Hybrid molecular modeling and experimental study of structure and reaction kinetics at interface between electrode and polymer electrolyte phases

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0933393ZhouProject SummaryAlthough great efforts have been focused on developments of more effective and/or low cost electrocatalysts and polymer electrolytes for polymer electrolyte fuel cells (PEFC) in the last 30 years, the essential technical requirements for performance, durability, and cost have not been satisfied. One of the major barriers for PEFC technology is the very slow reaction kinetics and high activation polarization for the oxygen reduction reaction (ORR) at the cathode. The fact that the ORR exchange current density at the Pt/Nafion interface is about 3 orders of magnitude lower than that at the Pt/sulfuric acid interface suggests that the coupling between an electrocatalyst and an electrolyte is critical. This provides a perfect case for theoreticians to study and elucidate the mystery with respect to interfaces. Therefore, a unified approach is proposed to focus on the electrocatalyst/electrolyte couple rather than the electrocatalyst and polymer electrolyte separately. Intellectual Merits: The objectives of this research are to elucidate the fundamental mechanisms that cause the orders of magnitude differences in reaction kinetics between different electrocatalyst/electrolyte couples, and to establish a cost effective methodology for designing and computer-testing more effective and/or low cost electrocatalyst/electrolyte couples for PEFCs. To reach the objectives, a high throughput hybrid atomistic simulation methodology will be developed and it will be assisted by in situ X-ray absorption analysis to define the atomic structure or electric double layer (EDL) structures. This methodology will be used to evaluate the electrochemical charge transfer and polarization in ORR at the electrocatalysts/polymer electrolyte interface in contrast to the electrocatalysts/liquid electrolyte (e.g.H2SO4) interface. The unified approach in electrocatalyst and polymer electrolyte research is novel and has the potential to improve our understanding of the fundamental mechanisms of the EDL between an electrocatyst and a polymer electrolyte and the charge transfer characteristics. Furthermore, the proposed research will also promote the fundamental understanding of all other electrochemical systems that involve solid-state electrolytes, such as high performance lithium-ion batteries, photoelectrochemical cells, and supercapacitors. Broader impact: The proposed work will (1) enhance ongoing PhD research programs on PEFCs and solid-state supercapacitors by providing new tools of molecular modeling techniques to the study of energy conversion processes; (2) attract, encourage, and support outstanding undergraduate students to pursue a PhD study; (3) integrate the information on molecular simulation into curricula of the courses taught by the PI and Co-PI; (4) integrate the information into regular community education tasks; and (5) promote education of female and minority students.