Power Density Of Cell Research Articles

Fabrication and optimization of LSM infiltrated cathode electrode for anode supported microtubular solid oxide fuel cells

In this study, anode supported microtubular solid oxide fuel cells (SOFCs) with LSM (lanthanum strontium manganite) catalyst infiltrated LSM-YSZ (yttria stabilized zirconia) cathodes are developed to increase the density of triple/three phase boundaries (TPBs) in the cathode, thereby to improve the cell performance. For this purpose, two different porous YSZ layers are formed on the dense YSZ electrolyte, i.e., one is with co-sintering while the other one is not. Incorporation of LSM into these porous YSZ layers is achieved via dip coating of a sol-gel based infiltration solution. The effects of the fabrication method for porous YSZ, LSM solution dwelling time and the thickness of the porous YSZ layer on the cell performance are experimentally investigated and optimized in the given order. A reference cell having a conventional dip coated cathode prepared by mixing the commercial LSM and YSZ powders is also fabricated for comparison. The results show that among the cases considered, the highest peak power density of 0.828 W/cm2 can be obtained from the cell, whose single dip coated porous electrolyte layer co-sintered with the dense electrolyte is impregnated with LSM for a dwelling time of 45 min. On the other hand, the peak power density of the reference cell is measured as only 0.558 W/cm2. These results reveal that ∼50% increase in the maximum cell performance compared to that of the reference cell can be achieved by LSM infiltration after the optimizations.

Identification of internal polarization dynamics for solid oxide fuel cells investigated by electrochemical impedance spectroscopy and distribution of relaxation times

Reliability and durability are two major problems restricting for Solid oxide fuel cells (SOFCs) industrial applications. To ensure the long-term stability, understood the internal operation mechanism of SOFC was necessary. The polarization curve combined with the distribution of relaxation times (DRT) method to analyze the electrochemical impedance spectroscopy (EIS) was used to identify the SOFCs modulation and degradation effect through the excitation frequency. Dynamic evolution of carbon deposition process and specific time constants were determined employing EIS and DRT. Special attention was paid to the dependency between the complex reaction processes that occur during the different operation of SOFC. The corresponding frequencies of concentration and activation polarization resistances in EIS were investigated under various gas compositions. The high concentration polarization resistance caused by the addition of nitrogen and hydrogen starvation was the key limiting factor for high cell power density. The total polarization resistance increased from 1.50 Ω/cm2 to 5.26 Ω/cm2 when the H2:N2 ratio decreased from 1:0 to 1:5. The anode did not deteriorate due to the poisoning of Ni particles in a short-term tested under 0.5 A/cm2 current density when the fuel was methane.

Nanofibrous La0.7Sr0.3FeO3-δ-SDC cobalt-free composite cathode for proton-conducting solid oxide fuel cell

In order to prepare high-efficiency solid oxide fuel cells (SOFCs) at medium temperature, continuous La0.7Sr0.3FeO3-δ (LSF) nanofibers with average diameter of 57 nm and uniform pores are prepared as cathode. At 700 °C, the minimum Rp of cathode is 0.066 Ω cm2, the maximum power density (MPD) of single cell is 1180 mW cm−2, and the corresponding open circuit voltage (OCV) is 1.04 V. By reconstructing the microstructure of cobalt-free cathode, the electrochemical performance of H+-SOFC prepared by La0.7Sr0.3FeO3-δ-Sm0.2Ce0.8O2-δ (LSF-SDC) composite cathode has been greatly improved, which provides an effective method for obtaining porous nanocathodes as well as low-cost, high-performance H+-SOFC.

