At last: orbital-free DFT simulations of semiconductors and transition metals
Professor Emily Carter, Princeton University, USA
Professor Paul Madden FRS, University of Oxford, UK
First principles electrochemistry
Professor Michiel Sprik, University of Cambridge, UK
The electrodes in electrochemical cells are interfaces between electronic and ionic conductors converting one type of charge transport into the other. Experimental electrochemistry has developed a range of current-voltage measurement techniques to probe this process. Atomistic modelling is not yet ready for this challenge, or at least we, using electronic structure based methods, are not. Electrochemical interfaces also act as capacitors, which can be charged (electrified). This can be studied under open circuit conditions (zero current). Here computational methods have more of a chance and considerable progress has been made in the calculation of open circuit electrode potentials. This talk is a brief overview of the efforts of our group focusing on the level alignment at transition metal oxide interfaces including the dependence on the pH of the electrolytic solution*.
* In collaboration with Jun Cheng, Marialore Sulpizi and Joost VandeVondele
First principles simulations of metal oxide electrodes for water oxidation
Professor Annabella Selloni, Princeton University, USA
Water splitting on metal oxide surfaces has attracted enormous interest for decades. While a great deal of work has focused on titanium dioxide (TiO2), recently other oxides, e.g. cobalt and Ni/Fe mixed oxides, have emerged as promising candidates for use as anode materials in electrochemical water splitting. In this talk I shall discuss various aspects of water oxidation on metal oxide surfaces, including the changes in composition and structure of the material under electrochemical environment and the mechanism of the first proton-coupled-electron transfer at the oxide/water interface in the presence of a photoexcited hole. In particular, I shall provide evidence that the first proton and electron transfers at the water/TiO2 interface are not concerted but rather represent two separate processes.
Modeling ion adsorption and dynamics in nanoporous carbon electrodes
Dr Mathieu Salanne, Paris (Université Pierre et Marie Curie), France
The recent demonstration that in supercapacitors ions from the electrolyte could enter sub-nanometer pores increasing greatly the capacitance opened the way for valuable improvements of the devices performances. Despite the recent experimental and fundamental studies on that subject, the molecular mechanism at the origin of this capacitance enhancement is still not quite clear. We report here molecular dynamics simulations including two key features: the use of realistic electrode structures comparable with carbide-derived carbons and the polarization of the electrode atoms by the electrolyte. This original design of an electrochemical cell allows us to recover capacitance values in quantitative agreement with experiment and to gain knowledge about the local structure and dynamics of the ionic liquid inside the pores. Then, from the comparison between planar (graphite) and porous electrodes, we propose a new mechanism explaining the capacitance enhancement in nanoporous carbons. We also set up some simulations where, starting from 0V, an electric potential is applied between the electrodes. It is then possible to follow the dynamical aspects of the charging of supercapacitors.
- Merlet, Rotenberg, Madden, Taberna, Simon, Gogotsi and Salanne, Nat. Mater., 11, 306 (2012)
- Merlet, Pean, Rotenberg, Madden, Simon and Salanne, J. Phys. Chem. Lett., 4, 264 (2013)
- Merlet, Rotenberg, Madden and Salanne, Phys. Chem. Chem. Phys., 15, 15781 (2013)
- Merlet, Pean, Rotenberg, Madden, Daffos, Taberna, Simon and Salanne, Nat. Commun., doi : 10.1038/ncomms3701 (2013)