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Slow oxygen reduction reaction (ORR) involving proton transport remains the limiting factor for electrochemical performance of proton-conducting cathodes. To further reduce the operating temperature of protonic ceramic fuel cells (PCFCs), developing triple-conducting cathodes with excellent electrochemical performance is required. In this study, K-doped BaCo0.4Fe0.4Zr0.2O3−δ (BCFZ442) series were developed and used as the cathodes of the PCFCs, and their crystal structure, conductivity, hydration capability, and electrochemical performance were characterized in detail. Among them, Ba0.9K0.1Co0.4Fe0.4Zr0.2O3−δ (K10) cathode has the best electrochemical performance, which can be attributed to its high electron (e−)/oxygen ion (O2−)/H+ conductivity and proton uptake capacity. At 750 °C, the polarization resistance of the K10 cathode is only 0.009 Ω·cm2, the peak power density (PPD) of the single cell with the K10 cathode is close to 1 Wcm−2, and there is no significant degradation within 150 h. Excellent electrochemical performance and durability make K10 a promising cathode material for the PCFCs. This work can provide a guidance for further improving the proton transport capability of the triple-conducting oxides, which is of great significance for developing the PCFC cathodes with excellent electrochemical performance.

This work introduces a significant Co-free cathode material for proton-conducting solid oxide fuel cells (H-SOFCs) and offers a deep understanding of the effect of K-doping on the ability of absorption and transportation of oxygen ions and protons.

During the past decade proton exchange membrane fuel cells (PEMFCs) as one kind of the potential clean energy sources for electric vehicles and portable electronic devices are attracting more and more attentions. Although Nafion® membranes are considered as the benchmark of proton exchange membranes (PEMs), the drawbacks of Nafion® membranes restrict the commercialization in the practical application of PEMFCs. As of today, the attention is to focus on developing both high-performance and low-cost PEMs to replace Nafion® membranes. In all of these PEMs, sulfonated poly(arylene ether ketone)s (SPAEKs) and sulfonated poly(arylene ether sulfone)s (SPAESs) are the most promising candidates due to their excellent performance and low price. In this review, the efforts of SPAEK and SPAES membranes are classified and introduced according to the chemical compositions, the microstructures and configurations, as well as the composites with polymers and/or inorganic fillers. Specifically, several perspectives related to the modification and composition of SPAESs and SPAEKs are proposed, aiming to provide the development progress and the promising research directions in this field.

The commercialization of solid oxide fuel cells (SOFCs) can be significantly promoted with the direct utilization of methane, which is the primary component in natural gas and the second most abundant anthropogenic greenhouse gas. However, carbon deposition on most commonly used Ni-based anode is the bottle-necking issue inhibiting long-term stability of direct methane SOFCs. To avoid such a problem, methane is typically reformed (internally or externally) in SOFCs. Considering the cost, system simplification, coking resistance, and material selection, the on-cell catalytic reforming layer (OCRL) is one of the most promising designs for direct methane SOFCs. Reforming catalytic materials are typically consisted of active component, substrate and catalytic promoter, all of which have a significant impact on the catalytic activity, sintering resistance and coking resistance of methane reforming catalysts. This review summarizes the influence of the various components, some common OCRL materials and their applications in direct methane SOFCs, reforming and coking resistance mechanism, as well as the remaining challenges. The effective utilization of OCRL plays a pivotal role in promoting the development of direct methane SOFCs and the commercialization of SOFCs.

SOFC (solid oxide fuel cell, SOFC) is recognized to be efficient green energy technology in the 21st century. However, when hydrocarbons are directly used as fuel, carbon deposition is easy to occur in Ni-based anode, thus losing electrochemical catalytic activity. Fuel pre-reforming is also called on-cell reforming of hydrocarbons, which has been a promising solution for alleviating the carbon deposition problem in cermet anodes to varying degrees. And the key factor is to find an efficient and stable fuel reforming catalyst. Perovskite oxides have stable structure, highly catalytic activity and adjustable thermal expansion coefficient for using on the cells, showing great potentials of application for fuel reforming. In this paper, we summarize the application of perovskite catalyst in CH4 fuel reforming based on the research of our group and other scholars, and puts forward the corresponding views and perspective, especially in perovskite catalyst with Ni exsolution.

