Proton-conducting Solid Oxide Research Articles

High-Temperature Mechanical–Conductive Behaviors of Proton-Conducting Ceramic Electrolytes in Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (P-SOFCs) are widely studied for their lower working temperatures than oxygen-ion-conducting SOFCs (O-SOFCs). Due to the elevated preparation and operation temperatures varying from 500 °C to 1500 °C, high mechanical stresses can be developed in the electrolytes of SOFCs. The stresses will in turn impact the electrical conductivities, which is often omitted in current studies. In this work, the mechanical–conductive behaviors of Y-doped BaZrO3 (BZY) electrolytes for P-SOFCs under high temperatures are studied through molecular dynamics modeling. The Young’s moduli of BZY in fully hydrated and non-hydrated states are calculated with different Y-doping concentrations and at different temperatures. It is shown that Y doping, oxygen vacancies, and protonic point defects all lead to a decrease in the Young’s moduli of BZY at 773 K. The variations in the conductivities of BZY are then investigated by calculating the diffusion rates of protons in BZY at different triaxial, biaxial, and uniaxial strains from 673 K to 873 K. In all cases, the diffusion rate present a trend of first increasing and then decreasing from compression state to tension state. The variations in elementary affecting factors of proton diffusion, including hydroxide rotation, proton transfer, proton trapping, and proton distribution, are then analyzed in detail under different strains. It is concluded that the influences of strains on these factors collectively determine the changes in proton conductivity.

Construction of more oxygen vacancies of BaCo0.4Fe0.4Zr0.2O3-δ for high-performance proton-conducting solid oxide fuel cell cathodes

The cathodic catalytic activity for the oxygen reduction reaction (ORR) plays a critical role in determining the performance of proton-conducting solid oxide fuel cells (P-SOFCs). BaCo0.4Fe0.4Zr0.2O3-δ (BCFZ) has emerged as a promising cathode for P-SOFCs due to its triple-phase conductivity. Nevertheless, its suboptimal proton conductivity and hydration ability at intermediate temperatures prevent it from achieving the anticipated ORR catalytic activity. To address these limitations, this study explores the enhancement of electrocatalytic activity in BCFZ through alkali metal doping and A-site defect construction. The effects of such modifications on oxygen surface exchange kinetics and ORR catalytic activity are systematically investigated. The findings reveal that BCFZ exhibits relatively low parameters in terms of electronic conductivity, oxygen ion conductivity, oxygen vacancy concentration, kchem, and Dchem. Conversely, these parameters are markedly improved in A-site deficient BCFZ (D-BCFZ) and Na/K-doped BCFZ. Consequently, the enhancement of these properties yields a significant increase in ORR catalytic activity, with D-BCFZ demonstrating the best electrochemical performance. Specifically, P-SOFC with D-BCFZ cathode achieves an Rp value of just 0.073 Ω cm2 and a Pmax value of 0.928 W cm-2 at 650 °C. This study provides theoretical insight into the mechanisms by how alkali metal doping and defect construction enhance the ORR catalytic activity of BCFZ. These findings offer valuable guidance for the development and optimization of high-performance P-SOFC cathodes.

Tailoring SrFeO3 cathode with Ta and F allows high performance for proton-conducting solid oxide fuel cells

To customize the traditional SrFeO3 (SFeO) cathode for proton-conducting solid oxide fuel cells (H-SOFCs), a Ta cation and F anion co-doping approach is suggested. It has been discovered that Ta-doping can enhance the oxygen vacancy content and the protons' and oxygen's diffusion capacities, enabling improved H-SOFC performance. Ta-doping alone, however, only modestly enhances the cathode's performance, which is still below that of many newly created cathodes. The F anion co-doping is further introduced to further improve performance, resulting in the formation of the SrFe0.9Ta0.1O2.9F0.1 (SFeTOF) cathode. When SFeTOF is compared to the single Ta-doping material, its proton and oxygen diffusion properties are further improved, demonstrating the efficacy of using Ta and F co-doping for SFeO. Consequently, the fuel cell utilizing the SFeTOF cathode for H-SOFCs displays a fuel cell output of 1559 mW cm−2 at 700 °C, notably higher than the fuel cell that uses SFeO or Ta-doped SFeO cathodes. The performance is likewise impressive among the H-SOFC cathodes that are now in use. Moreover, the fuel cell utilizing the SFeTOF cathode demonstrates sufficient operational stability in operating conditions, establishing SFeTOF as a reliable and effective cathode for H-SOFCs.

