• Energy Research

To optimize the interface of the catalyst layer (CL) and gas diffusion layer (GDL) in polymer electrolyte membrane fuel cells (PEMFCs), microporous layers (MPLs) with different decorative patterns were prepared. Carbon paper treated with polytetrafluoroethylene was used as a substrate for the coating of MPLs. To accelerate water removal and gas permeation, ammonium chloride was utilized to improve the porous structure of MPLs. Owing to the recrystallization and pyrolysis of ammonium chloride with different contents, the surface of MPLs exhibited point-, line-, and flowerlike patterns. Membrane electrode assemblies (MEAs) were assembled to evaluate the performance of MPLs with different decorative patterns. From measurements, an MEA containing a porosity-graded MPL (MPL-G) with a flowerlike pattern exhibited the best electrochemical performance. It is because that graded porosity accelerates the removal of excessive water. The flowerlike pattern facilitates the diffusion of the reactant gas at the interface of the catalyst layer and MPL. With the measurement of segmented cell technology, such MEAs revealed an improved redispersion of reactant gases. Furthermore, the produced water was compressed to the gas outlet, providing a larger active region for reaction. These results indicate that pattern design of MPLs is a promising strategy to improve the mass-transfer efficiency at the interface of the catalyst layer and gas diffusion layer.

Fuel cells, designed for mobile applications, should feature compact and low-weight designs. This study describes a design process that fulfills the specific needs of target applications and the production process. The key challenge for this type of metallic bipolar plate is that the combination of two plates creates three flow fields, namely an anode side, a cathode side, and a coolant. This illustrates the fact that each cell constitutes an electrochemical converter with an integrated heat exchanger. The final arrangement is comprised of plates with parallel and separate serpentine channel configurations. The anode and cathode sides are optimized for operation under dry conditions. The final plate offers an almost perfect distribution of coolant flow over the active area. The high quality of this distribution is almost independent of the coolant mass flow, even if one of the six inlet channels is blocked. The software employed (OpenFOAM and SALOME) is freely available and can be used with templates.

A numerical simulation of the Jülich F-design Solid Oxide Fuel Cells stack is conducted by means of an original mathematical model. The model is implemented in the open source toolbox, OpenFOAM. This cell/stack level model is a key component of a programme to develop a fully integrated multi-scale fuel cell modelling capability, from nano-scale through to system level. It is intended to share the resulting software with other parties openly. Substantial experimental data is available for the Jülich F-design; Stack configuration, flow conditions, interconnector geometries and porous electrode properties prescribed in the numerical model are based on field experiments. The numerical model generates distributions of fluid flow, species concentrations, current density and temperature. The results of the simulations are compared against experimental data obtained from short stacks.

Abstract A three-dimensional (3D) lattice Boltzmann model is applied to simulations of the dynamic process of liquid water moving through the gas diffusion layer, processed by covering the fibers with polytetrafluorethylene (PTFE), in polymer electrolyte membrane fuel cells. The PTFE content and two through-plane distribution styles were analyzed regarding their impact on the liquid water's flow behavior. The total saturation curves show that the water's breakthrough times are affected by these two factors. Different characteristic shapes of local saturation curves are observed with different types of PTFE distribution. The dynamic elevation plots of water fronts show that certain PTFE distribution styles can be of advantage to fuel cell efficiency.

Applied energy 288, 116561 (2021). doi:10.1016/j.apenergy.2021.116561 Published by Elsevier Science, Amsterdam [u.a.]

Metallic flow field plates, also called bipolar plates, are an important component of fuel cell stacks, electrolyzers, hydrogen purification and compression stacks. The manufacturing of these plates by means of stamping or hydroforming is highly suitable for mass production. In this work, a toolbox is created that is suitable for a screening process of different flow field design variants. For this purpose, the geometry and computational mesh are generated in an automated manner. Basic building blocks are combined using the open source software SALOME, and these allow for the construction of a large variant of serpentine-like flow field structures. These geometric variants are evaluated through computational fluid dynamics (CFD) simulations with the open source software OpenFOAM. The overall procedure allows for the screening of more than 100 variants within one week using a standard desktop computer. The performance of the flow fields is evaluated on the basis of two parameters: the overall pressure difference across the plate and the relative difference of the hydrogen concentration at the outlet of the channels. The results of such a screening first provide information about optimum channel geometry and the best choice of the general flow field layout. Such results are important at the beginning of the design process, as the channel geometry has an influence on the selection of the metal for deep drawing or hydroforming processes.

Code stability is a matter of concern for three-dimensional (3D) fuel cell models operating both at high current density and at high cell voltage. An idealized mathematical model of a fuel cell should converge for all potentiostatic or galvanostatic boundary conditions ranging from open circuit to closed circuit. Many fail to do so, due to (i) fuel or oxygen starvation causing divergence as local partial pressures and mass fractions of fuel or oxidant fall to near zero and (ii) nonlinearities in the Nernst and Butler–Volmer equations near open-circuit conditions. This paper describes in detail, specific numerical methods used to improve the stability of a previously existing fuel cell performance calculation procedure, at both low and high current densities. Four specific techniques are identified. A straight channel operating as a (i) solid oxide and (ii) polymer electrolyte membrane fuel cell is used to illustrate the efficacy of the modifications.