Bismuth vanadate (BiVO4) has been one of the most promising candidates for solar water splitting while still suffers from poor bulk charge transport that limits its solar to hydrogen conversion efficiency. We demonstrate in this work an efficient strategy for boosting bulk charge transport of BiVO4 through the facile impregnation of as-prepared BiVO4 photoanode in the precursor solution of ultrathin BiOI nanosheets. Such impregnation creates increased oxygen vacancies in the bulk of BiVO4 through the reduction of V5+ to V4+ by I−, which greatly improves bulk separation efficiency for BiVO4-BiOI up to 65.9 % at 1.23 VRHE from the original 51.9 % of pure BiVO4. Moreover, the decoration of the BiOI nanosheets on BiVO4 photoanode is also beneficial for addressing the carrier dynamics at surface due to the matched energy levels of BiOI nanosheets and BiVO4. The introduced plenty of oxygen vacancies in the bulk of BiVO4 and the built-in electric field in BiVO4-BiOI synergistically improve the photocurrent density at 1.23 VRHE up to 3.88 mA cm-2. We believe that such facile impregnation strategy will pave an alternative way to the development of highly efficient BiVO4 photoanode.

Coking is a major issue with the traditional Ni-based anodes when directly oxidizing CH4 in solid oxide fuel cells (SOFCs). Dry reforming to convert CH4–CO2 into CO–H2 syngas before entering Ni-based anode may potentially be an effective and economical method to address the coking problem. Consequently, an on-cell reforming layer outside the Ni-based anode is expected to offer a unique solution for direct CH4–CO2 SOFCs without coking. In this study, Ni-GDC anode-supported cells with and without a Sr2Co0.4Fe1.2Mo0.4O6-δ (SCFM) layer outside the anode support have been fabricated and evaluated using either H2 or CH4–CO2 as fuel. Both types of cells show excellent electrochemical performance when H2 is used as fuel, and the SCFM layer has negligible impact on the cell performance. When CH4–CO2 is used as fuel, however, the electrochemical performance and durability of the cells with the SCFM layer are much better than those without the SCFM layer outside the Ni-GDC anode, indicating that the SCFM layer can efficiently perform dry reforming. This unique on-cell dry reforming design enables direct CH4–CO2 solid oxide fuel cells and offers a very promising route for energy storage and conversion.

A solid oxide fuel cell (SOFC) is a clean, efficient energy conversion device with wide fuel applicability. Metal-supported solid oxide fuel cells (MS-SOFCs) exhibit better thermal shock resistance, better machinability, and faster startup than traditional SOFCs, making them more suitable for commercial applications, especially in mobile transportation. However, many challenges remain that hinder the development and application of MS-SOFCs. High temperature may accelerate these challenges. In this paper, the existing problems in MS-SOFCs, including high-temperature oxidation, cationic interdiffusion, thermal matching, and electrolyte defects, as well as lower temperature preparation technologies, including the infiltration method, spraying method, and sintering aids method, are summarized from different perspectives, and the improvement strategy of existing material structure optimization and technology integration is put forward.

La0.5(Ba0.75Ca0.25)0.5Co0.8Fe0.2O3-δ, a simple perovskite cathode material with high electrical conductivity (940 S cm−1 at 600 °C) and impressive surface catalytic activity, was prepared and used in proton-conducting solid oxide fuel cells. As its thermal expansion coefficient is higher than that of the electrolyte material BaZr0.1Ce0.7Y0.1Yb0.1O3-δ, they were combined and used as a composite cathode. The crystal structure, chemical compatibility, electrical conductivity, cell performance, and the oxygen reduction reaction of the cathode material were explored, and we found that the single fuel cell developed with the composite cathode achieved excellent electrochemical performance, with both a low polarization resistance and high peak power density (0.044 Ω cm2 and 1102 mW cm−2 at 750 °C, respectively). Outstanding stability was also achieved, as indicated by a long-term 100-h test. Additionally, the rate-limiting steps of the oxygen reduction reaction were the oxygen adsorption, dissociation, and diffusion processes.

