Steam Gasification of PEMFC Catalysts: An Endothermal Process to Create Accessible Carbon Support Morphologies

Abstract

Platinum catalysts supported on porous carbons are considered state-of-the-art for proton-exchange membrane fuel cells (PEMFCs) due to their ability to protect Pt nanoparticles within the internal pores of the primary carbon particles. This shielding enables high oxygen reduction reaction (ORR) activity by separating the Pt particles from ionomer contact and endows them with greater resilience against voltage cycling-induced degradation. However, the pore enclosure impedes oxygen diffusion to internal platinum particles at high current densities, incurring significant voltage losses particularly at low cathode loadings (∼0.07 mgPt cm−2). Such transport bottlenecks can be mitigated by localized oxidation, a thermal post-treatment enabling Pt particles to etch open the surrounding pore space via Pt-catalyzed carbon oxidation. The strong exothermicity of this reaction, however, is challenging for process scale-up. We explore Pt-catalyzed steam gasification of Pt/Ketjenblack as an endothermal, but otherwise functionally similar post-treatment to increase catalyst accessibility. Connecting physico- and electrochemical characterizations of steam-gasified catalysts, we identify the generation of mesopore volume to be crucial for high current density performance and efficient oxygen transport. Ultimately, locally oxidized and steam-gasified catalysts reveal subtle differences in their respective etching mechanisms, resulting in marginally less efficient pore opening, but also better ORR activity retention for steam gasification.