Universal Activity Volcano for 2e- and 4e- Reduction of Oxygen on Metal Surfaces
In this talk, we will address the issue of 2e− versus 4e− reduction of oxygen on metal surfaces. Using a detailed thermodynamic analysis based on density functional theory calculations, we show that to a first approximation an activity descriptor, ΔGOH*, the free energy of adsorbed OH*, can be used to describe trends for the 2e− and 4e− reduction of oxygen. We demonstrate the existence of a universal activity volcano shown in the Figure and find quite a remarkable agreement between the predictions of the model and experimental results spanning nearly 30 years.[2-4]
 Fuel Cell Catalysis: A Surface Science Approach, Marc Koper and Andrzej Wieckowski, (2009)
 V. Viswanathan, H. A. Hansen, J. Rossmeisl, and J. K. Nørskov, ACS Cat., (2012) 2, 1654-1660.
 V. Viswanathan, H. A. Hansen, J. Rossmeisl, and J. K. Nørskov, J. Phys. Chem. Lett., (2012) 3, 2948-2951.
 H. A. Hansen, V. Viswanathan and J. K. Nørskov, (submitted).
Fig 1: Activity volcanoes for the 2e− and 4e− reduction of oxygen are shown in red and blue respectively. The source of the experimental data for the 2e− and 4e− reduction of oxygen are listed in ref. . The experimental value of the limiting potential, UL, is determined by the half-wave potentials for the 4e− reduction and by the onset of ring current for the 2e− reduction. The activity of (111) and (100) surfaces has been plotted in circles and squares, respectively.