• Catalyst
• non-noble metal
• ORR
• PEMFC
• PGM-free
• supported nanoparticles
• ZrO2

Low-temperature proton-exchange-membrane fuel cells (PEMFCs) are promising energy conversion devices that, in recent years, have been successfully deployed in several vehicles. Besides the numerous advantages, however, they are still too expensive for mass commercialization. To build a fuel cell stack, in fact, a considerable amount of Pt is required, especially at the cathode electrode, where the oxygen reduction reaction (ORR) takes place. Thus, considerable research effort is focused on reducing or completely eliminating noble metal content. One approach is to use cheap and abundant materials, the so-called platinum-group-metal-free (PGM-free) catalysts. Although they are less active than platinum, their price allow to use higher loading, so that the ORR is facilitated.
The most promising candidates demonstrated so far employ N-coordinated Fe as active species, embedded in a matrix of carbon (Fe-N-C catalysts). Aiming at a higher stability in acidic electrolyte than Fe-N-C based compounds, the purpose of this thesis work was to prepare and characterize PGM-free catalysts for the ORR based on carbon-supported ZrO2 nanoparticles.
These metal oxide species are stable in acid solution and their discrete ORR activity was already reported from Ken-ichiro Ota research group, which is studying group IV and V metal-oxide-based compounds since past 10 years.
The active sites for the reaction are not completely understood yet, but there is the hypothesis that they are correlated to the presence of oxygen vacancies or uncoordinated metal sites on the surface of the oxide.
Literature reports the creation of oxygen vacancies in the oxide when either iron or copper are incorporated in ZrO2. For this reason, during this work, Fe- and Cu-doped zirconia has been synthetized starting from soluble metal (Zr, Fe and Cu) phthalocyanines as organometallic precursors.
After impregnation on carbon black, the samples were heat treated to form the oxide nanoparticles. A series of samples were synthesized with different heat treatment conditions and doping-metal loadings. Structural characterization of the samples was primarily done by X-ray diffraction technique and secondly by transmission electron microscopy. For the Fe-doped ZrO2, the samples were analyzed by 57Fe-Mössbauer spectroscopy to monitor the Fe phases and the Fe incorporation.