Stability and Degradation of Pt/C Catalysts Explored with IL-TEM

Abstract

Industrial application of fuel cells, while, hopefully, inevitable, is still hindered by various aspects, one of them being the issue with oxygen reduction reaction (ORR) catalysts. Current state of the art platinum catalysts, while extraordinarily active, still have a long way to go when it comes to stability. In this work we have decided to tackle this problem by employing FW200 carbon black as a support for platinum nanoparticles. The carbon support was treated in 3000 °C to obtain highly ordered, graphitic structure. We’ve discovered that our catalyst, while initially exhibiting lower electrochemical surface area (ECSA) than it’s commercial, Vulcan-based counterpart, degraded with substantially slower rate than the industrial catalyst. We’ve came to that conclusion after subjecting the catalysts to accelerated degradation tests (ADT) on the rotating ring disk electrode in various potential ranges and performing ECSA and activity measurements during and after said tests. Additionally, to explore degradation mechanisms of the catalysts we’ve used identical localization transmission electron microscopy (ILTEM). This technique allows us to track the behaviour of each platinum nanoparticle, before and after electrochemical measurements, by performing ADT on TEM grids covered with catalyst. ILTEM experiments allowed us to prove, that the crystalline structure of graphitized FW200 hinders nanoparticles’ movement across the carbon support, leading to increased resistance to agglomeration. We used inductively coupled plasma optical emission spectroscopy to investigate platinum dissolution’s part in reducing catalyst activity by measuring the amount of platinum left in electrolyte after ADT. Lastly, we’ve investigated the influence of heat treatment in 3000 °C on the structure and electronic properties of the FW200 carbon black using Raman spectroscopy and X-ray photoelectron spectroscopy. Thorough electrochemical and structural study of platinum catalyst deposited on graphitized FW200 carbon black allowed us to confirm, that our material is highly competitive, in the terms of stability, to commercially available Vulcan-based catalysts. We also think that ILTEM, while exceptionally powerful, is still quite an underutilized technique and we would like to present how joint efforts of microscopists and electrochemists can push the boundaries of knowledge in ORR electrochemistry.