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Published January 28, 2017 | Supplemental Material
Journal Article Open

Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells


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 H_2O 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.

Additional Information

© 2017 the Owner Societies. Received 24th November 2016, Accepted 20th December 2016, First published online 21 Dec 2016. This work was supported by National Science Foundation (CBET 1512759, program manager Robert McCabe). We thank Dr Ted Yu for helpful discussions. Author contributions: T. C. and W. A. G. proposed the ideas; T. C., Q. A. and S. M. carried out the simulations; T. C. H. X. and B. M. analyzed the results, and the manuscript was written by T. C. and W. A. G. The authors declare no competing financial interests.

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