Ce was successfully doped into the A site of La0.9Mn0.8Ni0.2O3 (LMN) with 5 mol% doping content (LCMN-05), and the obtained LCMN-05 acted as a catalyst for dry reforming. After reduction in 5% H2–N2 stream at 800 °C, the Ni particles were successfully exsolved on the surface. The H2-TPR, XPS and solid EPR results demonstrated that the Ce substitution facilitated the reducible properties of the perovskites, as well as the oxygen transfer. Furthermore, it promoted the reduction to high extents with more oxygen vacancies left behind. Thus, the reduced LCMN-05 showed stable conversions of CH4/CO2 above 90% at 750 °C for 50 h without coking. While for the reduced LMN, it had a rapid deactivation with the amount of carbon fibers when the temperature rose from 700 °C to 750 °C. The LCMN-05 displayed a whole perovskite structure after the test, which guaranteed the strong interaction between the exsolved Ni and perovskite substrate. However, the structure of LMN was destroyed in a reducing atmosphere at high temperature, which explained the different performances of the two catalysts. The introduction of Ce increased the amount of oxygen vacancies and avoided the excessive reduction of Mn3+, thus improving the structural stability and ensuring the catalytic activity of reduced LCMN-05.

LaCrO3-based ceramic interconnects (ICs) are currently employed in tubular solid oxide cells (SOCs), but they are facing challenges in manufacturability, durability, and cost, primarily due to Cr v...

Zn-doped PrBa0.9Ca0.1Co2-xZnxO5+δ (PBCCZx) with x equaling 0, 0.05, 0.10, 0.15, and 0.2, designated as PBCCZ00, PBCCZ05, PBCCZ10, PBCCZ15, and PBCCZ20, respectively, are prepared and investigated in the aspects of crystal structure, thermal expansion behavior, defect chemistry, and electrochemical performance as the cathode of proton-conducting solid oxide fuel cells (H–SOFCs). With the increase of the content of doped Zn, the thermal expansion coefficient of PBCCZx remains unchanged essentially. But the bulk and surface concentrations of oxygen vacancy are increased, and the maximum power density (MPD) of the cells at 750 °C with PBCCZx-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) composite cathodes are improved from 335 (x = 0) to 876 (x = 0.15) mW cm−2. With the PBCCZ15-BZCYYb cathode, the MPD of the cell increases with temperature from 299 mW cm−2 at 600 °C to 876 mW cm−2 at 750 °C with a reduction of cell polarization resistance from 0.68 to 0.04 Ω cm2 accordingly.

Lowing the operating temperature can greatly promote the commercialization of solid oxide fuel cells (SOFCs), however it also results in a significant increase in cell impedance, which is the bottleneck for the development of intermediate temperature SOFCs (IT-SOFCs). Major hurdles in developing conventional single-phase cathode materials for IT-SOFCs are poor electrochemical performance or durability. The investigation of new cathode materials or the optimization of the existing cathodes is imminent for the development of IT-SOFCs. Among them, core-shell structured cathode can combine the advantages of multiple components, and has been demonstrated with excellent oxygen reduction reaction (ORR) catalytic activity and long-term stability. This review summarizes the recent research progress on core-shell structured cathode for enhanced electrochemical performance, long-term stability, CO2 tolerance and Cr tolerance. Furthermore, the future directions are discussed from a perspective of materials design, preparation and characterization. Core-shell structured cathodes are expected to play an increasingly critical role in the commercialization of IT-SOFCs.

In this study, we successfully synthesized double perovskite-type oxide NdBa0.5Ca0.5Co1.5Fe0.5O5+δ (NBCCF) using a conventional wet chemical method as the oxygen electrode for reversible solid oxide electrochemical cells (RSOCs). The polarization resistance (Rp) of the composite electrode NBCCF-Gd0.1Ce0.9O2 (GDC) is only 0.079 Ω cm2 at 800 °C under air. The single cell based on NBCCF–GDC electrode displays a peak power density of 0.941 W/cm2 in fuel cell mode and a low Rp value of 0.134 Ω cm2. In electrolysis cell mode, the cell displays an outstanding oxygen evolution reaction (OER) activity and shows current density as high as 0.92 A/cm2 with 50 vol% AH (Absolute Humidity) at 800 °C and applied voltage of 1.3 V. Most importantly, the cell exhibits admirable durability of 60 h both in electrolysis mode and fuel cell mode with distinguished reversibility. All these results suggest that NBCCF is a promising candidate electrode for RSOC.

