Thermally Pretreated 46% Pt/Vulcan XC72: Characterisation by TGA/DSC/TEM and Cyclic Voltammetry

Abstract

We report a study of thermal stability and impact of thermal pretreatment procedures for 46% Pt/Vulcan XC72 (Tanaka) fuel cell catalyst. Stability in air and in inert gas (nitrogen, argon, helium) has been investigate by thermal gravimetric analysis (TGA), TGA-mass spectrometry (TGA-MS) and differential scanning calorimetry (DSC). Two distinct low temperature mass loss processes (100-200 and 285-300 degrees C) were observed, each exhibiting unique pretreatment temperature dependencies. TGA-MS data in helium show fragment ions that suggest the thermal degradation processes are associated with decomposition of materials such as processing aids. Transmission electron microscopy (TEM) reveals a modest increase in average Pt nanoparticle size upon thermal pretreatment. After a pretreatment protocol based on TEM and thermal characterisation (300 degrees C/15 min, N-2), the electrochemically active surface area did not increase. At the kinetically controlled potential region (E>0.8 V) there was a small drop in current density for treated 46% Pt/C in comparison with as-received catalyst. The slowing in ORR kinetics is significant. Apparently, the removal of organic components, which would improve mass transport, is negated by increased nanoparticle size.