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The development of proton, oxygen‐ion, and electron mixed conducting materials, known as triple‐conduction materials, as cathodes for proton‐conducting solid oxide fuel cells (H‐SOFCs) is highly desired because they can increase fuel cell performance by extending the reaction active area. Although oxygen‐ion and electron conductions can be measured directly, proton conduction in these oxides is usually estimated indirectly. Because of the instability of cathode materials in a reducing environment, direct measurement of proton conduction in cathode oxide is difficult. The La0.8Sr0.2Sc0.5Fe0.5O3–δ (LSSF) cathode material is proposed for H‐SOFCs in this study, which can survive in an H2‐containing atmosphere, allowing measurement of proton conduction in LSSF by hydrogen permeation technology. Furthermore, LSSF is discovered to be a unique proton and electron mixed‐conductive material with limited oxygen diffusion capability that is specifically designed for H‐SOFCs. The LSSF is an appealing cathode choice for H‐SOFCs due to its outstanding CO2 tolerance and matched thermal expansion coefficient, producing a record‐high performance of 2032 mW cm−2 at 700°C and good long‐term stability under operational conditions. The current study reveals that a new type of proton–electron mixed conducting cathode can provide promising performance for H‐SOFCs, opening the way for developing high‐performance cathodes. [ABSTRACT FROM AUTHOR]

Abstract: Ba0.5Sr0.5(Co0.8Fe0.2)1−xTixO3− δ (x=0, 0.05, and 0.1) materials were successfully prepared via an improved solid-state reaction route in an attempt to get better chemical stability for Ba0.5Sr0.5Co0.8Fe0.2O3− δ (BSCF). Stability tests showed that the novel Ti-doping strategy can effectively increase the chemical stability for Ba0.5Sr0.5Co0.8Fe0.2O3− δ in CO2-containing environments. The larger the Ti doping amount, the better the chemical stability. Ti-doped samples showed only a slight increase in area specific resistance (ASR) values, as shown from electrochemical tests performed on symmetrical cells. Therefore, anode-supported single fuel cells using BaZr0.4Ce0.4Y0.2O3− δ (BZCY) as the electrolyte and BZCY-Ba0.5Sr0.5(Co0.8Fe0.2)0.9Ti0.1O3− δ as the composite cathode, were fabricated and tested. The measured maximum power density values were 181, 116, and 49mWcm−2 at 700, 600, and 500°C, respectively. [Copyright &y& Elsevier]

By modifying the proton conductor BaTbO 3 with the element Co, it is discovered that the solubility of Co in BaTbO 3 is restricted to 20 mol.%, and phase segregations happen for high Co doping concentrations in BaTbO 3. The fabrication of nominal BaTb 0.5 Co 0.5 O 3 results in the in-situ development of the heterostructure cathode composed of BaTb 0.8 Co 0.2 O 3 +BaCoO 3. The critical role of the interface between BaTb 0.8 Co 0.2 O 3 and BaCoO 3 in enhancing fuel cell performance is to accelerate charge transfer kinetics, thereby enabling proton-conducting solid oxide fuel cells (H-SOFCs) to operate at higher performance levels than cells employing BaTb 0.8 Co 0.2 O 3 or BaCoO 3 cathodes alone. Furthermore, the favorable chemical stability of the BaTb 0.8 Co 0.2 O 3 +BaCoO 3 nanocomposite is maintained, thereby enhancing the fuel cell's operational stability. This research suggests that unanticipated phase segregation may occasionally improve the performance of the cathode, thereby presenting an interesting approach to cathode design in H-SOFCs. [ABSTRACT FROM AUTHOR]

