Trimetallic Alloys as an Electrocatalyst for Fuel Cells: The Case of Methyl Formate on Pt₃Pd₃Sn₂

The shift toward renewable energy sources plays a central role in the quest for a circular economy. In this context, methyl formate (MF) has garnered attention as a compelling hydrogen carrier and alternative fuel, because of its remarkable characteristics (energy density, ease of storage and transport, and low boiling point). In this study, DFT calculations supported by online electrochemical mass spectroscopy (OE-MS) were performed to investigate the MF electro-oxidation (MFEO) on Pt₃Pd₃Sn₂ (111). The DFT calculations provide insight into the role of Pt, Pd, and Sn atoms in MFEO. Pt and Pd together provide a preferred active site for initiating MFEO through the O-H bond scission, and Sn plays an essential role in the mitigation of CO through oxygenation or water activation. By comparing the reaction energies and activation barriers for all possible reactions in MFEO, the suggested path necessitates a minimum energy of 0.14 eV to initiate the MFEO. This value was supported by the experimental results, showing that the oxidation wave of MF starts at 0.15 V (70 °C). Density functional theory (DFT) results, supported by OE-MS, indicate that the hydrolysis of MF prior to MFEO is not preferred on Pt₃Pd₃Sn₂ (111) surfaces, although the formation of methanol is plausible via a CH₃O intermediate. Among the three small organic molecules (SOMs) studied─MF, methanol, and formic acid─MF has the lowest activation energy for the initial bond breaking that starts the whole oxidation process (0.13 eV), compared to formic acid (0.45 eV) and methanol (0.61 eV); thus, MF is the preferred fuel on Pt₃Pd₃Sn₂ (111).