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Designing a high‐performance cathode is essential for the development of proton‐conducting solid oxide fuel cells (H‐SOFCs), and nanocomposite cathodes have proven to be an effective means of achieving this. However, the mechanism behind the nanocomposite cathodes' remarkable performance remains unknown. Doping the Co element into BaZrO3 can result in the development of BaCoO3 and BaZr0.7Co0.3O3 nanocomposites when the doping concentration exceeds 30%, according to the present study. The construction of the BaCoO3/BaZr0.7Co0.3O3 interface is essential for the enhancement of the cathode catalytic activity, as demonstrated by thin‐film studies using pulsed laser deposition to simulate the interface of the BCO and BZCO individual particles and first‐principles calculations to predict the oxygen reduction reaction steps. Eventually, the H‐SOFC with a BaZr0.4Co0.6O3 cathode produces a record‐breaking power density of 2253 mW cm−2 at 700°C. [ABSTRACT FROM AUTHOR]

Abstract A microwave sintering technique is reported for fabricating co-sintered proton-conducting solid oxide fuel cells. With this method, high-quality ceramic electrolyte membranes can be prepared at 1100 °C, thus enabling the fabrication of entire cells in a single step. The microwave sintering method not only enhances electrolyte densification but also improves the cathode/electrolyte interface, which is critical for improving fuel cell performance. The power output of the co-sintered cell prepared under the microwave conditions (up to 449 mW cm−2 at 700 °C) was significantly higher than that of the cell fabricated using the traditional co-sintering method (approximately 292 mW cm−2 at the same temperature). Electrochemical analysis revealed that the enhanced electrolyte density and the improved cathode/electrolyte interface achieved by using the microwave sintering technique decrease both the ohmic resistance and the polarisation resistance of the cell, leading to good fuel cell performance. [ABSTRACT FROM AUTHOR]

Abstract NiO is used as a sintering aid to modify BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ by an external addition method and by an internal doping strategy to improve the sinterability of BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ. In both cases, the modified BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ materials show an improved sinterability compared with the original BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ. However, doping BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ with NiO to form BaZr 0.1 Ce 0.66 Ni 0.04 Y 0.2 O 3-δ is found to be an effective strategy to significantly improve the electrolyte properties. The BaZr 0.1 Ce 0.66 Ni 0.04 Y 0.2 O 3-δ sample shows a high density and large grain size after sintering at a relatively low temperature (1400 °C). Electrochemical studies reveal that the doping strategy offers a high proton conductivity in both the bulk and across grain boundaries. The conductivity of BaZr 0.1 Ce 0.66 Ni 0.04 Y 0.2 O 3-δ sintered at 1400 °C is observed to be higher than that of BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ sintered at 1600 °C. With BaZr 0.1 Ce 0.66 Ni 0.04 Y 0.2 O 3-δ as the electrolyte, a proton-conducting solid oxide fuel cell displays a large peak power density of 477 mW cm-2 at 600 °C and a high electrolyte membrane conductivity of 6.3 × 10−3 S cm−1. Highlights • NiO was used as the dopant for BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ proton-conducting oxide. • High sinterability with improved conductivity was achieved. • The doping strategy showed advantages over the traditional approach of using NiO. • The cell with BaZr 0.1 Ce 0.66 Ni 0.04 Y 0.2 O 3-δ electrolyte showed a high performance. [ABSTRACT FROM AUTHOR]

