase composition, and electrical conductivity of the La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolyte. A review paper [57] on sintering aids for gallate electrolytes demonstrated that the use of sintering aids enables the production of denser ceramics or the reduction in the final sintering temperature.
There is a paucity of studies that examine the impact of sintering aids on the characteristics of redox-stable electrodes utilized in symmetrical electrochemical cells. In [58], the influence of CuO, MnO2, and Fe2O3 on the properties of Ba2FeMoO6 electrodes was examined, and it was determined that copper oxide represents the most effective sintering aid for ferrite-molybdate. In [59], it was noted that the utilization of copper oxide as a sintering aid for strontium ferrite-based electrodes for symmetrical cells results in enhanced electrochemical activity of the electrodes.
In our previous study, we initiated the development of an approach to the chemical design of electrochemical cells with a close ionic composition of the electrolyte and electrodes. To this end, we conducted a series of studies on a gallate-based electrolyte in which part of the gallium cations was replaced by iron cations, bringing it closer to the chemical composition of La0.6Sr0.4FeO3−δ electrodes [60]. The purpose of this study was to examine the impact of an iron oxide as a sintering aid on the transport properties of the electrolyte, specifically on the bulk and grain boundary resistance as a function of the sintering temperature and on the electrochemical activity of La0.6Sr0.4FeO3-δ electrodes. In the context of electrode material research, we also performed a comparative analysis of the efficiency of iron oxide versus the more extensively studied CuO sintering aid.

2. Materials and Methods

In order to prepare the electrolyte with the composition of La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM), a conventional solid-state method was applied using La2O3 (99.9 wt.%), SrCO3 (99.99 wt.%), Ga2O3 (99.9 wt.%) and MgO (99.5 wt.%). The starting compounds were mixed in isopropanol and ground in a PM 100 planetary ball mill (Retsch®, Haan, Germany), and then dried and annealed at 1000 °C for 6 h in air, followed by regrinding in the ball mill. The resulting powder was pressed and sintered for 6 h to obtain dense ceramic samples and the sintering temperatures were 1350, 1400, and 1450 °C. For the samples with a sintering aid, 0.5 wt.% Fe2O3 (99.9%) was added to the powder before pressing and mixed in the planetary mill followed by sintering. Similarly, the solid-state method and the same starting compounds were used in the synthesis of La0.6Sr0.4FeO3−δ (LSF) electrode powder. The first synthesis step was performed at 900 °C for 3 h, and the final sintering step was performed at 1150 °C for 2 h in air. The electrode powder was then ground to an average particle size of about 5 µm with the addition of sintering aids of 3 wt.% Fe2O3 or 3 wt.% CuO.
The samples for high-temperature measurements were prepared in the button type with symmetrical electrodes and the supporting LSGM electrolyte. In order to measure the performance of the electrolyte, the electrodes were made of platinum and sintered at 1050 °C for 2 h. To evaluate the performance of the electrodes, LSF electrodes were fabricated on the base of electrolyte buttons. The electrode ink, which was prepared by mixing an organic binder with the LSF powder, was applied to both sides of LSGM using the print-screen method and sintered at temperatures of 1050, 1100, and 1150 °C.
The X-ray powder diffraction analysis was carried out using a D/MAX-2200 diffractometer (Rigaku Corporation, Takatsuki, Japan) with CuKα-radiation (λ(Kα) = 1.5406 Å, 40 kV, 30 mA) at room temperature in ambient air. The microstructure of the electrolyte and electrolyte/electrode boundary was analyzed by scanning electron microscopy (SEM) using MIRA 3 (Tescan, Brno, Czech Republic) and KYKY-EM8200 (KYKY Technology Co., Ltd., Beijing, China) electron microscopes.
An investigation of the high-temperature performance of the LSGM electrolyte was carried out using impedance spectroscopy with the P-40X instrument (Elins, Chernogolovka, Russia) over a temperature range of 200–550 °C in atmospheres with various oxygen partial pressures (pO2 = 0.21 and 10−22 atm). A high-temperature Pt/YSZ/Pt pump, located in a discrete furnace and operating at 800 °C, was used to remove oxygen from the air. The contributions of the bulk and grain boundary resistance to the total resistance of the LSGM electrolyte were determined using ZView software, version 2.80 (Scribner Associates Inc., Southern Pines, NC, USA).
The electrochemical performance of LSF electrodes was investigated through impedance spectroscopy, using a Solartron FRA-1260 and EI-1287 (Ametek, Hampshire, UK) in both air and wet (3 vol.% H2O) hydrogen atmospheres. For the distribution of relaxation time (DRT) analysis of the impedance spectra, the original software based on Tikhonov’s regularization was utilized.

3. Results

3.1. XRD Certification

X-ray diffractograms of the investigated LSGM and LSF powders are shown in Figure 1. The powders were found to be single phase. The stability of LSF in pure hydrogen atmosphere was also verified. The chemical and structural stability of LSF in a hydrogen atmosphere is an important property for studying the electrochemical activity of LSF electrodes (these data are shown below). The results showed that no impurity phases are formed in LSF after 24 h of exposure at 800 °C in a hydrogen atmosphere (purity of at least 99.99 vol.%). The compatibility of LSF + LSGM (mass ratio 1/1) was also tested at 1150 °C for 2 h, which corresponds to the sintering conditions of LSF electrodes. The XRD study of the LSGM + LSF powder showed some minor peaks in 30° regions (Figure 1), which can be attributed to SrLaGa3O7 and/or SrLaGaO4 phases [26,61]. The formation of magnesium-free phases has been observed in many studies [62,63,64]. Taking into account the minor concentration of these phases (not exceeding 1 wt.%), it can be reasonably assumed that its presence will not affect the primary properties of the LSF electrodes. It is also important to note that the sintering additives (copper and iron oxides) examined in this study are reduced to metal in a reducing atmosphere. These results will not be presented here, as they represent basic data. However, a discussion of this topic will be provided later in the paper.

