It has long been recognized that shape and material composition directly influences function on the nanoscale. Moreover, there has been a consistent demand for the synthesis of complex nanostructures over the past few years due to new applications often relying on nanostructures' shapes in determining the material's chemical and physical properties. However, while the combined control of materials and shapes is the cornerstone of engineering and manufacturing at the nanoscale, these controls are still challenging to implement within one standard manufacturing method. The coil structure with three-dimensional helicity and periodicity is one of the topologies existing in many natural materials that can offer various exotic applications. In particular, nanoscale artificial coil manufacturing is pioneering new areas that have not been shown before in applications such as bio and energy fields. Their characteristics enable the unique physicochemical properties resulting from the shape as well as the existing qualities. Nevertheless, despite massive efforts, the process of realizing the nanoscale coil shape is indeed a complex matter, along with the limitation in its materials and shape. Therefore, the method for synthesizing nanocoils of various shapes and materials remains a problem to be actively resolved. In this study, we developed a strategy to synthesize hollow nanocoils using several electrochemical strategies throughout the entire process. After synthesizing a sacrificial CoFe nanocoil (NC) by an electrochemical method in a nanopore frame, the hollow reaction was carried out using an interfacial reaction at the solid-liquid interface in colloidal solutions. We designed an interfacial reaction at the solid-liquid interface to synthesize hollow nanocoils (HNCs) with various compositions and surface morphologies based on the control of galvanic exchange between the metal cations and the Kirkendall effect between the metal cations and phosphate anions. Metal precursors with different reduction pathways are converted into single or multi-component forms at the sacrificial CoFe NC interface. To show the application potential of hollow nanocoils, we combined Mn-based multi-component HNC with 4 nm-size Mn3O4 to increase the active site to increase the oxygen evolution reaction (OER) catalyst efficiency relative to consisting of only nanoparticles at neutral pH.

Electrochemical strategies for fabricating hollow nanocoils and their interfacial reactions in colloidal solution

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ACS Fall 2022

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