Different transition metals are employed to tune the Y-doped BaZrO 3 proton conductor, resulting in the new BaZr 0.125 Y 0.125 M 0.75 O 3 (M = Cu, Mn, Ni, Zn, Co, and Fe) compositions as cathodes for proton-conducting solid oxide fuel cells. Only Co and Fe dopants can yield pure phases, whereas the use of other dopants results in impurities. Further experimental studies and first-principles calculations show that using Fe dopant has some advantages over Co-doped material, such as increased oxygen vacancies, lower proton migration energy barriers, and faster proton and oxygen diffusion kinetics. The fuel cell employing the BaZr 0.125 Y 0.125 Fe 0.75 O 3 (BZYFe) cathode has a larger fuel cell output than the fuel cell using the BaZr 0.125 Y 0.125 Co 0.75 O 3 (BZYCo) cathode. Furthermore, the CO 2 adsorption energy on the BZYFe surface is larger than that at the BZYCo surface, indicating that BZYFe has significantly better chemical stability than BZYCo. The long-term stability of the fuel cell demonstrates that the fuel cell with the BZYCo cathode is degrading. In contrast, the BZYFe cell has good operating stability. Given its phase purity, fuel cell performance, and stability, the Fe element is an appropriate dopant for altering BZY and creating a new cathode. • BaZr 0.125 Y 0.125 M 0.75 O 3 (M = Cu, Mn, Ni, Zn, Co, and Fe) were prepared. • Only Co and Fe dopants can generate pure phases. • BaZr 0.125 Y 0.125 Co 0.75 O 3 and BaZr 0.125 Y 0.125 Fe 0.75 O 3 cathodes yielded similar cell performance. • The cell using BaZr 0.125 Y 0.125 Fe 0.75 O 3 cathode showed better operational stability. [ABSTRACT FROM AUTHOR]

Pr 1.85 M 0.15 NiO 4+x (M represents Ba, Sr, or Ca) materials were prepared and evaluated as cathodes for protonic ceramic fuel cells (PCFCs). Compared with the Sr and Ba doping methods, the Ca-doping approach slightly enhanced the generation of interstitial oxygen and the surface catalytic activity in Pr 2 NiO 4. Furthermore, Ca-doping decreases the distance between O atoms in the lattice compared with the Sr and Ba-doped Pr 2 NiO 4 , facilitating the movement of charge carriers. Consequently, PCFCs employing Ca-doped Pr 2 NiO 4 cathodes achieve a much greater power density of 1279 mW cm−2 at 700 °C compared to fuel cells employing Sr-doped or Ba-doped Pr 2 NiO 4 cathodes. Furthermore, a PCFC employing a Ca-doped Pr 2 NiO 4 cathode exhibited excellent long-term stability under working conditions and operated continuously for over 280 h without any discernible deterioration. These results indicate that the Ca-doped Pr 2 NiO 4 cathode is a stable and effective candidate for PCFCs. [ABSTRACT FROM AUTHOR]

Manganate cathodes have good stability, but their performance at intermediate temperatures is not satisfactory, restricting the application for proton-conducting solid oxide fuel cells (H–SOFCs). A new composition, Pr 0.25 Nd 0.25 Sr 0. 5 MnO 3-δ (PNSM), is proposed to solve this problem. First-principles calculations indicate PNSM should have better performance than the classical Sr-doped LaMnO 3 (LSM) cathode by favoring the formation of oxygen vacancies and proton defects. Experimental studies indicate that the PNSM material can be successfully synthesized and show good chemical stability. The H–SOFC using the single-phase PNSM cathode shows improved performance than that using the traditional LSM cathode, demonstrating the prediction from the theoretical calculations. Further optimizing the cell structure, an encouraging performance of 1266 mW cm−2 at 700 °C is obtained, which is larger than many other manganates cathode-based H–SOFCs. The performance is even comparable to many high-performing cathodes for H–SOFCs, indicating PNSM is an efficient cathode material for H–SOFCs. [ABSTRACT FROM AUTHOR]

A Sr-deficiency approach is utilized to adjust the composition of the standard Sr 2-x Fe 1.5 Mo 0.25 Sc 0.25 O 6 (SFMS) material, with the goal of improving the performance of the SFMS cathode in proton-conducting solid oxide fuel cells (H–SOFCs). The Sr-deficiency concentration is restricted to 10% at the Sr site, and an increase in Sr-deficiency leads to the formation of more oxygen vacancies. However, the presence of increased oxygen vacancies does not consistently enhance the diffusion capabilities of charge carriers. The excess of oxygen vacancies impedes the movement of oxygen and protons. The optimal oxygen and proton transport capabilities are achieved when the Sr-deficiency level is set at 5%. Specifically, this is observed in the compound Sr 1.9 Fe 1.5 Mo 0.25 Sc 0.25 O 6 (S1.9FMS). The enhanced oxygen and proton diffusion kinetics enable H–SOFCs to achieve exceptional performance when employing the S1.9FMS cathode, reaching a power density of 1709 mW cm−2 at 700 °C with a low polarization resistance of 0.023 Ω cm2. The fuel cell's output exceeds that of many previously reported H–SOFCs. Furthermore, the fuel cell utilizing the S1.9FMS cathode not only exhibits excellent fuel cell performance but also maintains reliable operational stability. This indicates that employing the Sr-deficiency technique with an appropriate level of deficiency is a successful approach to enhance the cathode performance for H–SOFCs. • A Sr-deficiency approach was used to tailor Sr 2-x Fe 1.5 Mo 0.25 Sc 0.25 O 6 (SFMS). • The Sr-deficient SFMS showed improved oxygen and proton diffusion kinetics. • A high fuel cell performance was obtained with the Sr 1.9 Fe 1.5 Mo 0.25 Sc 0.25 O 6 cathode. • Good stability was retained for the Sr 1.9 Fe 1.5 Mo 0.25 Sc 0.25 O 6 cathode. [ABSTRACT FROM AUTHOR]

