Optimal Ratio Identification for Formic Acid Oxidation in Pd–Sn–Ir Catalyst Arrays

The Pd–Sn–Ir catalyst array was prepared using the concept of combinatorial methods, and the optimal catalyst composition for catalytic formic acid oxidation was rapidly screened using electrochemical scanning microscopy (SECM). Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed that the elemental composition of the Pd–Sn–Ir catalysts matched the molar concentration ratios of the precursor solution. Among the Pd–Sn–Ir catalyst arrays, the optimal composition was identified as the Pd₆₀Sn₂₀Ir₂₀ catalyst. The Pd₆₀Sn₂₀Ir₂₀ electrode exhibits higher mass and specific activities for formic acid oxidation than the pure Pd electrode. Additionally, the Pd₆₀Sn₂₀Ir₂₀ catalyst shows superior CO desorption capability. The incorporation of Sn lowers the Pd d-band center, thereby weakening the adsorption of reaction intermediates, while Ir promotes the enrichment of surface hydroxyl species, facilitating intermediate oxidation at lower potentials. As a result, the combined addition of Sn and Ir significantly enhances the catalytic performance for formic acid oxidation and effectively improves the long-term stability of the catalyst.