Identical‐location Transmission Electron Microscopy of Pt Nanoparticle Electrocatalysts Using Iridium‐coated Au Grids for Fuel Cell Durability Tests Simulating Start‐up and Shutdown Conditions

Abstract

AbstractIn an identical‐location TEM (IL‐TEM) analysis of an electrocatalyst, an Au grid is usually selected owing to its chemical stability under potential cycling conditions. A potential cycle between 1.0 and 1.5 V is applied to the catalyst‐cast Au grid for cathode durability testing that simulates the start‐up and shutdown conditions of fuel cells. Because of the redox potential of Au (1.36 V vs. RHE), the grid dissolves and redeposits on the catalyst under the applied potential, making it complicated to evaluate the catalyst nanoparticle shape and size after degradation. We fabricated an Au grid coated with an iridium oxide layer (Ir‐coated Au grid) to suppress the dissolution of Au. The Ir‐coated Au grid with carbon support was compared to the Au grid to confirm the effect of the iridium oxide layer. No Au deposition was observed, even after 3000 cycles at 60 °C for the Ir‐coated Au grid, but Au was deposited on carbon on the Au grid after 1000 cycles. Consequently, the alkylamine‐modified Pt nanoparticle catalyst (unwashed catalyst) was observed along with the Ir‐coated Au grid using IL‐TEM under durability tests simulating start‐up and shutdown conditions. A catalyst with less alkylamine content was prepared by butylamine washing (washed catalyst) and observed using IL‐TEM for comparison. The Pt nanoparticles of the washed catalyst aggregated and changed their morphology after 1000 cycles, while the alkylamine‐modified nanoparticles of the unwashed catalyst almost maintained their original size and shape up to 1000 cycles. The Ir‐coated gold grids allow proper IL‐TEM analysis of catalysts in durability tests without the interference of Au dissolution.