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Recently, flow fields of proton exchange membrane fuel cell with three-dimensional (3-D) structure are attracting attentions due to their merits on mass transfer and water management. Among them the most representative one is 3-D fine mesh flow field (3-D flow field). In this study, the morphology of 3-D flow field is reconstructed based on optical microscope image to discuss the single- and two-phase flow characteristics. It is found that the air guidance effect of 3-D baffles contributes to the reactant transport. Meanwhile, a separated liquid-gas transport phenomenon is observed, which reduces the liquid coverage area on gas diffusion layer surface and provides a larger passage area for mass transfer. Furthermore, the effects of air inlet velocity, droplet size and baffle contact angle are discussed. It is found that unless the air velocity is too low, the droplet tends to overcome surface tension and move to above-baffle …