Co3O4 nanocubes with exposed (001) planes were prepared and employed for use as first-generation Sr-doped LaMnO3 (LSM) cathodes in solid oxide fuel cells to improve the cell performance. Theoretical simulations suggest that the Co3O4 (001) plane has the smallest oxygen adsorption and oxygen dissociation energies compared with other planes, thus favouring cathode reactions in solid oxide fuel cells (SOFCs). Experimental studies consistently demonstrate that a cell using an LSM cathode made with Co3O4 nanocubes with selective (001) surfaces exhibits a peak power density of 500 mW cm−2 at 600 °C, while the power output for a cell using unselective (commercial) Co3O4 nanoparticles is only 179 mW cm−2 at the same temperature. The electrochemical study indicates that the use of Co3O4 nanoparticles with exposed (001) surfaces obviously accelerates the cathode reactions and thus decreases the polarisation resistance, which is the key to improving fuel cell performance. This study demonstrates the feasibility of using the crystal planes of metal oxides to improve the fuel cell performance and provides a new way to design SOFC cathodes. [ABSTRACT FROM AUTHOR]

This study proposes a new Pr 0.25 Nd 0.25 Ca 0.5 MnO 3-δ (PNCM) cathode material for protonic ceramic fuel cells (PCFCs). As demonstrated by first-principles calculations, the Ca-doping strategy can promote oxygen vacancy formation and accelerate the oxygen reduction reaction (ORR) compared to the conventional Sr-doping method. Additional experiments reveal the doping of Ca can enhance the proton and oxygen diffusion abilities compared with the traditional Sr-doped material. Consequently, the PCFC with single-phase PNCM cathode produces a high peak power density of 1232 mW cm-2 at 700 °C, which is significantly greater than the cell with Sr-doped cathode, which only produces 749 mW cm-2 under the same testing conditions. The PNCM cathode inherits the excellent stability of manganate cathodes, allowing the fuel cell to exhibit good stability under operational conditions. PNCM is a new and promising cathode material for PCFCs due to its excellent fuel cell performance and stability. [ABSTRACT FROM AUTHOR]

Transition metal elements were employed to customize the standard Sr 2 Fe 1.5 Mo 0.5 O 6 (SFM) material, with the goal of improving the performance of the SFM cathode in proton-conducting solid oxide fuel cells (H–SOFCs). Sr 2 FeMo 0.5 X 0.5 O 6 (X = Ni, Co, Mn, Zn) materials were prepared, but it was discovered that only the dopants Ni and Co can form a pure phase, whereas the dopants Mn and Zn produced an obvious secondary phase. When comparing oxygen vacancies and oxygen diffusion kinetics, utilizing the Co-dopant exhibited clear advantages. The Co-doped SFM had a higher oxygen vacancy content and faster oxygen diffusion kinetics than both the standard and Ni-doped SFM cathodes. The energy barrier for the oxygen reduction reaction (ORR) at the Co-doped SFM cathode was 0.76 eV, which was much lower than that for the SFM and Ni-doped SFM, which were 5.52 and 2.28 eV, respectively. As a result, the Co-doped SFM's cathode reaction was greatly accelerated, resulting in a high fuel cell performance of 1306 mW cm−2 at 700 °C. This finding suggests that using the appropriate dopant can alleviate the low-performance problem of the traditional SFM cathode, resulting in a promising cathode option for H–SOFCs. • Sr 2 FeMo 0.5 X 0.5 O 6 (X = Ni, Co, Mn, Zn) cathodes were proposed for H–SOFCs. • The Co dopant showed more advantages compared with other dopants. • The Sr 2 FeMo 0.5 Co 0.5 O 6 cathode delivered high fuel cell performance. • The mechanism for the enhanced cathode performance was revealed. [ABSTRACT FROM AUTHOR]

