Electrochemical chlorine evolution at rutile oxide (110) surfaces

Abstract

Based on density functional theory (DFT) calculations we study the electrochemical chlorine evolution reaction on rutile (110) oxide surfaces. First we construct the Pourbaix surface diagram for IrO(2) and RuO(2), and from this we find the chlorine evolution reaction intermediates and identify the lowest overpotential at which all elementary reaction steps in the chlorine evolution reaction are downhill in free energy. This condition is then used as a measure for catalytic activity. Linear scaling relations between the binding energies of the intermediates and the oxygen binding energies at cus-sites are established for MO(2) (M being Ir, Ru, Pt, Ti). The linear relations form the basis for constructing a generalized surface phase diagram where two parameters, the potential and the binding energy of oxygen, are needed to determine the surface composition. We calculate the catalytic activity as function of the oxygen binding energy, giving rise to a Sabatier volcano. By combining the surface phase diagram and the volcano describing the catalytic activity, we find that the reaction mechanism differs depending on catalyst material. The flexibility in reaction path means that the chlorine evolution activity is high for a wide range of oxygen binding energies. We find that the required overpotential for chlorine evolution is lower than the overpotential necessary for oxygen evolution.

A theoretical evaluation of possible transition metal electro-catalysts for N2reduction

“…We will assume that the onset of a signicant reaction rate occurs at a potential where the initial and nal states of an elementary step have the same free energy, ∆G = 0. This approach has been successfully applied to other electrochemical reactions [30,38,39,53]. First, we focus on the associative mechanism, which is analogous to the mechanism in the enzyme.…”

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…In the case of the hydrogen evolution reaction, it is Pt, 51,68 and in the case of the chlorine evolution reaction, it is RuO 2 . 69 6748 | Energy Environ. Sci., 2012, 5, 6744-6762…”

“…k This situation contrasts with a two-electron reaction, such as hydrogen evolution or chlorine evolution, which only involves one intermediate. [68][69][70] As for the oxygen reduction reaction, the ''perfect'' catalyst would have a flat free energy diagram at the equilibrium potential. Given that only one intermediate needs to be taken into account, such a catalyst can be found easily.…”

Beyond the volcano limitations in electrocatalysis – oxygen evolution reaction

“…15 The cus sites can be identified with surface metal cations which form (n À 1) bonds with oxygen (where n is the number of oxygen bonds formed by the given cation in the bulk). Only cus sites allow for formation of reactive ''atop'' positions essential for the formation of strongly adsorbed intermediates.…”