(560cq) Potential Dependent Kinetic Barriers of Oxygen Reduction Reactions (ORR) on Pt (111)

Authors: 
Sharma, S., Brown University
Peterson, A. A., Brown University
Oxygen reduction reactions (ORR) have been extensively studied in the past few decades owing to their application in proton exchange membrane fuel cells (PEMFCs). Despite the high efficiency, sustainability and environment friendly operation of PEMFCs, they are known to suffer from the slow rate of ORR at the cathode. Although, an ideal electrochemical reaction should generate 1.23 VRHE per electron, the typical operating potential for electro-catalytic ORR on Pt(111) surface is observed below 0.9 VRHE. First principle thermodynamic atomistic calculations [1-2] using Density Functional Theory (DFT) have shown a presence of high over-potential of ORR on Pt(111) due to the strong binding of the reaction intermediates like O* and HO*. However, the reason behind the sluggish kinetics of ORR remains unclear and ambiguous in the literature.

In this study, we employ a kinetic study using DFT along with the Solvated Jellium (SJ) model [3] – a method developed in our group – to study the potential dependence of the elementary steps of ORR via both dissociative and associative mechanism using density functional theory. The aim of the study is to understand the kinetics of ORR at different potentials and relevant coverages. We further comment on the dominance of either associative or dissociative mechanisms at different operating conditions.

[1] Norskov, J. K. et Al, Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode J. Phys. Chem. B, 2004, 108 (46), pp 17886–17892

[2] Sharma S. et al, Face-centered tetragonal (FCT) Fe and Co alloys of Pt as catalysts for the oxygen reduction reaction (ORR): A DFT study, J. Chem. Phys. 150, 041704 (2019)

[3] Kastlunger, G. et al, Controlled-Potential Simulation of Elementary Electrochemical Reactions: Proton Discharge on Metal Surfaces, J. Phys. Chem. C 122 (24), 12771 (2018)