LaNi 0.5 Fe 0.5 O 3-δ (LNF) is a viable option for the cathode of solid oxide fuel cells (SOFCs), however, its performance in proton-conducting SOFCs (H–SOFCs) is not sufficient. In this work, an Sc-doped method to increase the cathode performance of conventional LNF for H–SOFCs is proposed. Although the Sc cation can be doped at the Ni site or the Fe site in LNF, which led to the formation of pure phase materials, first-principles calculations indicate that the formation of the LaNi 0.4 Sc 0.1 Fe 0.5 O 3-δ (LNSF) material has more advantages than the formation of the LaNi 0.5 Fe 0.4 Sc 0.1 O 3-δ (LNFS) material, even though the same Sc-doping level is employed. Compared to Sc-free LNF, LNSF provides superior fuel cell performance. At 700 °C, the LNSF cell generates a peak power density of 1534 mW cm−2, double that of the LNF cell. In addition, employing the LNSF cathode reduces the cell's polarization resistance, indicating that the Sc-doping strategy paired with selecting the doping site is an effective method for reusing LNF in high-performance H–SOFCs. • Sc cations can be doped at the Fe or Ni sites in LaNi 0.5 Fe 0.5 O 3-δ (LNF). • The site occupation at the Ni site shows advantages compared with that at the Fe site. • Sc-doped LNF shows better performance than the Sc-free one. • The performance of the cell using LaNi 0.4 Sc 0.1 Fe 0.5 O 3-δ is better. [ABSTRACT FROM AUTHOR]

As a cathode material for proton-conducting SOFCs (H–SOFCs), a novel MnCo 1.9 Sb 0.1 O 4 (MCSO) spinel material was suggested. The MCSO material was effectively produced, and it demonstrated excellent phase stability at elevated temperatures and chemical stability against CO 2 and H 2 O. Doping Sb into the MnCo 2 O 4 (MCO) allowed for enhanced proton diffusion and surface exchange, as evidenced by electrical conductivity relaxation tests. In addition, an oxygen-vacancy-rich surface was developed for the MCSO material, resulting in the possibility of a high cathode oxygen reduction reaction activity. The MCSO material was examined in the H–SOFC application, and the fuel cell with an MCSO cathode attained a high power density of 1380 mW cm−2 at 700 °C. At 700 °C, the cell employing the Sb-free MCO cathode, which had a comparable cell microstructure to the MCSO cell, only obtained a peak power density of 836 mW cm−2. The higher cell performance resulted from the Sb-modified MCO cathode's increased catalytic activity. In addition, the MCSO cell displayed excellent operational stability under fuel cell operating conditions, indicating that MCSO is a novel and effective spinel cathode for H–SOFCs. • A new MnCo 1.9 Sb 0.1 O 4 (MCSO) spinel was proposed for H–SOFCs. • Doping Sb into MnCo 2 O 4 (MCO) enhanced proton diffusion and surface exchange. • MCSO improved the cathode activity compared with Sb-free MCO. • A high performance was obtained for the fuel cell using MCSO cathode. [ABSTRACT FROM AUTHOR]

By synthesizing the nominal Pr x Sr 0.5 MnO 3-δ materials (x = 0.5, 0.6, 0.7, 0.8), new Pr 0.5 Sr 0.5 MnO 3-δ (PSM50)+PrO 2−x composite cathodes for proton-conducting solid oxide fuel cells (SOFCs) were developed. The structure analysis and morphology observations verified the exsolution of PrO 2−x particles, and the amount of exsolved PrO 2−x increased with the amount of Pr in Pr x Sr 0.5 MnO 3-δ. An H-SOFC with a Pr 0.7 Sr 0.5 MnO 3-δ (PSM70) cathode enabled the highest reported fuel cell output for H-SOFCs with manganate cathodes. The construction of a PSM50/PrO 2 heterostructure interface can reduce the formation energy of oxygen vacancies, hence accelerating the cathode oxygen reduction reaction (ORR) kinetics, as confirmed by oxygen diffusion and surface exchange experiments. The excellent electrochemical performance was combined with its good chemical stability against CO 2 and H 2 O, allowing a stable operation of the cell for over 100 h, indicating that PSM70, which was in fact PSM50 +PrO 2−x , was a highly efficient and durable cathode material for H-SOFCs. [ABSTRACT FROM AUTHOR]