3.2. Electrolyte Performance

The following section examines the electrochemical behavior of the LSGM electrolyte. Figure 2 illustrates the temperature-dependent electrical conductivity of LSGM samples under atmospheres with various oxygen partial pressures. It can be observed that, under all investigated conditions, an increase in sintering temperature and the addition of the Fe2O3 sintering aid correlates with an improvement in electrical conductivity. However, the activation energy of electrical conductivity remains almost unchanged (Table 1).
To obtain a better understanding of the influence of sintering temperature and introduction of the sintering aid on electrical conductivity of the electrolyte, the contributions of grain bulk and grain boundaries to the electrolyte’s conductivity were determined. At temperatures below 400 °C, two semicircles, corresponding to the bulk and grain boundary resistances, can be clearly observed on the impedance spectra (insert in Figure 3a). Thus, impedance data were analyzed according to the equivalent circuit (RQ)bulk(RQ)gb. Using the obtained values of the resistances, conductivities of the grain bulk and the grain boundaries were calculated (Figure 3a–d). One can see that in both atmospheres, the bulk conductivity remains almost the same, while grain boundary conductivity strongly depends on sintering temperature and Fe2O3 addition. Both the increase in sintering temperature and introduction of the sintering aid led to an increase in the grain boundary conductivity. Activation energy values of bulk and grain boundary conductivity are close for all the samples and conditions, and remain almost the same for all the cases (Table 1). Figure 3e,f also summarize the total, bulk and grain boundary conductivity for all the samples and conditions at a constant temperature. The addition of Fe2O3 along with sintering at 1400 °C results in a conductivity even higher than that after sintering at 1450 °C without the sintering aid. Further improvement can be achieved with sintering at 1450 °C. Sintering at 1350 °C is not enough even with the Fe2O3 addition.
Microscopic examination of chipped electrolyte samples showed that individual grains are difficult to distinguish in this case (Figure 4). In contrast, the relief of the chip surface is clearly visible, which is especially pronounced for the sample sintered at 1350 °C without a sintering aid. This indicates weaker intergranular contact and, consequently, lower grain-to-grain conductivity.

3.3. Electrochemical Performance of the Electrodes

The following section examines the electrochemical behavior of La0.6Sr0.4FeO3−δ (LSF) electrodes in contact with the LSGM electrolyte, with a focus on the impact of the sintering aids, sintering temperature of the electrode, and gas environment. This study compares two sintering aids: copper oxide, as a widely used sintering aid, and iron oxide, which closely aligns with the chemical composition of the electrode. As previously stated in the experimental section, this study did not vary the mass fraction of the sintering additive. Instead, electrodes were produced with only 3 wt.%, in accordance with the previously obtained data [59]. The designation of the electrodes is provided in Table 2. It should be noted that the production of a high-quality LSF electrode in the range of sintering temperatures 1000–1250 °C was not possible without the use of sintering aids. The electrode exhibited poor adhesion, crumbled, and did not conduct an electric current. Attempts to measure electrochemical performance were unsuccessful.
In the studies of LSF electrodes with the sintering aids, it was demonstrated that the polarization resistance in air is significantly dependent on the sintering temperature (Figure 5a). Therefore, at a study temperature of 800 °C, the polarization resistance exhibited a four-fold variation as a function of the sintering temperature. The 1050-Cu sample exhibited the most favorable outcomes, with a value of approximately 0.25 Ω cm2, while the 1150-Cu sample demonstrated the least favorable outcomes, with a value of approximately 1 Ω cm2. The 1050-Fe electrode demonstrated intermediate-quality results, exhibiting a polarization resistance of approximately 0.45 Ω cm2 at 800 °C. It is noteworthy that the slope of the temperature dependence (activation energy) of the polarization resistance of electrodes with copper oxide and iron oxide addition was found to be relatively high, approximately 140 kJ/mol, and exhibited minimal dependence on the sintering temperature, suggesting the potential for these electrode materials in the high-temperature region. For a more detailed understanding of how the sintering temperature affects the electrode reaction mechanism, impedance spectra and DRT functions calculated from them were considered (Figure 5b and Figure 5c, respectively). For all investigated electrodes, the spectra are a single half-circle with no visual separation into semicircles. However, despite the visual similarity of the spectra, the obtained DRT functions differ significantly. Thus, the 1000-Cu sample is characterized by the presence of a split peak in the frequency range of 2–100 Hz. For electrodes 1050-Cu and 1100-Cu, the DRT functions register only one main peak with a frequency at the maximum of about 1 Hz. For these samples, minor peaks of very low intensity are also present; we do not consider them since the contribution of these stages to the polarization resistance is not significant. For 1150-Cu, two peaks are found, one of low intensity at 1 Hz and one with high intensity at 0.1 Hz. A distinct trend can be observed in the case of utilizing copper oxide as a sintering aid. The nature of the rate-determining steps of the oxygen reduction reaction changes with increasing sintering temperature, and their specific frequencies are shifted to the low-frequency region. In the case of the 1050-Fe sample, the DRT function is comparable to that of the 1000-Cu, albeit exhibiting a slight shift towards the high-frequency region (Figure 5c). This behavior can be attributed to the higher melting temperature of iron oxide in comparison to copper oxide. The number of peaks and their relaxation frequencies, as derived from the DRT functions, allow us to hypothesize about the nature of the stages that limit the rate of the oxygen reduction reaction. In the case of the 1000-Cu sample, these processes are observed at the electrode/electrolyte boundaries and between the electrode particles. They appear to be related to the slow transport of electrons and/or oxygen ions across the boundaries, which can be attributed to the low sintering temperature of the electrode and the poor quality of the interfacial boundaries. As the sintering temperature increases, the electrode adhesion increases and the rate of electron and ion transport across the boundaries increases. For electrodes sintered at higher temperatures of 1050-Cu and 1100-Cu, the rate-determining stage of oxygen reduction is the interfacial exchange of electrode oxygen with the gas phase [39]. The DRT function for the 1150-Cu sample exhibits a low-frequency peak, which is characteristic of gas diffusion processes [65]. This peak is a consequence of a notable reduction in electrode porosity at the sintering temperature of 1150 °C. Consequently, the porosity estimation derived from micrographs using the ImageJ software (version 1.51j8) package indicated a value of approximately 62% for the 1050-Cu sample and approximately 35% for the 1150-Cu sample (Figure 5d).
As previously stated in the Introduction, symmetrical electrochemical cell electrodes must operate efficiently in both oxidizing and reducing atmospheres. Accordingly, we proceeded to examine the electrochemical behavior of LSF electrodes in a wet hydrogen atmosphere. Figure 6a illustrates the temperature dependence of the polarization resistance of LSF electrodes in a wet hydrogen atmosphere. A comparison of these data with the results presented in Figure 5a reveals that the sintering temperature and the type of sintering aid exert disparate effects on electrode performance in different atmospheres. In particular, the polarization resistance of the samples with copper oxide was observed to increase with an elevated sintering temperature. The lowest polarization resistance was observed for the 1000-Cu sample, reaching approximately 1.7 Ω cm2 at 800 °C. Conversely, the highest polarization resistance was recorded for the 1150-Cu sample, approximately 6.5 Ω cm2 at the same temperature. It is noteworthy that the polarization resistance of the 1050-Fe electrode exhibited the highest performance among all studied samples, reaching approximately 1.3 Ω cm2 at 800 °C. The results demonstrated that the activation energy of the polarization resistance in a wet hydrogen atmosphere is nearly identical to that observed in air (Figure 5a and Figure 6a). This finding suggests that the rate of the hydrogen oxidation reaction may be constrained by the same processes that regulate the oxygen reduction reaction. Figure 6b presents a comparison of the polarization resistance for all investigated electrodes in various atmospheres at 800 °C. From the perspective of utilizing the electrodes in symmetrical cells, electrode 1050-Fe demonstrates the most effective performance. It exhibits the most optimal values of polarization resistance in both oxidizing and reducing atmospheres. A comparison of the obtained values of polarization resistance for 1050-Fe with the literature data for electrodes of symmetrical electrochemical devices reveals that it is on a par with the majority of the studied ferrites, with the exception of the most promising materials for symmetrical electrodes based on strontium ferrite-molybdate (Table 3).
A comparison of the electrochemical impedance spectra of 1050-Fe in oxidizing and reducing atmospheres reveals significant differences (Figure 7a). The DRT functions calculated from these spectra revealed that the primary discrepancies in the mechanisms of hydrogen oxidation and oxygen reduction reactions are associated with the emergence of a high-frequency process of considerable intensity in the reducing atmosphere. In contrast, the remaining peaks were previously observed on the DRT function for the oxidizing atmosphere and exhibited only minor alterations following the transition to the reducing atmosphere. A consideration of the DRT functions for all the studied samples in the atmosphere of wet hydrogen reveals that, according to a rough approximation, the mechanism of hydrogen reduction at all the studied electrodes is essentially the same. This is in contrast to the air atmosphere, where shifts of peaks or the appearance of new ones are observed. Instead, in the wet hydrogen atmosphere, only changes in peak intensity are evident (Figure 7b). The high-frequency peak is characterized by the greatest intensity changes. Given the relaxation frequency of this peak, it can be posited that this process represents a stage of charge transfer at the triple-phase boundary. This assertion is indirectly corroborated by the capacitance value calculated from the impedance spectrum, which is approximately 5 × 10−6 F/cm2. This stage is localized at the three-phase electrolyte/electrode/gas boundary. It can therefore be reasonably assumed that with the increase in the sintering temperature, there is an increase in the area of contact between the electrolyte and the electrode, and the extent of the triple-phase boundary decreases. This leads to an increase in the resistance of this stage. As illustrated in Figure 5c in an oxidizing atmosphere, this step in the DRT function is absent. This is due to the fact that LSF exhibits markedly enhanced oxygen and electronic conductivities in an oxidizing atmosphere, allowing this stage to be localized at the electrode/gas dual-phase boundary. The remaining stages of the electrode reaction for hydrogen oxidation are analogous to those observed previously for the oxygen reaction and include the particles’ adsorption, interfacial exchange with the gas phase, and the gas diffusion stage. It is noteworthy that in the case of a wet hydrogen atmosphere, the response from the gas diffusion stage is registered for all electrodes, which is a distinctive feature of the hydrogen atmosphere due to the high coefficient of interdiffusion of the gas mixture in comparison to the air [78]. The reasons why the DRT functions for 1000-Cu and 1050-Fe were similar have been previously stated and appear to be related to the higher melting point of iron oxide compared to copper oxide, which affects the microstructure of the electrode and its adhesion to the electrolyte. It is also noteworthy that in a wet hydrogen atmosphere, both sintering aids are reduced to metal. As evidenced by [79], iron exhibits slightly greater activity in the dissociative adsorption reaction of hydrogen compared to copper. This results in a slightly higher activity of the 1050-Fe electrode compared to that of the 1000-Cu electrode in a wet hydrogen atmosphere.

