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For present solid oxide fuel cells (SOFCs), rapid performance degradation is observed in the initial aging process, and the discussion of the degradation mechanism necessitates quantitative analysis. Herein, focused ion beam-scanning electron microscopy was employed to characterize and reconstruct the ceramic microstructures of SOFC anodes. The lattice Boltzmann method (LBM) simulation of multiphysical and electrochemical processes in the reconstructed models was performed. Two samples collected from industrial-size cells were characterized, including a reduced reference cell and a cell with an initial aging process. Statistical parameters of the reconstructed microstructures revealed a significant decrease in the active triple-phase boundary and Ni connectivity in the aged cell compared with the reference cell. The LBM simulation revealed that activity degradation is dominant compared with microstructural degradation during the initial aging process, and the electrochemical reactions spread to the support layer in the aged cell. The microstructural and activity degradations are attributed to Ni migration and coarsening. [ABSTRACT FROM AUTHOR]

The aim of the paper is to examine the performance of molten carbonate fuel cell, which is supplied with a raw bioethanol, i.e. bioethanol which origins directly from fruit fermentation, without pre-treatment of fermentation products. The composition of raw bioethanol was precisely determined and then the impact of raw bioethanol on the degradation of molten carbonate fuel cells was examined. Steam to carbon ratio of the biofuel has been determined as 5.7 (in comparison to stoichiometry of reaction) which allowed for estimation of hydrogen production during steam reforming process taking place in the anode channel. The results in the form of current-voltage curve was obtained and compared with the same fuel cell fed with pure hydrogen, while the amount of hydrogen was defined as identical with the one after steam reforming of biofuel taking place in the nickel anode channel. Relevant literature studies were focused on the purified fuel or examination of the impact of individual components. Our study proved carbon deposition is not a problem, however solid particles contamination in fermentation product makes it impossible to use fuel cell fueled with fermentation product for longer periods, and prior to supplying fuel cell the bioethanol purification is required. A raw biofuel with its impurities did not have any impact on the anode and current collector surface from physical point of view, but Electrochemical Impedance Spectroscopy analysis shows visible increase of ohmic loses. • Homemade first generation bioethanol composition have been examined. • Manufactured bioethanol has been delivered directly to the MCFC anode without purification. • Performance of MCFC fueled with impure bioethanol has been investigated. • Effect of steam reforming for hydrogen generation and steam to carbon ratio were evaluated. • Pollution on the anode after cell operation was investigated with SEM and EIS. [ABSTRACT FROM AUTHOR]

Commercial Li-ion batteries typically incorporate a small amount of high-capacity silicon (Si)-based materials in the composite graphite-based anode to increase the energy density of the battery. However, very little is known about the effects of Si on the fast-charging behavior of composite anodes. Herein, we examine the effects of the Si/graphite ratio in the composite anode on the fast-charging behavior of full cells. We show that addition of Si increases the rate capability from 1C to 8C and improves the capacity retention in early cycles at 6C due to reduced overpotential in constant current charging cycles. The impacts of Si content on fast-charging aging were identified by Post-Test characterization. Despite realizing benefits of available capacity and reduced Li plating at 6C, silicon–electrolyte interactions lead the time-dependent cell performance to fade quickly in the long term. The Post-Test analysis also revealed the thickening of the electrode and nonuniform distribution of electrolyte decomposition products on the Si-containing anodes, as well as the organic-rich solid electrolyte interphase (SEI), which are the factors behind cell degradation. Our study sheds insight on the advantages and disadvantages of Si/graphite composite anodes when they are used in fast-charging applications and guides further research in the area by designing an optimized composition of Si incorporated in a mature graphite matrix. [ABSTRACT FROM AUTHOR]