BaSrInFeO 5 (BSIF), a new cathode material for proton-conducting solid oxide fuel cells (SOFCs), is designed based on the modification of the Ba 2 In 2 O 5 proton conductor with Sr and Fe cations. Compared with the Ba 2 In 2 O 5 proton conductor tailored with only Fe cations (Ba 2 InFeO 5 , BIF), doping Sr can improve the chemical stability and also benefit the formation of oxygen vacancies. The proton mobility is also improved with Sr-doping, which is confirmed by first-principles calculations and experimental studies. An H-SOFC using the BSIF cathode generates a relatively high peak power density of 1192 mW cm-2 at 700 oC, which is superior to many cells in previous reports. First-principles calculations find that the cathode oxygen reduction reaction (ORR) energy barrier for BSIF is significantly lower than that for BIF. Although Ba 2 In 2 O 5 is less studied, the derived cathode materials can still present decent performance, probably offering new material selections for H-SOFCs. [ABSTRACT FROM AUTHOR]

In this study, both cathode powder preparations and fuel cell fabrications for proton-conducting solid oxide fuel cells (H–SOFCs) were performed using the microwave sintering technique. The microwave sintering approach produced Sr 2 Fe 1.5 Mo 0.25 Sc 0.25 O 6-δ (SFMS) cathode particles with a lower phase formation temperature and smaller grain size than the standard muffle furnace sintering method. The advantages of microwave sintering were also recognized during the fuel cell manufacturing process. Using the same electrolyte and anode, conventional sintering and microwave sintering were used to produce SFMS cathodes, resulting in varied fuel cell performance. The fuel cell output of the conventionally sintered cell was 1312 mW cm−2 at 700 °C, whereas the power density of the microwave-prepared cell achieved 1452 mW cm−2 under the same testing conditions, which was also higher than the performance of a number of recently reported H–SOFCs. Surface chemistry research revealed that microwave sintering generated more oxygen vacancies (Vo). Calculations based on first-principles indicated that the greater surface abundance of Vo increased the oxygen reduction reaction (ORR) activity. The benefits of microwave sintering can be discovered in both the powder preparation and cell construction stages, making it an intriguing and simple way to enhance the performance of H–SOFCs. [ABSTRACT FROM AUTHOR]

A new spinel oxide CoFe 1.9 Li 0.1 O 4 (CFLO) has been synthesized as a cathode material for proton-conducting solid oxide fuel cells. CFLO has good structure stability up to 900 °C. In addition, the material can survive in both CO 2 and steam-containing atmospheres. Compared with the Li-free sample, the Li-doping strategy significantly regulates the material's electronic structure. The low valence of Li leads to the increased amount of Fe and Co cations with higher valences. Furthermore, doping Li creates more oxygen vacancies at the material surface, which benefits the oxygen reduction reaction (ORR). The improved cathode performance for CFLO has been demonstrated that a cell using CFLO cathode reaches a peak power density of 1052 mW cm−2 at 700 °C. The cell performance is 60% larger than the Li-free cell, and similar results can be detected at other testing temperatures. In addition, the CFLO cell shows good long-term stability in the working condition. This study proposes the Li-doping strategy to modify spinel oxides and also provides a new spinel oxide as a high-performing cathode for H–SOFCs. [ABSTRACT FROM AUTHOR]

U cations were immobilized in the traditional Sr 2 Fe 2 O 6-δ (SFO) oxide, which was subsequently evaluated as a cathode for proton-conducting solid oxide fuel cells (H–SOFCs). Experimental studies indicated that the U cations could be incorporated into the SFO lattice, forming the new Sr 2 Fe 1.5 U 0.5 O 6-δ (SFUO) oxide material. The SFUO material exhibited improved chemical stability than the SFO material, preventing the formation of carbonates after treatment in a CO 2 atmosphere. Although the total electrical conductivity was decreased with the U-doping, the surface catalytic activity of SFUO was improved compared with SFO, which was demonstrated by first-principles calculations. The subsequent electrochemical studies indicated that an H–SOFC using the SFUO cathode showed higher fuel cell output and smaller polarization resistance than the SFO cathode. The present study demonstrated that SFO could locate U cations in the lattice, and the produced SFUO oxide exhibited improved performance, suggesting the utilization of SFO cathode in the harsh environment (such as U-containing conditions) would be possible, and the electrochemical performance of the fuel cell is not reduced. [ABSTRACT FROM AUTHOR]

