Understanding the Performance Increase of Catalysts Supported on N-Functionalized Carbon in PEMFC Catalyst Layers

Abstract

Applying nitrogen-modified carbon support in proton exchange membrane fuel cells (PEMFCs) has been attracting increasing interest due to the resulting performance enhancement. In the present study, we attempted to uncover the origin and gain a deeper understanding of the different N-modification processes, whose influences are responsible for the improvement. By utilizing chemically modified Ketjenblack supports comprising altered fraction of N-functionalities, we investigated the underlying mechanism of the drastically reduced voltage losses under fuel cell operation conditions. In all, we demonstrate the key role of support modification induced by ammonia in strengthened support/ionomer interactions and alter physico-chemical properties of the carbon support contributing towards enhanced MEA performance. With the use of X-ray photoelectron spectroscopy, we show unambiguous evidences that not all N modified surfaces yield the desired performance increase. Rather, the latter depends on a complex interplay between different electrochemical parameter and catalyst properties. We want to emphasize the ionomer/support interaction as one important factor for enhanced ionomer distribution and present a prove of a direct interaction between the ionomers´ sidechains and N-functional groups of the support.

Synergy between Intermetallic Pt Alloy and Porous Co–N4 Carbon Nanofibers Enables Durable Fuel Cells with Low Mass Transport Resistance

“…The increased pyridine N content suggests the formation of Co−N x /C sites and could also enhance the static interaction between PCNF and sulfonic groups in Nafion, which is beneficial to the homogeneous distribution of ionomer throughout the catalysts. 44,45,47 X-ray absorption spectroscopy (XAS) was used to characterize the local environment and electronic structure of the catalysts. The valence change of Pt can be analyzed based on the intensity of the white line in near-edge X-ray absorption spectra (XANES, Figure 3c).…”

Stability challenges of carbon-supported Pt-nanoalloys as fuel cell oxygen reduction reaction electrocatalysts

“…This results in improved MEA performances, especially in the more relevant dry operating conditions. 27,[188][189][190] However, the second main development direction focuses on finding new, better alternatives to CBs. Since the first graphene isolation in 2004 by A. Geim and K. Novoselov, 191 graphene and its derivatives emerged as a potential substitute for CBs as catalyst support.…”

Effect of Substrate Surface Charges on Proton Conduction of Ultrathin Nafion Films

“…This speculation is supported by some experimental observations. Ott et al , introduce NH x or N groups to the surface of the carbon support, which would introduce positive charges to the carbon support. The enhanced interactions between the positively charged carbon surface and sulfonic acid groups of ionomers were proved by X-ray photoelectron spectroscopy (XPS), and the decreased proton resistance of the cathode CL was found at low relative humidity.…”