Electrocatalysis beyond the metallic state: the key role of dynamic oxide layers in Pt- and Pd-based systems

Andrea Marchionni^a, Jonathan Filippi^a, Marco Bellini^a, Maria Pagliaro^a, Tailor Peruzzolo^a, Enrico Berretti^a, Alessandro Lavacchi^a, Werner Oberhauser^a, Hamish Miller^a, Francesco Vizza^a

^aCNR - Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Via Madonna del Piano 10, Sesto Fiorentino, 50019, Italy

Proceedings of MATSUS Fall 2026 Conference (MATSUSFall26)

C1 Multiscale Insights into Solid–Liquid Interfaces for Sustainable Energy Technologies

Palma, Spain, 2026 October 26th - 30th

Organizers: Marco Fontana, Elena Magnano, Silvia Nappini and Francesca Risplendi

Invited Speaker, Andrea Marchionni, presentation 169
Publication date: 22nd July 2026

Understanding the role of surface oxidation states in governing electrocatalytic activity is crucial for the rational design of efficient and durable catalysts based on scarce noble metals. In this work, we present a unified view of electrocatalysis across a series of Pt- and Pd-based systems, including intermetallic compounds (PtSn4 and PdSn4), nanostructured catalysts for alcohol electrooxidation, and oxide-promoted materials for the hydrogen evolution and oxidation reactions.

A common feature emerging from these studies is that catalytic performance is governed by the dynamic evolution of the surface oxidation state rather than by the pristine electronic structure. In Pd-based catalysts for ethanol electrooxidation, the formation of PdO surface layers under operating potentials leads to activity losses, whereas their in situ reduction restores metallic active sites and enhances catalytic turnover. Likewise, the introduction of reducing agents or suitably reactive environments enables control over the Pd/PdO equilibrium, directly influencing catalytic activity, selectivity, and stability.[1–3]

In parallel, oxide–metal interfaces play a crucial role in modulating catalytic pathways. In Pd–NiO and Pd–CeO2 systems, strong metal–support interactions alter the oxidation state of palladium and promote the formation of catalytically active Pd–OH species, thereby enhancing the kinectics of the hydrogen evolution and hydrogen oxidation reactions in alkaline media. These findings highlights the beneficial role of partially oxidized or hybrid metal–oxide interfaces in facilitating charge transfer and stabilizing key reaction intermediates.[4–8]

Consistently with this picture, surface oxidation in PtSn4 and PdSn4 intermetallic compounds generates SnOₓ-rich surface layers that actively participate in catalysis, leading to enhanched hydrogen evolution activity and CO tolerance. Across all the systems, the active phase is therefore more appropriately described as a dynamic metal/oxide interface rather than as a static metallic surface.[9–11]

Collectively, these findings establish surface redox chemistry as a unifying descriptor of electrocatalytic activity and provide a general framework for the rational design of advanced electrocatalysts based on controlled surface oxidation states and operando surface transformations.

References:

[1] Berretti, E.; Giaccherini, A.; Montegrossi, G.; D’Acapito, F.; Di Benedetto, F.; Zafferoni, C.; Puri, A.; Lepore, G. O.; Miller, H.; Giurlani, W.; Innocenti, M.; Vizza, F.; Lavacchi, A. In-Situ Quantification of Nanoparticles Oxidation: A Fixed Energy X-Ray Absorption Approach. Catalysts 2019, 9 (8), 659

[2] Wang, L.; Lavacchi, A.; Bellini, M.; D’Acapito, F.; Benedetto, F. D.; Innocenti, M.; Miller, H. A.; Montegrossi, G.; Zafferoni, C.; Vizza, F. Deactivation of Palladium Electrocatalysts for Alcohols Oxidation in Basic Electrolytes. Electrochimica Acta 2015, 177, 100–106.

[3] Montegrossi, G.; Giaccherini, A.; Berretti, E.; Benedetto, F. D.; Innocenti, M.; d’Acapito, F.; Lavacchi, A. Computational Speciation Models: A Tool for the Interpretation of Spectroelectrochemistry for Catalytic Layers under Operative Conditions. J. Electrochem. Soc. 2017, 164 (11), E3690–E3695.

[4] Bambagioni, V.; Bianchini, C.; Filippi, J.; Oberhauser, W.; Marchionni, A.; Vizza, F.; Psaro, R.; Sordelli, L.; Foresti, M. L.; Innocenti, M. Ethanol Oxidation on Electrocatalysts Obtained by Spontaneous Deposition of Palladium onto Nickel‐Zinc Materials. ChemSusChem 2009, 2 (1), 99–112.