Commercial Li-ion batteries typically incorporate a small amount of high-capacity silicon (Si)-based materials in the composite graphite-based anode to increase the energy density of the battery. However, very little is known about the effects of Si on the fast-charging behavior of composite anodes. Herein, we examine the effects of the Si/graphite ratio in the composite anode on the fast-charging behavior of full cells. We show that addition of Si increases the rate capability from 1C to 8C and improves the capacity retention in early cycles at 6C due to reduced overpotential in constant current charging cycles. The impacts of Si content on fast-charging aging were identified by Post-Test characterization. Despite realizing benefits of available capacity and reduced Li plating at 6C, silicon–electrolyte interactions lead the time-dependent cell performance to fade quickly in the long term. The Post-Test analysis also revealed the thickening of the electrode and nonuniform distribution of electrolyte decomposition products on the Si-containing anodes, as well as the organic-rich solid electrolyte interphase (SEI), which are the factors behind cell degradation. Our study sheds insight on the advantages and disadvantages of Si/graphite composite anodes when they are used in fast-charging applications and guides further research in the area by designing an optimized composition of Si incorporated in a mature graphite matrix.

Potassium-sulfur (K-S) batteries are one of the promising high-energy-density candidates beyond current lithium-ion batteries. Nevertheless, in practice, the utilization of K-S batteries is largely hindered due to the dissolution and shuttle effect of the cathode redox intermediates and the scarcity of an effective anode protection layer in conventional electrolytes. Herein, electrolyte engineering is applied to formulate an ether-based localized high-concentration electrolyte (LHCE) for the first time in a K-S cell with the mitigated parasitic effect of polysulfide dissolution and shuttle and the tuned anode-electrolyte interface property. A nonsolvating and polysulfide-stable fluoroether is sieved as a cosolvent in such an LHCE, which possesses the ultralow polysulfides solubility due to less roaming solvents and thus alleviates the polysulfides shuttle effect. The anion-derived solid electrolyte interphase enriched in inorganic components is constructed due to the strengthened cation-anion interplay in the primary solvation sheath and highlighted with accelerated interfacial kinetics in a K-S cell. It is validated that the proposed LHCE unlocks the theoretical capacity of the K-S cell based on the conversion between S and K 2 S 3 . It is further revealed that the lifespan is limited to the anode corrosion with severe cosolvent degradation caused by limited solvating solvent compatibility with metallic K, and the inevitable byproduct accumulation at the S cathode. The K-S cell based on the designed LHCE could achieve a prolonged lifespan with a reversible capacity of 448 mA h/g s after 80 cycles with an elaborate cathode design. This work shines a light on the electrolyte design perspective for full utilization and an in-depth mechanistic understanding of high-energy-density K-S batteries.

Although using an air cathode is the goal for superoxide‐based potassium‐oxygen (K‐O2) batteries, prior studies were limited to pure oxygen. Now, the first K‐air (dry) battery based on reversible superoxide electrochemistry is presented. Spectroscopic and gas chromatography analyses are applied to evaluate the reactivity of KO2 in ambient air. Although KO2 reacts with water vapor and CO2 to form KHCO3, it is highly stable in dry air. With this knowledge, rechargeable K‐air (dry) batteries were successfully demonstrated by employing dry air cathode. The reduced partial pressure of oxygen plays a critical role in boosting battery lifespan. With a more stable environment for the K anode, a K‐air (dry) battery delivers over 100 cycles (>500 h) with low round‐trip overpotentials and high coulombic efficiencies as opposed to traditional K‐O2 battery that fails early. This work sheds light on the benefits and restrictions of employing the air cathode in superoxide‐based batteries. [ABSTRACT FROM AUTHOR]

The growth of nickel (Ni) particles in the porous anode is one of the most critical issues in solid oxide fuel cells (SOFC). It reduces the density of triple-phase boundaries (TPBs) over time and increases the polarization resistance of SOFC. Most of the three-dimensional models that are used to simulate this phenomenon in detail are numerically exhausting and as such intractable for on-line applications. This work presents a two-dimensional, microstructural model of reduced complexity as a trade-off between the numerical load and the level of detail. The model of Ni agglomeration is based on the power-law coarsening theory. The resulting model was validated by comparing the relative density of TPBs and the cell voltage to the experimentally measured values. It was shown that the calculated values closely fit the measured data. The advantage of the proposed model is that it takes lower computational load during the simulation compared to the complex phase field models and is suitable for estimation of SOFC electric performance over time. [ABSTRACT FROM AUTHOR]