Numerical study of PEMFC heat and mass transfer characteristics based on roughness interface thermal resistance model

The thermal contact resistance (TCR) is the main component of proton exchange membrane fuel cell (PEMFC) thermal resistance due to the existence of surface roughness between the components of PEMFC, and the influence of TCR is often ignored in traditional three dimensional PEMFC simulations. In this paper, the heat and mass transfer characteristics including polarization curve, power density curve, temperature distribution, membrane water content distribution, membrane current density are studied under different component surface roughness conditions, and finally the effect of each TCR on the PEMFC performance is studied. It is found that under the same operating conditions, the TCR makes the radial heat transfer of the PEMFC decrease, and the temperature of the membrane electrode and the temperature difference of each component of the PEMFC is higher than that of the model without TCR. When the surface roughness of components in the PEMFC equals 1 μm, 2 μm, 3 μm, the cell current density decreases by 6.56%, 12.46% and 17.17% respectively when the output cell voltage equals 0.3 V, and the cell power density decreases by 3.64%, 7.54%, 13.14% respectively when the cell current density equals 1.2 A·cm−2. When the TCR between the CL and PEM equals 0.003 K·m2·W−1, 0.005 K·m2·W−1, 0.01 K·m2·W−1, the cell current density is increased by 2.30%, 3.65%, 6.74% respectively under the condition that the output cell voltage equals 0.3 V, and the cell power density is increased by 1.24%, 1.85%, 3.10% respectively when the cell current density equals 1.2 A·cm−2. The results show that the numerical simulation of PEMFC cannot ignore the effect of TCR.

Alternating Flow Field Design Improves the Performance of Proton Exchange Membrane Fuel Cells.

The flow field structure of a proton exchange membrane fuel cell (PEMFC) is a determining factor for improving the cell power density. In this study, a universal alternating flow field design for the first time is proposed, which arranges structural units with different flow resistances in an alternating way to significantly improve the gas transfer rate into the electrode, with the advantages of easy machining and low pumping loss. Based on the design, it is proposed and tested large-scale fuel cells with three novel flow fields by combining a parallel channel, baffled channel, serpentine channel, and narrowed channel. The results show that the design can significantly enhance the gas supply efficiency and that the novel baffled flow field improves the PEMFC performance by 23% with low pumping loss. The design employed in the study offers additional options for flow field optimization and contributes to the early achievement of next-generation ultrahigh power density fuel cells.

K-doped BaCo0.4Fe0.4Zr0.2O3−δ as a promising cathode material for protonic ceramic fuel cells

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.

Improved performance of nafion membranes by blending ultra-high molecular weight polyvinylidene fluoride

Proton exchange membrane (PEM) is developing towards thin thickness and high mechanical strength for extraordinary performance proton exchange membrane fuel cells (PEMFCs). However, the commercial membrane such as Nafion can hardly satisfy the practical application of PEMFCs because of high gas crossover and low mechanical strength when the thickness is less than 20 μm. Here, a reinforced composite membrane (denoted as P110-PFSA) was synthesized by blending poly(vinylidene fluoride)(PVDF) featured with high molecular weight of Mw= 1100000 g mol-1 into perfluorosulfonic acid resin (PFSA). The P110-PFSA with the thickness of 15 μm exhibits tensile strength of over 33 MPa because the PVDF with high molecular weight forms a higher density of hydrogen bonds with PFSA, resulting in a reinforcement of the bonding strength between PVDF and PFSA. H2/O2 fuel cell performance with the P110-PFSA shows more than 1170 mW cm-2 fed with H2 at 70 °C and 100% RH much better than that with Nafion 211. Direct methanol fuel cell power densities of the blent PEM are 92, 61, 50, 28 and 15 mW cm-2 fed with 2, 6, 10,16 and 20 M methanol solution respectively at the anode.

Supramolecular Anchoring of Polyoxometalate Amphiphiles into Nafion Nanophases for Enhanced Proton Conduction.