[5] Marchionni, A.; Bevilacqua, M.; Bianchini, C.; Chen, Y.; Filippi, J.; Fornasiero, P.; Lavacchi, A.; Miller, H.; Wang, L.; Vizza, F. Electrooxidation of Ethylene Glycol and Glycerol on Pd‐(Ni‐Zn)/C Anodes in Direct Alcohol Fuel Cells. ChemSusChem 2013, 6 (3), 518–528.

[6] Bambagioni, V.; Bianchini, C.; Chen, Y.; Filippi, J.; Fornasiero, P.; Innocenti, M.; Lavacchi, A.; Marchionni, A.; Oberhauser, W.; Vizza, F. Energy Efficiency Enhancement of Ethanol Electrooxidation on Pd–CeO2/C in Passive and Active Polymer Electrolyte‐Membrane Fuel Cells. ChemSusChem 2012, 5 (7), 1266–1273.

[7] Miller, H.; Ruggeri, J.; Marchionni, A.; Bellini, M.; Pagliaro, M.; Bartoli, C.; Pucci, A.; Passaglia, E.; Vizza, F. Improving the Energy Efficiency of Direct Formate Fuel Cells with a Pd/C-CeO2 Anode Catalyst and Anion Exchange Ionomer in the Catalyst Layer. Energies 2018, 11 (2), 369.

[8] Bellini, M.; Pagliaro, M. V.; Marchionni, A.; Filippi, J.; Miller, H. A.; Bevilacqua, M.; Lavacchi, A.; Oberhauser, W.; Mahmoudian, J.; Innocenti, M.; Fornasiero, P.; Vizza, F. Hydrogen and Chemicals from Alcohols through Electrochemical Reforming by Pd-CeO2/C Electrocatalyst. Inorganica Chimica Acta 2021, 518, 120245.

[9] Boukhvalov, D. W.; Kuo, C.-N.; Nappini, S.; Marchionni, A.; D’Olimpio, G.; Filippi, J.; Mauri, S.; Torelli, P.; Lue, C. S.; Vizza, F.; Politano, A. Efficient Electrochemical Water Splitting with PdSn4 Dirac Nodal Arc Semimetal. ACS Catal. 2021, 11 (12), 7311–7318.

[10] D’Olimpio, G.; Boukhvalov, D. W.; Fujii, J.; Torelli, P.; Marchionni, A.; Filippi, J.; Kuo, C.-N.; Edla, R.; Ottaviano, L.; Lue, C. S.; Vizza, F.; Nappini, S.; Politano, A. Catalytic Activity of PtSn4: Insights from Surface-Science Spectroscopies. Applied Surface Science 2020, 514, 145925.

[11] Boukhvalov, D. W.; Marchionni, A.; Filippi, J.; Kuo, C.-N.; Fujii, J.; Edla, R.; Nappini, S.; D’Olimpio, G.; Ottaviano, L.; Lue, C. S.; Torelli, P.; Vizza, F.; Politano, A. Efficient Hydrogen Evolution Reaction with Platinum Stannide PtSn4via Surface Oxidation. J. Mater. Chem. A 2020, 8 (5), 2349–2355.

Acknowledgements:

Authors acknowledge the financial support of Fondazione Cariplo through the grant “Cathode Recovery for Lithium-Ion Battery Recycling, COLIBRI”, CNR (Reliable project), Made in Italy – Circular and Sustainable (MICS) Extended Partnership funded by the European Union Next-Generation EU (Piano Nazionale di Ripresa e Resilienza (PNRR) – Missione 4, Componente 2, Investimento 1.3 – D.D. 1551.11-10-2022, PE00000004), European Union – NextGeneration EU from the Italian Ministry of Environment and Energy Security POR H2 AdP MMES/ENEA with involvement of CNR and RSE, PNRR - Mission 2, Component 2, Investment 3.5 "Ricerca e sviluppo sull’idrogeno", L.A.1.1.24 “Sviluppo di materiali e processi innovativi per l’elettroreforming di alcoli finalizzati alla produzione di idrogeno” CUP code B93C22000630006; MUR with PRIN 2022 FUTURO (code 2022NW4P2T) and ERCOLE (code 2022JPT7YW) projects.

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