CeO2/rGO co-catalysts for PEMFCs

CeO2/rGO co-catalysts for PEMFCs L. Iacobini1*, N. Carboni1, J. Montero1, V. Naticchioni2, M.A. Navarra1,3 1Dept. of Chemistry, Sapienza University of Rome, Rome, 00185, Italy 2ENEA, CR-Casaccia, Via Anguillarese 301, 00123, Rome, Italy 3hydro-Eco Research Center, Sapienza University of Rome, Via A. Scarpa,16, 00161, Rome, Italy *luna.iacobini@uniroma1.it Hydrogen has become, especially during the recent years, one of the protagonists on the continuous race towards sustainable and clean energy sources. Following this trend, proton-exchange membrane fuel cells (PEMFCs) are electrochemical devices able to directly convert chemical energy into electricity by the total reaction 𝐻2(𝑔)+ 1 2 O2  H2O (𝑔/𝑙), producing only water as by-product. The very high efficiency of these systems (~60%) compared to combustion systems (~30%) encourages their study and their development. Anyways, PEMFCs have some problems to overcame, the main one is related to the low kinetics of the oxygen reduction reaction (ORR) that occurs on the cathode side and that requires the employment of a catalyst to enhance the kinetics and at the same way reduce the overpotential of the process. The best choice in terms of catalytic activity for this type of fuel cells is Platinum, but it is very expensive (~$28.95 per gram) due to its low abundance and it suffers, like other noble metals, for very easy passivation and contamination. For this reason, the demand for a cheaper alternative is of paramount importance. Here, 𝐶𝑒𝑂2/𝑟𝐺𝑂 (reduced-Graphene Oxide) is proposed as a promising additive to the commercial Pt/C catalyst, aimed to reduce the Platinum loading and enhance the catalyst efficiency [2]. The 𝐶𝑒𝑂2 has been synthetized generating oxygen vacancies (namely, 𝐶𝑒𝑂2-δ) that act as catalytic centers where the reduction of the oxygen can take place [1]. Moreover, thanks to its hygroscopicity, 𝐶𝑒𝑂2 can help in the cell water management and reduce flooding effects. This non stoichiometric compound acts also as an oxygen radical scavenger, thanks to the 𝐶𝑒3+-to-𝐶𝑒4+ conversion consuming unwanted peroxides of the complex ORR [1]. Despite all these good qualities, it is known that cerium ions may become soluble in water, migrating from the electrode towards the membrane in which they can form ionic interaction with the anionic sulfonic groups of the acidic polymer, thus reducing the proton conductivity. The 𝑟𝐺𝑂 is found to be a good choice to get a better stability of the ceria and, according to its reduction degree, it can promote good electrical conductivity and provide high surface area for a more efficient catalyst deposition. Synthesis, physical-chemical characterizations, and electrochemical tests, both ex-situ by rotating disk electrode analysis and in-situ by FC performances evaluation, will be presented in this work, proving the effect of the 𝐶𝑒𝑂2/𝑟𝐺𝑂 on the ORR kinetics. Acknowledgements: The financial support of ENEA within the PNRR POR H2 - Mission 2 – Component 2 – Investment 3.5, is gratefully acknowledged (Project title: “Synthesis and characterization of low-cost alternative catalysts for low-temperature fuel cells. References [1] L. Mazzapioda, G. Moscatelli, N. Carboni, S. Brutti, M.A. Navarra, ChemElectroChem, Volume 10, (2023) 9. [2] P. Salarizadeh, M.B. Askari, H. Beydaghi, M. Rastgoo-Deylami, S. M. Rozati, JPhysChemSolids, Volume 159 (2021) 8.