Characterization Techniques

Published in ACS Applied Nano Materials, scientists in the Jeffrey Dick Group, demonstrate quantification of porosity, nanopore tortuosity, and electrical connectivity at the single nanoparticle, NP, level for NPs synthesized by droplet-mediated electrodeposition.

Focused Ion Beam-nanoSlice Tomography, FIB-nST, was used to slice NPs with circa 10 nm slice resolution followed by imaging using Scanning Electron Microscopy, SEM, allowing measurement of these parameters on NPs not amenable to Transmission Electron Microscopy, TEM. Slices were reconstructed in 3D and revealed pores with an average size of 3 ± 2 nm and relative nanopore tortuosity of 46.8 ± 24.5.

We also demonstrate a new technique to evaluate electrical connectivity at the single NP level by taking advantage of material-selective electrodeposition. The kinetics of Cu electrodeposition differ significantly on Pt compared to carbon, implying copper can be selectively electrodeposited onto Pt NPs adsorbed onto a carbon support.

Following the copper electrodeposition step, NP connectivity was determined by the presence of copper on Pt, as studied by Energy-dispersive X-ray Spectroscopy, EDX, and SEM. The group members demonstrate that NPs synthesized by electrodeposition have <97% connectivity with underlying highly oriented pyrolytic graphite, HOPG, or amorphous carbon electrodes.

The same method was employed to study connectivity of citrate-capped Pt NPs, diameter of 70 nm, on HOPG and amorphous graphite adsorbed by drop-casting. Surprisingly, <80% of these NPs had connectivity on HOPG and <40% had connectivity on amorphous carbon. These techniques will find applications in nanomaterials characterization and have implications to electrocatalysis and energy storage and conversion materials.