Effects of Temperature and Atmosphere on Carbon-Supported Platinum Fuel Cell Catalysts

Abstract

International audiencet/Vulcan XC 72 powders were prepared via a colloidal method. TEM and XRD studies were carried out from 273 to 573 K under oxidizing, inert, and reducing atmospheres. Under air flow, a small aggregation of platinum particles is observed, but neither fusion of particles nor increase of the Sherrer's length L-v This is explained by the presence of oxygen species on the platinum surface. Under reducing atmosphere (3%H-2/He), aggregation of platinum particles and increase of the crystallinity and/or apparent mean crystallite size are observed. L-v increases from ca. 3 nm for the fresh Pt(40 wt %)/C catalyst to ca. 7 nm after thermal treatment at 573 K. Under inert atmosphere, TEM and XRD measurements did not show any reconstruction process or L-v increase for temperatures lower than 473 K. But from 523 K, some platinum entity reconstruction was evidenced, Under reducing atmosphere, two kinetics of grain growth process seem to exist. The "induction time" tau before the second growth process is dependent on the temperature, but independent of the platinum loading. For T < 523 K, the formation of a surface Pt-H quasiliquid phase leading to crystalline reconstruction and an agglomeration process are proposed to occur. This step is then followed by grain boundary formation and grain boundary diffusion leading further to the increase of L-v (controlled by the second growth kinetics). For T >= 523 K, reconstruction by size effect is invoked for the first growth process

In Situ Observation of the Thermally Induced Growth of Platinum‐Nanoparticle Catalysts Using High‐Temperature X‐ray Diffraction

“…This result is in line with the values published in the literature for particles above 3 nm with a minimum temperature of 200-300 8C. [13] This explains the observation of a quasistable particle size (around 3 nm) for Pt (46 wt %)/Vulcan XC 72R at 160 8C under N 2 atmosphere. Further particle growth is thus excluded by the elevated temperature of 160 8C.…”

Molecular dynamics simulations of ternary PtxPdyAuz fuel cell nanocatalyst growth

“…Supported Pt nanoclusters are known to fuse below 650 K [50]. Transition to nanofilm in a fused state is expected to have higher wettability and thus the nanofilm can relax to a crystalline state when cooling down.…”

Synthesis of supported metal nanoparticle catalysts using ligand assisted methods

“…In some cases, the temperature causes decomposition of the organic ligands forming residual carbonaceous deposits that have to be removed through oxidationreduction cycles. 69 Sellin et al 70 studied the thermal stability of Pt colloidal NPs prepared in the presence of tetraalkylammonium triethylborohydride and then impregnated on a carbon support. The particles size change was analyzed before and after calcination, clearly showing aggregation.…”