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Gallic acid, known for its biological activity contributing to human health, including antioxidant, anti-inflammatory, anticancer, and antimutagenic properties, was the focus of this study. The solubility of gallic acid was experimentally measured in pure and mixed solvents of water, ethanol, and acetic acid and predicted using the COSMO-SAC model and the Hansen solubility parameter. The Hansen solubility parameter method predicted a higher solubility of gallic acid in pure water than in pure ethanol, and in a mixed solvent, it predicted the maximum solubility at 80% water content, showing different results from the experimental data trends. However, using the molar volume obtained from COSMO calculations resulted in a tendency that matched the experimental results. The results revealed higher solubility in ethanol compared to water, with the solubility in mixed solvent falling within the range between them. Using the same method, the Hansen solubility parameter obtained was applied to acetic acid/water and acetic acid/ethanol mixtures, and similar trends were observed compared to experimental data. In particular, gallic acid in the acetic acid/water mixture solvent exhibited maximum solubility, and this phenomenon was well-predicted. As the temperature increased, solubility in both pure and mixed solvents also increased. While the COSMO-SAC model effectively captured this trend, the predicted solubility values were slightly lower than the experimental data. The solubility trends depending on solvent types were confirmed by comparing the σ-profiles of each compound. The σ-profile of gallic acid closely resembled that of ethanol, and this result led to higher solubility than water and acetic acid. The maximum solubility in ethanol/water and acetic acid/water mixed solvents could be anticipated when two solvents with significant differences in their σ-profiles are mixed in an appropriate ratio.

For the high performance of a fuel cell where a bipolar plate (BP) is applied, rectangular channel, microchannel width, micro-rib, enough channel quantity, adequate channel depth, and innovative flow field design should be realized from a configuration standpoint. In this study, a stainless-steel BP with a microchannel flow field is fabricated with a powder bed fusion (PBF) 3D printer to improve fuel cell performance. A BP with a triple serpentine flow field, rectangular channel, 300 μm channel width, 300 μm rib, and 500 μm channel depth is designed. The print is completed perfectly until the flow field. The bending phenomenon due to thermal deformation does not occur in the BP fabricated by designing the thickness at 2 mm. Performance tests are conducted using fabricated stainless-steel BPs. The current density value is 1.2052 A/cm2 at 0.6 V. This value is higher by 52.8% than the BP with 940 μm channels (rectangle, 940 μm ribs, and 500 μm channel depth). In addition, the value is higher by 24.9% than a graphite BP with 940 μm channels (rectangle, 940 μm ribs, and 1000 μm channel depth). The current density values are measured at 0.6 V for 260 h.