To meet escalating energy demands and address environmental concerns, it is imperative to develop energy conversion technologies that are both sustainable and efficient. Unitized regenerative fuel cells (URFCs) provide efficient energy storage and conversion through the seamless integration of fuel cells and electrolyzers. A study of the effect of varying Gas Diffusion Layer (GDL) thicknesses from 270 to 420 µm on URFC’s performance is presented. The study is performed by developing mathematical numerical modeling and simulation using a finite element analysis-based software COMSOL Multiphysics 5.6 and validation with past literature experimental results. In this study, reactant gas distribution within URFCs is compared in fuel cell and electrolysis modes. Electrolysis performance with varied GDL thicknesses showed negligible change between load voltages of 1.25 to 1.45 V, whereas fuel cell performance variations reached significant values at 0.65 V due to mass transport losses. The intricate interaction between GDL thickness, reactant gas distribution uniformity, and cell performance is elucidated by analyzing reactant gas transport resistances. While thicker GDLs exhibit lower non-uniformity in reactant distribution in fuel cells, moderate-thickness GDLs exhibit excellent uniformity in electrolysis. Specifically, in this work, the A3 series of GDLs by JNTG incorporates a microporous layer (MPL) of carbon nanofibers for fuel cells, with the numerical suffix indicating increasing GDL thickness. For A3-20 GDL (270 µm), A3-30 GDL (320 µm), and A3-40 GDL (420 µm) round trip efficiencies of simulated URFCs are 36%, 43.75%, and 38.9%, respectively, at 500 mA/cm2. A3-30 (320 µm) GDL is recommended as the optimal choice for URFCs, as it effectively balances reactant transport, water management, and electrochemical performance, ensuring high round-trip efficiency and system stability.
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