4. Conclusions

In this study, we investigated the effect of iron oxide as a sintering aid on the performance of a highly conductive electrolyte based on lanthanum gallate and La0.6Sr0.4FeO3−δ electrodes, which are promising components of symmetrical electrochemical devices on solids. It was demonstrated that the use of 0.5 wt.% Fe2O3 as a sintering aid for the La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte leads to a significant increase in the grain boundary conductivity by forming better grain-to-grain contact. For the La0.6Sr0.4FeO3−δ electrode material, a comparative study of the copper oxide sintering aid was additionally performed. It was shown for the first time that the nature of the sintering aid and the sintering temperature exert disparate effects on the activity of electrodes, depending on the gas environment (air or hydrogen). The findings demonstrate that the nature of the rate-determining stages of the electrode reactions of hydrogen oxidation and oxygen reduction can be altered based on the sintering temperature. Among the electrodes studied, La0.6Sr0.4FeO3−δ with 3 wt.% Fe2O3 at a sintering temperature of 1050 °C exhibited optimal activity in both the oxidizing and reducing media.

Author Contributions

Investigations, formal analysis, writing—original draft preparation, E.G. and E.A.; conceptualization, methodology, investigation, writing—original draft preparation, E.A. and D.O.; conceptualization, supervision, acquisition of funding, writing—review and editing, D.O. All authors have read and agreed to the published version of the manuscript.

Funding

The study was funded by a grant of the Russian Science Foundation (grant number 24-19-00040), https://rscf.ru/project/24-19-00040/ (accessed on 4 September 2024).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author/s.