The electrospinning technique was employed to prepare the La 0.5 Sr 0.5 Mn 0.875 Zn 0.125 O 3-δ (LSMZn) cathode for proton-conducting solid oxide fuel cells (H–SOFCs). Although the fiber structure can be obtained with the electrospinning technique for the LSMZn precursor, the fiber structure disappeared after the calcination procedure, leading to the formation of fine LSMZn nano-powders. It was found that the electrospun LSMZn can reach a pure phase after firing at 1100 °C, whereas the traditional sol-gel prepared LSMZn required a calcination temperature of 1150 °C. Furthermore, the electrospun LSMZn had a smaller particle size and richer oxygen vacancy than the traditional sol-gel LSMZn. First-principles calculations indicated that the oxygen vacancy-rich surface promoted the cathode reaction. The H–SOFC using the single-phase electrospun LSMZn generated a power density of 1122 mW cm−2 at 700 °C. The performance was not only larger than the sol-gel LSMZn cell reported in this study but also larger than previous H–SOFCs using the single-phase Mn-based cathodes, suggesting the electrospinning technique was an effective method to produce high-performing cathodes for H–SOFCs. [ABSTRACT FROM AUTHOR]

A Zn-doping strategy was employed to modify the Ruddlesden-Popper (R–P) structure oxide La 2 NiO 4+x to improve hydration and proton diffusion ability. First-principles calculations indicated the formation of interstitial oxygen instead of oxygen vacancy is favorable for Zn-modified and Zn-free La 2 NiO 4+x. The doping of Zn significantly lowered the hydration energy for La 2 NiO 4+x and decreased the proton migration barrier. The electrical conductivity relaxation confirmed that the Zn-modified La 2 NiO 4+x sample had a higher proton diffusion rate than the Zn-free sample. Furthermore, the Zn-doping strategy did not alter the thermal expansion behavior of the material, and both Zn-modified and Zn-free La 2 NiO 4+x samples showed a similar thermal expansion coefficient value, which was also close with the electrolyte materials. As a result, the Zn-modified La 2 NiO 4+x exhibited suitability as the cathode for proton-conducting solid oxide fuel cells (H–SOFCs). An H–SOFC using the Zn-modified La 2 NiO 4+x showed a relatively high peak power density of 1070 mW cm-2 at 700 °C, significantly larger than that La 2 NiO 4+x -based H–SOFCs reported previously. [ABSTRACT FROM AUTHOR]

[Display omitted] • The new Pr 0.5 Sr 0.5 Fe 0.9 Mn 0.1 O 3 cathode was prepared. • The Mn-doping method mitigated the high thermal expansion of Pr 0.5 Sr 0.5 FeO 3. • The oxygen vacancy formation and proton diffusion were improved with Mn-doping. • Better fuel cell performance was obtained with the cathode using Mn-doping. The traditional Pr 0.5 Sr 0.5 FeO 3 (PSF) cathode is customized with Mn cations to generate the new Pr 0.5 Sr 0.5 Fe 0.9 Mn 0.1 O 3 (PSFMn) cathode for proton-conducting solid oxide fuel cells (H-SOFCs). Compared to the PSF oxide, the new PSFMn has a reduced thermal expansion, making it more compatible with electrolytes. Furthermore, Mn-doping enhances oxygen vacancy production in PSF, as revealed by experimental and first-principle calculations. More crucially, doping Mn into PSF improves proton diffusion kinetics, resulting in quicker proton diffusion and surface exchange. As a result, the H-SOFC with the PSFMn cathode achieves an output of 1446 mW cm−2 at 700 °C, but the PSF cell only achieves fuel cell performance of 1009 mW cm−2. The fundamental cause of the increased cell performance is the significantly reduced polarization resistance, implying that using the Mn-doping strategy enhances the cathode kinetics of conventional PSF cathodes for H-SOFC. [ABSTRACT FROM AUTHOR]

A series of W doped Pr 0.5 Ba 0.5 (Co 0.7 Fe 0.3)O 3-δ (PBCF) are prepared and characterized as cathodes for proton-conducting solid oxide fuel cell (H–SOFC). The enhancement of proton migration and formation ability through W doping significantly increases the cell performance and it is further verified by the density functional theory (DFT) simulation, presenting the high valence element doping can be a potential approach for the design of cathode. • W doped PBCF at proper concentration can form Single and double perovskite composites. • The performance of H-SOECs is highly improved by applying this novel element. • Proton migration and transportation energies are calculated using DFT method. [ABSTRACT FROM AUTHOR]

