Periodic Reporting for period 1 - GRAPHIL (Exploring the Interface Between Ionic Liquids and Graphene : Elucidating Structure and Electronic Properties)
Reporting period: 2016-03-01 to 2018-02-28
The principal objective of the research is to find out the detailed structure of ionic liquid (IL) thin films in contact with graphene and graphite using scanning probe microscopy. This research employs state of the art microscopy to unravel the interfacial structure of a series of ILs in order to understand the changes in the adsorbed ion layers as a function of change in the constituent ions. The fundamental information obtained from the microscopy measurements is employed to assess the influence of the interfacial structure of the ILs on graphene electronic structure by using Raman spectroscopy.
The main goal of the project is to understand the interface of the ionic liquids/graphene and its impact on electronic structure of graphene. The project has been executed according to the work packages and the following conclusions were made:
Nanostructure of the ionic liquids at IL/graphene interface largely depends on the nature of the anion. In the case of imidazolium-based ILs having large and weakly associating anions (Tf2N), cation dominates on the surface. In contrast to this, for imidazolium-based ionic liquids with small and strongly associating anions (BF4), both the ions (cation and anion) adsorb on to the surface. The major difference between the geometric organization of these ionic liquids at the interface can be rationalized by considering the size of both anions.
Impact of the nanostructure of the ionic liquids on graphene is also mostly governed by the type of anion present in ionic liquids. To some extent the cation also plays a mild role on electronic structure of graphene. Imidazolium-based ionic liquids with Tf2N anion could not alter the properties of graphene. However, non-aromatic pyrrolidinium cations having Tf2N anion show mild influence on graphene properties, specifically the longer alkyl chains present on the cation. The observed results can be rationalized by considering charge delocalization, which is more prominent in the case of the imidazolium cation than the pyrrolidinium. In contrast to these ionic liquids, imidazolium-based ionic liquids with BF4 anion have strong influence on the graphene electronic structure. The impact of BF4 ionic liquids gradually increases with increasing alkyl chain length on the imidazolium cation. In other words, significant influence has been observed in the case of longer alkyl chains present on the imidazolium cation.
In totality, the execution of the project has provided the fundamental information on IL/graphene interface and its impact on electronic structure of graphene. This project report is one of the first steps in developing comprehensive fundamental understanding of IL/graphene interface which will be potentially useful for improving the capacitance of graphene-based supercapacitors.
Exploitation and dissemination of results:
The findings which are obtained during the project will be disseminated through various activities. For instance, publications in peer-reviewed journals, through conferences and outreach activities such as Re@ct and Open day at University. The aim of the Re@ct is to inform students about the opportunities that a research career may provide them in the future, to promote research careers among youngsters and dispel stereotypes about researchers and research. Open day at University is a unique opportunity to give the general public a flavor on what we are doing in our laboratories in the Department of Chemistry. In addition, for us it is also an occasion to have a look at the activities of colleagues in other departments.
The fundamental information attained from this project is valuable for manipulating the properties of IL/graphene composites. Essentially, the insight gained from this research is valuable in the engineering of interface structures, which in turn will provide a better handle on the efficiency of energy storage devices derived from these materials. Knowledge of the interfacial structure of ionic liquids on graphene is further helpful for tuning the work function of graphene. In other words, ionic liquids have a significant effect on the density of states of graphene which in turn affects the capacitance of supercapacitors.
Apart from the above-mentioned, ionic liquids also have other exceptional physicochemical properties such as non-flammable and high thermal stability. These properties further make them suitable electrolytes for batteries. For instance, Lithium-ion batteries are widely using in variety of electronic devices. However, their implementation for energy storage and in vehicle applications has been slowed by safety concerns surrounding the use of large-scale lithium cells. Undesired reactions between the battery components and the liquid organic electrolyte, triggered by unpredictable events such as short circuits or local overheating, lead to an exothermic reaction of the electrolyte with the electrode materials, producing a rapid increase of the battery temperature and, eventually, to fire or explosion. The unique properties of ionic liquids may help to solve the problem as they are practically non-flammable, which is a significant safety asset. The replacement of the conventional, flammable and volatile, organic solutions with ionic-liquid-based, lithiumion- conducting electrolytes may greatly reduce, if not prevent, the risk of thermal runaway.