Electro-oxidation of ethanol on PtRh surfaces partially covered by Sn

In this work we prepare Pt75Rh25 electrodeposits in a reproducible way and modified them with different Sn contents by spontaneous deposition. When these materials are used as electrocatalysts for the ethanol oxidation reaction in acidic medium, they reveal a global activity that is strongly sensitive to the Sn content. The best performance is observed for theta(sn) = 0.11, followed by high Sn coverages while the poorer results are observed for intermediary Sn contents. By using in situ FTIR spectroscopy the results are rationalized in terms of two superficial domains that generate acetic acid in two potential regions. The net electrocatalytical response seems to be the consequence of the compromise between these two electrochemical routes. Conversely, the production of CO2 is scarcely affected by the Sn content, and no synergy is apparent from the combination of Pt, Rh and Sn, which is probably because the later deposition of Sn does not promote a close contact between the metals. (C) 2019 Elsevier Ltd. All rights reserved.