Pt Catalysts Supported on Polybenzimidazole-Grafted Graphene for PEMFCs

The performance of a PEMFC is dominated by its catalyst performance, which depends on the size and distribution of the catalyst on the surface of the carbon support. A functionalized carbon support allows better dispersion of the catalyst nanoparticles, which can reduce the aggregation of metal nanoparticles and, consequently, improve the catalyst performance.¹ Graphene is single-atomic-layer-thick carbon atoms arranged in a hexagonal lattice, which is the thinnest catalyst support for Pt catalyst nanoparticles. Graphene has many advantages over conventional carbon black catalyst support, like high electronic conductivity, surface area, mechanical strength, and excellent stability.² All of these unique properties make the graphene as an ideal candidate for Pt catalyst support in polymer electrolyte fuel cells (PEFCs).³ In this work, covalently-functionalized graphene with polybenzimidazole (PBI) was employed as the catalyst support. The Pt nanoparticles were uniformed deposited onto graphene/PBI due to a strong interaction between PBI and Pt. Such Pt catalyst supported on the PBI grafted graphenes will benefit the MEA for PBI membrane based PEMFCs.  The synthesized catalysts were characterized using rotating disk electrode (RDE) for their elctrocatalytic performance.

 The Cyclic voltammetry (CV) curves of graphene/PBI supported Pt catalyst at a scan rate of 20 mV/s in N₂-saturated 0.1 M HClO₄ is shown in Figure 1. The electrochemical active surface area (ECSA) was calculated to be about 55 m²_Pt/g_Pt, which is comparable with that of commercial E-TEK Pt/C catalyst (58 m²_Pt/g_Pt). The high ECSA value suggests the uniform distribution of Pt on the surface of graphene/PBI. Accelerated degradation tests (ADT) were also evaluated by monitoring the changes in electrochemical surface area during voltage cycling between 0.6 V and 1.2 V at a scan rate of 20 mV/s in N₂-saturated 0.1 M HClO₄. After 1000 cycles, a relatively surface area loss of more than 81% was observed in commercial catalyst. In comparison, the relative surface area loss of graphene/PBI supported Pt catalyst was 57%. The increase in the stability of catalyst may result from the strong binding of Pt nanoparticles onto PBI-grafted graphene. In conclusion, the high ECSA and excellent durability of graphene/PBI supported Pt catalyst illustrates the advantage of polybenzimidazole-grafted graphene as a catalyst support in PEMFCs.