Advanced proton exchange membranes (PEMs) are highly desirable in emerging sustainable energy technology. However, the further improvement of commercial perfluorosulfonic acid PEMs represented by Nafion is hindered by the lack of precise modification strategy due to their chemical inertness and low compatibility. Here, we report the robust assembly of polyethylene glycol grafted polyoxometalate amphiphile (GSiW11) into the ionic nanophases of Nafion, which largely enhances the comprehensive performance of Nafion. GSiW11 can coassemble with Nafion through multiple supramolecular interactions and realize a stable immobilization. The incorporation of GSiW11 can increase the whole proton content in the system and induce the hydrated ionic nanophase to form a wide channel for proton transport; meanwhile, GSiW11 can reinforce the Nafion ionic nanophase by noncovalent cross-linking. Based on these synergistic effects, the hybrid PEMs show multiple enhancements in proton conductivity, tensile strength, and fuel cell power density, which are all superior to the pristine Nafion. This work demonstrates the intriguing advantage of molecular nanoclusters as supramolecular enhancers to develop high-performance electrolyte materials.

Influence of Radial Flows on Power Density and Gas Stream Pressure Drop of Tubular Solid Oxide Fuel Cells

The development of solid oxide fuel cells (SOFCs) for powering vehicles requires high power densities. The radial flows generated by the insert structures in SOFC fuel channels could improve the power density by facilitating the fuel to enter the porous anode for electrochemical reactions. In this paper, we developed a 2D axisymmetric numerical model to examine the influence of a convergent conical ring insert on the flow and mass transfer characteristics in a tubular SOFC. The mass transfer conductance of fuel was analyzed and proposed to quantify the performance of different insert designs. The effects of the radius and offset angle of the convergent conical ring insert were examined and analyzed. We demonstrate that increasing the insert radius could increase the fuel mass transfer conductance and effectively improve the net output power of the tubular SOFC by 12% while the offset angle of the inserts exhibits a negligible impact on the fuel mass transfer conductance. Increasing the offset angle could help reduce the gas-phase pressure drop in fuel channels by 42%. The present study helps improve our understanding of the relationship between fuel mass transfer conductance and electrochemical reactions. It also proposes channel design methods based on mass transfer conductance for high-power-density solid oxide fuel cells.

Sodium titanate nanowires for Na+‐based hybrid energy storage with high power density

AbstractIt is crucial to enhance the rate capability of the titanium‐based materials for fulfilling their promising potential as the anode materials of sodium‐ion batteries (SIBs). Herein, Mn‐doped sodium titanate (Mn‐NTO) nanowires with homogeneously distributed ultrathin carbon nanosheets (Mn‐NTO@C) are synthesized by a one‐step salt‐template‐assisted method, showing much‐enhanced power density. The as‐prepared Mn‐NTO@C demonstrates the realization of hybrid energy storage, which reconciles the diffusion‐controlled behavior with the pseudocapacitive‐controlled behavior. It has been revealed that the Mn heteroatoms can raise the proportion of Na2Ti3O7 phase with the expanded crystal lattice, facilitating the diffusion‐controlled insertion/extraction process of sodium ions. Meanwhile, the hybrid morphology of Mn‐NTO nanowires and carbon nanosheets provides a promoted structure stability. As a result, the assembled Na||Mn‐NTO@C half‐cells work well at an extreme current density of 24 A g−1 for 10 000 cycles with a capacity retention of 95.2%. Moreover, the Mn‐NTO@C||Na3V2(PO4)3 (NVP) full cells exhibit an attenuation of only 0.0015% per cycle at 20 A g−1 for over 10 000 cycles, and the energy density and power density of the full cells reach an ultrahigh level of 262 Wh kg−1 and 16.3 kW kg−1, respectively.

Strategic Approach for Frustrating Charge Recombination of Perovskite Solar Cells in Low-Intensity Indoor Light: Insertion of Polar Small Molecules at the Interface of the Electron Transport Layer

In this study, we propose a strategic interface engineering method for optimizing the power density and power conversion efficiency (PCE) of perovskite solar cells (PVSCs) under low-intensity indoor light conditions. The insertion of a polar bathocuproine (BCP) layer at the electron transport interface significantly improved the photovoltaic properties, in particular, the fill factor and open circuit voltage, in a low-intensity light environment. Based on the systemic characterizations of surface trap states and carrier dynamics using Kelvin probe force microscopy, we revealed that BCP facilitated efficient charge carrier separation and electron extraction under low-intensity light illumination due to surface passivation and dipole-induced suppressed charge recombination. The beneficial role of BCP enabled excellent indoor PCEs of 27.04 and 35.45% under low-intensity light-emitting diode and halogen lights, respectively. Modification of the electron transport layer interface using polar molecules is a simple but highly effective method for optimizing the indoor performance of PVSCs.