Solid oxide fuel cells with high-temperature proton conductors (HTPCs) as the electrolyte have attracted intensive attention for years; however, the mechanism for proton transfer in HTPCs remains u...

Solid oxide fuel cells (SOFCs) can directly operate on hydrocarbon fuels such as natural gas; however, the widely used nickel-based anodes face grand challenges such as coking, sulfur poisoning, and redox instability. We report a novel double perovskite oxide Sr2Co0.4Fe1.2Mo0.4O6-δ (SCFM) that possesses excellent redox reversibility and can be used as both the cathode and the anode. When heat-treated at 900 °C in a reducing environment, double perovskite phase SCFM transforms into a composite of the Ruddlesden-Popper structured oxide Sr3Co0.1Fe1.3Mo0.6O7-δ (RP-SCFM) with the Co-Fe alloy nanoparticles homogeneously distributed on the surface of RP-SCFM. At 900 °C in an oxidizing atmosphere, the composite transforms back into the double perovskite phase SCFM. The excellent oxygen reduction reaction catalytic activity and mixed ionic-electronic conductivity make SCFM an excellent cathode material for SOFCs. When SCFM is used as the anode, excellent performance and stability are achieved upon either direct oxidation of methane as a fuel or operation with sulfur-containing fuels. The excellent redox reversibility coupled with outstanding electrical and catalytic properties manifested by SCFM will enable a broad application in energy conversion applications.

In this paper, we study the perovskite La0.6Sr0.4Fe0.9Mn0.1O3-δ (LSFM) as both the cathode and anode in a symmetrical solid oxide electrolysis cell (SOEC) for direct high-temperature electrolysis of pure CO2. The cell with a configuration of LSFM-GDC|GDC||YSZ||GDC|LSFM-GDC performs with perfect electrochemical properties with a polarization resistance of 0.068 Ω·cm2 and a current density of 1.107 A/cm2 at 800 °C and 1.744 A/cm2 at 850 °C under an operating voltage of 2.0 V. The corresponding CO production rate at 800 °C and 2.0 V is 6.438 mL/(min·cm2). These results confirm that La0.6Sr0.4Fe0.9Mn0.1O3-δ can act as an excellent electrode material in a symmetrical SOEC for electrolysis of pure CO2.

Two Co-alloy-coated steels with 1.0 wt% and 3.0 wt% Mn content were subjected to 1000 h of thermal exposure (750 °C) in air. The coated alloys displayed an increased oxidation rate as the Mn content varied between 1.0 wt% and 3.0 wt%. And Co coating was thermally converted into a three-layer structure composed of Cr-rich oxide (inner layer), mixed oxide with Co, Fe, Mn and Cr (middle layer) and doped Co3O4 spinel oxide (outer layer). Regardless of the Mn content, only a small amount of Mn was incorporated in the Co3O4 spinel. The area specific resistance for the Co-coated Fe-Cr containing 1.0 wt% Mn was as low as 5.37 mΩ cm2 subsequent to oxidation (lasting for 1000 h). Compared to the cathode with the uncoated alloy present, the polarization resistance of the cathode in the presence of the Co-coated alloy increased very slowly under the conditions of open circuit potential set as 750 °C and 200 h, and Cr deposition on the cathode surface declined noticeably. This showed that the Co coating effectively inhibited outward diffusion of Cr to poison the cathode during long-term exposure.

Formation energy, crystal structure and electronic structure of C, N doped anatase TiO2 are calculated based on the density functional theory of plane-wave ultrasoft pseudopotential. Results indicate that, due to doping of the C or N atoms in anatase TiO2, the lattice distorts obviously. The substitution of C tends to Ti site while N tends to O site. All the substitutions lead to the red shift of the optical absorption and increasing coefficient of light absorption. When N concentrations are 2.08% and 3.13% in N-doped TiO2, the highest photocatalytic activity is obtained, while it is 2.08% for C-doped one.