A Model Based Analysis of Alkaline Membrane Fuel Cells
Authors: Rasin Igal G , Page Miles , Dekel Dario R. , Brandon Simon 
Published: February 2020

Alkaline Membrane Fuel Cells (AMFCs), also known as Hydroxide Exchange Membrane Fuel Cells (HEMFCs), Anion Exchange Membrane Fuel cells (AEMFCs) or Alkaline Anion Exchange Membrane Fuel Cells (AAEMFCs), have emerged as an attractive alternative to the more established Proton Exchange Membrane Fuel Cells (PEMFCs) as well as to the traditional alkaline systems (involving a liquid electrolyte). Advantages of AMFCs include the possibility of implementing cheaper catalyst materials as compared to those utilized in PEMFCs, as well as the superior nature of the solid polymer (rather than a liquid) electrolyte which reduces the negative impact of carbon dioxide on performance and resolves issues of electrolyte leakage. However, although advantageous, several challenges still exist in the development of AMFCs. These are related to a number of issues including membrane durability, catalyst performance and cost, as well as water management within the cell. The last issue, although important also in PEFMCs, is especially challenging in the case of AMFCs due to the nature of the electrochemical reactions which involve water production in the anode as well as its consumption in the cathode.

Although experimentally based research has been successful in advancing the understanding and development of AMFCs, theoretical and computational investigations of these systems offer important perspectives not easily obtained via experiments. In particular, a robust modeling approach offers the possibility for inexpensive (albeit simulated) analyses of system sensitivity to a wide range of parameters, the ability to test design modifications and the opportunity for in depth analysis of cell failure (or poor performance) by direct viewing of the distribution of relevant dependent variables (e.g. water uptake/concentration, current generation rate, temperature) throughout the system thus possibly locating the type, position and time of failure (or reduction in performance).

In this contribution we will present our approach to continuum modeling of an alkaline membrane fuel cell. We have developed a transient model in which we account for different phenomena including the transport of several relevant chemical species, heat transfer, electrochemical reactions, gas flow, and electrical performance; three-dimensional system geometry and related effects are also addressed by the model when necessary. Our focus is on investigating behavior and performance of realistic systems. To this end, we make it a point to validate our model against experimental results while minimizing (as much as possible) the use of fitted parameters; see e.g. Fig. 1 in which our computed IV curve, obtained using essentially one fitting parameter, is plotted alongside the corresponding experimentally measured data (taken from [1]).

We will discuss the model as well as the numerical approach, used in the solution of the relevant equations, involving explicit finite difference and Lattice Boltzmann methods. The robustness of the model will be demonstrated, in part, by the (simulated) reproduction and elucidation of experimental data published by Kaspar et.al. [1] (e.g. the IV curve shown in Fig. 1 and mentioned above). These and other results from our computational analyses (to be presented in this contribution) are mainly focused on questions of water management, it's sensitivity to several system parameters and its impact on system performance and stability.

[1] R.B. Kaspar, M.P. Letterio, J.A. Wittkopf, K. Gong, S. Gu, Y. Yan, J. Electrochemical Soc., 162(6) F483 (2015)

Figure 1