Importance of pyrolysis programs in enhancing the application of microalgae-derived biochar in microbial fuel cells

Nitrogen-doped (N-doped) biochar was prepared by pyrolyzing lipid-extracted microalgae residues under 800 °C for 2 h with different temperature increasing rates (single-segment programs: 3–8 °C/min for room temperature-800 °C; two-segment programs: 5–8 °C/min for room temperature-500 °C and 3 °C/min for 500–800 °C). The obtained biochar was used for oxygen reduction reactions and microbial fuel cell applications. Interestingly, biochar prepared by two-segment programs achieved better performances than those prepared by single-segment programs with higher onset potentials in oxygen reduction reactions and higher maximal power densities in microbial fuel cell. This is likely because the applied two-segment programs improved the porous structure and enhanced the formation of pyridinic N in the biochar. Notably, applying the optimal program (5–8 °C/min for room temperature-500 °C and 3 °C/min for 500–800 °C) obtained biochar with a maximal oxygen reduction reactions onset potential of 0.877 V and a maximal microbial fuel cell power density of 843.6 mW·m−2, both of which are higher than values achieved using Pt/C. This study suggests that simply improving the pyrolysis program for N-rich biomass pyrolysis is promising for producing high-performance N-doped biochar for microbial fuel cells.

Composite electrolyte with Ruddlesden-Popper structure Sm1.2Sr0.8Ni0.6Fe0.4O4+δ for high-performance low temperature solid oxide fuel cells

Ruddlesden-Popper (R–P) structure oxide has been widely used as the electrode material in low temperature solid oxide fuel cells (LT-SOFCs) because of its high catalytic activity and excellent oxygen transport performance, while the studies on this material served as the electrolyte of LT-SOFCs is rarely reported. Herein, the R–P P-type semiconductor Sm1.2Sr0·8Ni0·6Fe0·4O4+δ (SSNF) oxide material was prepared and then used as electrolyte by constructing P–N heterostructure with the N-type semiconductor Sm0.075Nd0.075Ce0·85O2-δ (SNDC) oxide material. Experimental results showed that the developed 5SSNF-5SNDC composite electrolyte exhibited a high ionic conductivity of 0.201 S·cm−1 along with remarkable fuel cell power density of 1056 mW·cm−2 at 550·°C. The constructed P–N heterostructure helps to improve the oxygen ion conductivity and thus the electrochemical properties. These results demonstrate that P–N heterojunctions constructed from oxide materials with highly catalytically active R–P structures exhibit excellent electrolyte performance. This work provides a new perspective for developing advanced electrolytes of LT-SOFCs.

A Co-Axial Microtubular Flow Battery Cell with Ultra-High Volumetric Power Density

