| AVS 60th International Symposium and Exhibition | |
| Nanometer-scale Science and Technology | Tuesday Sessions |
| Session NS+AS+EN+SS-TuA |
| Session: | Nanoscale Catalysis and Surface Chemistry |
| Presenter: | B. Koel, Princeton University |
| Authors: | X. Yang, Princeton University J. Hu, University of California, Irvine R.Q. Wu, University of California, Irvine B. Koel, Princeton University |
| Correspondent: | Click to Email |
Sluggish kinetics of the electrochemical reduction of molecular oxygen (ORR) in polymer electrolyte membrane fuel cells (PEM-FCs) requires a continued search for advanced catalysts. Our work combines synthesis and characterization of well-defined, multimetallic model catalysts in UHV and direct evaluation of their catalytic performance in an electrochemical cell accessible by a multifunctional ambient-pressure antechamber and sample transfer system. Surface structures and electronic properties [#] [#] of these electrocatalysts were characterized by LEED, AES, LEIS, XPS, and STM. We found previously that Pd3Fe(111) annealed at high temperature is highly active for ORR, but may lose activity due to slow dissolution of Fe. To address this issue, we developed a method to improve the stability while maintaining high activity of the catalyst involving a submonolayer amount of Au at the surface. While bulk gold is catalytically inactive, the surface prepared by submonolayer amounts of Au deposited on a Pd/Pd3Fe(111) substrate was discovered to be highly active for the ORR, more active than Pt(111). The activity was strongly dependent on the Au coverage, with the highest activity found near 0.5-monolayer Au. The high activity and durability of this Au-modified Pd3Fe(111) surface is associated with formation of 2D nanostructures at the step edges at the surface, small nano-islands, which were revealed by STM. DFT calculations of O2 adsorption on these 2D Au islands and of Au diffusion barriers to the top of Au terraces with and without O and O2 were used to provide a more thorough understanding of the origin of the high catalytic activity of this system. We found that adsorbed oxygen atoms can enhance diffusion in Au protrusions, resulting in a 3D Au nanostructure that can lead to O2 dissociation. In this work, we not only discovered a potential candidate for non-Pt catalysts to replace Pt cathode catalysts for the ORR, but also identified conditions for activating gold for use in practical electrocatalysts.
B.E.K. acknowledges support by NSF Grant No. CHE-1129417. R.W. acknowledges support by NSF Grant No. CHE-0802913 and computing time at XSEDE.