On the morphological stability of supported Pt nanoparticle ensembles in electrochemical environments
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Final Report Abstract
In this project, different novel catalyst support materials were investigated with regard to their possible potential as Pt support in polymer electrolyte fuel cells. Several different types of metal oxides have been tested for such use in the past and it has been found out that metal oxides are able to provide the required properties for a stable support. Moreover, metal‐support interactions based on electronic effects are known to enhance the overall catalyst stability. In this project, Indium Tin Oxide (ITO), Rutheniumoxide Titaniumoxide (RTO) and Antimony‐doped tin oxide (ATO) were investigated as alternative electrocatalyst supports and compared to state‐of‐art commercial carbon supported catalysts. A deeper understanding under operating (so‐called “in situ”) conditions by advanced synchrotron‐based techniques such as X‐ray diffraction and absorption was the focus of these studies. Excellent structural and morphological stability of Pt nanoparticles was found for the RTO support in three different catalyst loadings when a stress test was applied to simulate the lifetime regime of the fuel cell. The oxidic support stabilizes the Pt particles, but the reductive conditions during the stress test could account for Pt active site poisoning by support ions in the atomic scale. A relatively similar behavior was found for Pt/ITO catalyst, in which again the oxide support stabilizes the Pt in terms of particle and crystallite size as well as weight fraction. Support degradation during the LP‐AST in the form of Ostwald ripening and dissolution was found to affect the catalytic activity of Pt. In the HP‐AST, simulating start‐up/shut‐down cycles of a fuel cell, the Pt/ITO system shows overall superior stability with stable Pt and metal oxide component. In a third study, these two oxide‐supported electrocatalyst were compared to Pt/C reference system with respect to Pt oxidation. By in situ X‐ray absorption and Pt dissolution experiments it was successfully shown that Pt/C shows the highest and Pt/RTO the lowest tendency towards the formation of PtOx‐species, predicting a superior stability of the oxide supported electrocatalysts. In another approach, IrOx on a mesoporous ATO support showed excellent electrocatalytic stability in a constant current stability test which was attributed to electron donation from the support due to the strong metal support interactions. The studies conducted in this project show, that the choice of electrocatalyst and knowledge about its properties especially under working conditions is tremendous in order to develop a stable and highly efficient fuel cell.
Publications
- Unravelling Degradation Pathways of Oxide‐Supported Pt Fuel Cell Nanocatalysts under In Situ Operating Conditions, Adv. Energy Mater
Henrike Schmies, Arno Bergmann, Jakub Drnec, Guanxiong Wang, Detre Teschner, Stefanie Kühl, Daniel J. S. Sandbeck, Serhiy Cherevko, Martin Gocyla, Meital Shviro, Marc Heggen, Vijay Ramani, Rafal E. Dunin‐Borkowski, Karl J. J. Mayrhofer, and Peter Strasser
(See online at https://doi.org/10.1002/aenm.201701663) - Electrochemical Catalyst Support Effects and Their Stabilizing Role for IrOx Nanoparticle Catalysts during the Oxygen Evolution Reaction, J. Am. Chem. Soc. 138 (38), 12552–12563 (2016)
Hyung‐Suk Oh, Hong Nhan Nong, Tobias Reier, Arno Bergmann, Manuel Gliech, Jorge Ferreira de Araujo, Elena Willinger, Robert Schlögl, Detre Teschner, and Peter Strasser
(See online at https://doi.org/10.1021/jacs.6b07199)