Flow batteries are a promising energy storage solution. However, the footprint and capital cost need to be further reduced for flow batteries to be commercially viable. The flow cell, where electron exchange takes place, is a central component in flow batteries. Improving the volumetric power density of the flow cell (W/Lcell) can reduce the size and cost of flow batteries. While significant progress has been made on flow battery redox, electrode and membrane materials to improve energy density and durability, conventional flow batteries based on planar cell configuration exhibit a large cell size with multiple bulky accessories such as flow distributors, resulting in low volumetric power density. In this talk, I will introduce a new co-axial microtubular (CAMT) flow battery cell configuration that significantly improves volumetric power density by reducing the membrane-to-membrane distance by almost 100 times and eliminating completely the bulky flow distributors. Using zinc-iodide chemistry as a demonstration, our CAMT cell shows peak charge and discharge power densities of 1322 W/Lcell and 306.1 W/Lcell compared to average charge and discharge power densities of < 60 W/Lcell and 45 W/Lcell of conventional planar flow battery cells. The battery cycled for more than 220 hours, corresponding to > 2,500 cycles at off-peak conditions. Furthermore, the CAMT cell has been demonstrated to be compatible with zinc-bromide, quinone-bromide, and all-vanadium chemistries. The CAMT flow cell represents a device-level revolution to enhance the volumetric power of flow batteries and potentially reduce the size and cost of the cells and the entire flow battery.Publication:https://chemrxiv.org/engage/chemrxiv/article-details/62070e98bd05a04ae103fa7e Figure 1

Simulation of Cathode Catalyst Durability Under Fuel Cell Vehicle Operation - the Effect of Temperature

Fuel cell vehicles (FCVs) emerge to be promising candidates to produce clean power for the transportation sector in order to tackle climate change issues. Although the commercialization of polymer electrolyte membrane fuel cells (PEMFCs) has progressed in the past few decades, there are still obstacles to address, including high cost and limited hydrogen infrastructure. For heavy duty transportation applications, the PEMFC durability is also not yet proven, and extrapolating from lab data to real-world field operating conditions remains a significant challenge [1].In this work, the cathode catalyst degradation in PEMFCs is studied to make an estimation of fuel cell durability in the FCV application. The well-known Butler-Volmer approach is utilized to model platinum dissolution and redeposition, platinum oxidation and platinum ion formation during the fuel cell operation [2]. First, the model is calibrated with the results presented by Ferreira et al. [3] at 80℃; the calibrated model is then validated with Kocha’s results [4] to demonstrate the model’s capability of generating reliable results at different temperatures. In order to realistically predict the cathode degradation pattern and lifetime, the real-life fuel cell operating conditions should be obtained. Therefore, a drive cycle recorded based on a real-life transit bus operation in the city of Victoria is utilized to calculate the input fuel cell voltage profile. The procedure to calculate fuel cell operating voltage profile using the drive cycle has been thoroughly explained by Ahmadi and Kjeang [5]. This procedure employs Newton’s second law to calculate the required cell power density considering the air flow drag force counteracting the vehicle thrust. Finally, polarization curves representing the fuel cell performance are used to calculate the fuel cell voltage profile with the determined required cell power density. Polarization curves measured under a range of temperatures are employed to adequately reflect the effect of temperature on the fuel cell performance. The cell active area is considered to be 500 cm2 and the stack is assumed to contain 225 cells, representing a nominal stack power of 74 kW at 80℃. The fuel cell operation and degradation are simulated at three different temperatures: 60, 70, and 80℃. The change of remaining electrochemically active surface area (ECSA) with time is calculated as the output of the model.Temperature highly affects the electrochemical reactions of platinum dissolution in several ways. First, it affects the Tafel slope in the platinum dissolution reaction. Second, it substantially impacts on platinum degradation reaction rate constant [6]. The Arrhenius approach is taken in this study to apply the effect of temperature on the reaction rate constants. Fuel cell voltage loss over time is determined by assuming simple Tafel kinetics. The cathode lifetime is calculated at 0.6 A/cm2 and is estimated by considering 10% voltage drop as the failure criterion. Fig. 1 shows the simulated change of remaining ECSA over time and the resulting fuel cell lifetime for the three different cell temperatures. The results indicate that the cathode lifetime increases 168% when the cell temperature drops from 80℃ to 60℃ due to a significantly lower platinum degradation rate at 60℃. The results show relatively low cathode catalyst lifetimes for a transit bus. The reason is attributed to the bus drive cycle used as the model input. The drive cycle contains a great portion of deceleration and idling time which leads to a fuel cell operation close to open circuit voltage (OCV), thus experiencing a high degradation rate.In this regard, the present modeling framework could become a useful tool for fuel cell and FCV developers to predict lifetime for new products and systems prior to commercial release. Scientifically, the present model can also be used to further explore key influencing factors on fuel cell durability and develop more durable cell, stack, and system designs for a targeted FCV application. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

