A new geometric method based on two-dimensional transmission electron microscopy for analysis of interior versus exterior Pd loading on hollow carbon nanofibers

Hallow carbon nanofibers (CNFs) are being explored as catalyst supports because of their unique properties; catalytic activities with both interior and exterior metal loadings are being evaluated. Electron tomography (3D transmission electron microscopy, 3D TEM) has been used to estimate internal versus external loading of metal nanoclusters. However, this method is time consuming and requires a specialized TEM. We prepared three hollow CNF supported Pd samples with various Pd localizations, and developed a geometric analysis method based on 2D TEM images to estimate Pd internal versus external loading percentages. Results show the similar localization for the same sample in terms of the number, surface area, and mass of Pd nanoclusters but distinct values for different samples. To test our method, we compare results for one segment of a CNF using both 3D scanning transmission electron microscopy (3D TEM) and our new 2D geometic analysis method. Agreement is within 15.1%. Our results also agree with 3D TEM results from the literature for similarly prepared Pd on CNFs (within 5.6%). Our geometric analysis method is proposed as a more straightforward and fast way to evaluate metal nanocluster localizations on tubular supports.