Electrochemical processing of discrete nanoparticle ions

High quality, purified nanoparticles are required for both fundamental scientific studies and technological applications in a variety of (hierarchical) functional materials. Carbon nanotubes are an archetypical nanoparticle with enormous promise if the remaining processing hurdles can be overcome. One recent route addresses this challenge by using chemical charging in metal-ammonia solutions to form "nanotubide" anions. Charging uniquely provides an approach to true thermodynamic equilibrium solutions of single walled nanotubes, and has proved to offer a means both to remove amorphous carbon and to separate metallic from semiconducting fractions; this technology has already been licensed commercially and is the subject of a new venture. However, having developed this methodology, we realised that the challenging alkali metal-ammonia solution can be avoided by using pure electrochemical charging. This approach represents an entirely new strategy for nanoparticle processing, through electrochemical dissolution and subsequent electrodeposition of discrete nanoparticle ions. We believe that the approach will be general and may be applicable to a variety of electrochemically stable, conductive nanoparticles, likely including noble metal systems, graphene, and some transition metal chalcogenides; it offers unrivalled control of charge density and chemical potential. The results raise fundamental scientific questions about the possibility of discrete nanoparticle electrochemistry and potential analogies to traditional atomic/ionic systems. They also suggest opportunities for new large scale manufacturing processes involving nanoparticles, particularly purification (fractionation), functional coatings or co-deposition of composites/hybrids. It is worth noting that many large scale industrial processes rely on electrochemical approaches, including the purification of copper, and electrowinning of aluminium. The nanoparticle ions themselves offer opportunities for further chemical reactions or assembly. As an example, nanotubide anions are reactive to electrophiles, offering a means to generate functionalised individual species in high yield. The ability to manipulate charge density and potential accurately, coupled with an understanding of the complex density of states of these materials, will allow this new chemistry to be understood, controlled and exploited.
In short, this project will explore a new direction: the scientific challenges and technological opportunities enabled by the formation of well-defined discrete ions through electrochemical processing.

This grant aims to exploit a recent discovery that nanoparticles can be dissolved electrochemically, in a manner analogous to smaller atomic or molecular ions. Whilst the phenomena of electron transfer, reduction/oxidation, and dissolution/deposition are similar, there are also differences relating to the nature of the band structure in nanoparticulate systems. It will drive forward both the understanding and the potential applications of the approach. The fundamental aspects will be of interest to physical chemists, electrochemists, and nanomaterials scientists, as they try to understand and characterise the basic phenomenology of these systems. The resulting nanoparticulate ions, represent an intriguing new class of polyelectrolytes or electrostatically-stabilised colloids, depending on the nature of the particle. As well as a scientific challenge, there is an opportunity to develop new manufacturing processes for preparing and modifying nanoparticles. Electrodeposition and other methods of charge-driven assembly will offer new means to prepare well-defined functional assemblies. Different systems will be explored to identify the range and variety of relevant systems. In the context of nanocarbons (especially nanotubes and graphenes), electrochemical processing is a particularly appealing means to isolate individual species without damage, which is normally challenging. The resulting ions, with well-defined chemical potential and charge density, provide a means for chemists to control and understand the nature of the reactivity of these species, which represent a complex family of molecular structures. The varying redox potentials of the dissolved species also suggests a convenient means to separate them without damage, and at large scale, a vital aspect for a wide range of applications including flexible electronics, solar cells, flat panel displays, sensors, and supercapacitors. Many of these applications offer societal benefits in terms of new functions, energy management, or environmental monitoring. Naturally, success commercial exploitation of these opportunities provides economic benefits. This New Directions grant will ensure that the currently world-leading knowledge and momentum in this new concept is maintained and developed to maximise its influence on both science and application.