Investigation of samarium and neodymium co-doped BaCeO3 electrolyte for proton-conducting solid oxide fuel cells

BaCe0.8Sm0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) powder was prepared using the glycine-nitrate combustion method, its crystal structure, microscopic morphology and electrochemical properties were investigated. X-ray diffraction analysis showed that the BaCe0.8Sm0.2-xNdxO3-δ powder with orthorhombic perovskite structure could be obtained after calcined at 1150 °C. Scanning electron microscopy showed that BaCe0.8Sm0.2-xNdxO3-δ sintered samples exhibited a dense structure. Electrochemical impedance tests showed that the substitution of Nd3+ improved the electrical conductivity of the BaCeO3-based electrolyte materials. The proton conductivity of BaCe0.8Sm0.15Nd0.05O3-δ samples reaches a maximum value of 0.035 S cm−1 in a wet air environment at 700 °C.

Efficient ammonia conversion in proton conducting fuel cells: Combined application of dendritic anodes and nanofiber catalysts

Ammonia, with its high hydrogen content, serves as an optimal carbon-free medium for indirect hydrogen storage, making it ideal for fuel cells. Nevertheless, the limited anodic catalytic activity of Proton-conducting solid oxide fuel cells (PCFCs) significantly hampers NH3 utilization efficiency and overall performance. This study introduces efficient nano-catalysts deposited onto dendritic anodic microchannels, leading to the formation of an in-situ ammonia decomposition reactor for internal ammonia gas conversion. Compared to conventional cells, this cell, equipped with a catalyst bed, shows a 25% increase in peak power density and a 20%–30% enhancement in NH3 utilization efficiency. Additionally, ammonia undergoes efficient decomposition on anodic metallic nickel, which prevents nickel nitridation and improves cell stability. The augmented stability of these cells is evidenced by their prolonged operational lifespan under constant current conditions, extending from 63 to 108 h, thus marking a substantial enhancement in the system's durability and reliability.

Advancements in sustainable proton-conducting electrochemical cells: Direct recycling of sintered nickel oxide-doped barium zirconate half cells

The ongoing evolution in energy production and conversion technologies has brought solid oxide electrochemical cells (SOCs) to the forefront, recognized for their high efficiency and environmental benefits. However, establishing sustainable and scalable manufacturing processes for SOCs presents formidable challenges, including sourcing large-scale raw materials and implementing effective recycling methods for spent cells and manufacturing scraps. In response, we demonstrate closed-loop direct recycling of proton-conducting solid oxide electrochemical half cells, incorporating active comminution and cell regeneration using the recycled materials. This innovative approach achieves over 92 % material recovery and an impressive 100 % recovery in full cell performance, addressing a significant gap in current sustainable manufacturing practices while setting a new standard for the industry. This technology not only addresses a significant gap in current sustainable manufacturing practices but also sets a precedent for future advancements in the sustainable SOC field, potentially influencing broader practices in the recycling of multi-functional ceramics.

Cross-stacking crystal structural configuration of integrated cathode materials for proton-conducting solid oxide fuel cells

Cross-stacking crystal structural configuration of integrated cathode materials for proton-conducting solid oxide fuel cells

P2M systems based on proton-conducting solid oxide cells: Future prospects and costs of renewable methanol production

As consequence of the transition towards sustainable energy sources, the future production of liquid energy carriers (e.g. methanol) via H2 supply pathways utilizing water electrolyzers (power-to-liquid) will most likely be based on fluctuating grid electricity or islanded renewable inputs. As a result, these production processes are subject to fluctuating operating conditions and varying production capacities, ultimately leading to uncertainties with respect to their process economics and profitability. Therefore, the impact of different electricity supply-side scenarios (static grid and intermittent grid or renewable supply) on the production economics of power-to-liquid processes needs to be assessed thoroughly for the upcoming decades. Methanol is considered as an essential base chemical which is widely known for its versatility and broad potential use contexts in future chemical industries and energy storage applications. Methanol production pathways powered by renewable electricity sources, also known as power-to-methanol processes, are characterized by low specific life-cycle emissions and are therefore of paramount interest. One possible renewable process chain features proton-conducting high temperature electrolyzers combined with a direct hydrogenation of CO2. In this paper, a techno-economic forecast study of this process chain is presented and specific production costs of renewable methanol under different electricity supply scenarios are determined and discussed for the years 2030 and 2050. The studies showed that flexible grid-supported scenarios through direct spot-market participation and renewable scenarios based on wind onshore production enable the largest production cost reduction potential in the upcoming decades. Minimum production costs of 740 € t−1MeOH (2030) and 415 € t−1MeOH (2050) are determined for a flexible operation of the system with spot-market participation, benefitting from times of low or even negative electricity prices. Among the renewable production scenarios, islanded power-to-methanol systems coupled to wind onshore plants were identified as the most beneficial configuration with ascertained production costs as low as 820 € t−1MeOH and 353 € t−1MeOH by 2030 and 2050, respectively.

