The flow field is an integral part of a proton exchange membrane fuel cell. In this work, three flow-field designs, including straight parallel, multiple channel serpentine, and single channel serpentine, are studied systematically to investigate their effects on fuel cell performance. To evaluate the characteristics of each design, relative humidity and flow rate are parametrically adjusted to evaluate performance experimentally. A finite element-based 3D steady state, single phase COMSOL computational model is employed to analyze reactant distribution and fuel cell performance. The single channel serpentine exhibits the best performance under the greatest variety of operating conditions, but also experiences the highest inlet-outlet pressure differentials. This study shows that parallel channel design has more evenly distributed reactant concentration, but is prone to liquid water accumulation, which requires high flow rate to remain stable operation under wet conditions. In summary, the multiple channel serpentine design can provide a reasonable balance between pressure drop and flow distribution with robust fuel cell operation.
A 1-D electrochemical model for a solid oxide electrolysis cell (SOEC) is developed and validated using published experimental data. The model combines thermodynamics, kinetic, ohmic, and concentration overpotentials to predict cell performance. For the anode-supported SOEC, good agreement is obtained between the model and experimental data, with ohmic loss being the major contributor to the cell's total overpotential. Both kinetic and concentration losses are less significant due to high-temperature operation. Due to the dominating performance loss, reducing the anode thickness is effective in diminishing the cell potential. Overall, this simple 1-D model can be employed as a design tool to evaluate component design and estimate system performance for industrial applications.
Owing to the sluggish oxygen reduction reaction (ORR), high-performance catalysts like Pt-based alloys are widely used to render the reaction practically useful in systems like fuel cells. Nonetheless, high costs and technical complications associated with such catalysts have encouraged the exploration of alternative ORR catalysts like heteroatom-doped carbon nanomaterials. To improve the catalytic activity of carbon, earlier studies used boron, nitrogen, phosphorus, sulfur, and selenium as dopants. In this paper, we perform density functional theory (DFT) calculations to explore the potential of halogens (X = F, Cl, Br, I) substituted within the two-dimensional structure of graphene. We also validate some of the results of previous experimental and theoretical studies on halogen-doped graphene. For example, we compare halogen adsorption and band structures of the resulting halogen-doped materials, as well as the possible influence of atomic size and atomic interactions (e.g., Br2/Br interactions, polyiodide formation) on their experimentally observed properties. Based on the resulting electronic and structural information, we then identify which among the buckled and planar forms of halogen-substituted graphene show the most promise for ORR activity. Finally, we compare this method of doping with previously studied methods like adsorption and edge-halogenation to provide additional insight on halogen doping.
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