A Zn-doping strategy is employed to tailor the LaNi 0.5 Fe 0.5 O 3-δ material to improve its performance for proton-conducting solid oxide fuel cells (H–SOFCs). Zn can partially replace Ni in the LaNi 0.5 Fe 0.5 O 3-δ lattice to form LaNi 0.4 Zn 0.1 Fe 0.5 O 3-δ material. In contrast, ZnO secondary phase can be detected if attempts are made to partially replace Fe with Zn, and the nominal composition LaNi 0.5 Fe 0.4 Zn 0.1 O 3-δ cannot be obtained. First-principles calculations indicate that the Zn-doping method lowers the formation energy of oxygen vacancy and decreases the hydration energy, benefiting its application as the cathode for H–SOFCs. As a result, the H–SOFC with the LaNi 0.4 Zn 0.1 Fe 0.5 O 3-δ cathode generates a peak power density of 1226 mW cm−2 at 700 °C. In contrast, the peak power density for the cell using the Zn free LaNi 0.5 Fe 0.5 O 3-δ cathode only reaches 722 mW cm−2 at the same testing temperature. The polarization resistance of the cell with the LaNi 0.4 Zn 0.1 Fe 0.5 O 3-δ cathode is reduced to 0.043 Ω cm2 at 700 °C, which is one of the smallest reported for H–SOFCs using cobalt-free cathodes. The high fuel cell performance coupled with the low polarization resistance for the Zn-modified LaNi 0.5 Fe 0.5 O 3-δ suggests that the Zn-doping strategy would be an interesting way to promote the performance of the cobalt-free LaNi 0.5 Fe 0.5 O 3-δ material for H–SOFCs. • A new LaNi 0.4 Zn 0.1 Fe 0.5 O 3-δ material has been prepared. • Zn-doping improved the material's properties for H–SOFCs. • High cell performance of 1226 mW cm−2 at 700 °C was obtained with the new cathode. • First-principles calculations were used to reveal the mechanism. [ABSTRACT FROM AUTHOR]

The application of traditional MIEC cathode material Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) in the solid oxide fuel cell (SOFC) field is limited due to its susceptibility to CO 2 and high thermal expansion coefficient. Therefore, improving the stability of BSCF cathode in CO 2 -containing environments and the matching degree between BSCF and electrolyte are the key factors to achieve its excellent electrochemical and stable performance for intermediate temperature solid oxide fuel cells (IT-SOFCs). Herein, the cathode materials Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2-x Ta x O 3-δ (X = 0, 0.1, 0.2) are successfully prepared and the effects of Ta-doped content are investigated systematically. With the increase of Ta-doped content, the thermal expansion coefficient of BSCF 0.2-x T x decreases from 25.1 × 10−6 K−1 to 16.5 × 10−6 K−1, which indicated that Ta-doped enhanced the combination of cathode material and electrolyte. In single-cell applications, the maximum power density of 926.4 mW cm−2 and the lowest polarization resistance of 0.06 Ω cm2 at 700 °C are achieved. Furthermore, theoretical calculations show that the CO 2 adsorption energy of BSCFT is 0.12 eV higher than that of BSCF, indicating that BSCFT exhibited improved resistance to CO 2 corrosion compared with BSCF. It is indicated that the Ta-doping strategy has the advantage of improving both the performance and stability of BSCF cathode materials. • BSCF cathode materials doped with different concentrations of Ta were prepared. • The good stability of Ta-doped BSCF cathode materials were confirmed. • The effect of Ta doping on CO 2 resistance was analyzed by theoretical calculations. • BSCF 0.1 T 0.1 material achieved excellent fuel cell performance with good stability. [ABSTRACT FROM AUTHOR]

• DFT calculations used for H-SOFCs are briefly reviewed. • The advantages of using DFT calculations are clarified. • Limitations and future developments are discussed. Density functional theory (DFT) calculations have been widely used to investigate insights for electrochemical materials, but its application in proton-conducting solid oxide fuel cells has just started a few years ago. Despite the limited time, the DFT calculation is regarded as a powerful tool to anticipate the properties of the proton-conducting oxides with success, bring insights into the material design that promotes the electrochemical performance of the cells. Furthermore, the DFT calculation provides a solution to reveal the potential proton conduction in the cathode materials for proton-conducting solid oxide fuel cells that is difficult to achieve by experimental approaches. However, some limitation for the current DFT application has also been observed. This mini-review briefly documents the application of DFT calculations for the cathodes of proton-conducting solid oxide fuel cells, focusing on the exploration of new cathode materials with high electrochemical performance. Both success stories and the current limitations have been presented, aiming to arouse the attention of the community for this interesting method. [ABSTRACT FROM AUTHOR]

