Simulation of a Full Fuel Cell Membrane Electrode Assembly Using Pore Network Modeling

Abstract

A pore network model has been applied to a both sides of a fuel cell membrane electrode assembly. The model includes gas transport in the gas diffusion layers and catalyst layers, proton transport in the catalyst layers and membrane, and percolation of liquid water. This paper presents an iterative algorithm to simulate a steady state isothermal cell with a 3D pore network model for constant voltage boundary condition. The proposed algorithm provides a simple method to couple the results of the anode and the cathode sides by iteratively solving the uncoupled equations of the transport processes. It was found that local water blockages at the GDL/CL interface not only affect concentration polarization, but also might change ohmic polarization of the cell. Depending on the liquid water configuration in the porous electrodes, the protons generated in the anode need to travel longer paths to reach the active sites of the cathode; consequently, the IR loss will be increased in the presence of liquid water. This finding highlights the strength of pore network models which resolve discrete water blockages in the electrodes. Polymer electrolyte membrane fuel cells are one of the key technologies required to realize a sustainable energy economy because they provide energy storage. A typical PEMFC is a stack of electrochemical cells, and the heart of each is a sandwich of several porous layers around a thin polymer electrolyte membrane, referred to as a membrane-electrode assembly (MEA). In the typical arrangement each side consists of a gas diffusion layer (GDL), and a catalyst layer (CL). The GDL is usually a carbon-fiber based paper and acts as a spacer to allow gaseous reactants to reach regions of the catalyst layer under the flow field ribs, and as a bridge to allow electron access to catalyst sites over the flow field channels. The CL is composed of a mixture of ionomer such as Nafion and carbon-supported platinum catalyst particles, and is adhered to the surface of the membrane as a porous coating around 10-20 μm thick. The ionomer phase in the CL allows protons to reach the catalyst sites, while the carbon particles provide pathways for electrons, and the porosity allows transport of gaseous reactants (oxygen and hydrogen) and product (water). Under some conditions the cathode produces liquid water, which can accumulate in the pore spaces, blocking the access to the reaction sites. Liquid water can also be found on the anode side, for instance if temperature fluctuations occur since the hydrogen is humidified. Understanding the role of liquid water and its impact on fuel cell operation has been a longstanding challenge for the industry.1-3 Complete water removal from the cell is not an option because the currently used membrane materials must be hydrated to function.When electrical current is drawn, several sources of voltage loss are incurred due to the inefficiencies of current generation and transport processes. Voltage losses can be broken into three categories: activation polarization η act , ohmic polarizat...

Coupled continuum and condensation–evaporation pore network model of the cathode in polymer-electrolyte fuel cell

“…(11) and (12) combined with Eqs. (25) and (26). This gives the boundary condition to be applied for the computation of the thermal, gas and electrical transfers inside the GDL.…”

“…A coupled continuum-PN models is also presented in Ref. [25]. This model couples a threedimensional PNM in the GDL to continuous models in the other layers for anode and cathode sides.…”

Versatile and efficient pore network extraction method using marker-based watershed segmentation

“…Percolation theory describes the sequence and pattern of an invading phase, which can be incorporated into the network transport calculations. Taken together, this means that PNMs can be used to study complex multiphase flow problems in large domains, such as entire catalyst pellets [19], electrodes [20], and paper [21]. Developing faithful pore network models of materials is thus essential for the study and advancement of many technologies.…”

Stochastic Analysis of the Gas Flow at the Gas Diffusion Layer/Channel Interface of a High-Temperature Polymer Electrolyte Fuel Cell

“…The GDL/channel interface was investigated by Yu et al [34], who analyzed irregular contact angles of water droplets at the GDL surface and their pattern when they passed the GDL/channel interface at several positions. The relevance of the interface for multi-scale simulations was shown by Qin et al [35,36] and Aghihi et al [37], who used pore network modeling (PNM) to bridge the scales (still on water transport in low temperature PEFCs). Niu et al [38] coupled the LBM in the porous GDL structure with OpenFOAM simulations in the air channel.…”