The anodic degradation process of carbon fibres (CFs) in carbon-fibre-reinforced-polymer (CFRP) composites was first examined under varying operating currents, particularly in the pore solution of seawater and sea sand concrete. A range of analytical techniques were employed to provide insights into the formation and characteristics of the decomposition products generated in the electrolyte and precipitate. The electrochemical reactions of anions and carbon occurred under the different potential significantly influence the corrosion behaviour of CFRP. The production of diverse forms and quantities of carbon oxides primarily arises from the oxidative deterioration of CFs' graphitic structure. These results reveal the anodic degradation behaviour of CFs, which contributes to the anodic degradation mechanism of CFRP materials, especially when exposed to different current levels in high-chloride and high-alkaline conditions. • Anodic degradation mechanism of carbon fibres in CFRP composites was studied. • Applied current affects quantity, morphology, and structure of degradation products. • Anode degradation of CFRPs is mainly driven by electrochemical corrosion of CFs. [ABSTRACT FROM AUTHOR]

The growth of nickel (Ni) particles in the porous anode is one of the most critical issues in solid oxide fuel cells (SOFC). It reduces the density of triple-phase boundaries (TPBs) over time and increases the polarization resistance of SOFC. Most of the three-dimensional models that are used to simulate this phenomenon in detail are numerically exhausting and as such intractable for on-line applications. This work presents a two-dimensional, microstructural model of reduced complexity as a trade-off between the numerical load and the level of detail. The model of Ni agglomeration is based on the power-law coarsening theory. The resulting model was validated by comparing the relative density of TPBs and the cell voltage to the experimentally measured values. It was shown that the calculated values closely fit the measured data. The advantage of the proposed model is that it takes lower computational load during the simulation compared to the complex phase field models and is suitable for estimation of SOFC electric performance over time.

Ni-YSZ anodes for Solid Oxide Fuel Cells are vulnerable to microstructural damage during redox cycling leading to a decrease in the electrochemical performance. This study quantifies the microstructural changes as a function of redox cycles at 800 °C and associates it to the deterioration of the mechanical properties and polarisation resistance. A physically-based model is used to estimate the triple-phase boundary (TPB) length from impedance spectra, and satisfactorily matches the TPB length quantified by FIB-SEM tomography: within 20 redox cycles, the TPB density decreases from 4.63 μm −2 to 1.06 μm −2 . Although the polarisation resistance increases by an order of magnitude after 20 cycles, after each re-reduction the electrode polarisation improves consistently due to the transient generation of Ni nanoparticles around the TPBs. Nonetheless, the long-term degradation overshadows this transient improvement due to the nickel agglomeration. In addition, FIB-SEM tomography reveals fractures along YSZ grain boundaries, Ni-YSZ detachment and increased porosity in the composite that lead to irreversible mechanical damage: the elastic modulus diminishes from 36.4 GPa to 20.2 GPa and the hardness from 0.40 GPa to 0.15 GPa. These results suggest that microstructural, mechanical and electrochemical properties are strongly interdependent in determining the degradation caused by redox cycling. [ABSTRACT FROM AUTHOR]

Nickel/zirconia-based nanostructured electrodes for solid oxide fuel cells suffer from poor stability even at intermediate temperature. This study quantifies the electrochemical and microstructural degradation of nanostructured electrodes by combining 3D tomography, electrochemical impedance spectroscopy (EIS) and mechanistic modeling. For the first time, the electrochemical degradation of nanostructured electrodes is quantified according to the fractal nature of the three-phase boundary (TPB). Using this hypothesis an excellent match between modeling and the electrochemical response is found. The origin of the degradation in microstructure and electrochemical performance can be found in the initial fractal roughness of the TPB at a length scale not detectable with state-of-the-art tomography at 30 nm resolution. This additionally implies that the hydrogen electro-oxidation takes place within 4 nm from the geometric TPB line, revealing that the electrochemical reaction zone cannot be regarded anymore as a one-dimensional line when dealing with nanoparticles. [ABSTRACT FROM AUTHOR]

