Dr Xiao Hua and PhD student Matthew Leesmith of Lancaster’s Chemistry Department have been working alongside colleagues at the University of Cambridge in order to develop supercapacitor technologies with greater energy storage. The results of their most recent experiments – published in the journal Science – have led to the discovery that supercapacitors with a “messier” carbon structure have a significantly higher capacity to store energy than those with a neater or more “ordered” carbon structure.

An emerging technology, supercapacitors were first conceptualised in the 1970s as an alternative to lithium-ion batteries, storing energy electrostatically rather than through chemical reactions. They are comprised of a surface area of electrodes (typically made of carbon) soaked in electrolytes. These electrolytes – substances that are naturally positively or negatively charged when dissolved in water – generate an electric field whilst the superconductor is charging, which is then released through a circuit as a current of electricity when discharged.

Supercapacitors are more thermally-stable than their lithium-ion counterparts, last longer, and are faster at charging and discharging their energy than standard batteries. However, the problem of capacitance has long been an issue for supercapacitors, with their ability to store energy being severely limited when compared to batteries, making it difficult for them to be used in electric vehicles and similar applications.

The teams at Lancaster and Cambridge have therefore been investigating ways that the carbon structures used in supercapacitors could be modified in order to allow them to increase their storage. Until recently, the vast majority of research into supercapacitors has been focused on the impact of the porosity of the carbon on capacitance, but NMR spectroscopies carried out on carbon-based electrodes at Cambridge found a lack of correlation between the size of pores and the energy capacitance of the supercapacitors.

The Lancaster team therefore performed a cutting-edge technique called pair distribution function (PDF) via a laboratory X-ray scattering facility that was recently established in the Electrochemistry and Surfaces research group. Using this technique, they were able to probe an average atomic structure of a given carbon electrode and evaluate its degree of "disorder" to assist the Cambridge team's NMR result. They found that it was the degree of deviance from a regular crystalline structure within the carbon – rather than just pore size – that was a bigger factor in the storage ability of the supercapacitor.

On the findings, Dr Xiao Hua said: “With respect to this paper, what is important about that work is that it provides a new direction for materials scientists to develop mesoporous carbon with higher capacitance. As a supercapacitor electrode, the atomic structure of mesoporous carbon remains a challenge to characterize due to an ambiguity in defining its atomic structure order and disorder - to say it in another way "the degree and nature of messiness". This paper suggests that the structure "disorder" or "messiness" of mesoporous carbon likely plays a more critical role than previously believed. In turn, it means that a strategic design of future carbon electrodes should have an emphasis on structure disorder.”