Acknowledgments

The study was, in part, carried out using the equipment of the Shared Access Center of “Composition of Compounds” at the IHTE UB RAS. The authors are grateful to Tamara Kuznetsova and Anastasia Tkachyk for their research assistance.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Talukdar, A.; Chakrovorty, A.; Sarmah, P.; Paramasivam, P.; Kumar, V.; Yadav, S.K.; Manickkam, S. A review on solid oxide fuel cell technology: An efficient energy conversion system. Int. J. Energy Res. 2024, 2024, 6443247. [Google Scholar] [CrossRef]
  2. Chasta, G.; Himanshu; Dhaka, M.S. A review on materials, advantages, and challenges in thin film based solid oxide fuel cells. Int. J. Energy Res. 2022, 46, 14627–14658. [Google Scholar] [CrossRef]
  3. Dunyushkina, L.A. Solid oxide fuel cells with a thin film electrolyte: A review on manufacturing technologies and electrochemical characteristicses. Electrochem. Mater. Technol. 2022, 1, 20221006. [Google Scholar] [CrossRef]
  4. Demin, A.K.; Bronin, D.I. Solid state electrochemical devices for hydrogen energy. Electrochem. Mater. Technol. 2023, 2, 20232016. [Google Scholar] [CrossRef]
  5. Zong, S.; Zhao, X.; Jewell, L.L.; Zhang, Y.; Liu, X. Advances and challenges with SOEC high temperature co-electrolysis of CO2/H2O: Materials development and technological design. Carbon Capture Sci. Technol. 2024, 12, 100234. [Google Scholar] [CrossRef]
  6. Lahrichi, A.; El Issmaeli, Y.; Kalanur, S.S.; Pollet, B.G. Advancements, strategies, and prospects of solid oxide electrolysis cells (SOECs): Towards enhanced performance and large-scale sustainable hydrogen production. J. Energy Chem. 2024, 94, 688–715. [Google Scholar] [CrossRef]
  7. Guo, S.; Jiang, L.; Li, Y.; Zhong, P.; Ismail, S.A.; Norby, T.; Han, D. From electrolyte and electrode materials to large-area protonic ceramic fuel cells: A review. Adv. Funct. Mater. 2024, 34, 2304729. [Google Scholar] [CrossRef]
  8. Osinkin, D.; Tropin, E. Hydrogen production from methane and carbon dioxide mixture using all-solid-state electrochemical cell based on a proton-conducting membrane and redox-robust composite electrodes. J. Energy Chem. 2022, 69, 576–584. [Google Scholar] [CrossRef]
  9. Rosensteel, W.A.; Ricote, S.; Sullivan, N.P. Hydrogen permeation through dense BaCe0.8Y0.2O3−δ–Ce0.8Y0.2O2−δ composite-ceramic hydrogen separation membranes. Int. J. Hydrog. Energy 2016, 41, 2598–2606. [Google Scholar] [CrossRef]
  10. Kalyakin, A.S.; Volkov, A.N.; Gorshkov, M.Y. Stability and reproducibility of solid electrolyte amperometry sensors at the analysis of hydrogen in nitrogen-containing gas mixtures. Electrochem. Mater. Technol. 2024, 3, 20243026. [Google Scholar] [CrossRef]
  11. Starostin, G.; Volkov, A.N.; Kalyakin, A.S.; Medvedev, D.A. High-temperature gas sensors based on proton-conducting ceramic oxides. A brief review. Ceram. Int. 2024, 50, 37449–37459. [Google Scholar] [CrossRef]
  12. Kalyakin, A.S.; Volkov, A.N.; Mirzayants, D.P. Stability and reproducibility of the amperometric sensors for oxygen concentration analysis in the nitrogen gas mixtures. Electrochem. Mater. Technol. 2024, 3, 20243027. [Google Scholar] [CrossRef]
  13. Abdalla, A.M.; Azad, A.T.; Madian, A.B.; Omeiza, L.A.; Subramanian, Y.; Wei, B.; Taweekun, J.; Khairat Dawood, M.M.; Azad, A.K. All-protonic fuel cell designs and developments fuelled by ammonia. Environ. Sci. Pollut. Res. 2024, 31, 46769–46789. [Google Scholar] [CrossRef] [PubMed]
  14. Kumar, A.; Vibhu, V.; Bassat, J.M.; Nohl, L.; de Haart, L.G.J.B.; Bouvet, M.; Eichel, R.A. Ammonia as a potential energy vector in the burgeoning hydrogen economy. ChemElectroChem 2024, 11, e202300845. [Google Scholar] [CrossRef]
  15. Thyssen, V.V.; Vilela, V.B.; de Florio, D.Z.; Ferlauto, A.S.; Fonseca, F.C. Direct conversion of methane to C2 hydrocarbons in solid-state membrane reactors at high temperatures. Chem. Rev. 2022, 122, 3966–3995. [Google Scholar] [CrossRef]
  16. Omeiza, L.A.; Kabyshev, A.; Bekmyrza, K.; Kuterbekov, K.A.; Kubenova, M.; Zhumadilova, Z.A.; Subramanian, Y.; Ali, M.; Aidarbekov, N.; Azad, A.K. Constraints in sustainable electrode materials development for solid oxide fuel cell: A brief review. Mater. Sci. Energy Technol. 2025, 8, 32–43. [Google Scholar] [CrossRef]
  17. Omeiza, L.A.; Kuterbekov, K.A.; Kabyshev, A.; Bekmyrza, K.; Kubenova, M.; Afroze, S.; Bakar, S.A.; Azad, A.K. Limitations and trends on cobalt-free cathode materials development for intermediate-temperature solid oxide fuel cell- an updated technical review. Emergent Mater. 2024, 1–6. [Google Scholar] [CrossRef]
  18. Pikalova, E.Y.; Kalinina, E.G.; Pikalova, N.S. Recent advances in electrophoretic deposition of thin-film electrolytes for intermediate-temperature solid oxide fuel cells. Electrochem. Mater. Technol. 2023, 2, 20232011. [Google Scholar] [CrossRef]
  19. Zamudio-García, J.; dos Santos-Gómez, L.; Losilla, E.R.; Marrero-López, D. Exploring alkali metal doping in solid oxide cells materials: A comprehensive review. Chem. Eng. J. 2024, 493, 152832. [Google Scholar] [CrossRef]
  20. Hadi, N.H.; Somalu, M.R.; Samat, A.A.; Muchtar, A.; Baharuddin, N.A.; Anwar, M. A review on the preparation of anode materials and anode films for solid oxide fuel cell applications. Int. J. Energy Res. 2021, 45, 14357–14388. [Google Scholar] [CrossRef]
