Grantee Research Project Results
A Method for Through-Plane Measurement of Species Concentration in Porous Electrodes for Fuel Cells and BatteriesEPA Grant Number: FP917154
Title: A Method for Through-Plane Measurement of Species Concentration in Porous Electrodes for Fuel Cells and Batteries
Investigators: Epting, William K.
Institution: Carnegie Mellon University
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2010 through August 31, 2013
RFA: STAR Graduate Fellowships (2010) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Science & Technology for Sustainability: Energy
Polymer electrolyte membrane (PEM) fuel cells and lithium-ion (Li-ion) batteries, backed by a sustainable energy infrastructure, present an opportunity for a transportation sector free of harmful emissions and the volatility of the global oil market. However, through-plane mass transport issues in the porous electrodes of both PEM fuel cells and Li-ion batteries remain a substantial hurdle to bring the costs of these technologies to market-ready levels. This research aims to experimentally characterize mass transport through the thickness of these porous electrodes, fundamentally enhancing the understanding of mass transport limitations, reaction kinetics, and degradation mechanisms. The data will also be applied to properly validate theoretical electrode models.
This work addresses the fundamental understanding of chemical transport in the reaction zones of fuel cells and batteries. Improvements in these technologies could drastically reduce vehicle emissions. For example, understanding how oxygen travels in a fuel cell electrode will guide the design of lower cost fuel cells. This work uses a micro-scale electrochemical approach to take measurements in electrodes. Key findings will be analyses of reactions and degradation, and validation of theoretical models.
This research will use a micro-structured electrode scaffold (MES) to measure the concentration of reactive chemical species at discrete intervals through the thickness of a porous electrode—a measurement that has not been previously demonstrated. The MES allows layers of sensing electrodes to come into contact with the porous electrode from the side. The sub-micron thick sensing layers are employed as ultra-microelectrodes to perform electroanalytical concentration-sensing techniques, such as pulsed amperometric detection. The MES concept will initially be applied to PEM fuel cells and later to Li-ion batteries as well as battery chemistries for grid-scale renewable energy storage.
At high fuel cell operating currents, the oxygen reactant concentration distribution in the cathode is expected to shift towards the gas diffusion layer (where the oxygen enters the electrode) and away from the electrolyte membrane. The distributions will be compared with predictions from porous electrode models, providing a measure of model accuracy and directions for improving the relevant theory. The technique will be used to elucidate the effect of concentration distribution on the evaluation of reaction kinetics parameters. Measurements of degradation species, such as hydrogen peroxide in PEM fuel cells, will enhance fundamental understanding of the degradation processes that are responsible for PEM fuel cells not reaching durability targets. These measurements are particularly important in next-generation electrodes using inexpensive non-platinum-group-metal catalysts, as mass transport and degradation are particularly troublesome issues in such electrodes. In Li-ion batteries, enhanced understanding of reactant transport will guide the design of thick electrodes with high energy density and power density.
Potential to Further Environmental/Human Health Protection
As the U.S. depends almost entirely on oil for transportation, that sector accounts for nearly a third of U.S. CO2 emissions, and gives rise to local pollution issues and foreign oil dependence. Widespread adoption of electric vehicles using any combination of PEM fuel cells and Li-ion batteries would cut transportation sector CO2 emissions dramatically, and almost completely if they are backed by sustainably generated electricity and hydrogen. Furthermore, local pollution from automobile traffic leads to health issues in high population areas—an issue that will be mitigated by the zero tailpipe emissions of fuel cell and battery electric vehicles.