Pd-Au nanostructured electrocatalysts with tunable compositions for formic acid oxidation

The green transition requires new strategies to develop active and stable nanomaterials for energy conversion. We describe, for the first time, the preparation of Pd-Au bimetallic nanocatalysts using a surfactant-free electrodeposition method in a deep eutectic solvent (DES) and test their electrocatalytic performance for the formic acid oxidation reaction (FAOR). We use choline chloride plus urea DES to tune the composition of Pd and Au in the bimetallic nanostructures, as well as their morphology and active surface area. We measure the increase in the electrochemically active surface area (ECSA) of the prepared Pd-Au bimetallic surfaces by Cu underpotential deposition (UPD). Our results indicate a surface area increase of 5 to 12-fold compared to Pd and PdAu extended polycrystalline electrodes. We observe that the higher activity of Pd-Au nanostructures is principally due to its increased active area. Our results also reveal that Pd-Au nanostructures with ca. 50% of Pd and Au display the best activity and stability in relation to the Pd mass loading proving the synergy between Pd and Au in the bimetallic catalyst. We highlight that an in-depth analysis of the ECSA, as well as surface and electronic structure effects in bimetallic nanostructures, are crucial aspects for the rationalization of their catalytic properties.