2021 Annual Meeting

(164v) Molecular Dynamics Simulation of Nafion Configurations to Improve O2 Transport

Authors

Wang, X. - Presenter, Rose-Hulman Institute of Technology
Fuel cell technology is key to the advancement of a sustainable energy economy. Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are particularly promising. Its relatively high power density and low cost makes the PEMFC an ideal candidate for small applications, such as transportation, backup power units and distributed power generation. PEMFCs rely on an ion-conductive polymer to facilitate energy-producing electrochemical reactions. This ion-conductive polymer is known colloquially as an ionomer, and serves manifold purposes in the PEMFC, including ion transport from anode to cathode, and oxygen transport to the surface of platinum coated catalyst particles. The focus of this research is the latter, and considers what structural modifications can be made to a production ionomer (Nafion) to improve oxygen transport.

Findings indicate that oxygen transport is hindered by a high-density ionomer layer which forms at the surface of the catalyst particle. The formation of this layer is due to the adsorption of charged species on the ionomer to platinum particles on the catalyst surface. Structural modification of the ionomer is the most obvious way to mitigate this problem. The design space of such modified ionomers is too large to be thoroughly examined through experiments, so computer simulation techniques are used. Here, it makes the most sense to use the time-dependent Molecular Dynamics (MD) technique, given that oxygen transport is time dependent.

Preliminary MD simulations indicate that bulky dioxolane groups on the ionomer main chain, in conjunction with shorter side-chains (the chain which connects charged species to the ionomer backbone), result in lower density at the ionomer-catalyst interface. Further simulations will clarify whether this lower density corresponds to improved oxygen transport. Should these modifications correspond to an improvement in oxygen transport, use of the modified ionomer in PEMFCs would likely result in dramatically improved reaction dynamics at the catalyst surface. This could yield more durable, higher output fuel cells.