(33f) Optimization of Cathode Layer for Polymer Electrolyte Fuel Cells

We adopt an agglomerate catalyst layer (CL) model, and
recast it into a condensed form, for optimization of polymer electrolyte fuel
cell (PEFC) cathodes. This model captures the essential features in transport
processes within the gas diffusion layer (GDL) and accounts for chemical species,
proton, and electron transport processes along the CL width, as well as, transport
and reaction processes within an individual agglomerate particle in CL. Our reformulated
model possesses two limiting behaviors with simpler physics, the
pseuodo-homogenous model and a model with negligible polymer-electrolyte
membrane (PEM) film thickness agglomerates. The model equations are discretized
using a finite difference method and the resulting nonlinear program is linked
to a state-of-the-art interior point optimization algorithm, IPOPT [1].

Platinum (Pt) minimization for a specified cell current
density is performed, and optimal Pt distribution along CL width is obtained that
maximizes the current density by solving multi-zone partial differential equation-constrained
optimization problem. For special limiting cases, we have verified, both the
simulation and optimization results obtained by Secanell et al.[2,3]. Optimal
distribution of parameters was obtained along the CL width using IPOPT by
solving the 2^N partial differential equations-constrained
optimization problem. Our preliminary results show an exponential decay of Pt
mass along the CL width from CL-PEM to the CL-GDL interfaces. The decay rate depends
strongly on the current density of operation, and increases with current
density. We further examined optimal conditions for minimum Pt usage and intend
to generalize our analysis to multi-objective optimization for maximizing
current density and minimizing Pt amount simultaneously.

Our procedure provides a fast, robust, and efficient
solution methodology, which is suitable for system level optimization of PEFC
devices.

References:

1. Wächter A, Biegler LT. On the implementation of an interior-point filter line-search algorithm for large-scale nonlinear programming. Math Program. 2006;106:25-57.
2. Secanell M, Carnes B, Suleman A,  Djilali N. Numerical optimization of proton exchange membrane fuel cell cathodes. Electrochimica Acta. 2007;52:2668-2682.
3. Secanell M, Karan K, Suleman A,  Djilali N. Multi-variable optimization of PEMFC cathodes using an agglomerate model. Electrochimica Acta. 2007;52:6318-6337.