Circumventing the Sabatier Principle in Electrocatalysis: the Case of Oxygen Reduction Reaction on Au(100) in Alkaline Medium

Abstract

The barriers for elementary steps in the oxygen reduction reaction (ORR) catalyzed on Au(100) in alkaline solution are mapped out by ab initio molecular dynamics simulations. Due to the relatively weak binding energy of O2 and oxygenated species, the calculated O−O dissociation barrier at ~0.5 eV is indeed considerably higher than the association barrier (< 0.1 eV) to form adsorbed HOO*, pushing ORR towards the thermodynamically less favorable 2e− pathway. However, the kinetics is changed above the equilibrium potential for the association channel ~0.7 V (RHE) where the 2e− pathway is switched off. Thereafter, the 4e− pathway becomes active as the O−O dissociation barrier at ~0.5 eV is not prohibitive. For the subsequent reduction steps, the weak binding energies of oxygenated species on Au(100) are actually an advantage, making Au(100) as good an ORR catalyst as Pt. It also makes the outer sphere electron transfer to O2 as the eventual rate determining step, as supported by the j-E polarization curve, showing a small ORR current extending close to the overall 4e− ORR equilibrium potential of 1.23 V. It provides an example on how the ORR activity volcano curve based on the Sabatier Principle can be circumvented in electrocatalysis.

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“…However, in the ORR, bulk gold single-crystal electrodes with orientations of (111), (110), and (100) show promising behavior. As a result, the ORR efficiency of the Au(100) electrode in alkaline media is comparable to that of platinum [ 28 ]. To achieve a large specific surface area and lower the cost, gold is frequently dispersed across a nanoparticle form that is adsorbed onto a hard surface [ 29 , 30 ].…”