FIELD-DIRECTED FABRICATION OF HIERARCHICAL STRUCTURES TOWARD ELECTROCHEMICAL APPLICATIONS

Abstract

The ubiquity of hierarchical structures in nature indicates an inherent advantage to having morphological features comprised of multiple length scales. Such structures help maximize interfacial surface area, allowing for efficient chemical reactions and mass transport despite volumetric constraints. In electrochemical applications such as batteries, supercapacitors, electrolysis, fuel cells, catalysis etc. there is a similar necessity to maximize electrochemically active surface area to facilitate facile charge and mass transport. Inspired by examples in nature, this work seeks to develop scalable fabrication techniques to obtain hierarchically structured high-performance electrodes for electrochemical applications, with a focus on energy applications. Particular emphasis was laid on improving oxygen evolution reaction and hydrogen evolution reaction catalyst performance in alkaline electrolytic water splitting, an extremely promising technology for a sustainable clean energy future. Utilizing field-directed nanomaterial assembly techniques such as electrophoretic deposition, electrodeposition, and magnetophoresis, a variety of carbon nanotube, metal and mixed-metal hydroxide based hierarchical nanocomposites geared towards superior electrochemical performance were prepared. By virtue of the intimate attachment between various components within the deposits, synergistic performance enhancements could be exploited, greatly reducing water splitting overpotentials. Such high performance catalysts produced with earth abundant materials are critical to the large-scale viability of this technology. Additionally, these field-directed assembly techniques offer control over nanomaterial orientation in the deposits. Through rational choice of deposition technique, deposition parameters, and material selection, extreme surface wetting properties such as superhydrophobicity, superhydrophilicity, underwater superaerophobicity and superoleophobicity could be induced in some of the deposits. The ideas demonstrated in this work are broadly applicable toward the improvement of a variety of next generation electrochemical applications.