Electrochemical processing of discrete nanoparticle ions

Lead Research Organisation: Imperial College London
Department Name: Dept of Chemistry

Abstract

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.

Planned Impact

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.

Publications

10 25 50
 
Description The fundamental understanding of nanotube and other nanocarbon anions, their solubility and chemical reactivity, was developed. These highly unusual species are both molecularly specific and have a complex, continuum density of states. The charge density on the nanoion species was found to be controlled by (electro)chemical potential leading to complicated selective dissolution and precipitation behaviours, combining the effects of the density of states and polyelectrolyte phenomenology. In addition, the degree of charging was found to control reactivity, and was related to redox potential of reagents. Electrochemical dissolution of undamaged / unfunctionalised graphene was found to be challenging but routes to functionalised dispersions were established. As well as negatively charged 'nanotubide' anions, positively charged 'nanotubium' cations can be prepared and manipulated. The discharge of these nanoion species was controlled using a variety of metallic and organic species, providing means to prepare grafted nanocarbons, functional hybrids, and to remove the excess charge without functionalization. These reactions also illustrate the unusual fundamental chemistry of these systems.
Exploitation Route The theory of nanoions / giant polyelectrolytes will benefit from further experimental and computational studies, to understand the nature of charging and solvation. A wide range of applications are possible for true solutions of undamaged/unfunctionalised nanomaterials. Nanotubides and other nanocarbons species are immediately useful for transparent conductors to replace ITO, as well as other thin film electronics applications, electrochemical electrodes (fuel cells, supercapacitors, etc), catalyst supports, etc. Charged nanocarbons are also effective for producing individualised functionalised species, relevant to many applications from composites to protein nucleants. Many of these opportunities are under development. More recently, related strategies have been applied to analogous systems with a range of compositions, although in many cases the changes are more localised; nevertheless, new theory is still required.
Sectors Aerospace, Defence and Marine,Chemicals,Electronics,Energy,Environment,Pharmaceuticals and Medical Biotechnology,Transport

 
Description The understanding of reductively charged nanocarbons, investigated during this grant, supported the launch of a commercial product targeted at the electronics industry in 2013. Further developments of the technology are anticipated.
First Year Of Impact 2013
Sector Chemicals,Electronics
 
Description Linde 
Organisation Linde Group
Country Global 
Sector Private 
PI Contribution Developed a technology in partnership and licensed to the company
Collaborator Contribution Technical discussion, hiring a group member, supplying samples and information
Impact Licensed technology and product release.
 
Description Thomas Swan and Co Ltd 
Organisation Thomas Swan and Co Ltd
Country United Kingdom 
Sector Private 
PI Contribution Long standing partnership developing technology and licensing it
Collaborator Contribution Development of synthesis and processing routes relevant to new company products. Advice and discussion. CASE studentships (3)
Impact New nanomaterials products.
 
Title PREPARATION OF FUNCTIONALISED MATERIALS 
Description New method to dissolve / functionalise nanotubes and graphene using charge 
IP Reference WO2015071441 
Protection Patent application published
Year Protection Granted 2015
Licensed Yes
Impact .
 
Title Purification method 
Description Purification of nanomaterials using a chemical charging method 
IP Reference WO2012131294 
Protection Patent granted
Year Protection Granted 2013
Licensed Yes
Impact .