Abstract
Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.
Highlights
The modern scenario for the automotive transportation sector is seeing more and more stringent emission regulations for traditional internal combustion engine vehicles (ICEV), relevantly increasing the powertrain cost due both to the complexity of the after-treatment devices and/or by the coupling with an electric motor for hybrid powertrains
The interest towards carbon-free solutions for mobility is the motivation for a renewed attention on the possible uses of hydrogen as an energetic vector. It can be used either as a combustible fuel for ICEV or to produce electricity in proton exchange membrane fuel cells (PEMFC): While in the former strategy the peak formation of harmful nitrous oxide (NOx ) emerges as the most relevant obstacle, in the latter one water and low-temperature heat are the only by-products of on-board electricity generation, thanks to the absence of a thermal/combustion cycle
A constant value is maintained at the anodic side, since the dissociation voltage losses of hydrogen are usually orders of magnitude lower than that of oxygen, whereas a semiempirical law was adopted for the cathode, able to consider the load of the catalyst layer and the catalyst surface roughness and morphology
Summary
The modern scenario for the automotive transportation sector is seeing more and more stringent emission regulations for traditional internal combustion engine vehicles (ICEV), relevantly increasing the powertrain cost due both to the complexity of the after-treatment devices (particulate filter, catalytic reduction systems, etc.) and/or by the coupling with an electric motor for hybrid powertrains. Among the multiple types of fuel cells, PEMFC are receiving significant research and investment attention for the use in the transportation sector, mainly because of their low-temperature operation (in the range 340 K–380 K), good suitability for frequent startstop cycles, and for the absence of corrosive substances (e.g., liquid acid) Their core component is a solid polymeric membrane impermeable to fluids, able to separate the hydrogen oxidation reaction (HOR, at the anode) and the oxygen reduction reaction (ORR, at the cathode). Despite PEMFC being a well-established type of fuel cell, the complex interplay of physical and chemical processes that are key to a highly-efficient operation are still not fully understood, as is the role of materials on the overall cell performance To fulfill this knowledge gap, computational fluid dynamics (CFD) modelling allows the numerical simulation of all the fluid/heat/charge transport phenomena, offering the incomparable possibility to identify limiting processes and driving the design and development of highefficiency PEMFC. An improved formulation of the cathodic exchange current density will be implemented, and conclusive guidelines on comprehensive 3D-CFD models will be provided
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