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J. Electrochem. Soc. 2014, volume 161, issue 14, F1323-F1329.
Qingying Jia1, Keegan Caldwell2, Joseph M. Ziegelbauer3, Anusorn Kongkanand3, Frederick T. Wagner3, Sanjeev Mukerjee1, and David E. Ramaker2,
- Department of Chemistry & Chemical Biology, Northeastern University, Boston, Massachusetts 02115, USA and
- Department of Chemistry, George Washington University, Washington, DC 20052, USA and
- Electrochemical Energy Research Lab, General Motors Research & Development, Warren, Michigan 48090, USA
Abstract
We present experimentally observed molecular adsorbate coverages (e.g., O(H), OOH and HOOH) on real operating dealloyed bimetallic PtMx (M = Ni or Co) catalysts under oxygen reduction reaction (ORR) conditions obtained using X-ray absorption near edge spectroscopy (XANES). The results reveal a complex Sabatier catalysis behavior and indicate the active ORR mechanism changes with Pt–O bond weakening from the O2 dissociative mechanism, to the peroxyl mechanism, and finally to the hydrogen peroxide mechanism. An important rearrangement of the OOH binding site, an intermediate in the ORR, enables facile H addition to OOH and faster O–O bond breaking on 111 faces at optimal Pt–O bonding strength, such as that occurring in dealloyed PtM core-shell nanoparticles. This rearrangement is identified by previous DFT calculations and confirmed from in situ measured OOH adsorption coverages during the ORR. The importance of surface structural effects and 111 ordered faces is confirmed by the higher specific ORR rates on solid core vs porous multi-core nanoparticles.