Manipulating cathode composition to enhance performance of proton-conducting solid oxide fuel cells through indium doping

One current research direction in proton-conducting solid oxide fuel cells (H–SOFCs) focuses on developing triple-phase conducting cathodes. By optimizing the cerium and indium ratio and adjusting the phase composition of barium ferrate cathode materials, improved power density is achieved in single cells with BaCe0.21Fe0.64In0.15O3-δ (BCFI15) as the cathode, reaching a peak power density of 1473 mW cm−2 at 700 °C. Density functional theory calculations (DFT) further support that the incorporation of indium through doping effectively reduces the energy barrier for proton transition, thereby enhancing proton absorption capability and electrochemical reactivity.

Bridging the Gap between fundamentals and efficient devices: Advances in proton-conducting oxides for low-temperature solid oxide fuel cells

Low-temperature solid oxide fuel cells (LT-SOFCs) represent a cutting-edge solution in the domain of clean energy, poised to revolutionize electricity generation for both stationary and mobile applications. At the core of LT-SOFCs lies the proton-conducting solid oxide electrolyte, a subject of extensive exploration and advancement. This comprehensive review investigates the evolution of proton-conducting solid oxide electrolytes for LT-SOFCs, exploring the landscape from fundamental materials to diverse device architectures. The review meticulously examines three pivotal dimensions: 1) strategies for fine-tuning the properties and structures of ceramics and proton-conducting oxides, 2) advancements in techniques for protonic-conducting fuel cells (PCFCs), and 3) an exploration of the opportunities and challenges intrinsic to the progression of electrolyte-based PCFCs. By elucidating the advancements made in optimizing conductivity, chemical stability, sinterability, and electron-blocking characteristics of proton-conducting electrolytes, this review offers invaluable insights into the state-of-the-art for LT-SOFC technology. Furthermore, it casts a forward-looking perspective, envisioning the future trajectory of proton-conducting electrolyte research and its potential to reshape the landscape of LT-SOFC technology. By providing a comprehensive overview of past achievements and future prospects, this review serves as a valuable resource for researchers, engineers, and stakeholders, guiding them towards the realization of efficient and sustainable energy solutions.

BaZr0.1Ce0.7Y0.1Yb0.1O3-δ particles embedded PrBa0.5Sr0.5Co1.5Fe0.5O5+δ hollow nanofibers with 3D fast transmission path as oxygen electrode for proton-conducting solid oxide electrolysis cell

To address the challenge of low-temperature catalytic activity of oxygen electrodes, a high-activity triplex ionic conductor material, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF), is prepared using electrospinning. The preparation PBSCF and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) nanofibers composite electrodes are used with different composite methods to improve the catalytic activity and the proton transport pathway within the electrode. The results show that PBSCF@BZCYYb prepared by PBSCF and BZCYYb pre-mixed one-step electrospinning has high porosity and 3D interwoven continuous transmission path, exhibiting minimal polarization impedance on symmetric cells. The electrolysis cell with PBSCF@BZCYYb|BZCYYb|NiO-BZCYYb (active layer) |NiO-BZCYYb (support layer) structure shows electrolysis current densities of 775.4 mA cm−2 under 1.3 V at 650 °C with 20%H2O+80%Air atmosphere. Additionally, during the constant voltage electrolysis, the cell shows acceptable stability in 60 h at 650 °C, considered to be a promising oxygen electrode material in this work.