  21. Pikalova, E.Y.; Guseva, E.M.; Filonova, E.A. Short review on recent studies and prospects of application of rare-earth-doped La2NiO4+δ as air electrodes for solid-oxide electrochemical cells. Electrochem. Mater. Technol. 2023, 2, 20232025. [Google Scholar] [CrossRef]
  22. Ahmed, N.; Devi, S.; Dar, M.A.; Ibrahim, S.K.M.; Sharma, A.; Sharma, N.; Paul, S.; Ahamed, S.R. Anode material for solid oxide fuel cell: A review. Indian J. Phys. 2024, 98, 877–888. [Google Scholar] [CrossRef]
  23. Rafique, M.; Nawaz, H.; Shahid Rafique, M.; Bilal Tahir, M.; Nabi, G.; Khalid, N.R. Material and method selection for efficient solid oxide fuel cell anode: Recent advancements and reviews. Int. J. Energy Res. 2019, 43, 2423–2446. [Google Scholar] [CrossRef]
  24. Porotnikova, N.; Osinkin, D. Segregation and interdiffusion processes in perovskites: A review of recent advances. J. Mater. Chem. A 2024, 12, 2620–2646. [Google Scholar] [CrossRef]
  25. Horita, T. Chromium poisoning for prolonged lifetime of electrodes in solid oxide fuel cells—Review. Ceram. Int. 2021, 47, 7293–7306. [Google Scholar] [CrossRef]
  26. Erpalov, M.V.; Tarutin, A.P.; Danilov, N.A.; Osinkin, D.A.; Medvedev, D.A. Chemistry and electrochemistry of CeO2-based interlayers: Prolonging the lifetime of solid oxide fuel and electrolysis cells. Russ. Chem. Rev. 2023, 92, RCR5097. [Google Scholar] [CrossRef]
  27. Balabanov, S.S.; Belyaev, A.V.; Novikova, A.V.; Permin, D.A.; Rostokina, E.Y.; Yavetskiy, R.P. Densification peculiarities of transparent MgAl2O4 Ceramics—Effect of LiF sintering Additive. Inorg. Mater. 2018, 54, 1045–1050. [Google Scholar] [CrossRef]
  28. Frage, N.; Kalabukhov, S.; Sverdlov, N.; Kasiyan, V.; Rothman, A.; Dariel, M.P. Effect of the spark plasma sintering (SPS) parameters and LiF doping on the mechanical properties and the transparency of polycrystalline Nd-YAG. Ceram. Int. 2012, 38, 5513–5519. [Google Scholar] [CrossRef]
  29. Meir, S.; Kalabukhov, S.; Froumin, N.; Dariel, M.P.; Frage, N. Synthesis and densification of transparent magnesium aluminate spinel by SPS processing. J. Am. Ceram. Soc. 2009, 92, 358–364. [Google Scholar] [CrossRef]
  30. Li, J.; Wang, C.; Wang, X.; Bi, L. Sintering aids for proton-conducting oxides—A double-edged sword? A mini review. Electrochem. Commun. 2020, 112, 106672. [Google Scholar] [CrossRef]
  31. Hostaša, J.; Picelli, F.; Hříbalová, S.; Nečina, V. Sintering aids, their role and behaviour in the production of transparent ceramics. Open Ceram. 2021, 7, 100137. [Google Scholar] [CrossRef]
  32. Bi, L.; Traversa, E. Synthesis strategies for improving the performance of doped-BaZrO3 materials in solid oxide fuel cell applications. J. Mater. Res. 2014, 29, 1–15. [Google Scholar] [CrossRef]
  33. Hagy, L.S.; Ramos, K.; Gelfuso, M.V.; Chinelatto, A.L.; Chinelatto, A.S.A. Effects of ZnO addition and microwave sintering on the properties of BaCe0.2Zr0.7Y0.1O3-δ proton conductor electrolyte. Ceram. Int. 2023, 49, 17261–17270. [Google Scholar] [CrossRef]
  34. Zeng, T.; Jia, L.; Chen, Z.; Yang, M.; Luo, R. Effects of Bi2O3–CuO additives on microstructure and microwave properties of low-temperature-sintered NiCuZn ferrite ceramics. Ceram. Int. 2024, 50, 6388–6394. [Google Scholar] [CrossRef]
  35. Zhang, G.; Zheng, G.; Huang, Z.; Bao, X.; Shi, C.; Yang, X.; Zhou, J.; Chen, T.; Wang, S. The effect of Fe2O3 sintering aid on Gd0.1Ce0.9O1.95 diffusion barrier layer and solid oxide fuel cell performance. Int. J. Hydrogen Energy 2023, 48, 21908–21919. [Google Scholar] [CrossRef]
  36. Mehranjani, A.S.; Cumming, D.J.; Sinclair, D.C.; Rothman, R.H. Low-temperature co-sintering for fabrication of zirconia/ceria bi-layer electrolyte via tape casting using a Fe2O3 sintering aid. J. Eur. Ceram. Soc. 2017, 37, 3981–3993. [Google Scholar] [CrossRef]
  37. Zhang, T.S.; Ma, J.; Kong, L.B.; Chan, S.H.; Hing, P.; Kilner, J.A. Iron oxide as an effective sintering aid and a grain boundary scavenger for ceria-based electrolytes. Solid State Ionics 2004, 167, 203–207. [Google Scholar] [CrossRef]
  38. Liu, Z.G.; Ouyang, J.H.; Ren, Z.; Sun, K.N.; Zhou, Y. Influence of Fe2O3 addition on the densification and oxygen ion conductivity of the GdSmZr2O7 ceramic. J. Eur. Ceram. Soc. 2014, 34, 3735–3740. [Google Scholar] [CrossRef]
  39. Porotnikova, N.M.; Ananyev, M.V.; Osinkin, D.A.; Khodimchuk, A.V.; Fetisov, A.V.; Farlenkov, A.S.; Popov, A.I. Increase in the density of Sr2Fe1.5Mo0.5O6-δ membranes through an excess of iron oxide: The effect of iron oxide on transport and kinetic parameters. Surf. Interfaces 2022, 29, 101784. [Google Scholar] [CrossRef]
  40. Kuzmin, A.V.; Lesnichyova, A.S.; Tropin, E.S.; Stroeva, A.Y.; Vorotnikov, V.A.; Solodyankina, D.M.; Belyakov, S.A.; Plekhanov, M.S.; Farlenkov, A.S.; Osinkin, D.A.; et al. LaScO3-based electrolyte for protonic ceramic fuel cells: Influence of sintering additives on the transport properties and electrochemical performance. J. Power Sources 2020, 466, 228255. [Google Scholar] [CrossRef]
