(168b) Session Keynote: Gas-Transport Limitations in Electrochemical Energy-Conversion Technologies

The issue of transport phenomena is omnipresent in various electrochemical energy-conversion technologies. There is a need to understand and optimize the various means for products and reactants, whether gas, liquid, or ions to get to and away from the reaction sites. Such transport often results in concentration polarization and ohmic effects in various electrochemical cells. Mathematical modeling and advanced diagnostics are ideally suited to elucidate and explore the impacts of transport phenomena on device performance.

In this talk, we will discuss current research questions and issues related to transport phenomena in various electrochemical energy-conversion technologies including solar fuel generators, polymer-electrolyte fuel cells, and redox flow batteries. These various technologies share very similar architectures of typically ion-conducting polymer membranes sandwiched between thin catalyst layers that are porous electrodes. Key in many of these technologies is the need to get the reactant gas to the reaction site within the porous electrodes. In this respect, two main technologies will be explored, namely, vapor-fed solar-fuel generators and polymer-electrolyte fuel cells. If time permits, exploration of ion transport and selectivity in redox flow batteries will be discussed.

For polymer-electrolyte fuel cells, the drive to decrease the amount of active catalyst has resulted in additional, unexpected mass-transport losses to the reaction site. It is believed that these losses are due to gas transport through the ionomer film covering the particles. In this talk, we will discuss measurement at limiting current of these resistances as well as the associated ionomer film morphology to help shed the light on this issue.

For solar-fuel generators, the need to remove the inherent carbon-dioxide transport and solubility issues drives the exploration of gas-diffusion electrodes. In this talk, we will explore how the various transport limitations come into play and how the structure of electrode dictates product selection and yield.

Acknowledgement

This work was funded by the Department of Energy under contract number DE-AC02-05CH11231.