A proton-conducting solid oxide fuel cell for co-production of ethylene and power via ethane conversion

A proton-conducting solid oxide fuel cell for co-production of ethylene and power via ethane conversion

A-site cation deficient SrTa0.1Fe0.9O3-δ as a bi-functional cathode for both oxygen ion- and proton-conducting solid oxide fuel cells

In order to accelerate the widespread application of solid oxide fuel cells (SOFCs), especially proton-conducing solid oxide fuel cells (PCFCs), it is crucial to develop a cathode material with high activity for the oxygen reduction reaction (ORR), excellent long-term stability and CO2 tolerance. Herein, an A-site deficient cobalt-free (Co-free) perovskite oxide Sr0.95Ta0.1Fe0.9O3-δ (S0.95TF) is prepared by introducing cation deficiencies into SrTa0.1Fe0.9O3-δ (STF), and it proves to be a highly active cathode. The increased oxygen vacancies, the decreased thermal expansion coefficient (TEC) value and improved CO2 tolerance, efficiently enhance electrochemical performance and durability during long-term stability testing. As a result, the area specific resistance (ASR) values of S0.95TF at 600 °C are only 0.095 and 0.42 Ω cm2 with the Sm0.2Ce0.8O1.9 (SDC) and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolytes, respectively. In addition, both of the single cells with S0.95TF cathodes, based on different electrolytes, can function stably for 200 h without obvious performance decrease. These results clearly demonstrate that S0.95TF is a highly promising candidate for both oxygen ion-conducting SOFCs and PCFCs.

Coordinated optimization of methanol utilization and in-situ cracking reforming in proton-conductive solid oxide fuel cells

Proton-conductor solid oxide fuel cells (PC–SOFCs) have demonstrated innovative capabilities in energy applications, particularly for the efficient transformation of biomass fuels into hydrogen for power generation. Methanol, a readily available and economical biomass fuel with a high hydrogen content, has shown significant potential for waste utilization and energy recovery. Consequently, this study employed methanol as a fuel for PC-SOFCs and investigated the optimal operating conditions through meticulously designed experiments. This study also enhanced the cell performance through the co-reforming of steam and methanol, demonstrating that the introduction of steam during the methanol-reforming process significantly improved cell efficiency. At a 30 % methanol fuel concentration and a 700 °C operating temperature, co-reforming increased the maximum power density (MPD) from 0.269 to 0.352 W cm−2. Additionally, integrating Ru-GDC nanofiber catalysts into the anodic dendritic microchannels enabled the creation of an in-situ catalytic cracking reactor, further boosting MPD to 0.412 W cm−2. The catalyst-equipped cell demonstrated stable operation for continuous 102 h at a current density of 0.6 A cm−2, with no performance decline, thereby confirming the exceptional long-term stability of the system.

Manipulating Nb-doped SrFeO 3− δ with excellent performance for proton-conducting solid oxide fuel cells

Manipulating Nb-doped SrFeO _{3− <i>δ</i>} with excellent performance for proton-conducting solid oxide fuel cells

A dual modification strategy of highly active catalytic cathode for proton-conducting solid oxide fuel cell with Ni-doped PrBaFe1.9Mo0.1O6-δ

The cathode catalytic activity and stability in a temperature range of 550–700 °C is crucial to the development of proton-conductive solid oxide fuel cells (PCFCs). A facile dual-modification strategy is developed for the design of Ni-doped PrBaFe1.9Mo0.1O6-δ (PBFMN), composed of a major perovskite and a minor NiO phases, as a cobalt-free cathode. The composite cathode PBFMN exhibits high catalytic activity and stability. Computational simulation indicates that the perovskite phase increases the oxygen vacancies and enhances the proton transfer, while nickel oxide nanoparticles improve oxygen adsorption and dissociation. The fuel cell with as-prepared PBFMN reached a peak power density 1.23 W cm−2 at 700 °C. The improved performance of the cell is mainly due to the fast ORR kinetics. This work provides a new insight into the design of cobalt-free cathode for a PCFC.

Co-precipitation process as an effective and viable route for proton-conducting solid oxide fuel cell applications

BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb) is one of the most popular electrolyte materials in proton ceramic fuel cells (PCFCs). The synthesizing method and properties of BCZYYb powders have a significant impact on the sintering activity of electrolyte materials. In this work, the BCZYYb electrolyte was synthesized by ammonium bicarbonate co-precipitation method (CPT), and was compared with the powder produced by solid-state reaction (SSR) and sol-gel (SG) methods. XRD results show the BCZYYb powder synthesized by the CPT method belongs to orthorhombic crystal system with a space group of Pmcn (No. 62) and the refined lattice parameters are a = 8.774 Å, b = 6.173 Å, and c = 6.203 Å. In humid air atmosphere, the total conductivity at 650 °C and the activation energy for the BCZYYb powder prepared via the CPT method was 2.1 × 10−2 S cm−1 and 0.46 eV, respectively, as compared with 1.9 × 10−2 S cm−1 and 0.45 eV for the SSR method, and 1.8 × 10−2 S cm−1 and 0.44 eV for the SG method. Under similar testing conditions, the measured peak power densities were 0.51, 0.35, and 0.40 W cm−2 at 650 °C for the anode supported PCFCs using electrolyte powder prepared via CPT, SSR and SG methods, respectively, which proves the CPT method is an effective and viable route for PCFCs applications.

