Connectivity and ION Conductions in Fuel Cell Membranes Probed by Tunneling Atomic Force Microscopy

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, and co-funding from the Polymers Program in the Division of Materials Research, Professor Steven Buratto and his group at University of California-Santa Barbara are utilizing conductive atomic force microscopy (c-AFM) to image ion conductance and pore connectivity in proton exchange membranes (PEM) used in PEM fuel cells on a nanometer length scale and at the level of a single pore channel. PEM fuel cells, which convert chemical energy into electricity using an electrochemical cell, can be used as efficient power sources, offering high power density and low environmental impact. Critical to fuel cell performance is the polymer electrolyte membrane, which is an efficient proton conductor but an electric insulator. A detailed understanding of proton conduction, in terms of the size and distribution of the chemical domains responsible for transport, is crucial to both a complete understanding of fuel cell performance and a systematic approach to improving the performance. To this end, c-AFM will be used to correlate phase and current images taken on an operating half fuel cell and determine the fraction of electrochemically-active aqueous surface domains. The PI and his group will also image the nanoscale domain morphology and connectivity as a function of (1) the environmental conditions that more accurately reflect those of an operating fuel cell such as high temperature and low relative humidity, (2) the membrane type and composition, and (3) the proximity of the catalyst particles to the ion channels. The results of these experiments will be used to gain a fundamental understanding of ion conductance in PEM fuel cells and provide inspiration and insight into the development of the next-generation membranes materials.The possibility of producing power with efficiency greater than internal combustion engines, and with environmentally benign byproducts, makes fuel cells an important player in the field of alternative energy and sustainability, especially if the reactants are derived from renewable resources. Students working on this project will be exposed to this alternative source of power, help optimize industrial processes that produce polyelectrolyte membranes, and provide important insight into the discovery of new membrane materials. In addition, students will be trained in state-of-the-art scanned probe microscopy and nano-characterization techniques. Researchers supported by this grant (including PIs) will also be active in outreach to K-12 schools in the Santa Barbara area. Researchers working on this project also plan to develop a demonstration of an operating fuel cell that will be included in the currently active outreach program in the chemistry department here at UCSB. In addition, they will visit high schools in the Santa Barbara and Ventura Counties three times per year to discuss their research and its impact as well as to promote science education.