The microwave sintering strategy was for the first time adopted to prepare proton-conducting electrolyte membranes for solid oxide fuel cells. The preparation of a dense proton-conducting BaCe 0.7 Zr 0.1 Y 0.2 O 3-δ (BCZY) electrolyte membrane can be achieved at 1200 °C with the microwave sintering method. In sharp contrast, a BCZY sample prepared at 1200 °C using the conventional thermal sintering method was found to be porous. In comparison with a dense BCZY sample prepared at 1400 °C using the conventional sintering method, the microwave-sintered BCZY electrolyte showed an improved proton conductivity, which is beneficial for fuel cell applications. Experimental results showed that the microwave sintering method enabled a homogenous elemental distribution and a suppression of barium evaporation, leading to the conductivity improvement in both bulk and grain boundaries. With the microwave sintered BCZY film as the electrolyte, a proton-conducting solid oxide fuel cell delivered a maximum power density of 838 mW cm −2 at 700 °C with an electrolyte film conductivity as high as 1.4 × 10 −2 S cm −1 . This study suggests that the microwave sintering method is a promising strategy to prepare electrolyte membranes at a relatively low temperature with high conductivity, which could advance the development of proton-conducting solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Several proton conductive ceramic oxides are evaluated for potential application in ceramic-NiO composite anodes for proton-conducting La 0.99 Ca 0.01 NbO 4 (LNO) electrolyte-based fuel cells. Chemical compatibility tests show that most of the existing proton-conducting oxides are unfavorable for application in LNO electrolyte-based fuel cells because of undesirable reactions at high temperatures. Further considering the chemical compatibility with NiO and the ability to promote the densification of the deposited LNO electrolyte, LNO-NiO composite anode proves to be the only suitable anode candidate. With humidified hydrogen (∼3%H 2 O) as the fuel and static air as the oxidant, fuel cells based on LNO electrolyte film deposited on LNO-NiO anodes show a peak power density of 24 mW cm −2 at 750 °C, this value being one of the largest ever reported for LNO-based cells. Further investigation reveals that the polarization resistance of the cell is the major contribution to the total cell resistance, limiting the overall cell performance. [ABSTRACT FROM AUTHOR]

Y-doped BaZrO 3 (BZY) electrolyte films are successfully fabricated by utilizing the driving force from the anode substrate, aiming to circumvent the refractory nature of BZY materials. The BZY electrolyte film on the high shrinkage anode becomes dense after sintering even though no sintering aid is added, while the BZY electrolyte remains porous on the conventional anode substrate after the same treatment. The resulting BZY electrolyte shows a high conductivity of 4.5 × 10 − 3 S cm − 1 at 600 °C, which is 2 to 20 times higher than that for most of BZY electrolyte films in previous reports. In addition, the fuel cell with this BZY electrolyte generates a high power output of 267 mW cm − 2 at 600 °C. These results suggest the strategy presented in this study provides a promising way to prepare BZY electrolyte films for fuel cell applications. [ABSTRACT FROM AUTHOR]

Proton-conducting oxides offer a promising way of lowering the working temperature of solid oxide cells to the intermediate temperate range (500 to 700 °C) due to their better ionic conductivity. In addition, the application of proton-conducting oxides in both solid oxide fuel cells (SOFCs) and sold oxide electrolysis cells (SOECs) provides unique advantages compared with the use of conventional oxygen-ion conducting conductors, including the formation of water at the air electrode site. Since the discovery of proton conduction in some oxides about 30 years ago, the development of proton-conducting oxides in SOFCs and SOECs (the reverse mode of SOFCs) has gained increased attention. This paper briefly summarizes the development in the recent years of R-SOFCs with proton-conducting electrolytes, focusing on discussing the importance of adopting chemically stable materials in both fuel cell and electrolysis modes. The development of electrode materials for proton-conducting R-SOFCs is also discussed. [ABSTRACT FROM AUTHOR]

A chemically stable electrolyte structure was developed for proton-conducting SOFCs by using two layers of stable BaZr0.7Pr0.1Y0.2O3−δ to sandwich a highly-conductive but unstable BaCe0.8Y0.2O3−δ electrolyte layer. The sandwiched electrolyte structure showed good chemical stability in both CO2 and H2O atmosphere, indicating that the BZPY layers effectively protect the inner BCY electrolyte, while the BCY electrolyte alone decomposed completely under the same conditions. Fuel cell prototypes fabricated with the sandwiched electrolyte achieved a relatively high performance of 185mWcm−2 at 700°C, with a high electrolyte film conductivity of 4×10−3 Scm−1 at 600°C. [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]

