The role of electrolyte/cathode interfacial structure on performance of proton exchange membrane fuel cells

Proton exchange membrane fuel cells are an alternative energy conversion device that may efficiently convert chemical energy to electrical energy for use as motive power in transportation applications. Inefficiencies in these devices are associated with the energetics of specific chemical processes and constrain their performance. The current state-of-the-art devices can not simultaneously meet efficiency, power output, cost, and durability targets. A majority of the performance losses are allocated to processes at the oxygen reduction cathode, where power/efficiency losses, non-optimum utilization of expensive platinum catalyst, and sensitivity to the reactant oxygen stream relative humidity challenge the development of practical devices. These losses can, in part, be attributed to imperfect design of the Pt catalyst particle-polymer electrolyte interface. However, current attempts to improve the design of this interface are limited by a lack of fundamental understanding of its role in dictating device performance. The complexity inherent in this interface and the need to characterize it under operating conditions limit the ability of experimental techniques to link interfacial structure to PEMFC performance.

Intellectual Merit: The research objectives of the proposed work are to (1) appropriately model the membrane/cathode electrocatalytic interface in a proton exchange membrane fuel cell (PEMFC) using both molecular dynamics and quantum-mechanical methods; (2) to describe the influence of humidity and electrochemical potential on the structure of this interface and on oxygen reduction reaction kinetics; and (3) to estimate the losses in PEMFC performance due to a non-ideal electrolyte/electrode interfacial structure. A propose multi-scaled, integrated molecular modeling approach to understand the influence of electrode/electrolyte interfacial structure on oxygen reduction reaction rates is proposed. Molecular dynamics (MD) will be used to probe the structure of this interface as a function of electrode potential and hydration. Quantum-mechanical (QM) methods will be used to quantify the dependence of the elementary oxygen reduction reaction kinetics on this interfacial structure. Method advances in both the application of MD and QM methods to the electrochemical interface will be developed. Collectively, these methods will establish the rate of reaction as a function of hydration and electrode potential, which is directly linked to the PEMFC efficiency and power output. Therefore, the structure of this interface can be linked to PEMFC performance losses thus providing the fundamental structure-performance relationships needed to improve device design.

Broader Impact: The proposed work will (1) integrate research efforts in the molecular modeling of energy conversion devices currently concentrating separately on membrane materials and electrode design by probing the interface between these components; (2) enhance ongoing research by training graduate students in the application of molecular modeling techniques to the study of energy conversion processes; and (3) to extend this training beyond the perspective research groups through the development of an advanced course in this area; to involve undergraduates from under-represented groups in research using molecular modeling techniques early in their collegiate careers . An advanced course in molecular modeling emphasizing energy applications will be developed. The modules developed for this course will be made available and publicized to the technical community. Graduate student researchers will receive advanced technical training with additional emphasis on the effective communication of research results. Additionally, components of the proposed study will be offered as research projects through established Penn State programs to recruit and motivate women and minority undergraduate students towards research careers utilizing computational techniques.