Characterization of platinum nanoparticles for fuel cell applications by single particle inductively coupled plasma mass spectrometry.

The most effective utilization of platinum (Pt) in fuel cells is achieved through the use of nanoparticles (NPs) that offer a large electrochemically active surface area. Because the stability of NPs decreases as they become smaller, their size and size distribution must be known in order to optimize the catalysts' durability, while offering high catalytic activity. Single particle inductively coupled plasma mass spectrometry (spICPMS) can quantify the mass of metallic NPs suspended in aqueous medium, which can then be converted into a size if the NPs' shape, density and composition are known. In this study, for the first time, spICPMS was compared to transmission electron microscopy (TEM) for the characterization of 10 nm Pt NPs. After verifying the accurate sizing of commercial Pt NPs with diameters of 30, 50 and 70 nm, spICPMS with solution calibration was applied to laboratory-synthesized 10 nm Pt NPs possessing a near spherical shape and 10 ± 2 nm diameter according to TEM. The same NPs were also analyzed by spICPMS with Pt size calibration using Pt NPs standards. Irrespectively of the calibration strategy, spICPMS measured the entire population of 659 Pt NPs (6-65 nm), while TEM analyzed the 500 Pt NPs that appeared isolated in the field of view (6-18 nm). Analysis of the size distribution histograms revealed that the modal and mean diameters were respectively 10 and 11 ± 2 nm using solution calibration, and 12 and 13 ± 2 nm using particle size calibration. Both of these mean diameters are in agreement with the TEM measurements according to a Student's t-test at the 95% confidence level, demonstrating that spICPMS, with a size detection limit of 6 nm, can accurately quantify 10-nm Pt NPs while at the same time analyzing the entire sample.