Abstract: A BaZr0.4Ce0.4Y0.2O3− δ (BZCY)-NiO anode functional layer was added between the BZCY electrolyte and the BZCY-NiO anode substrate to investigate its effect on the performance of single cells. With BaZr0.4Ce0.4Y0.2O3− δ (BZCY) as the electrolyte and composite BZCY-Ba0.5Sr0.5(Co0.8Fe0.2)0.9Ti0.1O3− δ as the cathode material, anode-supported electrolyte fuel cells were fabricated and tested. The single cell without an anode functional layer generated maximum power densities of 181, 138, 116, 77, and 49mWcm−2 at 700, 650, 600, 550, and 500°C, respectively, whereas those for the single cell with an anode functional layer significantly improved up to 281, 243, 194, 145, and 95mWcm−2 at the same temperatures, almost doubling the power output. Electrochemical impedance spectroscopy (EIS) measurements for these two cells revealed that the addition of the anode functional layer reduced the contact resistance as well as the polarization resistance for the cell, resulting thus in the improved cell performance. [Copyright &y& Elsevier]

Abstract: In3+ was used as dopant for BaZrO3 proton conductor and 30 at%-doped BaZrO3 samples (BaZr0.7In0.3O3-δ , BZI) were prepared as electrolyte materials for proton-conducting solid oxide fuel cells (SOFCs). The BZI material showed a much improved sinteractivity compared with the conventional Y-doped BaZrO3. The BZI pellets reached almost full density after sintering at 1600°C for 10h, whereas the Y-doped BaZrO3 samples still remained porous under the same sintering conditions. The conductivity measurements indicated that BZI pellets showed smaller bulk but improved grain boundary proton conductivity, when compared with Y-doped BaZrO3 samples. A total proton conductivity of 1.7×10−3 Scm−1 was obtained for the BZI sample at 700°C in wet 10% H2 atmosphere. The BZI electrolyte material also showed adequate chemical stability against CO2 and H2O, which is promising for application in fuel cells. [Copyright &y& Elsevier]

Abstract: Proton-conducting BaCeO3 membranes with different In-doping levels (from 10 to 30%) were fabricated on NiO-based anode substrates. Indium, which was only used as a trivalent element to create oxygen vacancies in BaCeO3 previously, was found to have the function of stabilizing BaCeO3 in this study. The In-doped BaCeO3 showed improved chemical stability against CO2, while even the traditional BaCeO3 substituting with a small amount of Zr decomposed in the same environment. Furthermore, unlike other strategies for stabilizing BaCeO3, the supported In-doped BaCeO3 membrane became dense after firing at relatively low temperatures. We also investigated the influences of the sintering temperatures and the In-doping levels on the densification and the electrical properties of the supported BaCeO3 membranes, which revealed that the In-doping strategy increased both the chemical stability and sinterability for BaCeO3 with little loss of electrical performance. [Copyright &y& Elsevier]

Abstract: Proton-conducting solid oxide fuel cells (SOFCs), consisting of BaCe0.7In0.3O3−δ (BCI30)-NiO anode substrates, BCI30 anode functional layers, BCI30 electrolyte membranes and BCI30-LaSr3Co1.5Fe1.5O10−δ (LSCF) composite cathode layers, were successfully fabricated at 1150°C, 1250°C and 1350°C respectively by a single step co-firing process. The fuel cells were tested with humidified hydrogen (∼3%H2O) as the fuel and static air as the oxidant. The single cell co-fired at 1250°C showed the highest cell performance. The impedance studies revealed that the co-firing temperature affected the interfacial polarization resistance of a single cell as well as its overall electrolyte resistance. [Copyright &y& Elsevier]

Abstract: A high In-dopant level BaCeO3 material was used as an electrolyte for a proton-conducting solid oxide fuel cell (SOFC). Indium behaved as an ideal dopant for BaCeO3, which improved both the chemical stability and sinterability for BaCeO3 greatly. The anode supported BaCe0.7In0.3O3−δ (BCI30) membrane reached dense after sintering at 1100°C, much lower than the sintering temperature for other BaCeO3-based materials. Additionally, the BCI30 membrane showed adequate chemical stability against CO2 compared with the traditional rare earth doped BaCeO3. The BCI30-based fuel cell also showed a reasonable cell performance and a good long-term stability under the operating condition. Besides, the LaSr3Co1.5Fe1.5O10−δ (LSCF) was also evaluated as a potential cathode candidate for a proton-conducting SOFC. [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]

