Relevance to Published Work

The origin of PtsCo activity towards the oxygen reduction reactions has been the subject of numerous studies. Among the scenarios advanced are  

The latter is not inconsistent with the data given here. 

A combined LEISS-AES-EC study was earlier undertaken at crystalline PtsCo and PtsNi alloy surfaces. It was reported that, when PtsCo and PtsNi were annealed at 1000 K, only Pt atoms existed on the outermost layer the latter was referred to as a Pt skin. This particular observation is not in agreement with the result here that Co actually co-exists with Pt at the outermost layer. Interestingly, when the PtsCo surface in the earlier study was lightly sputtered, approximately 25% of the sputtered material was Co this result suggests that Co is in fact present at the topmost layer. Why a discrepancy exists between the LEISS and depth-profile studies is unclear. But, for the difference between the present and previous LEISS work, the possibility exists that the interfacial be- 

The study of catalysis by mixed-metal electrodes is confronted with intricacies not encountered in work with single-metal surfaces. An important issue that is seldom addressed pertains to the character of the topmost layer of the electrocatalyst. Almost all of the stractural and compositional analysis undertaken have employed methods that provide information not only of the outermost layer but also of the sub-surface environment hence, ambiguities may reside in the results that lead to umeliable correlations between interfacial structure, composition and reactivity. 

In this article, the study of alloy electrodes by a combination of EC with LEISS is discussed. LEIS spectroscopy is unparalleled in its ability to interrogate only the outermost layer this is because of the repulsive nature of ion-atom interactions that serves to mask interactions between sub-surface species with the probe ions. LEISS is an established surface physics technique but its adoption in surface electrochemical investigations has not been pervasive. For the work reviewed here, an instrument that incorporates EC with LEISS, LEED, XPS and TPD was employed. 

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