Membrane electrode assemblies (MEAs) for proton exchange membrane fuel cell (PEMFC) applications must survive fuel starvation events which occur when the flow field becomes blocked by dust/debris/or ice (during freeze events) leading to high (>2 V) potentials at the anode. While most research has focused on optimizing these 'reversal' catalysts, recent work has also demonstrated that anode layer thickness/structure has an enormous impact on anode durability. In the present work, the impact of catalyst layer structure is studied in more detail, with a focus on understanding the mechanism for this improvement. The effect of both anode layer thickness as well as the spatial distribution of Ir within the anode layer is evaluated. The longest reversal time is found to result from thin layers, or placing the Ir adjacent to gas diffusion layer (GDL) interface. While both approaches lead to improved reversal times, reducing anode layer thickness is found to be a more promising approach as it results in less degradation during reversal, and is easier to manufacture vs. selectively placing the Ir adjacent to the GDL. [Display omitted] • Help to understand the role of anode thickness and IrO x distribution in anode layer. • Analyze the key factors affecting anode reversal time. • Recommendations for designs of anode layer are provided. [ABSTRACT FROM AUTHOR]

The triode fuel cell design and operation concept was applied as an alternative means for controlling and enhancing the carbon tolerance of state-of-the-art solid oxide fuel cell (SOFC) anodes. The triode cell configuration entails the introduction of a third electrode in addition to the anode and cathode, driven by an auxiliary circuit which is run in electrolytic mode. In this way the cell is forced to operate at controlled potential differences that are inaccessible under standard operation, and thus introduces a controllable variable into fuel cell operation. In the present study, the effectiveness of the triode approach was evaluated for the in situ control of the rate of carbon deposition in commercial multilayer NiO-GDC and NiO-YSZ SOFC anodes. The study involved typical and triode operation of SOFC button cells under CH steam reforming conditions, and it was found that the application of a small electrolytic current under triode operation resulted in significantly less carbon built-up on the anode compared to the standard SOFC operation. [ABSTRACT FROM AUTHOR]

In this research a cell stack with standard power output of 100 [W] was tested over a period of 3700 h. After the long-term operation a subsequent post-test analysis of the anode microstructure was conducted using a combination of focused ion beam and scanning electron microscopy. Obtained data was reconstructed into three-dimensional images, based on which the microstructure parameters were obtained. The microstructure parameters were quantified at three different locations in the selected cell; the inlet, the middle and the outlet. This is the first paper in the open literature, known to the authors, that uses the three dimensional microstructure reconstruction technique to evaluate the local evolution of a SOFC anode's microstructure. The obtained results indicate strong non-homogeneous microstructure morphology changes after long-term operation. [ABSTRACT FROM AUTHOR]

In this research a 100 W solid oxide fuel cells (SOFCs) stack was tested. After 3,700 hours of continuous operation a subsequent post-test analysis of the anodes' microstructure was conducted using a combination of focused ion beam and scanning electron microscopy. The obtained data was reconstructed into three-dimensional images, based on which the microstructure parameters were obtained. The microstructure parameters were quantified at nine different locations in the stack. The discussion focuses on tripe phase boundaries as the most important microstructure parameter strongly affecting the anode performance and degradation. The obtained results indicate strong non-homogeneous microstructure morphology changes after long-term operation. [ABSTRACT FROM AUTHOR]

Long-lasting solid oxide fuel cells (SOFC) rely upon an intact ionically conducting network in both the electrolyte and electrode. Understanding the impact of the high-temperature electrochemical operations on the possible nanostructure evolutions of ionic conductors is indispensable for the development of durable SOFC. Here we present possibly the first experimental evidence of space charge layer evolution of grain boundaries (GBs) of ionic conducting yttria-stabilized zirconia (YSZ) in a Ni/YSZ composite anode of SOFCs. Cells with identical Ni/YSZ composite anodes are either thermally treated or electrochemically operated using either dry or humidified H 2 fuel for up to 3,349 h. When operating under humidified H 2 fuel, a discrete core-shell structure is found to develop exclusively along the YSZ/YSZ GB planes. The core-shell structure is elliptically shaped elongated along the GB planes. The core has a lower mass with a Y-depleted ZrO 2-x with a cubic structure. The shell has a constant thickness of ∼1 nm and is Y-enriched. The nucleation and growth mechanisms of the core-shell structure are proposed in terms of the space charge layer evolution at YSZ GBs. The effect of the humidity in the fuel, the cell operating temperatures, and the current density on the formation of the core-shell structure is investigated. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The potential cycling of a polymer electrolyte fuel cell (PEFC) incorporating a reference electrode was carried out for 20h. After the potential cycling, the maximum power density decreased from 56.12mWcm−2 of the fresh membrane electrode assembly (MEA) to 47.64mWcm−2. Electrochemical impedance spectroscopy (EIS) was used to conduct an independent quantitative analysis of the anode and cathode degradation. The EIS results of the anode and cathode revealed the degradation properties after the potential cycling. For the anode, the charge transfer and mass transfer resistances significantly increased after the degradation procedure, indicating that a significant degradation occurred. However, for the cathode, it was demonstrated that a slight degradation occurred, because the charge transfer and mass transfer resistances slightly increased after the degradation procedure. The increase in the charge transfer resistance was attributed to the decrease in the Pt surface area, and the increased mass transfer resistance was considered to be due to the ionomer degradation. Meanwhile, the increase in the membrane resistance and decrease in the adsorption resistance were also observed after the degradation procedure. [Copyright &y& Elsevier]

