The development of Li-O2 batteries is being hampered by lack of understanding of the complexity of products formed on the air-cathode during reduction and oxidation. Spectroscopy is critical for identification of products and the understanding of the chemistry at the interface of electrodes. Moreover advanced in situ spectroelectrochemical techniques help us to comprehend these complex interfaces whilst under full electrochemical control. The goal of our work is to enable the uptake of this technology by fully understanding the reduction and oxidation pathways taking place in Li-O2 batteries.
Fundamental studies of dioxygen electrochemistry commonly require conductive supporting salts, such as tetraalkylammonium (TAA), to sustain redox processes in nonaqueous electrolytes. Electrochemical analysis of the formation and oxidation of superoxide on planar electrodes has shown a decrease in reversibility and lowering of the oxygen reduction rate constant when TAA cation alkyl chain length is increased. Probing interfacial regions on Au using in situ surface enhanced Raman spectroscopy (SERS) provides evidence that this is caused by the changing adsorption characteristics of TAA cations under negative potentials. These effects are heightened with longer alkyl chain lengths, therefore reducing the reversibility of superoxide formation and dioxygen evolution. From these observations it can be established that shorter chain TAA cations while retaining necessary conductive support: (1) enhance reversibility and rate of superoxide formation and oxidation and (2) for in situ SERS, have lower preference for adsorption, thus improving experimental detection of superoxide at the Au electrode interface.
Reorientation of Tetra-Alkyl Ammonium Ions at the Electrode Interface at ORR
Further reading: I.M. Aldous, L.J. Hardwick J. Phys. Chem. Lett. 5 (2014) 3924
Electrochemical and In Situ Studies of Electrode Interfaces
Spectroscopy is critical for identification of products and the understanding of the chemistry at the interface of electrodes. Moreover advanced in situ spectroelectrochemical techniques help us to comprehend these complex interfaces whilst under full electrochemical control. The group is active in the development of in situ Raman and IR techniques in partnership with Prof. Richard Nichols (Chemistry), as well as in situ synchrontron X-ray techniques in collaboration with Prof. Christopher Lucas (Physics).
Peled Model of the Solid Electrolyte Interphase: The solid electrolyte interphase is a complicated mixture of interfaces of inorganic and organic components created from reduction of electrolyte. It is electronically insulating, but ionic conducting, thus allowing the passage of Li+ ions. Its stability is crucial for the operation of the Li-ion battery.
Utilisation of Graphene-Enabled Materials in Batteries and Supercapacitors
Graphene is a one-atom-thick sheet of carbon atoms arranged in a honeycomb lattice. The exceptional physical properties of graphene have attracted enormous interest since its experimental isolation and initial characterisation in 2004, notably its intrinsically high surface area and its unique electronic properties, as manifested by its high conductivity. Amongst the myriad applications foreseen for this material, exploitation in electrochemical energy storage with supercapacitors or batteries ranks as one of the most prominent.
There are considerable challenges to be addressed en route to incorporating graphene into these energy storage devices, however, two specific problems, apparent in much of the vast body of recent work on graphene and energy storage, are:
The "graphene" is generally poor quality and variable dimensions.
- Frequently only minimal effort is made to control the architecture of the graphene in the resultant device.
We are actively collaborating with partners at the University of Manchester and at NTHU Taiwan to address these challenges.
Batteries for Stationary Energy Storage
Energy storage will become crucial for the smoothing out of supply and demand, allowing for a less centralised grid.
We are keenly researching battery materials, such as Li-ion and Na/MCl2 (or ZEBRA) chemistries, for stationary energy storage applications.