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]

Abstract: The thin membrane of BaCe0.8Sm0.2O3−δ (BCS) with high quality was successfully fabricated on porous NiO–BCS anode substrate through a novel in situ reaction method. The key part of this method is to directly spray well-mixed suspension of BaCO3, CeO2 and Sm2O3 instead of pre-synthesized BCS ceramic powder on the anode substrate. After sintering at 1400°C for 5h, the extremely dense electrolyte membrane in the thickness of 10μm is obtained. A single cell was assembled with La0.7Sr0.3FeO3−σ as cathode and tested with humidified hydrogen as fuel at 650°C. The open circuit voltage (OCV) and maximum power density respectively reach 1.04V and 535mW/cm2. Interface resistance of cell under open circuit condition was also investigated. [Copyright &y& Elsevier]

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]

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]

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]

Abstract The microwave sintering method is found to have advantages over the conventional thermal treatment method for preparing BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ powder. Comparing with the conventional thermal treatment, the microwave sintering method allows the solid material to be self-heated, enabling the formation of pure phase BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ powder at a relatively low temperature (900 °C) with a short dwell time of 1 h, while the same pure phase can only be formed at 1000 °C in an electric furnace. Importantly, the grain size for the microwave prepared BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ powder is much smaller than that of the conventionally thermal treated BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ powder. The small powder grain size is found to be beneficial for the densification and grain growth of the resultant electrolyte membrane during the electrolyte sintering procedure. A fuel cell fabricated using this electrolyte membrane with a conductivity of 7 × 10−3 S cm−1 delivers a power output of 791 mW cm−2 at 700 °C. Highlights • Microwave sintering was used to prepare BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ powder at 900 °C. • Microwave sintering allowed a small grain size of 25 nm for the as-prepared powder. • Microwave prepared BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ powder benefited the electrolyte preparation. • High electrolyte conductivity and desirable fuel cell performance were achieved. [ABSTRACT FROM AUTHOR]

By screening a series of La 0.5 Sr 0.5 MnO 3-δ (LSM)-La 0.5 Sr 0.5 FeO 3-δ (LSF) solid solutions using first-principles calculations, an optimal solid solution of LSM and LSF was chosen as the cathode for proton-conducting solid oxide fuel cells (H–SOFCs). In terms of oxygen vacancy formation energy, O 2 adsorption energy, bond length of adsorbed O 2 , and O p-band center, La 0.5 Sr 0.5 Mn 0.875 Fe 0.125 O 3 (LSMF125) and La 0.5 Sr 0.5 Mn 25 Fe 0.75 O 3 (LSMF75) exhibited superior properties. Subsequent experimental investigations revealed that the H–SOFC with the LSMF75 cathode performed better than the cell with the LSMF125 cathode. The structure analysis revealed that LSMF75 has both Mn and Fe cations on its surface, similar to the designs of several naturally occurring enzymes, hence the increased cathode activity. By improving the LSMF75 cathode further, the cell utilizing the LSMF75 cathode attained a peak power density of 1238 mW cm-2 at 700 °C, which was much greater than that of the cells using the LSM or LSF cathodes, illustrating the benefits of using the LSM-LSF solid solution. Additionally, the good chemical stability of the LSMF75 cathode was maintained, allowing for 150 h of stable operation under operational conditions. [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]

The BaCe 0 · 4 Zr 0 · 4 Y 0 · 2 O 3 (BCZY) was modified with the NiO sintering aid and prepared by a microwave sintering (MVS) method as the electrolyte for proton-conducting solid oxide fuel cells (H–SOFCs). The incorporation of NiO into the BCZY lattice improves the sinterability of the material, leading to the increase of the shrinkage from 3% to 26% after the high-temperature sintering. The dense BaCe 0 · 4 Zr 0 · 4 Y 0 · 15 Ni 0 · 05 O 3 (BCZYN) pellet can be obtained after sintering at 1500 °C, whereas the Ni-free BCZY is porous after sintering at the same condition. By further using the MVS method, the BCZYN can be densified at 1300 °C, which is 200 °C lower than conventional sintering. Furthermore, the microwave-sintered BCZYN has a higher conductivity than the conventionally sintered one due to the larger grain size. Using the MVS method in the H–SOFCs fabrication, the high porosity of the anode substrate can be retained. In contrast, the cell prepared by the conventional sintering (CS) method has a relatively dense anode, which is detrimental to gas fuel transportation. As a result, the microwave sintered cell exhibits an output of 1010 mW cm−2 at 700 °C, which is significantly larger than that for the conventionally sintered cell, being 535 mW cm−2 at the same testing condition, suggesting the advantage of using the MVS method for the fuel cell fabrication. [ABSTRACT FROM AUTHOR]