Commercial 18,650 lithium-ion batteries are cycled at different discharge current rates. It reveals that an accelerated capacity fade occurs for cells at a low discharge rate which is attributed to the loss of lithium inventory (LLI) from the differential voltage analysis (DVA). Cells using high discharge rates exhibit more kinetic loss at the same capacity retention from the analysis of impedance. Characterization techniques, i.e., post-mortem analysis including scanning electron microscopy (SEM) and ex-situ x-ray diffraction (XRD), galvanostatic tests, and in-situ XRD on half-cells made with cathodes and anodes retrieved from the 18,650 batteries, are used to further address the degradation factors. It indicates that the kinetic loss of the high discharge cells can be ascribed to the cathode where more particles are cracked and pulverized. Degradation on the anode is the primary reason for accelerated capacity fade occurring at the low discharge rate. The low discharge current deepens the discharge depth leading the graphite accessing into a higher potential over de-lithiation. Worse interphases and dense agglomerated structure are found from SEM images, which is deemed to result from the anode cycled at a high potential where large volumetric change happens as evidenced by the cycling of new anode half-cells. [Display omitted] • An accelerated capacity fade occurs for cells cycled at a low discharge rate. • Multiscale characterization techniques are used for mechanism investigation. • Cracked and pulverized cathode particles are related to battery kinetic loss. • The difference in discharge depth aggravates the anode working at a higher potential. • Worse anode morphology contributes to the accelerated battery capacity fade. [ABSTRACT FROM AUTHOR]

In-situ characterization of solid oxide fuel cells (SOFCs) under operating conditions is of great significance to mechanism studies on performance or long-term stability. In this study, real-time visualization of the two-dimensional gas distribution inside a large flat-tube SOFC is realized by built-in gas sampling tubes combined with external gas chromatography, validated by simulating calculation. The gas composition inside anode of the cell fueled with CH 4 /CO 2 is in-situ monitored during a 1000-h discharge test. Decrease in catalytic activity for methane dry reforming during the long-term test differs at different region of the cell, and is related with local carbon deposition and sintering of Ni particles. Based on these experimental results, the mechanism of cell performance degradation of the large flat-tube SOFCs under methane dry reforming conditions is discussed. • Gas composition within solid oxide fuel cell (SOFC) was in-situ monitored. • Long-term stability test of SOFC fueled with CH 4 /CO 2 was conducted for 1000 h. • Decrease of the catalytic activity for dry reforming of methane was detected. • Degradation was proved to be caused by carbon deposition and Ni sintering. [ABSTRACT FROM AUTHOR]

