Local Ordering Changes in Pt鈥揅o Nanocatalyst Induced by Fuel Cell Working Conditions
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- 作者：Giorgia Greco ; Agnieszka Witkowska ; Marco Minicucci ; Luca Olivi ; Emiliano Principi ; Sonia Dsoke ; Arianna Moretti ; Roberto Marassi ; Andrea Di Cicco
- 刊名：The Journal of Physical Chemistry C
- 出版年：2012
- 出版时间：June 14, 2012
- 年：2012
- 卷：116
- 期：23
- 页码：12791-12802
- 全文大小：616K
- 年卷期：v.116,no.23(June 14, 2012)
- ISSN：1932-7455
文摘
We present a detailed investigation of the changes in the local structure and chemical disorder induced by controlled potential cycling in Pt3卤未Co nanoparticles used as a catalyst in the proton exchange membrane fuel cell (PEMFC) technology. Various state-of-the art material science techniques were used to study the microscopic properties of those nanomaterials including ex-situ and in-situ X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). XAS double-edge multiple-scattering structural refinements of the Pt鈥揅o spectra were performed taking into account the reduction of coordination numbers and degeneracy of three-atom configurations resulting from the measured size distribution obtained by TEM and XRD. The effect of chemical disorder in the considered nanoalloy was also taken into consideration. The PEMFC performance appears to be related to specific changes of the microscopic structural properties of the nanocatalyst during the first operation hours, especially during a cell activation period. In operating PEMFCs a small amount of Co oxide, initially present in the nanoalloy (on the surface of particles), disappeared gradually. At the same time, interatomic Pt鈥揚t and Pt鈥揅o distances were slightly longer for higher current densities, while distance variances (蟽2) tended to decrease. Co鈥揅o distribution remained unchanged. By combining XRD and XAS data, we also found that after controlled potential cycling in PEMFC the stoichiometry of the considered alloy changed from the initial Pt3卤未Co to Pt4卤未Co. Comparison of XAS and XRD-extracted values of the Co atomic fraction indicated that mainly cobalt not fully alloyed with platinum dissolved, and this process occurred in the first degradation period. At the same time, no substantial aggregation processes and no change in the mean size of nanoparticles were observed for this alloy. Accelerated degradation test, lasting up to 150 h, showed structural and electrochemical catalyst stability. The observed increase of chemical and local structural order of the particle core alloy did not affect the ORR kinetics.