Effects of Ni-NCAL and Ni–Ag electrodes on the cell performances of low-temperature solid oxide fuel cells with Sm0.2Ce0·8O2-δ electrolyte at various temperatures

Three low-temperature solid oxide fuel cells are built using Sm0.2Ce0·8O2-δ (SDC) as the electrolyte. Cell A is symmetrical and features Ni–LiNi0.8Co0·15Al0·05O2 (Ni–NCAL) electrodes, Cell B comprises a Ni–NCAL anode and a Ni–Ag cathode, and Cell C is fabricated using a Ni–NCAL cathode and a Ni–Ag anode. The ohmic resistance and polarization resistance (Rp) of Cells B and C are significantly higher than those of Cell A. The reduction of NCAL at the anodes of Cells A and B yields LiOH and Li2CO3 phases, and the Ni particles generated on the surfaces of the NCAL particles improve the catalytic activity of the cells. Li2CO3–LiOH melts at temperatures >450 °C and penetrates the porous SDC electrolyte layer, causing its densification and abnormal grain growth and increasing its ionic conductivity to >0.2 S/cm at low temperatures. The high open-circuit voltages (OCVs) (0.970–1.113 V) of the cells during electrochemical measurements are ascribed to the Li2CO3–LiOH phase which serves as an electron-blocking layer for the SDC electrolytes. As the reduction of NCAL approaches completion, the anode comprises only Ni phase, which hinders the charge transfer process. The triple-phase-boundary (TPB) area at cathode of Cell B is significantly lower than that of Cell A; therefore, the catalytic activity of Cell B for the oxygen reduction reaction is lower than that of Cell A. Consequently, the maximum power density (MPD) of Cell B is less than half of that of Cell A. The large Rp value of Cell C is ascribed to its low TPB area at Ni–Ag anode which has no reaction with H2 during operation. No visible sintering of the SDC electrolyte layer is observed for Cell C; therefore, its ionic conductivity is considerably smaller than those of the electrolyte layers of Cells A and B. The OCVs of Cell C (0.281–0.495 V) are significantly lower than the typical OCVs of ceria-based SOFCs. This is attributed to the porous SDC electrolyte layer of Cell C. The large Rp values and the low OCVs contribute to the low MPDs of Cell C at various temperatures.

Electrochemical characteristics of Ca3Co4O9+δ oxygen electrode for reversible solid oxide cells

• Ca 3 Co 4 O 9+δ oxygen electrode shows superior durability under long-term operation. • Polarization promotes the electrochemical activity of Ca 3 Co 4 O 9+δ electrode. • Polarization improves the electrode/electrolyte interface. • The cell performance could be enhanced by 4 times by cathodic polarization. Reversible solid oxide cells (RSOCs) are clean electrochemical conversion devices that can flexibly operate between solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) patterns. Ca 3 Co 4 O 9+δ (CCO) material with a misfit-layered structure was successfully prepared and fully discussed as a oxygen electrode for RSOCs. The CCO electrode showed superior durability and excellent electrocatalytic activity for oxygen reactions. Both the ohmic and polarization resistances were decreased after alternating anodic and cathodic polarization for more than 100 h, demonstrated the activation of CCO electrode and an improvement of electrode/electrolyte interface. The peak power density of the single cell with CCO oxygen electrode was 614 mW·cm −2 after polarization at 500 mA·cm −2 for 4 h at 750 °C, which improved by 4 times than the unpolarized cell. The maximum electrolysis current density of 749 mA·cm −2 was obtained at 800 °C and 50 % water vapor, which corresponded to the hydrogen production rate of 311 mL·cm −2 ·h −1 . Results showed that CCO with good reversible polarization performance and long-term stability was a prospective oxygen electrode for RSOCs.

