Mitigating Electrode Deactivation Through Microstructural Design
- Author(s): McDevitt, Kyle McAnulty
- Advisor(s): Mohraz, Ali
- Mumm, Daniel R
- et al.
Increasing demands for energy storage and conversion has fueled research and development of next-generation electrochemical devices, including batteries, supercapacitors, and catalysts. Viability of technology beyond the proof-of-concept is dependent on the morphology and topology of the electrode, which should be carefully designed to maximize material utilization during operation. Despite the close relationship between microstructure and operational efficiency, there does not currently exist a single configuration that can be broadly applied across electrochemically active materials. The ideal microstructure is expected to have co-continuous and interpenetrating domains that have high interfacial area and present minimal resistance to ionic and electronic transport.
In the following dissertation, I present a technique to create such a structure through bicontinuous interfacially jammed emulsion gels (bijels), which are generated via spinodal decomposition and therefore confer characteristic microstructural qualities to derivative materials. Domain size distribution, interfacial curvature, tortuosity, and self-similarity are discussed in detail and compared quantitatively to alternative microstructures that have been proposed for electrochemical devices. These qualities are shown to influence material utilization in two specific applications, energy storage in zinc electrodes, and electrocatalytic water splitting for hydrogen generation.
Maintaining electronic conductivity in electrodes has been shown previously to delay capacity loss during repeated charge-discharge cycling. In the case of zinc anodes, converting the metallic material to the semiconducting zinc oxide creates heterogeneities in current distribution that inspire material reconfiguration and premature cell failure. Spinodal-like electrodes mitigate these effects by improving electronic accessibility of the active material and maintaining conduction pathways to a high degree of discharge compared to electrodes built with randomly sized features.
Homogeneous activity and co-continuity in an electrode are also advantageous in the electrocatalytic separation of water into constituent hydrogen and oxygen gases. Product desorption from the electrode is necessary to continue the reaction, but microstructural impediments to efficient removal result in the underutilization of active surfaces. Bijel templated electrodes improve gas transport through the same microstructural qualities discussed above and are shown to reduce energy losses associated with this inefficiency.