Optimization of 2-D Spatial Distributions of Pore Sizes, Platinum Content, and Nafion Amount in PEMFC

Abstract

Proton exchange membrane fuel cells (PEMFCs) provide a key technology to enable the transition to a zero-emission economy. In transportation applications, PEMFCs allow high-efficiency conversion of fuel to electricity, long range, and rapid refueling, all without pollution, noise, or other undesirable effects. However, cost remains one of the largest barriers to widespread adoption of PEMFC technologies. The goal of our research is to reduce PEMFC cost by optimizing the performance of the cell.In this presentation we focus on the numerical optimization of the microstructure of the anode and cathode catalyst and gas diffusion layers in low-temperature PEMFCs. Our approach consists of discretizing realistic PEMFC structures numerically and solving the following optimization problem on a finite element grid [1]: maxV(μPt, μN, μC, μ∈) μPt(r), μN(r),μC(r), μ∈(r) where V is the voltage of the cell at a specified current density, μPt, μN, μC, and μ∈ are the two-dimensional spatial distributions of the platinum, nafion, and carbon contents, and porosity, respectively. The above problem is solved using a modified steepest descent method in which the gradients of the cell voltage with respect to the local values of the platinum, nafion, carbon, and porosity distributions are computed efficiently using an adjoint method [2, 3]. The numerical algorithm is implemented in our finite element simulator, RandFlux [4], in which the derivatives of transport equations with respect to the state variables and the adjoint operator are computed efficiently using automatic differentiation.The figures present the optimized distribution of the platinum, nafion, pore fraction, and carbon as a function of the location in the cathode catalyst layer for a standard PEMFC with a membrane thickness of 25 mm, GDL thicknesses of 250 mm, and catalyst layer thicknesses of 15 mm. The 2-dimensional PEMFC is symmetric with respect to y=0.5 mm, has the opening between y=0.25 mm and 0.75 mm; the membrane is toward the left side of each figure, the gas diffusion layer (GDL) is toward the right side. The optimization was performed in order to increase the polarization of the cell at a current density of 0.5 A/cm2. We observe that it is optimum to increase the density of the platinum particles and the amount of the electrolyte near the membrane side of the catalyst layer and, in the same time, increase the porosity and carbon fraction near the gas diffusion layer. More results about the technique, the numerical implementation, and a number of fully optimized cells will be presented at the meeting.References Lamb and P. Andrei, ECS Transactions, 98, 67 (2020).J. Lamb, G. Mixon and P. Andrei, Journal of The Electrochemical Society, 164, E3232 (2017).J. Lamb and P. Andrei, ECS Transactions, 97, 671 (2020).RandFlux, Florida A&M University and Florida State University, http://www.eng.famu.fsu.edu/ms/RandFlux. Figure 1