An effort to develop new sustainable energy conversion and storage technologies has been ongoing in recent years within the field of electrocatalysis. At present, formic acid and methanol are among the most promising fuels for low-temperature fuel cells [1]. However, utilizing these carbon-based fuels yields one problem, namely the poisoning of the catalyst by carbon monoxide [2]. It was shown that it is possible to manage this issue by controlling atomic ensembles with specific geometric configurations in both electrochemical energy conversion and green electrosynthesis, giving importance to this type of systems for both purposes [2-4]. By creating atomic ensembles, it is possible to tune both activity and selectivity of electrochemical energy conversion reactions such as the oxygen reduction reaction [3,4]. In the case of more complex reactions involving different reaction intermediates and products, this approach could allow to selectively produce renewable chemicals and fuels.

This work aims to investigate the role of Pd atomic ensembles in electrocatalytic reactions such as formic acid oxidation. Pd electrodeposition on Au (111) single crystalline electrodes allows the formation of Pd atomic ensembles and monolayers that act as selective adsorption sites for reactants [5]. Herein, Pd deposition was investigated by electrodeposition of PdSO₄, K₂PdCl₄ in acidic medium relative to a surface alloy of Pd_1-x/Au_x. The alloy was prepared by engineering mixtures of both metal ions for the preparation of an atomic ensemble with a specific geometric configuration. Pd/Au (111) electrodes were characterized by electroanalytical techniques, allowing identification of the best method to modify the Au (111) electrode surface. Moreover, the chemical composition of the active phase was investigated by Angle-Resolved X-ray Photoelectron Spectroscopy (AR-XPS). The different reactivity of thin palladium monolayers is compared with the reactivity of selected monomers, dimers and trimers of palladium on gold. This can give insight on how tailoring the surface can improve the binding of selected reactants, improving the overall selectivity of the process. Ultimately, the design of bimetallic catalysts with geometric atomic ensembles holds promise towards enabling and adding insight to the fundamental understanding of sustainable electrocatalytic processes.