A new honeycomb-shaped La 0·5 Sr 0·5 Fe 0·9 P 0·1 O 3-δ (LSFP) material has been proposed as a cathode for proton-conducting solid oxide fuel cells (H–SOFCs). Compared with conventional LSFP, the honeycomb-shaped does not change the crystal structure or the electronic structure of the material but offers a much higher surface area. The unique honeycomb structure allows the easier diffusion of air and H 2 O evaporations in the cathode, thus benefiting the application of LSFP as a cathode for LSFP. The honeycomb LSFP cathode's fuel cell shows a peak power density of 1474 mW cm−2 at 700 °C, which is higher than the conventional LSFP cell. In addition, the fuel cell performance is also the highest ever reported for H–SOFCs based on the Sr-doped LaFeO 3 (LSF) cathodes, making a new life for the first-generation LSF cathode for H–SOFCs. The distribution of relaxation times (DRT) analysis for the cell reveals that the honeycomb-shaped cathode improves the oxygen reduction reaction (ORR) at the cathode, thus improving the cathode kinetics. • A honeycomb-shaped La 0·5 Sr 0·5 Fe 0·9 P 0·1 O 3-δ (LSFP) material has been prepared. • The honeycomb structure improved the surface area. • The cell using the honeycomb LSFP cathode showed higher fuel cell performance. • The performance enhancement mechanism was studied. [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]

Abstract: BaZr0.8−xPrxY0.2O3−δ (BZPYx, 0.1≤x≤0.4) perovskite oxides were investigated for application as cathode materials for intermediate temperature solid oxide fuel cells based on proton conducting electrolytes (protonic-SOFCs). The BZPYx reactivity with CO2 and water vapor was evaluated by thermogravimetric and X-ray diffraction analyses, and good chemical stability was observed for each BZPYx composition. Conductivity measurements of BZPYx sintered pellets were performed as a function of temperature and pO2 in humidified atmospheres, corresponding to cathode operating condition in protonic-SOFCs. Different conductivity values and activation energies were measured depending on the Pr content, suggesting the presence of different charge carriers. For all the compositions, the partial electronic conductivity, calculated from conductivity measurements at different pO2 , increased with increasing the temperature from 500 to 700°C. Furthermore, the larger the Pr content, the larger the electronic conductivity. BaZr0.7Pr0.1Y0.2O3−δ and BaZr0.4Pr0.4Y0.2O3−δ showed mostly pure proton and electron conductivity, respectively, whereas the intermediate compositions showed mixed proton/electronic conductivity. Among the two mixed proton/electronic conductors, BaZr0.6Pr0.3Y0.2O3−δ presented the larger conductivity, which coupled with its good chemical stability, makes this perovskite oxide a candidate cathode materials for protonic-SOFCs. [Copyright &y& Elsevier]

Abstract: The cermet consisting of electronic conductor Ni and proton conductor La2Ce2O7 (LDC) shows good chemical stability but poor hydrogen permeability. In order to improve the hydrogen permeability, novel Ni–La2−x Sm x Ce2O7 (x =0, 0.025, 0.05, 0.075, 0.1 and 0.2) cermets were developed for hydrogen separation. The results show that Sm element doping of LDC can affect the rate of hydrogen permeation, with Ni–La1.95Sm0.05Ce2O7 possessing the highest hydrogen permeation fluxes. [Copyright &y& Elsevier]

