Abstract
Nanocolumnar platinum thin films (Pt-TFs) were produced by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction electrocatalysts for polymer electrolyte membrane fuel cells. Conventional high-density Pt-TF prepared by low pressure sputtering was also studied for comparison. Pt-TFs were deposited on a microporous layer (MPL)-like surface composed of carbon particles to mimic catalyst-coated gas diffusion electrodes. Electron microscopy imaging revealed that HIPS Pt-TFs developed a cauliflower-like columnar microstructure, which originated from a shadowing effect during HIPS. This shadowing effect is enhanced on the rough surface of the MPL-like carbon that leads to the nano-cauliflower formation. With this approach, we also aimed to relate the catalyst performance obtained by benchtop tests directly to membrane electrode assembly test results. The electrochemically active surface area of Pt-TFs increased from 10 to 19 m2 g-1 with increasing sputter pressure. Specific activity of conventional high-density and nanocolumnar films were similar at ~600 μA cm-2, which is likely due to their similar crystal grain sizes, >5 nm. On the other hand, mass-specific (MA) activity values increased from ~0.06 A/mgPt for conventional Pt-TF to ~0.13 A/mgPt for HIPS Pt-TFs, which is consistent with the columnar microstructure of HIPS films providing a better catalyst utilization compared to conventional Pt-TF.
| Original language | English |
|---|---|
| Article number | 134508 |
| Journal | Journal of the Electrochemical Society |
| Volume | 167 |
| Issue number | 13 |
| DOIs | |
| State | Published - Jan 10 2020 |
Funding
This work was supported by Department of Energy under grant DE-EE0007652, Project ID FC157. TEM was performed at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy Office of Science User Facility. The UA Little Rock authors thank the UALR Center for Integrative Nanotechnology Sciences for helping with SEM imaging. The authors also thank Ion Power for providing half-MEAs for fuel cell tests.