  41. Starostina, I.A.; Starostin, G.N.; Akopian, M.T.; Vdovin, G.K.; Osinkin, D.A.; Py, B.; Maradesa, A.; Ciucci, F.; Medvedev, D.A. Insight into grain and Grain-boundary Transport of Proton-conducting Ceramics: A case Report of BaSn0.8Y0.2O3−δ. Adv. Funct. Mater. 2024, 34, 2307319. [Google Scholar] [CrossRef]
  42. Osinkin, D.; Bogdanovich, N. Sintering aid Strategy for promoting Oxygen reduction Reaction on High-performance Double-layer LaNi0.6Fe0.4O3–δ composite Electrode for devices Based on Solid-state Membranes. Membranes 2023, 13, 603. [Google Scholar] [CrossRef] [PubMed]
  43. Kolchugin, A.A.; Pikalova, E.Y.; Bogdanovich, N.M.; Bronin, D.I. The effect of copper on the properties of La1.7Ca0.3NiO4+δ-based cathodes for solid oxide fuel cells. Russ. J. Electrochem. 2015, 51, 483–490. [Google Scholar] [CrossRef]
  44. Kuzin, B.L.; Bogdanovich, N.M.; Bronin, D.I.; Yaroslavtsev, I.Y.; Vdovin, G.K.; Kotov, Y.A.; Bagazeev, A.V.; Medvedev, A.I.; Murzakaev, A.M.; Timoshenkova, O.P.; et al. Electrochemical properties of cathodes made of (La,Sr)(Fe,Co)O3 containing admixtures of nanoparticles of cupric oxide and intended for fuel cells with a solid electrolyte based on ceric oxide. Russ. J. Electrochem. 2007, 43, 920–928. [Google Scholar] [CrossRef]
  45. Md Harashid, M.A.; Chen, R.S.; Ahmad, S.H.; Ismail, A.F.; Baharuddin, N.A. Recent advances in electrode material for symmetrical solid oxide fuel cells and way forward sustainability based on local mineral resources. Int. J. Energy Res. 2022, 46, 22188–22221. [Google Scholar] [CrossRef]
  46. Gu, J.; Zhang, X.; Zhao, Y.; Alodhayb, A.; Sun, Y.; Bu, Y. Advances and challenges in symmetrical solid oxide electrolysis cells: Materials development and resource utilization. Mater. Chem. Front. 2023, 7, 3904–3921. [Google Scholar] [CrossRef]
  47. Zhu, K.; Luo, B.; Liu, Z.; Wen, X. Recent advances and prospects of symmetrical solid oxide fuel cells. Ceram. Int. 2022, 48, 8972–8986. [Google Scholar] [CrossRef]
  48. Istomin, S.Y.; Lyskov, N.V.; Mazo, G.N.; Antipov, E.V. Electrode materials based on complex d-metal oxides for symmetrical solid oxide fuel cells. Russ. Chem. Rev. 2021, 90, 644–676. [Google Scholar] [CrossRef]
  49. Yu, W.; Zhang, D.; Zhang, X.; Liu, T.; Wang, Y. Advanced Ru-Infiltrated Perovskite Oxide Electrodes for Boosting the Performance of Syngas Fueled Solid Oxide Fuel Cell. ChemElectroChem 2022, 9, e202200024. [Google Scholar] [CrossRef]
  50. Zhang, D.; Zhou, J.; Luo, Y.; Wang, Y.; Zhang, X.; Chen, X.; Liu, T.; Ding, M. Robust cobalt-free perovskite type electrospun nanofiber cathode for efficient electrochemical carbon dioxide reduction reaction. J. Power Sources 2023, 587, 233705. [Google Scholar] [CrossRef]
  51. Luo, Y.; Zhang, D.; Liu, T.; Chang, X.; Wang, J.; Wang, Y.; Gu, X.; Ding, M. In Situ Exsolution of Quaternary Alloy Nanoparticles for CO2-CO Mutual Conversion Using Reversible Solid Oxide Cells. Adv. Funct. Mater. 2024, 34, 2403922. [Google Scholar] [CrossRef]
  52. Liu, X.; Han, D.; Zhou, Y.; Meng, X.; Wu, H.; Li, J.; Zeng, F.; Zhan, Z. Sc-substituted La0.6Sr0.4FeO3-δ mixed conducting oxides as promising electrodes for symmetrical solid oxide fuel cells. J. Power Sources 2014, 246, 457–463. [Google Scholar] [CrossRef]
  53. Lu, C.; Niu, B.; Yu, S.; Yi, W.; Luo, S.; Xu, B.; Ji, Y. Efficient and stable symmetrical electrode La0.6Sr0.4Co0.2Fe0.7Mo0.1O3-δ for direct hydrocarbon solid oxide fuel cells. Electrochim. Acta 2019, 323, 134857. [Google Scholar] [CrossRef]
  54. Yang, Z.; Chen, Y.; Jin, C.; Xiao, G.; Han, M.; Chen, F. La0.7Sr0.3Fe0.7Ga0.3O3-δ as electrode material for a symmetrical solid oxide fuel cell. RSC Adv. 2015, 5, 2702–2705. [Google Scholar] [CrossRef]
  55. Larregle, S.C.; Baque, L.; Mogni, L. Effect of aid-sintering additives in processing of solid oxide fuel cells electrolytes by tape casting. Solid State Ionics 2023, 394, 116210. [Google Scholar] [CrossRef]
  56. Ha, S.B.; Cho, Y.H.; Kang, Y.C.; Lee, J.H.; Lee, J.H. Effect of oxide additives on the sintering behavior and electrical properties of strontium- and magnesium-doped lanthanum gallate. J. Eur. Ceram. Soc. 2010, 30, 2593–2601. [Google Scholar] [CrossRef]
  57. Gordeev, E.V.; Porotnikova, N.M. Approaches for the preparation of dense ceramics and sintering aids for Sr/mg doped lanthanum gallate: Focus review. Electrochem. Mater. Technol. 2023, 2, 20232022. [Google Scholar] [CrossRef]
  58. Ding, H.; Sullivan, N.P.; Ricote, S. Double perovskite Ba2FeMoO6−δ as fuel electrode for protonic-ceramic membranes. Solid State Ionics 2017, 306, 97–103. [Google Scholar] [CrossRef]
  59. Osinkin, D.A.; Lobachevskaya, N.I.; Bogdanovich, N.M. Effect of the copper Oxide sintering Additive on the electrical and electrochemical Properties of anode materials based on Sr2Fe1.5Mo0.5O6–δ. Russ. J. Appl. Chem. 2017, 90, 1686–1692. [Google Scholar] [CrossRef]
  60. Gordeev, E.; Belyakov, S.; Antonova, E.; Osinkin, D. Highly conductive Fe-doped (La,Sr)(Ga,Mg)O3−δ solid-state membranes for electrochemical application. Membranes 2023, 13, 502. [Google Scholar] [CrossRef]
  61. Kumar, S.; Chakraborty, A.; Kobi, S.; Gopalan, P.; Prasanna, T.R.S. Phase formation between La(Sr)Ga(Mg)O3 and Ce(La)O2 for solid oxide fuel cell applications. J. Am. Ceram. Soc. 2022, 105, 3625–3635. [Google Scholar] [CrossRef]
