Micropatterns applied to proton exchange membranes can improve the performance of polymer electrolyte fuel cells; however, the mechanism underlying this improvement is yet to be clarified. In this study, a patterned membrane electrode assembly (MEA) was compared with a flat one using electrochemical impedance spectroscopy and distribution of relaxation time analysis. The micropattern positively affects the oxygen reduction reaction by increasing the reaction area. However, simultaneously, the pattern negatively affects the gas diffusion because it lengthens the average oxygen transport path through the catalyst layer. In addition, the patterned MEA is more vulnerable to flooding, but performs better than the flat MEA in low-humidity conditions. Therefore, the composition, geometry, and operating conditions of the micropatterned MEA should be comprehensively optimized to achieve optimal performance.

The volume expansion of anode active materials in all-solid-state lithium-ion batteries strongly affects the dynamic change in the electrode structure and its activity in electrochemical reactions and mass transport. Thus, understanding the mechanisms and internal phenomena during the charging process with volume expansion is important. In addition, clarifying these phenomena contributes to the selection of the active material when creating the electrode structure. This study aimed to verify the effect of volume expansion of the active material in a porous electrode layer on the charging performance using a numerical simulation. In this calculation, for the electrochemical reaction transport analysis, equations were applied based on the porous electrode theory; for the structural deformation due to expansion, we expressed the change by controlling the structural parameters and built a model for simulation. From the simulation results, when the fastening pressure was small, the active material with a large volume expansion ratio exhibited a larger capacity. However, for a large fastening pressure, active materials with a large volume expansion ratio seemed not to be used. Although the volume expansion of the active material should be suppressed from the viewpoint of ion conduction network rupture, these results demonstrate that the influence of volume expansion effectively depends on the electrode creation conditions. This model will help to optimize the design of all-solid-state batteries and can be the key to further performance improvement.

The structure of the cathode catalyst layer (CCL) is critically important for improving the performance, durability, and stability of polymer electrolyte fuel cells (PEFCs). In this study, we designed CCLs with a three-dimensional (3D) structure that could increase the surface area of the CCLs to decrease their oxygen transfer resistance. The CCLs were fabricated using an inkjet printing method, and the electrochemical performance of the CCLs in a membrane electrode assembly was evaluated using an actual cell. The results showed that at high Pt loadings, the performance of the CCL with the 3D structure was superior to that of the flat structure. In particular, at a high current density, which is related to mass transport resistance, the two structures exhibited a significant difference in performance. At a Pt loading of 0.3 mg/cm2, the CCL with the 3D structure showed the highest maximum power density among all the CCLs investigated in this study. This indicates that the 3D structure decreases the oxygen transfer resistance of the CCL. Overall, the 3D structure provided improved morphological and microstructural characteristics to the CCL for fuel cell applications.