Co and Hf co-doped BaFeO3 cathode with obviously enhanced catalytic activity and CO2 tolerance for solid oxide fuel cell

It is essential to develop efficient and stable cathode materials operated at intermediate temperature for the application of solid oxide fuel cell. In this work, BaFeO3–δ based perovskite oxide was used to explore the influence of Co and Hf co-doping on the catalytic activity and CO2 tolerance of SOFC cathode materials. Among the series materials, BaCo0·2Fe0.7Hf0.1O3–δ (BC2FHO) shows excellent catalytic activity and CO2 stability. The EIS measurement shows that the polarization resistance (Rp) of BC2FHO is ∼0.04 Ω cm2 at 800 °C. In the CO2 tolerance test, the Rp decreases to ∼0.0435 Ω cm2 within 1 h after removing 10% CO2. The peak power density of the single cell with BC2FHO cathode are 1010.4, 649.4, and 256.6 mW cm−2 at 800, 700, and 600 °C, respectively. And the total degradation rate of the output voltage at 700 °C is only 0.009% h−1. The significantly enhanced activity and stability are attributed to Co and Hf co-doping. The incorporation of Hf allows BaFeO3 to obtain a highly symmetrical cubic structure with increased oxygen ion transport channels, which is conducive to promote the oxygen reduction reaction. In addition, Hf-doping can also increase the acidity to make the material resistant to CO2. The incorporation of Co improves the concentration of oxygen vacancies, which makes BC2FHO show excellent electrochemical performance.

On the Relative Importance of Li Bulk Diffusivity and Interface Morphology in Determining the Stripped Capacity of Metallic Anodes in Solid-State Batteries.

Lithium metal self-diffusion is too slow to sustain large current densities at the interface with a solid electrolyte, and the resulting formation of voids on stripping is a major limiting factor for the power density of solid-state cells. The enhanced morphological stability of some lithium alloy electrodes has prompted questions on the role of lithium diffusivity in these materials. Here, the lithium diffusivity in Li-Mg alloys is investigated by an isotope tracer method, revealing that the presence of magnesium slows down the diffusion of lithium. For large stripping currents the delithiation process is diffusion-limited, hence a lithium metal electrode yields a larger capacity than a Li-Mg electrode. However, at lower currents we explain the apparent contradiction that more lithium can be extracted from Li-Mg electrodes by showing that the alloy can maintain a more geometrically stable diffusion path to the solid electrolyte surface so that the effective lithium diffusivity is improved.

Effect of MgO and Fe2O3 dual sintering aids on the microstructure and electrochemical performance of the solid state Gd0.2Ce0.8O2-δ electrolyte in intermediate-temperature solid oxide fuel cells.

Solid state electrolytes have been intensively studied in the solid oxide fuel cells (SOFCs). The aim of this work is to investigate the effects of MgO and Fe2O3 dual sintering aids on the microstructure and electrochemical properties of solid state Gd0.2Ce0.8O2-δ (GDC) electrolytes, which are prepared by a sol-gel method with MgO and Fe2O3 addition to the GDC system. It is found that the addition of MgO and Fe2O3 can reduce the sintering temperature, increase densification and decrease the grain boundary resistance of the electrolyte. The 2 mol% MgO and 2 mol% Fe2O3 co-doped GDC (GDC-MF) exhibits the highest grain boundary conductivity. At 400°C, the grain boundary conductivity and total conductivity of GDC-MF are 15.89 times and 5.56 times higher than those of GDC. The oxygen reduction reaction (ORR) rate at the electrolyte/cathode interface of GDC-MF is 47 % higher than that of GDC. Furthermore, the peak power density of a single cell supported by GDC-MF is 0.45 W cm−2 at 700°C, 36.7% higher than that of GDC. Therefore, the GDC-MF should be a promising electrolyte material for intermediate-temperature solid oxide fuel cells (IT-SOFCs).