  62. Sepúlveda, E.; Mangalaraja, R.V.; Troncoso, L.; Jiménez, J.; Salvo, C.; Sanhueza, F. Effect of barium on LSGM electrolyte prepared by fast combustion method for solid oxide fuel cells (SOFC). MRS Adv. 2022, 7, 1167–1174. [Google Scholar] [CrossRef]
  63. Garcia-Garcia, F.J.; Tang, Y.; Gotor, Y.T.; Sayagués, M.J. Development by mechanochemistry of La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolyte for SOFCs. Materials 2020, 13, 1366. [Google Scholar] [CrossRef] [PubMed]
  64. Yoo, J.S.; Lee, S.; Yu, J.H.; Woo, S.K.; Park, H.; Kim, H.G. Fe doping effects on phase stability and conductivity of La0.75Sr0.25Ga0.8Mg0.2O3−δ. J. Power Sources 2009, 193, 593–597. [Google Scholar] [CrossRef]
  65. Almar, L.; Szasz, J.; Weber, A.; Ivers-Tiffee, E. Oxygen transport kinetics of mixed ionic-electronic conductors by coupling focused ion beam tomography and electrochemical impedance spectroscopy. J. Electrochem. Soc. 2017, 164, F289. [Google Scholar] [CrossRef]
  66. Zhang, D.; Zhang, K.; He, T.; Yu, N.; Zhao, Y.; Wang, Y.; Liu, T. Preparation and characterization of a redox-stable Pr0.4Sr0.6Fe0.875Mo0.125O3-δ material as a novel symmetrical electrode for solid oxide cell application. Int. J. Hydrog. Energy 2020, 45, 21825–21835. [Google Scholar] [CrossRef]
  67. Kong, X.; Zhou, X.; Tian, Y.; Wu, X.; Zhang, J.; Zuo, W. Niobium doped lanthanum calcium ferrite perovskite as a novel electrode material for symmetrical solid oxide fuel cells. J. Power Sources 2016, 326, 35–42. [Google Scholar] [CrossRef]
  68. Liu, F.; Zhang, L.; Huang, G.; Niu, B.; Li, X.; Wang, L.; Zhao, J.; Jin, Y. High performance ferrite–based anode La0.5Sr0.5Fe0.9Mo0.1O3–δ for intermediate-temperature solid oxide fuel cell. Electrochem. Acta 2017, 255, 118–126. [Google Scholar] [CrossRef]
  69. Zhao, L.; Chen, K.; Liu, Y.; He, B. A novel layered perovskite as symmetric electrode for direct hydrocarbon solid oxide fuel cells. J. Power Sources 2017, 342, 313–319. [Google Scholar] [CrossRef]
  70. Hou, Y.; Wang, L.; Bian, L.; Wang, Y.; Chou, K. Excellent electrochemical performance of La0.3Sr0.7Fe0.9Ti0.1O3 as a symmetric electrode for solid oxide cells. ACS Appl. Mater. Interfaces 2021, 13, 22381–22390. [Google Scholar] [CrossRef]
  71. Zhou, J.; Shin, T.; Ni, C.; Chen, G.; Wu, K.; Cheng, Y.; Irvine, J.T.S. In situ growth of nanoparticles in layered perovskite La0.8Sr1.2Fe0.9Co0.1O4-δ as an active and stable electrode for symmetrical solid oxide fuel cells. Chem. Mater. 2016, 28, 2981–2993. [Google Scholar] [CrossRef]
  72. Zhou, Q.; Yuan, C.; Han, D.; Luo, T.; Li, J.; Zhan, Z. Evaluation of LaSr2Fe2CrO9-δ as a Potential Electrode for Symmetrical Solid Oxide Fuel Cells. Electrochim. Acta 2014, 133, 453–458. [Google Scholar] [CrossRef]
  73. He, W.; Wu, X.; Dong, F.; Ni, M. A novel layered perovskite electrode for symmetrical solid oxide fuel cells: PrBa(Fe0.8Sc0.2)2O5+δ. J. Power Sources 2017, 363, 16–19. [Google Scholar] [CrossRef]
  74. Tian, D.; Lin, B.; Yang, Y.; Chen, Y.; Lu, X.; Wang, Z.; Liu, W.; Traversa, E. Enhanced performance of symmetrical solid oxide fuel cells using a doped ceria buffer layer. Electrochim. Acta 2016, 208, 318–324. [Google Scholar] [CrossRef]
  75. Gou, M.; Ren, R.; Sun, W.; Xu, C.; Meng, X.; Wang, Z.; Qiao, J.; Sun, K. Nb-doped Sr2Fe1.5Mo0.5O6-δ electrode with enhanced stability and electrochemical performance for symmetrical solid oxide fuel cells. Ceram. Int. 2019, 45, 15696–15704. [Google Scholar] [CrossRef]
  76. Lu, X.; Yang, Y.; Ding, Y.; Chen, Y.; Gu, Q.; Tian, D.; Yu, W.; Lin, B. Mo-doped Pr0.6Sr0.4Fe0.8Ni0.2O3-δ as potential electrodes for intermediate-temperature symmetrical solid oxide fuel cells. Electrochim. Acta 2017, 227, 33–40. [Google Scholar] [CrossRef]
  77. Meng, X.; Wang, Y.; Zhao, Y.; Zhang, T.; Yu, N.; Chen, X.; Miao, M.; Liu, T. In-situ exsolution of nanoparticles from Ni substituted Sr2Fe1.5Mo0.5O6 perovskite oxides with different Ni doping contents. Electrochim. Acta 2020, 348, 136351. [Google Scholar] [CrossRef]
  78. Osinkin, D.A. Identification of gas diffusion phenomena on highly active Ni–ceramic anodes using the DRT technique. J. Power Sources 2023, 571, 233085. [Google Scholar] [CrossRef]
  79. Rossmeisl, J.; Bessler, W.G. Trends in catalytic activity for SOFC anode materials. Solid State Ionics 2008, 178, 1694–1700. [Google Scholar] [CrossRef]
Applsci 14 08923 g001
Figure 1. XRD data for powders LSGM and LSF; for LSF after treatment in hydrogen atmosphere at 800 °C for 24 h; for mixture LSGM + LSF (mass ratio 1/1) sintered at 1150 °C for 2 h.
Figure 1. XRD data for powders LSGM and LSF; for LSF after treatment in hydrogen atmosphere at 800 °C for 24 h; for mixture LSGM + LSF (mass ratio 1/1) sintered at 1150 °C for 2 h.
Applsci 14 08923 g001
Applsci 14 08923 g002
Figure 2. Temperature dependences of the electrical conductivity for the investigated LSGM samples under atmospheres with various oxygen partial pressures: 0.21 atm (a); 10−22 atm (b).
Figure 2. Temperature dependences of the electrical conductivity for the investigated LSGM samples under atmospheres with various oxygen partial pressures: 0.21 atm (a); 10−22 atm (b).
Applsci 14 08923 g002
Applsci 14 08923 g003aApplsci 14 08923 g003b
