Egill Skúlason

Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt(111) electrode

We present results of density functional theory calculations on a Pt(111) slab with a bilayer of water, solvated protons in the water layer, and excess electrons in the metal surface. In this way we model the electrochemical double layer at a platinum electrode. By varying the number of protons/electrons in the double layer we investigate the system as a function of the electrode potential. We study the elementary processes involved in the hydrogen evolution reaction, 2(H(+) + e(-)) --> H(2), and determine the activation energy and predominant reaction mechanism as a function of electrode potential. We confirm by explicit calculations the notion that the variation of the activation barrier with potential can be viewed as a manifestation of the Brønsted-Evans-Polanyi-type relationship between activation energy and reaction energy found throughout surface chemistry.

Local density of states analysis using Bader decomposition for N2 and CO2 adsorbed on Pt(110)-(1 × 2) electrodes

Local density of states and electric charge in regions defined for individual atoms and molecules using grid based Bader analysis is presented for N(2) and CO(2) adsorbed on a platinum electrode in the presence of an applied electric field. When the density of states is projected onto Bader regions, the partial density of states for the various subregions correctly sums up to the total density of states for the whole system, unlike the commonly used projection onto spheres which results in missing contributions from some regions while others are over counted, depending on the radius chosen. The electrode is represented by a slab with a missing row reconstructed Pt(110)-(1 × 2) surface to model an edge between micro-facets on the surface of a nano-particle catalyst. For both N(2) and CO(2), a certain electric field window leads to adsorption. The binding of N(2) to the electrode is mainly due to polarization of the molecule but for CO(2) hybridization occurs between the molecular states and the states of the Pt electrode.

Modeling Electrochemical Reactions at the Solid-liquid Interface Using Density Functional Calculations.

Abstract Charged interfaces are physical phenomena found in various natural systems and artificial de- vices within the fields of biology, chemistry and physics. In electrochemistry, this is known as the electrochemical double layer, introduced by Helmholtz over 150 years ago. At this interface, between a solid surface and the electrolyte, chemical reactions can take place in a strong elec- tric field. In this presentation, a new computational method is introduced for creating charged interfaces and to study charge transfer reactions on the basis of periodic DFT calculations. The electrochemical double layer is taken as an example, in particular the hydrogen electrode. With this method the mechanism of forming hydrogen gas is studied. The method is quite general and could be applied to a wide variety of atomic scale transitions at charged interfaces.

Atomic scale simulations of heterogeneous electrocatalysis: recent advances

Graphical Abstract Abstract The methodology for atomic scale calculations of electrocatalysis in order to identify mechanisms and estimate reaction rates is reviewed. These include: (1) the application of an external electrical field or potential in density functional theory calculations, (2) the thermochemical model for estimating the onset potential of an electrochemical reaction, and (3) calculations of transition paths in atomic scale models of the electrical double layer. Hydrogen evolution reaction, oxygen reduction reaction as well as CO and N electrochemical reduction to form methane and ammonia are taken as examples. Calculations of reaction rates based on the estimation of the activation energy of elementary steps from minimum energy paths and transition state theory have been shown to provide accurate estimates of rates even for complex reactions and competing reaction mechanisms. There is room, however, for further improvements and some of those are also mentioned at the end of this mini-review.

Cyclic Voltammograms from First Principles

Cyclic voltammetry is perhaps the most important and widely utilized technique in the field of analytical electrochemistry. By measuring the current through an electrochemical cell as the cell potential is cycled an abundance of quantitative information regarding surface electrochemical phenomena can be obtained. For over 40 years, general and specific quantitative mathematical relationships have been developed to describe spectra recorded using cyclic voltammetry (1,2). Such expressions are crucial in the interpretation of measured data; however, in and of themselves such expressions offer little predictive ability.