Among the barriers to addressing oil security and greenhouse gas emissions are the cost and durability of fuel cells and batteries for alternative vehicles. Manufacturing and device models forecast that proton exchange membrane fuel cell (PEMFC) and lithium-ion (Li-ion) battery costs can be radically reduced with new electrode architectures having superior reactant transport properties. Presently, identifying optimal architectures is hampered by a lack of in situ measurements, limiting scientific understanding of the micro- and nano-scale coupling of electrochemistry and transport phenomena. To advance alternative vehicles and porous electrode science, in situ electrode diagnostics are needed to reveal limiting mechanisms, test theoretical models, and guide future designs.
The PI plans to establish micron-scale in situ analysis of porous electrodes using micro-structured electrode scaffold (MES) diagnostics and to apply them in advancing the science and engineering of fuel cell and battery electrodes. An MES is a multi-layer, planar substrate that surrounds a perpendicular column of electrode and contains spatially separated layers of thin-film sensing materials (e.g., Pt ultra-microelectrodes) that intersect the electrode?s side and extend to external instrumentation. The PI has some preliminary results, including the first spatially resolved measurements of ionic potential and oxygen within a PEMFC cathode. The planned education and outreach plan aims to recruit underrepresented groups into engineering and to prepare engineers for the expansion of electrochemical technology with vehicle electrification.
Intellectual merit: MES diagnostics are transformative in that they open the previously inaccessible electrode internals to direct in situ measurements. Existing diagnostics are not able to probe non-intrusively across the thickness of porous electrodes because the active layers are difficult to access and are very thin. In situ MES diagnostics allow representative through-plane transport; measure through-plane spatial distributions of potentials, currents, and concentrations; can achieve 1 micrometer resolution; and are broadly applicable. With MES diagnostics, the PI will address key scientific and engineering questions on coupling of transport and electrochemistry and the architecture of optimal electrodes, including: (1) identify and quantify the distinct transport resistances and degradation mechanisms in PEMFC electrodes, testing several hypotheses; (2) using functional through-plane grading and MES data, identify distributions of composition and structure that improve transport; (3) validate and advance leading agglomerate and pore-scale models; (4) identify new Pt-free electrode architectures that overcome the severe transport losses of current versions (if they become viable, Pt-free electrodes will radically alter fuel cell economics); (5) extend MES methods to Li-ion batteries to elucidate and minimize their cost-dictating transport resistances.
Broader impact: With their new measurement capabilities and broad applicability (e.g., to ultra-capacitors), MES methods will have impact on porous electrode research. The fuel cell and battery research addresses those challenges that support a wide range of future alternative vehicles to reduce oil reliance and emissions as well as supporting other key applications (e.g., renewable energy storage). The education and outreach plan?s key impacts are: (1) Preparing engineering students at Carnegie Mellon and beyond for future transitions to electrochemical power with a new ?breadboard? pedagogical approach and apparatus (BESA) that enhances education on energy systems and electrochemical devices with hands-on and project enhanced learning. A key emphasis is transferability to other institutions. (2) Recruiting underrepresented groups into engineering with interactive outreach activities with the portable BESA at community events and underserved schools and by ?What is Engineering?? workshops for teachers.
