A study on the surface reactivity of modified CeO2 ultra-thin films towards H2 dissociation.

Cnr Nano Modena
Massimo Rontani

Fuel cells are promising candidates for future power sources; especially low-temperature fuel cells such as proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are of major interest to the research community for portable, stationary, and transportation applications. The use of expensive platinum and platinum-based materials as electrocatalysts limits the commercialization of these fuel cells. Many efforts have been made to reduce the use of such expensive metals. In the recent past, ultra-thin metal-oxide based materials are being explored as new class of electrode materials for PEMFCs [1]. Ceria (CeO2), a reducible oxide is very interesting and can be a game changer in replacing the expensive platinum-based electrode materials. The reactivity of ceria towards H2 dissociation can be altered by doping it with cationic species such as Ag, Au and Cu. Ceria doped with such metals reduces the energy barrier for the dissociation of H2 and becomes a potential candidate for electrode material in fuel cells.


In this talk I will discuss a study of the reactivity of Cu-modified ultra-thin epitaxial CeO2 films on Pt (111) towards H2 dissociation in UHV conditions. The films are prepared by reactive MBE and XPS is used to study the changes in the oxidation state of Ce ions, O vacancy formation and hydroxyl group formation on the surface after thermal reduction cycles in H2. STM is being employed to understand the changes in surface morphology of the samples after each reduction cycle. Cu-modified ceria films showed a higher concentration of Ce3+ after thermal treatments under H exposure and a lower activation temperature (470 K-570 K) than the Ag-modified and pure CeO2 films previously investigated [2]. The observed reactivity of the films is higher in presence of a pure CeO2 buffer layer, due to confinement of Cu atoms on the surface, in agreement with theoretical predictions [3]. A significant increase in OH concentration on the surface is observed with the increase in thermal reduction temperature in H atmosphere. STM results show no significant changes on the surface morphology of Cu-modified ceria films after all reducing thermal treatments. The reactivity towards H2 dissociation will be compared also with that of Cu nanoparticles supported on the surface of a cerium oxide film.


[1] Kosmala, Tomasz, et al., ACS catalysis 8.3 (2018): 2343-2352
[2] S. Benedetti et al., ACS Appl. Mater. Interfaces 12, 27682 (2020)
[3] G. Righi et al. J. Phys. Chem. C 123, (2019) 9875


See the SLIDES of the presentation.