Revealing the Nanostructure of Mesoporous Fuel Cell Catalyst Supports for Durable, High-Power Performance

TL;DR

This study reveals that mesoporous carbon supports with microporous channels enhance oxygen transport and power performance in fuel cell catalysts, despite faster degradation, by optimizing nanoscale pore structure.

Contribution

It demonstrates that microporous channels in accessible porous carbons improve oxygen transport and fuel cell performance, providing insights into nanoscale catalyst support design.

Findings

Accessible porous carbons have larger, more numerous mesopores.

Oxygen transport primarily occurs through microporous channels.

Accessible carbons maintain high performance despite faster degradation.

Abstract

Achieving high power performance and durability with low Pt loadings are critical challenges for proton exchange membrane fuel cells. PtCo catalysts developed on new carbon black supports show promise by simultaneously providing good oxygen reduction kinetics and local oxygen transport. We investigate the role of nanoscale morphology in the performance of these catalysts supported on accessible (HSC-e and HSC-f) and conventional (Ketjen Black) porous carbons using 3D electron tomography, nitrogen sorption, and electrochemical performance measurements. We find that the accessible porous carbons have hollow interiors with mesopores that are larger and more numerous than conventional porous carbons. However, mesopore-sized openings (>2nm width) are too rare to account for significant oxygen transport. Instead we propose the primary oxygen transport pathway into the interior is through 1-2nm microporous channels permeating the carbon. The increased mesoporosity in the accessible porous carbons results in a shorter diffusion pathlength through constrictive, tortuous micropores in the support shell leading to lower local oxygen transport resistance. In durability testing, the accessible porous carbons show faster rates of electrochemical surface area loss, likely from fewer constrictive pores that would mitigate coarsening, but maintain superior high current density performance at end of life from the improved local oxygen transport.