To develop the manufacturing technology of electrochemical cells, such as polymer electrolyte fuel cell and lithium-air battery, it is necessary to elucidate the cell structure for realizing increase in power output, based on mass and heat transfer in the cell. This article introduces some results achieved by the authors’ researches, developing the structure of gas diffusion layer, micro-porous layer, and catalyst layer in a polymer electrolyte fuel cell, and the structure of air electrode in a lithium-air battery.

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  Understanding internal phenomena of porous electrode layer in Polymer electrolyte fuel cells （PEFCs） and Lithium-ion batteries （LIBs） has been required to reduction various resistance of electrochemical reaction and mass transport. However, it is difficult to know the internal condition under in-situ operating condition. Thus, the numerical simulation and digital transformation method are applicable to solve this problem. Porous structure and morphology in the porous electrode layer with nanometer to micrometer scale can be designed with these approaches. In this review, we provide an importance of the design of porous electrode layer and an overview for the simulation and digital transformation method of PEFC and LIB.

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  The vital importance of mechanical engineering approaches has been increasingly acknowledged in the research and development of electrochemical devices such as fuel cells and batteries because the coupled multi-species transport in their complex multicomponent structures is a key to explaining their macroscopic performance. In this article, novel fabrication techniques for solid oxide fuel cells（ SOFCs） to realize unique electrode microstructure with improved reaction and transport characteristics are overviewed with their theoretical backgrounds. The techniques include the meso-patterning on the electrode-electrolyte interface that increases the active reaction thickness, the nano-particle infiltration technique that enhances the electrochemical activity of the electrode without sacrificing the gas transport property, and the phase-inversion technique that introduces anisotropic pore structures in the electrode with significantly high gas transport properties.

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  To alleviate water flooding and membrane dryout in polymer electrolyte fuel cells （PEFCs）, it is necessary to elucidate mass transports and electrochemical reactions occurring in membrane electrode assemblies （MEAs） by various measurements and simulations and to design the optimum fuel cell structure for better water management. Our research group has developed several measurement techniques for investigating the liquid water behavior and quantifying the water vapor concentration within the flow channel and porous electrode of an operating PEFC based on cross sectional visualization, X-ray radiography and laser absorption spectroscopy. The details of their measurement methods and utilization examples were explained in this article.

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  Fabrication of structure from a slurry, which is a dispersion of materials in liquid, is a key technology to produce functional membranes and porous layers. In this review, fundamentals of fabrication from slurry and its applications to the fabrication of porous electrodes of polymer electrolyte fuel cells （PEFCs） are presented. Several scientific backgrounds including the agglomeration of particles in slurry, rheology, and transport phenomena in slurry during drying are introduced. Measurement techniques of particle size distribution, zeta potential, rheology and small angle X-ray/neutron scattering for evaluation of slurry are summarized. Several novel evaluation methods of slurry including impedance measurements and X-ray radiography are presented. Some experimental results with the application of the measurement techniques to evaluate dispersion state of materials in the slurry are presented. The formation of material distribution and porous structure of the electrode by slurry drying is explained. Finally, the importance of interaction between materials and fluids in the high-concentration slurry for fabrication is explained.

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