Tailored concave platinum nanocrystals for the selective electro-oxidation of formic acid

Abstract

The controlled synthesis of noble nanoengineered metal nanocrystals with uniform geometries has been a pivotal research focus, driven by their extensive applications in electrocatalysis. This study elucidates a facile synthesis of concave platinum nanocrystals (Pt-NCs) that exhibit high-index facets via a solvothermal method. The formation of distinct morphology was influenced by the addition of a surface modifier, i.e. Methylamine, significantly tuning the surface morphology with a 44% degree of concavity in Pt-NCs. In addition, microscopic investigations, including field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM), reveal their unique concave high-index faceted morphology. Furthermore, the powder X-ray diffraction (p-XRD) pattern confirms the crystal lattices of Pt-NCs. From the measured cyclic voltammograms, it is understood that Pt-NCs selectively choose a direct pathway for formic acid oxidation, whereas commercial Pt/C (i.e. Comm. Pt/C) is more prone to the indirect pathway. The critical role of high-index facets in improving catalytic performance in comparison to Comm. Pt/C, especially regarding Eonset for the formic acid oxidation and carbon monoxide (CO) tolerance, was discussed. The effect of temperature on formic acid oxidation for Pt-NCs and Comm. Pt/C was explored. Pt/NCs possesses a lower activation enthalpy (ΔH^‡) in comparison to Comm. Pt/C, indicating a preferential direct oxidation pathway. These insights present a promising pathway for developing advanced catalytic materials in energy conversion applications.