BaZr 0.8 Y 0.2 O 3-δ (BZY20) is found to react with Pt at high temperatures, although Pt is generally regarded as an inert material that prevents its reaction with many materials even at high temperatures. The reaction between BZY20 with Pt is difficult to be confirmed by X-ray diffraction (XRD) analysis as no observable secondary phase can be detected even after high-temperature treatment. However, the obvious color change of the fired BZY20 powder implies the potential reaction. Therefore, transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) and X-ray photoelectron spectroscopy (XPS) techniques are used to have an insightful analysis of the material. TEM-EDS result indicates that there is an existence of Pt element in the BZY20 powder after firing, suggesting a Pt diffusion into the BZY20 lattice. XPS analysis results further confirm the content of Pt4+ and Pt2+ in the BZY20 powder after firing and the content of Pt4+ increases with the increase of firing temperatures, and the increase of Pt4+ content lowers the O1s binding energy, which might be beneficial for the proton migration. [ABSTRACT FROM AUTHOR]

Abstract Nanofiber-structured La 2 NiO 4+δ (LNO) and LaNi 0.6 Fe 0.4 O 3-δ (LNF) cathodes, which were fabricated by an electrospinning technique, were used for proton-conducting solid oxide fuel cells (H-SOFCs) for the first time, aiming to develop high-performance cobalt-free cathodes for H-SOFCs. High porosity and large specific surface area of LNO, LNF nanofiber-structured cathodes were beneficial for the cathode reactions, resulting in an encouraging peak power density of 508 mWcm−2 and 551 mWcm−2 for LNO and LNF cathode cell at 700 °C, respectively. The nanofiber-structured cathodes showed a higher fuel cell performance and lower polarization resistance compared with that of the cell using corresponding powder cathode, suggesting the construction of nanofiber-structured cathode provided an alternative and promising route to prepare high performance cathodes for H-SOFCs. Graphical abstract Unlabelled Image Highlights • Nanofiber cathodes were used for proton-conducting SOFCs for the first time. • Two different nanofiber cathodes were used and investigated. • Nanofiber structure benefited the cathode reactions. • Cell with nanofiber cathodes showed higher performance than conventional cathodes. [ABSTRACT FROM AUTHOR]

A strategy of tailoring the ceramic cathode composite is presented to improve the performance of proton-conducting solid oxide fuel cells (SOFCs) prepared by a one-step co-firing process. Comparing to the conventional way of using BaCe 0.7 Zr 0.1 Y 0.2 O 3- δ (BCZY) in the composite cathode for BCZY-electrolyte based cells, the replacement of BCZY by BaZr 0.8 Y 0.2 O 3- δ (BZY) mitigates the reaction between the two ceramic phases in the composite cathode during the co-firing process and also keeps the cathode with sufficient porosity for ample gas diffusion which could assist in adequate cathode reactions. As a result, the BCZY-electrolyte based cell with Sm 0.5 Sr 0.5 CoO 3- δ (SSC)-BZY composite cathode shows a power output of 300 mW cm −2 at 600 °C, which is the largest ever reported for proton-conducting SOFCs prepared by a one-step co-firing process. The strategy of tailoring the composite cathode offers both small ohmic resistance and polarization resistance, providing a promising way to develop single-step co-fired proton-conducting SOFCs. [ABSTRACT FROM AUTHOR]

A facile strategy was proposed to synthesize Nb-containing BaCeO 3 -based material, which is a potential electrolyte for proton-conducting solid oxide fuel cells (SOFCs), via a wet chemical route while the conventional synthesis of Nb-containing oxides relied on the solid state reaction method due to the unavailability of suitable Nb-precursors such as Nb-nitrates resulting in a less desirable fuel cell performance when used as an electrolyte. The BaCe 0.7 Nb 0.1 Y 0.2 O 3 − δ (BCNY) electrolyte material in this study persisted a good chemical stability against CO 2 and exhibited good performance in the fuel cell application. The fuel cell with BCNY electrolyte film showed a high performance of 533 mW cm − 2 at 700 °C. This cell performance based on BCNY electrolyte was superior to that of many stable modified BaCeO 3 -based proton-conducting SOFCs where the electrolytes were tailored by other strategies. This result indicated that the strategy presented in this study could be an effective way to prepare a stable electrolyte for high performance proton-conducting SOFCs, which could advance the development of proton-conducting SOFCs. [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]