Towards highly dense electrolytes at lower sintering temperature (∼1200 °C): Optimization strategies for BaCe0.7Zr0.1CuxY0.2-xO3-δ in SOFCs

High-conducting and long-term stable proton-conducting electrolytes are of utmost importance. This study investigates the synthesis and characterization of BaCe0.7Zr0.1CuxY0.2-xO3-δ (BCZCuxY; x = 0, 0.005, 0.01, 0.02, 0.05, and 0.1) electrolytes tailored for proton-conducting solid oxide fuel cells (SOFCs). Through Cu2+ doping at the B-site of BaCe0.7Zr0.1Y0.2O3-δ (BCZY), a successful reduction of the sintering temperature to 1200 °C was achieved. BCZCu0.02Y exhibited a high relative density of approx. 98.1% at this temperature, but beyond 2 mol% Cu doping, the appearance of a BaCuO2 secondary phase adversely impacted conductivity. The electronic properties of BCZY and BCZCuxY are elucidated via partial density of states (PDOS) analysis, revealing optimized crystal structures and band gap reductions (from approx. 1.9 eV–1.1 eV) upon Cu doping. Notably, BCZCu0.02Y demonstrated a commendable conductivity, with values of 3.5 × 10−2 S. cm−1 in air and 4.8 × 10−2 S. cm−1 in a moist atmosphere at 750 °C. Remarkably, excellent electrochemical stability was observed in a moist hydrogen atmosphere for up to 450 h at 600 °C. Single cells incorporating BCZCu0.02Y electrolytes exhibited peak power densities of 380 mW/cm2 at 750 °C. The incorporation of 2 mol% Cu2+ in the BCZY lattice holds promise for achieving low-temperature sintering and high-performance proton-conducting SOFCs.

Multicomponent doping realized superior triple-conducting within cobalt-free Ruddlesden-Popper-type perovskite for Proton-conducting fuel cells cathode

Proton-conducting solid oxide fuel cells (H-SOFCs) are appealing for low-to-intermediate temperature operation due to their intrinsic lower activation energy and better ionic conductivity. Unfortunately, there are currently few acceptable and high-performing cathode materials available for H-SOFCs. Herein, we present a novel high performance multicomponent Ruddlesden-Popper (RP) type cathode Pr3Ni1.5Cu0.3Nb0.05Ta0.05Zr0.05Y0.05O7-δ (PNCNTZY) with superior triple conducting property. The multicomponent co-doping of Nb, Ta, Zr, and Y brings about the enhancement of configurational entropy and cocktail effect for improving H+/O2-/e- triple conductivity and oxygen vacancy concentration. Naturally, the ORR activity is improved by facilitated charge transfer and oxygen surface exchange, exhibiting reduced polarization resistance to just 0.24 Ω cm2 at 550 °C. When used as the cathode in H-SOFC single cells, excellent power production is demonstrated at 550 °C, with a peak power density of up to 0.84 W cm-2. Furthermore, the PNCNTZY sample shows adequate thermal compatibility with proton conductor electrolytes BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and then appropriate endurance durability (0.8 A cm-2 at 550 °C for about 250 h) due to their match of thermal expansion coefficient (TEC) brought about by the Co-free and partial replacement of larger-size elements. This extremely promising Co-free RP perovskite cathode for H-SOFCs produced by this work might provide a new type candidate and novel strategy for the commercialization of H-SOFCs.

A novel platinum modified barium zirconate-based electrolyte for enhanced solid oxide fuel cell performance

Pt modified BaZr0.76Y0.2Ni0.04O3 (BZYN) is fabricated and characterized as a stable electrolyte for proton-conducting solid oxide fuel cell (H-SOFC). The utilization of X-ray diffraction method (XRD) and transmission electron microscopy (TEM) enables the identification of the presence of platinum (Pt) in both the crystal lattice sites and the grain interface. This occurrence contributes to a reduction in grain boundary resistance. Consequently, this phenomenon improves the conductivity of the electrolyte. The electrochemical performance of the single cell with Pt-modified BZY electrolyte is improved by the reduction of ohmic resistance and enhancement of ion migration. This signifies a noteworthy advancement in the creation of more efficient and durable proton-conducting SOFCs.