title: Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells.
abstract: The sluggish oxygen reduction reaction (ORR) is a major impediment to the economic use of hydrogen fuel cells in transportation. In this work, we report the full ORR reaction mechanism for Pt(111) based on Quantum Mechanics (QM) based Reactive metadynamics (RμD) simulations including explicit water to obtain free energy reaction barriers at 298 K. The lowest energy pathway for 4 e-water formation is: first, *OOH formation; second, *OOH reduction to H2O and O*; third, O* hydrolysis using surface water to produce two *OH and finally *OH hydration to water. Water formation is the rate-determining step (RDS) for potentials above 0.87 Volt, the normal operating range. Considering the Eley-Rideal (ER) mechanism involving protons from the solvent, we predict the free energy reaction barrier at 298 K for water formation to be 0.25 eV for an external potential below U = 0.87 V and 0.41 eV at U = 1.23 V, in good agreement with experimental values of 0.22 eV and 0.44 eV, respectively. With the mechanism now fully understood, we can use this now validated methodology to examine the changes upon alloying and surface modifications to increase the rate by reducing the barrier for water formation.
authors.affiliation: Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, California 91125, USA. tcheng@caltech.edu anqi@caltech.edu xiao@caltech.edu merinov@wag.caltech.edu wag@wag.caltech.edu.
authors.forename: Tao
authors.identifier: http://orcid.org/0000-0003-4830-177X
authors.initials: T
authors.lastname: Cheng
authors.affiliation: Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, California 91125, USA. tcheng@caltech.edu anqi@caltech.edu xiao@caltech.edu merinov@wag.caltech.edu wag@wag.caltech.edu.
authors.forename: William A
authors.identifier: http://orcid.org/0000-0003-0097-5716
authors.initials: WA
authors.lastname: Goddard
authors.affiliation: Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, California 91125, USA. tcheng@caltech.edu anqi@caltech.edu xiao@caltech.edu merinov@wag.caltech.edu wag@wag.caltech.edu.
authors.forename: Qi
authors.identifier: http://orcid.org/0000-0003-4838-6232
authors.initials: Q
authors.lastname: An
authors.affiliation: Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, California 91125, USA. tcheng@caltech.edu anqi@caltech.edu xiao@caltech.edu merinov@wag.caltech.edu wag@wag.caltech.edu.
authors.forename: Hai
authors.identifier: http://orcid.org/0000-0001-9399-1584
authors.initials: H
authors.lastname: Xiao
authors.affiliation: Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, California 91125, USA. tcheng@caltech.edu anqi@caltech.edu xiao@caltech.edu merinov@wag.caltech.edu wag@wag.caltech.edu.
authors.forename: Boris
authors.initials: B
authors.lastname: Merinov
authors.affiliation: South Ural State University Lenina, 76, Chelyabinsk, Chelyabinsk Oblast, Russia. morozov72@gmail.com.
authors.forename: Sergey
authors.identifier: http://orcid.org/0000-0001-6226-5811
authors.initials: S
authors.lastname: Morozov