Symmetric cells have been developed to evaluate electrode degradation directly associated with solid electrolyte interphase (SEI) growth in Li-ion cells. This limits their applications to only certain anodes, such as graphite and Li 4 Ti 5 O 12. In this work, symmetric cells have been applied to investigate the degradation of high energy density anodes, such as Si-alloys, which undergo multiple degradation mechanisms, including mechanical failure and SEI growth. A Li inventory model has been developed to correlate the symmetric cell capacity fade and the multiple anode degradation mechanisms. Using symmetric cells with a pseudo-reference electrode, it was found that irreversible capacity caused by anode degradation can be partially compensated by a positive shift in electrode upper endpoint potential, which is key to interpreting degradation mechanisms. Importantly, a feasible method to measure Li consumption due to SEI growth on Si-alloys has been established using symmetric cells. This method could help battery researchers develop technologies to lower the SEI growth rate on Si-alloys. • Quantitative measurement of Si-based anode coulombic efficiency. • Electrolyte degradation and mechanical degradation independently measured. • Si-alloy coulombic efficiency measured independently in graphite blended electrodes. • Electrolyte degradation dependance on Si-alloy composition and cycling temperature. • New perspectives on symmetric cell use and data interpretation. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of trace (ppm) phosphine with the nickel/yttria stabilized zirconia (YSZ) anode of commercial solid oxide fuel cells has been investigated and evaluated for both synthesis gas and hydrogen fuels in an effort to examine P–Y reactions. The Ni poisoning effects reported in literature were confirmed and degradation was examined by electrochemical methods and post-test microstructural and chemical analyses. The results indicate that P-induced degradation rates and mechanisms are fuel dependent and that degradation of cells operated in synthesis gas (syngas) with phosphine is more severe than that of cells operated in hydrogen with phosphine. As reported in published literature, a cell operated in syngas containing 10ppm phosphine demonstrated significant microstructural degradation within the Ni phase, including formation of Ni–P phases concentrated on the outer layer of the anode and significant pitting corrosion in the Ni grains. In this research, a previously undetected YPO4 phase is observed at the YSZ/YSZ/Ni triple grain junctions located at the interface with the YSZ electrolyte. Tetragonal YSZ (t-YSZ) and cubic-YSZ (c-YSZ) domains with sizes of several tens of nanometers are also newly observed along the Ni/YSZ interface. These observations contrast with data obtained for a cell operated in dry hydrogen with phosphine, where no YPO4 phase is observed and the alternating t-YSZ and c-YSZ domains at the Ni/YSZ interface are smaller with typical sizes of 5–10nm. The data imply that electrolyte attack by P is a potentially debilitating mode of degradation in SOFC anodes, and that the associated reaction mechanisms and rates are worthy of further examination. [Copyright &y& Elsevier]

Abstract: Anode supported solid oxide fuel cells have been tested and the degradation over time was monitored and analyzed by impedance spectroscopy. Reproducibility of initial cathode, anode and electrolyte performance was obtained. Anode (Ni/YSZ) degradation was analyzed for tests applying p(H2O) of 0.2atm, 0.4atm and 0.6atm at 750°C and 0.75A/cm2. The anode degradation could be well described by the equation: R Ni,TPB(t)= R Ni,0 +ΔR∙(1−exp(− t / τ)). The initial resistance and total increase for the Ni–YSZ charge transfer resistance, R Ni,0 and ΔR, were similar for all tests (i.e. not directly correlated with p(H2O)), but the characteristic time, τ, for the anode degradation was significantly higher for the test at p(H2O)=0.2atm than at p(H2O) of 0.4atm and 0.6atm. [Copyright &y& Elsevier]

Abstract: The dependence of the degradation kinetics in Ni–CGO (cerium–gadolinium oxide) solid oxide fuel cell (SOFC) anodes upon salt evaporation is demonstrated operando with a custom built versatile reactor system. The system is based on evaporation and subsequent condensation of low concentration salt vapor aerosol mixtures representative of salt vapors typically present in biomass gasification processes. Fast changes in the charge transfer and ohmic resistance are observed in the anodes fuelled with a gas mixture containing a high KCl vapor concentration. Rapid condensation of salt vapors into the porous anode and partial delamination of the anode from the electrolyte surface because of salt deposits inside the porous anode is observed. The flexibility to produce vapor–aerosol mixtures with different concentrations and particle size distributions is proved, and suitability of these aerosols for anode testing in long term fuel cell test is evaluated. [ABSTRACT FROM AUTHOR]

Abstract: The effects of compositional and environmental parameters on the kinetics of microstructural degradation are investigated for porous Ni/CGO anodes in solid oxide fuel cells (SOFC). Improved methodologies of SEM-imaging, segmentation and object recognition are described which enable a precise quantification of nickel grain growth over time. Due to these methodological improvements the grain growth can be described precisely with a standard deviation of only 5–15nm for each time step. In humid atmosphere (60vol.% H2O, 40% N2/H2) the growth rates of nickel are very high (up to 140%/100h) during the initial period (<200h). At longer exposure time (>1000h) the growth rates decrease significantly to nearly 0%/100h. In contrast, under dry conditions (97vol.% N2, 3vol.% H2) the growth rates during the initial period are much lower (ca. 1%/100h) but they do not decrease over a period of 2000h. In addition to the humidity factor there are other environmental and compositional parameters which have a strong influence on the kinetics of the microstructural degradation. The nickel coarsening is strongly depending on the gas flow rate. Also the initial microstructures and the anode compositions have a big effect on the degradation kinetics. Thereby small average grain sizes, wide distribution of particle size and high contents of nickel lead to higher coarsening and degradation rates. Whereas the nickel coarsening appears to be the dominant degradation mechanism during the initial period (<200h) other degradation phenomena become more important during long exposure time (>1000h) in humidified gas. Thereby the evaporation of volatile nickel species may lead to a local increase of the Ni/CGO ratio. Due to the surface wetting of CGO a continuous layer tends to form on the surface of the nickel grains which prevents further grain growth and evaporation of nickel. These phenomena lead to a microstructural reorganization between 1000 and 2300h of exposure. This complex pattern of degradation phenomena also leads to a change of the amount of active microstructural sites that are important for catalytic reactions at the pore-nickel interfaces and for electrochemical reactions at the triple phase boundaries (TPB). [Copyright &y& Elsevier]

Abstract: An economical and environment friendly zinc–air system route is used for the synthesis of zinc oxide (ZnO) on a zinc (Zn) plate in room temperature. A Zn plate and a single air-cathode are used as the anode and cathode, respectively. It is found that the growth of ZnO increases with increasing electrolyte solution concentration until an optimum concentration is reached. A synthesis profile shows that the formation of ZnO in KOH+ZnO aqueous electrolyte occurs faster (about 500min) compared to KOH aqueous electrolyte solution (about 600min). The values of the plateau voltages for both electrolytes are ∼1.2V. A mixture of saturated ZnO powder in the KOH solution improves the microstructure, reduces the period of synthesis profile and decreases the degradation rate of the Zn plate. The field emission scanning electron microscopy observation shows that needle structures form. Energy dispersive X-ray spectroscopy and X-ray diffraction analysis confirmed that the needle structure is ZnO. [Copyright &y& Elsevier]

Defects-propagation in polymer electrolyte membrane fuel cells membrane electrode assemblies (MEA) is investigated via Accelerated Stress Tests (AST) combining load (hence potential) and load-driven humidity cycling, and open-circuit voltage. Customized MEA with lack of anode catalyst layer at two different locations -near the hydrogen inlet or outlet-are fabricated and subjected to the AST. Periodical electrochemical characterizations are performed using a segmented cell, enabling to track the cell performance and anode/cathode electrochemical surface area (ECSA) over the test period with a spatial resolution along the gas channels. These observations are completed by post mortem analyses of the MEA. The MEA accelerated degradation is obvious, with multiple impacts on the cell performance and materials. More specifically, the results brought first evidence of defects propagation, in term of anode ECSA loss, in the direction of the hydrogen flow. The cathode ECSA is also impacted, although seemingly homogeneously. Significant membrane thinning is observed for the defective segments, without propagation to the adjacent ones. Anode and cathode local potential monitoring during the AST reveals the absence of cathode high-potential excursion, in both the segments with/without initial defects: the membrane and anode accelerated degradation is governed by chemical mechanisms like gas crossover rather than electrochemical mechanisms induced by high-potential excursions. [Display omitted] • Anode active surface defects propagate in the direction of the hydrogen flow. • The cathode active surface is also impacted, but homogeneously. • Anode active surface defects entail significant membrane thinning. • Membrane thinning is likely governed mainly by chemical mechanisms. [ABSTRACT FROM AUTHOR]

