This study aims to develop a correlation equation between a porous electrode structure and the effective conductivity so as to design an optimal structure for a thick electrode layer of a ...high-capacity battery. We carried out a three-dimensional reconstruction of a lithium cobalt oxide and graphite electrode based on the cross-sectional images obtained via focused ion beam-scanning electron microscopy (FIB-SEM). The Li ion and electron conductivities are evaluated based on the effective conductive path determined from simulation and these values are compared with the experimental results obtained by electrochemical impedance spectroscopy carries out with a symmetric cell and the direct conductivity measurement under compression. Moreover, the amount of binder and the diameter of the active material particles are increased and decreased numerically using an actual reconstructed electrode structure, and the effect of those structures on the effective conductivity is examined. The most dominant factors that degrade ionic conductivity are the binder distribution and the particle morphology, respectively, in the cathode and anode, and a correlation equation with the function of porosity is obtained. These values are compared with those obtained by theoretical model equations, and the difference between the current effective ionic conductivity and the physical limiting value is determined.
•Effective ionic conductivity is evaluated by experiment, simulation and modeling.•Effects of binder volume and morphology in cathode are considered.•Effects of particle morphology and orientation in anode are considered.•Correlation equation of porous structure and ionic conductivity is obtained.•Difference between actual conductivity and physical limiting is understood.
It is important to reduce the oxygen diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas diffusion coefficient of CL is lower than MPL ...in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.
•The low gas diffusion coefficient of catalyst layer is studied by simulation.•Carbon black aggregate structure and ionomer adhesion are modeled.•Effect of porous structure with carbon agglomerate simulation model is studied.•The possibility to improve gas diffusion by structure design is understood.
In order to elucidate a porous structure consisting of carbon aggregate and ionomers, the agglomeration mechanism of carbon black in CL is examined based on the experimental results of particle ...diameter distribution of carbon black in CL ink with or without an ionomer and the transmission electron microscopy image of carbon black dispersion. A theoretical model of the attraction and repulsion between carbon particles is also discussed, and compared with experimental results. From this model and the measured particle distribution data, it is supposed that the structure with large isolated pores results from carbon black dispersion in CL slurry, and the interaction phenomenon of each carbon black particle depends on the weight ratio of ionomer and carbon. Furthermore, the carbon black aggregate and the agglomerate structure in CL are reproduced numerically, and the effects of the heterogeneous structure on gas diffusion performance are examined by simulations. These results suggest that gas diffusion performance depends on pore size and ionomer adhesion. In particular, ionomer migration near large pores strongly affects gas diffusion performance because of the existence of isolated pores. In addition, better gas diffusion needs a certain amount of pores of non-uniform sizes.
•Effects of solvent and ionomer on carbon agglomerate are considered.•Carbon aggregate and agglomerate structure is modeled with particle interaction.•Gas diffusion performance depends on pore size and ionomer adhesion.•Ionomer migration near large pores strongly affects gas diffusion performance.•Better gas diffusion needs a certain amount of ununiform-sized pores.
Abstract Background context Although explored in humans and animal models, the pathomechanisms of discogenic low back pain (LBP) remain unknown. Purpose The aim of this study was to review the ...literature about the pathomechanisms of discogenic LBP. Methods Animal models of discogenic pain and specimens from degenerated human intervertebral discs (IVDs) have provided clues about the pathomechanisms of discogenic LBP. Painful discs are characterized by a confluence of innervation, inflammation, and mechanical hypermobility. These three possible mechanisms are discussed in this review. Results Animal models and specimens from humans have revealed sensory innervation of lumbar IVDs and sensory nerve ingrowth into the inner layer of IVDs. Cytokines such as tumor necrosis factor-α and interleukins induce this ingrowth. Nerve growth factor has also been recently identified as an inducer of ingrowth. Finally, disc degeneration induces several collagenases; their action results in hypermobility and pain. Conclusions To treat discogenic LBP, it is important to prevent sensitization of sensory nerve fibers innervating the IVD, to suppress pathogenic increases of cytokines, and to decrease disc hypermobility.
