Materials Design Advanced Graduate Research Prize winner

Christopher Rochester wins the Materials Design Advanced Graduate Research Prize

From the start, Christopher Rochester showed himself an excellent PhD student: engaged, enthusiastic, eager to learn, interested not only in theory per se but in deep understanding of experiments, keen to explore new methods for solving the set problems. It was great pleasure for both of us to work with him as a junior colleague, rather than a student. But over the last year Chris has grown up considerably: if before it was about solving the set tasks, now he himself formulates the tasks and finds new ways for solving them. To the benefit of the joint research, Chris has become an independent, critical (and sceptical) collaborator who uses his own academic judgement to make strategic decisions and to steer the project.

Chris’s progress in his PhD was initially hampered by a number of mathematical difficulties that the model he was developing contained. However, these have since been overcome and Chris’s output has significantly increased attributed to the effort and time afforded by Chris to his work.

Chris is now able to generate new ideas and develop interesting and relevant directions to his work with little guidance. Since his Early Stage Assessment, Chris was first author on a paper published in ChemPhysChem on the electrostatic interactions between ions inside conducting nanopores. This work did not pass unnoticed: it has been recently verified and approved by DFT calculations carried out in Prof. W. Schmickler’s group in the University of Ulm, Germany. Since then Chris has completed further work to form two other articles, on the first of which he is currently working.

This paper will describe a model of electrode swelling in supercapacitors. This is practically a very important problem, because the unwanted ‘electroactuation’ or ‘breathing’ of the electrodes damages the supercapacitors. The way it is described in Chris’s work is very elegant, based on advanced analytical models of statistical mechanics (essentially mapped on some sophisticated versions of the Ising model). His work is a wonderful example of exploiting advanced analytical techniques to understand a puzzling phenomenon, which is the result of an interplay of interactions not easily disentangled. Competing electronic, steric effects, electrostatic, and elastic effects are considered and a mechanism of competition is proposed to explain why decreasing the size of the nanoscale pores in the electrode, causes its greater macroscopic deformation, as the supercapacitor is charged. The results are in good agreement with experimental data obtained in Volker Presser’s group in Saarbrucken.

The second paper will describe the differential capacitance of a supercapacitor with electrodes formed from ultra narrow pores when charged with cations and anions of different sizes, which is the reality when the electrolyte used is a room temperature ionic liquid.  The results will capitalize on the same formalism developed in the first paper, but it will also extend the model to the case of pores with variable ionophilicity, which currently poses a great challenge in energy storage material science, as it can dramatically improve energy storage in supercapacitors. Here Chris moves from Ising-like models to an extension of a three state Blum-Emery-Griffith model; Chris himself found that this is doable, and this will be a very valuable contribution to this research area. These results will be ahead of experiments, and will stimulate novel experimental work; if confirmed experimentally, they will be highly cited.

Chris has presented, quite successfully, talks about  different parts of his research at international workshops in Estonia, Paris, Cambridge and London and has started to build his own collaborations, directly interacting with experimentalists.

Alexei Kornyshev and Gunnar Pruessner