Figure 3. Temperature dependences of bulk (a,c) and grain boundary (b,d) conductivity for the investigated samples under pO2 = 0.21 atm (air) (a,b) and pO2 = 10−22 atm (c,d). Electrical conductivity of the investigated samples as a function of sintering temperature: bulk and grain boundary conductivity at 350 °C (e); total electrical conductivity at 550 °C (f).
Figure 3. Temperature dependences of bulk (a,c) and grain boundary (b,d) conductivity for the investigated samples under pO2 = 0.21 atm (air) (a,b) and pO2 = 10−22 atm (c,d). Electrical conductivity of the investigated samples as a function of sintering temperature: bulk and grain boundary conductivity at 350 °C (e); total electrical conductivity at 550 °C (f).
Applsci 14 08923 g003aApplsci 14 08923 g003b
Applsci 14 08923 g004aApplsci 14 08923 g004b
Figure 4. SEM images of chipped electrolyte samples. (a–c) LSGM; (d–f) LSGM + Fe2O3. Sintering temperature 1350 °C (a,d); 1400 °C (b,e); 1450 °C (c,f).
Figure 4. SEM images of chipped electrolyte samples. (a–c) LSGM; (d–f) LSGM + Fe2O3. Sintering temperature 1350 °C (a,d); 1400 °C (b,e); 1450 °C (c,f).
Applsci 14 08923 g004aApplsci 14 08923 g004b
Applsci 14 08923 g005
Figure 5. Temperature dependences of the polarization resistance of electrodes in air (a). Impedance spectra of electrodes in air at 800 °C (b). DRT functions calculated from the impedance spectra (c). SEM images of surface of 1050-Cu and 1150-Cu samples (d).
Figure 5. Temperature dependences of the polarization resistance of electrodes in air (a). Impedance spectra of electrodes in air at 800 °C (b). DRT functions calculated from the impedance spectra (c). SEM images of surface of 1050-Cu and 1150-Cu samples (d).
Applsci 14 08923 g005
Applsci 14 08923 g006
Figure 6. Temperature dependences of the polarization resistance of electrodes in wet hydrogen (a). Comparison of the polarization resistance for all investigated electrodes in different atmospheres at 800 °C (b).
Figure 6. Temperature dependences of the polarization resistance of electrodes in wet hydrogen (a). Comparison of the polarization resistance for all investigated electrodes in different atmospheres at 800 °C (b).
Applsci 14 08923 g006
Applsci 14 08923 g007
Figure 7. Impedance spectra and DRT functions for 1050-Fe electrode in various atmospheres at 800 °C (a). DRT functions for the investigated electrodes in the atmosphere of wet hydrogen at 800 °C (b).
Figure 7. Impedance spectra and DRT functions for 1050-Fe electrode in various atmospheres at 800 °C (a). DRT functions for the investigated electrodes in the atmosphere of wet hydrogen at 800 °C (b).
Applsci 14 08923 g007
Table 1. Activation energy of total, bulk and grain boundary conductivity for investigated LSGM samples (kJ/mol) under pO2 = 0.21 atm and pO2 = 10−22 atm.
Table 1. Activation energy of total, bulk and grain boundary conductivity for investigated LSGM samples (kJ/mol) under pO2 = 0.21 atm and pO2 = 10−22 atm.
Without Sintering AidWith Fe2O3 Sintering Aid
Sintering Temperature, °C135014001450135014001450
σtotal (0.21 atm)98 ± 1100 ± 1100 ± 194 ± 198 ± 199 ± 1
σbulk (0.21 atm)98 ± 1101 ± 2101 ± 196 ± 199 ± 1100 ± 1
σgb (0.21 atm)100 ± 199 ± 797 ± 591 ± 184 ± 586 ± 10
σtotal (10−22 atm)98 ± 1101 ± 1102 ± 198 ± 1101 ± 1102 ± 1
σbulk (10−22 atm)101 ± 2101 ± 1101 ± 1102 ± 2100 ± 1103 ± 2
σgb (10−22 atm)97 ± 195 ± 394 ± 495 ± 1100 ± 386 ± 7
Table 2. Designation of La0.6Sr0.4FeO3−δ electrodes with various sintering aids and sintering temperature.
Table 2. Designation of La0.6Sr0.4FeO3−δ electrodes with various sintering aids and sintering temperature.
№ of SampleSintering Temperature/°CSintering AidDesignation
110003 wt.% CuO1000-Cu
210503 wt.% CuO1050-Cu
311003 wt.% CuO1100-Cu
411503 wt.% CuO1150-Cu
510503 wt.% Fe2O31050-Fe
Table 3. Polarization resistances (Ω cm2) of various symmetrical electrodes in contact with LSGM electrolyte at 800 °C.
Table 3. Polarization resistances (Ω cm2) of various symmetrical electrodes in contact with LSGM electrolyte at 800 °C.
ElectrodeRη in AirRη in H2Ref.
La0.6Sr0.4FeO3−δ + 3wt.% Fe2O30.451.3This study
Pr0.4Sr0.6Fe0.875Mo0.125O3−δ1.021.6[66]
La0.9Ca0.1Fe0.9Nb0.1O3−δ0.241.46[67]
La0.5Sr0.5Fe0.9Mo0.1O3−δ-3.2[68]
PrBaMn1.5Fe0.5O5+δ0.220.68[69]
La0.3Sr0.7Fe0.9Ti0.1O3−δ0.0220.15[70]
La0.8Sr1.2Fe0.9Co0.1O4±δ0.291.14[71]
LaSr2Fe2CrO9−δ0.290.57[72]
PrBa(Fe0.8Sc0.2)2O5+δ0.050.18[73]
La0.8Sr0.2FeO3−δ0.480.92[74]
Sr2Fe1.4Nb0.1Mo0.5O6−δ0.0980.22[75]
Pr0.6Sr0.4Fe0.7Ni0.2Mo0.1O3−δ0.50.2[76]
Sr2Fe1.4Ni0.1Mo0.5O6−δ-0.78[77]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Gorgeev, E.; Antonova, E.; Osinkin, D. Sintering Aids Strategies for Improving LSGM and LSF Materials for Symmetrical Solid Oxide Fuel Cell. Appl. Sci. 2024, 14, 8923. https://doi.org/10.3390/app14198923

AMA Style

Gorgeev E, Antonova E, Osinkin D. Sintering Aids Strategies for Improving LSGM and LSF Materials for Symmetrical Solid Oxide Fuel Cell. Applied Sciences. 2024; 14(19):8923. https://doi.org/10.3390/app14198923

Chicago/Turabian Style

Gorgeev, Egor, Ekaterina Antonova, and Denis Osinkin. 2024. "Sintering Aids Strategies for Improving LSGM and LSF Materials for Symmetrical Solid Oxide Fuel Cell" Applied Sciences 14, no. 19: 8923. https://doi.org/10.3390/app14198923

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop