Theory and simulation of electrified interfaces

Professor Wolfgang Schmickler

ULM university, Germany

Professor Alexei Kornyshev

Imperial College London

Thursday 9th May 2019
Time: 4pm
Venue: Room G20, Royal School of Mines, Imperial College London
Contact: Ms Hafiza Bibi
Tel: 020 7594 7252

Ions in electrochemical nanostructures

Wolfgang Schmickler

In this ongoing project, we investigate the properties of ensembles of simple ions in thin nanotubes and -slits by a combination of density functional theory (DFT), statistical mechanics, and grand-canonical Monte Carlo. If we place alkali or halide atoms into these structures and run a DFT program the atoms become ionized, and the transferred charge resides as image charge on the walls. For nanotubes the electrostatic interactions can be characterized by the e ective image radius, which is the radius of a perfect metallic conductor which would yield the same distribution of the electrostatic potentials; for nanoslits an e ective image plane is used instead. These concepts make it possible to construct e ective Hamiltonians for ensembles of ions, which are solely based on DFT. In the corresponding grand- canonical ensemble both the electrode potential and the charge are well de ned. On this basis we investigate the storage of ions in nanostructures, calculate the ionic densities and the corresponding capacities as a function of the electrode potential. We compare our results with those of other researchers who have used classical DFT or Ising models.
An intriguing question is, if ions interact across the walls of carbon nanotubes. Un- expectedly, a Li+ ion placed inside a semiconducting carbon nanotube and a Li+ placed outside attract each other. This e ect is caused by the unique band structures of the tubes and a shift of the Fermi level caused by the presence of the ions. The e ect persists for conducting carbon tubes, but is noticeably smaller; it disappears for gold tubes.

L. Mohammadzadeh, A. Goduljan, F. Juarez, P. Quaino, E. Santos, W. Schmickler, On the energetics of ions in carbon and gold nanotubes, ChemPhysChem 17 (2016) 78.

W. Schmickler, A simple model for charge storage in a nanotube, Electrochim. Acta 173 (2015) 91.
W. Schmickler and D. Henderson, On the capacitance of narrow nanotubes, Phys. Chem. Chem. Phys., 19 (2017) 20393
F. Juarez, F. Dominguez-Flores, A. Goduljan, L. Mohammedzadeh, E. Santos, W. Schmickler, Defying Coulomb's law: A lattice-induced attraction between lithium ions. Carbon 139 (2018) 808.

Wolfgang Schmickler is Professor Emeritus at the Depart-ment of Theoretical Chemistry in Ulm and corresponding scientist of CONICET, Argentina. A theoretical physicist by training, he was introduced into electrochemistry by Profes- sor Wolf Vielstich at the University of Bonn. Since then he worked on manifold aspects of theoretical electrochemistry. Recently, together with his wife Dr. Elizabeth Santos, he has developed a theory for electrocatalysis. Amongst other awards, he received a Dr. h.c. of the National University of Cordoba, Argentina, the Alexander Kuznetsov Prize, of the International Society of Electrochemistry, and the Leloir Pri- ze of the Republic of Argentina.

Energy harvesting and storage with ionic liquids: the essential physics at the nanoscale

Alexei A. Kornyshev

The renewal of interest to fundamental mechanisms of energy storage in electrochemical supercapacitors was boosted by the progress in development of novel materials (mainly carbon based) for nanostructured electrodes. It was also affected by the booming research in room temperature ionic liquids that offers virtually unlimited number of new electrolyte combinations. Some of them have large potential windows that allow to charge capacitors to higher voltages and thereby store more energy. This material-science based progress had to be matched with detailed investigation of performance of such systems. In particular, exploiting ultrananoporous electrodes, with pores just about to accommodate one layer or one row of ions, can increase the interfacial area and thereby the stored energy, but what will be the capacitance-voltage dependence and the dynamics of charging of such electrodes? What are the laws of ion population of such pores under applied potential, and the conditions maximizing stored energy and power?

There was a considerable progress in this area over the last 10 years. Basic mechanisms of charge equilibria in ultrananoporous electrodes have been understood based on statistical theory of ion-ion and ion interactions in nano-confinement. The modes of charging dynamics have also been revealed based on kinetic theory and simulations. The talk will overview these advances, with a focus on the effects that theory explains or predicts, as well as highlight pressing questions for future experiments and theory.

Sister systems to supercapacitors are electroactuators. These can be and are being used for the conversion of time-dependent applied voltage into mechanical motion, or other way around –in reverse actuators for the conversion of the applied force into the AC current.  Such harvesters of mechanical work, draw currently attention in the context of AC-current generation from walking.  Physics of this class of systems will also be briefly reviewed.

One more related area is nanotribology, the subject related to minimizing energy losses. If time allowed, it will also briefly covered – the systems with electrotuneable lubricity with ionic liquid lubricants, in which friction can be turned on and off by applied voltage.  

With intention to overview this research area, the talk will still be focused on joint works of theoretical chemical physics team at Imperial and our partners at University of Strathclyde, University of Drexel, Virginia Tech, ORNL, FZ-Juelich, University of Tel Aviv, LPTL CNRS (France), HUST (China), and other groups, to be highlighted and acknowledged in the talk. Some papers of this series are listed below.

1. M.V.Fedorov and A.A.Kornyshev, Ionic liquids at electrified interfaces, Chem.Rev.114, 2978−3036 (2014).

2. S.Kondrat, A.Kornyshev, Charging dynamics and optimization of nanoporous supercapacitors, J.Phys.Chem.C 117, 12399-12406 (2013).

3. S.Kondrat, P.Wu, R.Qiao, A.A.Kornyshev, Accelerating charging dynamics in subnanometer pores, Nature Materials 13, 387-393(2014).

4. Y.He, J. Huang,B.G. Sumpter, A.A.Kornyshev, R.Qiao, Dynamic charge ctorage in Ionic liquids-filled nanopores: insight from a computational cyclic voltammetry study, J. Phys. Chem. Lett. 2015, 6, 22−30 (2015).

5. A.A.Lee, S.Kondrat, G.Oshanin, A.A.Kornyshev, Charging dynamics of a supercapacitor with narrow cylindrical nanopores, Nanotech. 25, #315401 (2014).

6. S. Kondrat, A.A.Kornyshev, Pressing a spring: what does it take to maximize the energy storage in nanoporous supercapacitors? Nanoscale Horizons, 1, 45-52 (2016).

7. A.A.Kornyshev, The simplest model of charge storage in single file metallic nanopores, Faraday Disc. 164, 117-133 (2013).

8. C.C. Rochester, G.Pruessner, A.A.Kornyshev, Statistical mechanics of `unwanted electroactuation' in nanoporous supercapacitors, Electrochim.Acta  174, 978-984 (2015).

9. G.Feng, X.Jiang, R.Qiao, A.A.Kornyshev, Water in ionic liquids at electrified interfaces: the anatomy of electrosorption, ACS Nano 8, 11685–11694 (2014).

10.  A.A.Lee, S.Kondrat, A.A.Kornyshev, Single-file charge storage in conducting nanopores, Phys.Rev.Lett. 113, #048701, 1-5 (2014).

11. O.Y.Fajardo, F.Bresme, A.A.Kornyshev, M.Urbakh, Electrotunable lubricity with ionic liquid nanoscale films, Sci.Rep. 5, 2045-2322 (2015).

12. O.Y.Fajardo, F.Bresme, A.A.Kornyshev, M.Urbakh, Electrotunable friction with Ionic liquid lubricants: how important is the molecular structure of the ions?,

J.Phys.Chem.Lett. 6, 3998-4004 (2015).

13. C.C.Rochester, S.Kondrat, G.Pruessner, A.A Kornyshev (2016), Charging ultrananoporous electrodes with size-asymmetric ions assisted by apolar solvent,

J.Phys.Chem.C 120, 16042-16050 (2016).

14. A.A. Kornyshev, R. Twidale, A.Kolomeisky, Current generating double layer shoe with a porous sole: ion transport matters, J.Phys.Chem.C 121, 7584-7595 (2017).

15. O.Y.Fajardo, F.Bresme, A.A.Kornyshev, M.Urbakh, Water in ionic liquid lubricants: friend and foe, ACS Nano, 11, 6825-6831 (2017).

16. S.Bi, R.X.Wang, S. Liu, J.W.Yan, B.W. Mao, A.A. Kornyshev, G.Feng,  Minimizing the electrosorption of water from humid ionic liquids on electrodes,                                                 Nature Comm. 9, #5222 (2018).

Alexei Kornyshev graduated from the Moscow Institute of Engineering Physics with a degree in theoretical nuclear physics. He matured as a scientist at the Frumkin Institute (Acad.Sci.) in Moscow, where he did his PhD (1974) in Theoretical Physics and DSc in Chemistry (1986), having worked there till 1991. In 1992 he was invited to Research Centre Jülich, Germany, where he then worked for 10 years leading a Theory Division in the Institute for Materials and Processes in Energy Systems, a position combined later with a Professorship of Theoretical Physics at the University of Düsseldorf. In 2002 he took Chair of Chemical Physics at Imperial College. His interests span widely in theoretical condensed matter chemical physics and its application to electrochemistry, biological physics, nanoscience, photonics and energy research, using methods of theoretical physics and computer simulations, and working in close collaboration with experimentalists. Recipient of many international and national awards and prizes, he is a Fellow of 5 learned societies, a Member of Royal Danish Academy of Science, and is on editorial boards of several physical and chemical journals. 


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