The reduction of oxygen transfer resistance through porous components consisting of a gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost ...and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas diffusion with a negative effect on performance. The relative diffusion coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative diffusion coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.
•Actual porous electrode structures of PEFC were made with FIB-SEM and X-ray CT.•Both gas diffusion results of calculations and experiments were almost same.•Equations of relative diffusion coefficient of each porous media were obtained.•Catalyst layer had low gas diffusion property depending on ionomer as expected.
A particle model for ionomer attachment on carbon black in a Polymer Electrolyte Fuel Cell (PEFC) catalyst layer was developed based the random walk method. Two different methods of particle ...attachment were used that resemble different catalyst ink preparation conditions: the solution method and the colloidal method. In the solution method, the simulation of attachment is conducted on the aggregate structures and in the colloid method, the attachment is simulated on the agglomerate structures. The distribution of carbon black, ionomer and void space was used in a multiscale electrochemical simulator that calculated the mass/charge transfer and reaction in the catalyst layer. The results of effective oxygen diffusion coefficients are consistent with experimental result and show why the Bruggeman correlation often is a poor approximation for upscaling the effective diffusive and conductive components in PEFC porous media. The solution method allowed for a better proton conduction through the ionomer but resulted in a thicker ionomer film that increased the oxygen diffusive resistance. However, solution and colloidal method resulted in similar cell performances. Our model can aid in the design to develop fuel cell catalyst layers with improved performance.
The resistance of the cathode oxygen reduction reaction in polymer electrolyte fuel cells must be reduced for improving the performance. Therefore, it is important to thoroughly understand the ...relationship between the heterogeneous structures and the cell performance. However, it is difficult to obtain such an understanding using experimental approaches and typical uniform porous simulations. In this study, numerical analysis was used to simulate a three-dimensional catalyst layer (CL) with carbon black (CB) aggregate structures and ionomer coating models, and a cathode reaction and mass transport simulation model incorporating the heterogeneous structure was developed. Moreover, the relationship between the electrode structure and the cell performance, including the reaction distribution and output performance, was examined. The current density distribution depended on the CB structure and ionomer adhesion shape. From the viewpoint of enhancing both the Pt utilization and the mass transport performance, an adequate heterogeneous pore structure in the CL is necessary. These results were used to determine the optimal material properties for the high performance cell.
•Simulation model in cathode catalyst layer with 3D structure was developed.•Heterogeneous structure with carbon black and ionomer was simulated.•Ionomer adhesion affect mass transport, and it cause reaction distribution.•Local reaction on Pt surface was changed to bi-modal distribution by agglomerate.•Effective Pt utilization in cathode was estimated by this simulation.
In polymer electrolyte fuel cells (PEFCs), an ionomer is needed to maintain the proton conductivity in the catalyst layer; however, it causes oxygen diffusion resistance because of its thickness on ...the platinum surface and the blockage of the void spaces. Therefore, understanding the ionomer distribution on a platinum/carbon black (CB) support catalyst is extremely important, because this knowledge can contribute to a reduction in the resistance for the cathode oxygen reduction reaction. In this study, a three-dimensional CB aggregate structure is simulated using numerical analysis with various experimental information (surface volume, aggregate size, and anisotropy); from the viewpoint of the roughness and morphology of CB, the ionomer distribution on its surface is simulated. The relationship between the ionomer content and the coverage of the ionomer on carbon is determined. Moreover, the effect of the surface structural properties on the ionomer distribution in the catalyst layer is studied using simulations. Based on the results, the relationship between the surface roughness and the ionomer connectivity is determined. The coverage and thickness of the ionomer do not change linearly upon changing its content. This condition strongly depends on the surface roughness. Insights gathered from this study can assist in designing optimum catalyst layer.
•Actual carbon black structure is simulated and the validity of this is confirmed.•Ionomer distribution on carbon black and in catalyst layer is estimated.•Correlation equation of ionomer thickness, coverage and conductivity are obtained.
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