(3u) Probing Interfacial Phenomena in Electrochemical Energy Devices

Interfaces are a critical component in electrochemical energy devices. Charge transfer and species transport/adsorption occur at electrode surfaces, processes which determine device performance. These processes are modulated by local interfacial phenomena: electrolyte breakdown during device operation to form a Solid Electrolyte Interface (SEI) in batteries, charged polymer adsorption to (and subsequent poisoning of) catalyst particles under applied potential in fuel cells, and spontaneous self-assembly of polymer/particle agglomerates in solution during slurry fabrication of electrodes are just three examples of the myriad ways in which interfacial phenomena control performance, structure, and operation of energy devices. Importantly, the electrode/electrolyte interface behavior is intimately tied to the chemical and physical identity of each constituent, rendering study of these interfaces complex, and thus, much remains unknown. I plan to focus my future career (first a postdoctoral position, followed by tenure-track faculty) on understanding these interfaces. For a postdoc appointment, I am seeking positions that would widen my experimental and theoretical capabilities and understanding of interfacial phenomena and colloidal science. The work would preferably have applications in electrochemical devices, but I am open to exploring other systems.

Research Experiences

My combination of interests in electrochemical energy technologies and interfacial phenomena led me to my graduate work in the Department of Chemical & Biomolecular Engineering at the University of California, Berkeley, where I am co-advised by Dr. Adam Weber (Lawrence Berkeley National Lab) and Professor Bryan McCloskey. My work focuses on understanding, predicting, and controlling hydrogen fuel-cell electrode structure. Fuel cells are promising energy conversion devices, but their economic feasibility is hampered by the prohibitively high cost of the electrodes (referred to as catalyst layers, CLs), and inefficiencies associated with them (transport resistances, underutilized platinum, etc.) The CLs are heterogeneous porous electrodes consisting of agglomerates of catalyst particles (platinum supported on carbon), bound with ion-conducting polymer (ionomer), separated by void space. An ideal CL maximizes the intersection of pore space necessary for gas transport, ionomer required for ion transport, and catalyst particles requisite for electron transport. While there have been significant advances in understanding structure-property relationships in CLs, there is considerably less effort focused on how to control and direct specific structures that would enabled optimized performance. Studies of the CL formation process have been almost entirely empirical, with little insights into the forces governing morphology. Therefore, my work aims to address this: by probing and understanding the interactions within the ink (dispersions of particles, ionomer, and solvent) from which these CLs are made, we can learn how and why specific structures and interfaces form, enabling control of the CL morphology and ionomer/particle interactions.

Using a variety of techniques, including light and x-ray scattering, electron microscopy, calorimetry, rheology, and quartz-crystal microbalance, I systematically study the interactions that control the complex multi-component phenomena in the ink. Over the past four years, I have had several projects that have explored different facets of these interactions. I’ve elucidated

• how solvent controls ionomer solution conformation and acidity
• how age and temperature alter conformation
• how this changing conformation modulates the way the ionomer adsorbs to surfaces
• the degree to which ionomer interacts with platinum versus carbon surfaces, and how surface modification of the catalyst particle (and varying platinum) content affect adsorption
• how all these parameters come together to affect agglomerate formation, size, and stability

I have also looked at a variety of ionomer and catalyst types that extend applicability of this work beyond traditional proton exchange membrane (PEM) fuel cell systems: experimental ionomer chemistries, alkaline ionomers, and catalyst particles used in electrolyzer systems. In addition to my experimental projects, I am working

• with Professor Clayton Radke to develop a theory to better analyze data of heterogeneous adsorbed polymer/solvent films obtained by quartz crystal microbalance with dissipation
• to extend Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory to account for critical interactions (hydrophobic, electrostatic, solvent-induced conformational changes, etc.) to model aggregation behavior in these ink systems

Ultimately, this work lends crucial insights in how we can engineer inks to control CL structures.

Prior to starting graduate school, my interests in electrochemistry were fostered during my four years working as an undergraduate researcher in Professor Alan West’s lab at Columbia University. In the Fall of my first year, I began work on a joint project with Scott Banta’s lab, developing a coupled electro-biochemical reactor. The Banta group was engineering A. ferooxidans, an iron-oxidizing bacteria, to use carbon fixed from atmospheric CO₂ to produce fuels and chemicals. By my second year I was independently responsible for the electrochemistry side of the project, while working with the much larger bio-side team. I designed and built an electrochemical reactor to reduce the oxidized iron growth media, and designed the pump system to enable continuous, closed-loop operation of the two reactors. To gain more experience, after two years I switched projects to research polarity-reversal charging protocols, with the aim of recovering capacity in spent lead-acid batteries. This work involved a combination of electrochemical techniques (battery cycling, electrochemical impedance spectroscopy) and material characterization (electron microscopy, x-ray diffraction).

My research experiences have given me a strong foundation in electrochemical engineering, colloidal science, and interfacial phenomena, and I am eager to enhance my skillset during a postdoctoral appointment.