Cheng Tao, Goddard William A, An Qi, Xiao Hai, Merinov Boris, Morozov Sergey
Materials and Process Simulation Center (MC139-74), California Institute of Technology, Pasadena, California 91125, USA.
South Ural State University Lenina, 76, Chelyabinsk, Chelyabinsk Oblast, Russia.
Phys Chem Chem Phys. 2017 Jan 25;19(4):2666-2673. doi: 10.1039/c6cp08055c.
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 HO 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.
缓慢的氧还原反应（ORR）是阻碍氢燃料电池在交通运输领域经济应用的主要因素。在这项工作中，我们基于量子力学（QM）的反应性元动力学（RμD）模拟报告了Pt(111)的完整ORR反应机理，该模拟包括明确的水，以获得298 K时的自由能反应势垒。4e水生成的最低能量途径是：首先，形成OOH；其次，OOH还原为HO和O；第三，O利用表面水进行水解生成两个OH，最后OH水合生成水。对于高于0.87伏（正常工作范围）的电势，水的生成是速率决定步骤（RDS）。考虑到涉及来自溶剂质子的埃利-里德（Eley-Rideal，ER）机理，我们预测在298 K时，对于低于U = 0.87 V的外部电势，水生成的自由能反应势垒为0.25 eV，在U = 1.23 V时为0.41 eV，这与实验值0.22 eV和0.44 eV分别非常吻合。由于现在已经完全理解了该机理，我们可以使用这种经过验证的方法来研究合金化和表面改性时的变化，以通过降低水生成的势垒来提高反应速率。
