Free Energy Profile of the ORR

Application of a negative overpotential, 0, shifts the reaction Gibbs energy of 

So far presented is a basic mechanistic picture of the ORR. It comprises discussions of potential-controlled formation of surface-adsorbed oxygen intermediates, alternative reaction pathways, and free energy profiles of typical stepwise reaction sequences. The overarching questions are How can these ingredients be cast into a consistent picture of the ORR at Pt-based catalystsl What controls the net rate of the reaction How are phenomenological parameters, which are employed in the Butler-Volmer equation, related to fundamental mechanisms and parameters  

a kinetic model of the ORR under steady-state conditions is discussed and analyzed. The focus is on the associative mechanism, involving the steps in Equations 3.40, 3.41, 3.42, and 3.45. The rate equations for these processes are 

In agreement with spectroscopic evidence (Wakisaka et al., 2010 Wang et al., 2007), negligible OORad coverage is assumed. Therefore, the back reaction in Equation 3.51, could be neglected. The back reaction for the second step. Equation 3.52, was neglected because OOHa is unstable and spontaneously reacts to form Oad and OHad (Rossmeisl et al., 2005, 2009). 

At steady state, reaction rates must fulfill the following balance vqrr = i i = V2 = V3 = -U4, representing three independent equations for the three coverage variables, assuming that ki P2 H ] 2 corresponds to Oooh 0. This assumption 

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