Alkaline Formate Oxidation with Colloidal Palladium–Tin Alloy Nanocrystals

The design of advanced catalysts for newer-generation fuel cells such as direct formate fuel cells (DFFCs) is an important milestone for energy generation and environmental sustainability. Formate as an alternative for alcohols in direct liquid fuel cells is gaining momentum since they can be regenerated from CO2, providing dual benefits of energy generation and carbon footprint reduction under the framework of the circular economy. Anticipating advantages from the oxyphilicity and lower electronegativity in tin (Sn)-alloyed palladium (Pd) crystals than to pure palladium catalysts (Pd/C), we developed effective nano-PdSn alloy crystals over carbon support (PdxSny/C) through a colloidal crystal growth scheme. The alloyed nanocrystals were characterized for the alkaline formate oxidation reaction (FOR) intended for their suitability as DFFC anode catalysts, and several-fold enhancement was observed with higher current density, lower onset potential, and enhanced stability compared to Pd/C. Density functional theory (DFT) calculations provided proper insights into the promotional effects upon appropriate alloying of Sn with Pd, with structural changes and the consequent modifications of the density of states, enhanced OHads in alkaline conditions, reduced intermediate poisoning (Hads and COads), and lowering of work function being identified as factors leading to excellent formate oxidation kinetics. The results obtained and detailed here could be used to design and process Pd nanocatalysts for better-performing DFFCs.