PrBaCo 2 O 5+δ (PBC) with high catalytic activity is identified as a prospective cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). However, its poor chemical stability hinders its application. To address this problem, a Ta-doping strategy was presented in this study. The cathode with Ta-doping PBC was applied in proton conducting SOFCs. And the influence of Ta-doping on the crystal structure, electrochemical performance, structure stability and electrical conductivity of PBC was investigated. The resistance to CO 2 of PBC at elevated temperature is significantly improved with Ta-doping. The electrochemical performance measurements indicated that a low Ta-doping concentration did not change the performance of the cells obviously, while large Ta-doping concentration could lower the fuel cell performance. • Tantalum element was successfully doped into the crystal lattice of PBC. • Ta-doped PBC was successfully applied in H–SOFC. • The resistance to CO 2 of PBC at elevated temperature is significantly improved with Ta-doping. [ABSTRACT FROM AUTHOR]

A Pr-doping strategy was used to improve traditional strontium-doped lanthanum ferrite oxides for proton-conducting solid oxide fuel cells (SOFCs). Three different samples, La 0.5 Sr 0.5 FeO 3- δ , La 0.25 Pr 0.25 Sr 0.5 FeO 3- δ , and Pr 0.5 Sr 0.5 FeO 3- δ ,were successfully prepared. The Pr content was shown to have an obvious influence on the hydration ability of the materials. Hydration was improved at higher Pr-contents, suggesting a promising cathode performance. However, the improved hydration ability did not always lead to an increased fuel cell performance, and it was found that the fuel cell performed best when an appropriate Pr-doping amount was used that resulted in a good compromise between protonic and oxygen-ion conduction. As a result, the optimized composition La 0.25 Pr 025 Sr 0.5 FeO 3- δ generated a high peak power density of 616 mW cm−2 and a low polarization resistance of 0.09 at Ω cm2 at 700 °C, which is an encouraging performance for a traditional cathode material. [ABSTRACT FROM AUTHOR]

In this study, we prepared a Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3- δ (BSCF) cathode layer for proton-conducting solid oxide fuel cells using microwave sintering. Unlike traditional sintering, which is carried out at 1000 °C for a few hours, the microwave sintering method allows the BSCF cathode layer to adhere well with the electrolyte layer after sintering at 900 °C for 10 min. This strategy helps the cathode layer maintain a microstructure favourable for cathode reactions and mitigate the potential diffusion of elements between it and the BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ electrolyte, leading to improved cell resistance. The cell with the BSCF cathode layer sintered by the microwave method has a power output of 0.96 W cm-2 at 700 °C, while the power output for the cell with a conventionally sintered cathode is 0.33 W cm-2. [ABSTRACT FROM AUTHOR]

Tailoring the electronic structure of the perovskite oxide could potentially allow dramatic improvements in the properties of cathode materials in proton-conducting solid oxide fuel cells (SOFCs). This has been demonstrated in the case of Mo-doped La 0.5 Sr 0.5 FeO 3-δ , where the electronic structure of the La 0.5 Sr 0.5 FeO 3-δ oxide has been changed with the Mo-doping, leading to a less strong metal-oxygen bond as well as a more active surface towards oxygen reduction. As a result, the more active oxygen atoms make the formation of oxygen vacancy and hydration that are critical for protonation more feasible. Furthermore, the electric field induced by Mo-doping provides an additional driving force for the movement of protons, accelerating the proton migrations in the oxide and thus improving the cathode performance. With the Mo-doped La 0.5 Sr 0.5 FeO 3-δ as the cathode, a proton-conducting SOFC exhibits an impressive fuel cell output of 1174 mW cm−2 at 700 °C that surpasses most of the cells using similar types of cathodes. This study not only provides a proper cathode material without involving cobalt and barium elements but also gives an understanding of the design of the cathode by tailoring the electronic structures. Image 1 • A new and proper way was proposed to design cathodes for proton-conducting SOFCs. • Tailoring electronic structure changed the properties of La 0.5 Sr 0.5 FeO 3-δ oxide. • Both experimental and theoretical studies were used to study the tailored cathode. • High performance was achieved with the designed La 0.5 Sr 0.5 Fe 0.9 Mo 0.1 O 3-δ cathode. [ABSTRACT FROM AUTHOR]