The operating properties of solid oxide fuel cells using Ni/scandia-stabilized zirconia (Ni–ScSZ) anodes under internal reforming conditions are investigated. A single-cell achieved a maximum power density of 0.64 W cm−2 at 900 °C in 97%CH4/3%H2O mixture fuel. The cell voltage during the power generation at 0.5 A cm−2 is stable in 97%CH4/3%H2O mixture fuel at 900 °C for at least 150 h. By contrast, degradation of anode performance and carbon deposition are found at 800 °C under the same conditions. These results suggest that carbon deposition is hindered more effectively at higher temperature under operation at high current density. [Copyright &y& Elsevier]

Fuel starvation events occur in proton exchange membrane fuel cells (PEMFCs) when the flow fields become blocked by ice or dust/debris from the environment. When this occurs, the electrons at the anode catalyst layer (ACL) must be generated by either water oxidation or carbon corrosion which forces the cell into a 'reversal' event. Such events rapidly degrade the anode catalyst layer, but can be mitigated through the use of reversal tolerant catalysts (RTCs) such as IrO x. While widely used in industry, this topic has not received significant attention in the literature. At the membrane electrode assembly (MEA)-level, there are two main approaches to evaluate reversal tolerance: 1) Galvanostatic and 2) Pulsing. In galvanostatic accelerated stress tests (ASTs), the current is held at a constant value until the cell voltage reaches a predetermined value. For pulsing ASTs, the MEA is put through short term 'reversal' conditions before going back to normal operating mode. These ASTs are in fact quite different in terms of the stress they put on the ACL. Here, we directly compare these two ASTs, showing that, when normalized for the same amount of total reversal time, the pulsing experiments result in more severe anode damage than galvanostatic testing. • Blockage of H 2 supply to the anode of a PEMFC results in severe anode damage. • This can be overcome with the use of a 'reversal tolerance catalyst' (RTC). • Accelerated stress testing (ASTs) are not widely standardized for RTCs. • A direct comparison of the two most common ASTs (Galvanostatic and Pulsing) is provided. • Recommendations for interpreting and choosing between these ASTs are provided. [ABSTRACT FROM AUTHOR]

The growth of nickel (Ni) particles in the porous anode is one of the most critical issues in solid oxide fuel cells (SOFC). It reduces the density of triple phase boundaries (TPBs) and increases the polarization resistance of SOFC. Most of the three-dimensional models, that are intended to simulate this phenomenon in detail, are numerically exhausting. Consequently, they are intractable for online monitoring applications. This work presents a reduced-complexity, two-dimensional, micro structural model as a trade-off between the numerical load and the level of modeling detail. The process of Ni agglomeration is described by applying the power-law coarsening theory. The resulting model is validated by comparing the relative density of TPBs and the cell voltage to the data that were measured on the real SOFC. It is shown that the cell voltage closely fits the measured values, rendering the model capable of calculating the electric performance of a SOFC system over time. The advantage of the proposed model is that it takes lower computational load during the simulation compared to the complex phase field models and is suitable to calculate the degradation of SOFC electric performances over the time. • Two-dimensional degradation model of solid oxide fuel cell (SOFC) is presented. • The nickel grain growth in the porous anode is modeled by using the power law. • The model is validated on data obtained by the measurement of real SOFC. • The calculated voltage of SOFC is in a good agreement with measured voltage. • The model is suitable to be applied for estimation of SOFC degradation. [ABSTRACT FROM AUTHOR]

Although using an air cathode is the goal for superoxide-based potassium-oxygen (K-O 2 ) batteries, prior studies were limited to pure oxygen. Now, the first K-air (dry) battery based on reversible superoxide electrochemistry is presented. Spectroscopic and gas chromatography analyses are applied to evaluate the reactivity of KO 2 in ambient air. Although KO 2 reacts with water vapor and CO 2 to form KHCO 3 , it is highly stable in dry air. With this knowledge, rechargeable K-air (dry) batteries were successfully demonstrated by employing dry air cathode. The reduced partial pressure of oxygen plays a critical role in boosting battery lifespan. With a more stable environment for the K anode, a K-air (dry) battery delivers over 100 cycles (>500 h) with low round-trip overpotentials and high coulombic efficiencies as opposed to traditional K-O 2 battery that fails early. This work sheds light on the benefits and restrictions of employing the air cathode in superoxide-based batteries., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)