Polybenzimidazole (PBI) Functionalized Nanographene as Highly Stable Catalyst Support for Polymer Electrolyte Membrane Fuel Cells (PEMFCs)

Abstract

Nanoscale graphenes were used as cathode catalyst supports in proton exchange membrane fuel cells (PEMFCs). Surface-initiated polymerization that covalently bonds polybenzimidazole (PBI) polymer on the surface of graphene supports enables the uniform distribution of the Pt nanoparticles, as well as allows the sealing of the unterminated carbon bonds usually present on the edge of graphene from the chemical reduction of graphene oxide. The nanographene effectively shortens the length of channels and pores for O 2 diffusion/water dissipation and significantly increases the primary pore volume. Further addition of p-phenyl sulfonic functional graphitic carbon particles as spacers, increases the specific volume of the secondary pores and greatly improves O 2 mass transport within the catalyst layers. The developed composite cathode catalyst of Pt/PBI-nanographene (50 wt%) + SO 3 H-graphitic carbon black demonstrates a higher beginning of life (BOL) PEMFC performance as compared to both Pt/PBI-nanographene (50 wt%) and Pt/PBI-graphene (50 wt%) + SO 3 H-graphitic carbon black (GCB). Accelerated stress tests show excellent support durability compared to that of traditional Pt/Vulcan XC72 catalysts, when subjected to 10,000 cycles from 1.0 V to 1.5 V. This study suggests the promise of using PBI-nanographene + SO 3 H-GCB hybrid supports in fuel cells to achieve the 2020 DOE targets for transportation applications. High stability is required for polymer electrolyte membrane fuel cells (PEMFCs) catalyst supports because they play a critical role in determining the overall durability of PEMFC systems.1 Carbon-based supports have been widely used to support Pt or Pt alloy catalysts in PEMFCs.2 High-surface-area carbon (HSAC) supports minimize the aggregation of the catalyst nanoparticles as HSAC provides more sites for catalyst to nucleate than low-surface-area-carbon (LSAC), thereby avoiding forming big aggregates. Thus, it increases the Pt utilization that leads to more active electro-catalysts with low platinum loadings (< 0.1 mg-Pt/cm 2 ), 2 yet HSAC is vulnerable for corrosion due to the increased surface area. Good electrical conductivity of the carbon materials provides good electron transport.3 In addition, the random aggregates of the primary carbon particles help the distribution of ionomer to access the active sites during the fabrication of membrane electrode assemblies (MEA), and also allow the construction of a highly porous catalyst layer that enables O 2 diffusion and the water dissipation in PEMFCs. The most commonly used carbon blacks in low temperature PEMFCs include Vulcan XC72 (Cabot Corp., USA), Black Pearls 2000 (Cabot Corp., USA) Ketjen Black EC300j (AkzoNobel Corp., the Netherlands), Ketjen Black EC600 (AkzoNobel Corp., the Netherlands), etc. These carbon blacks consist of inhomogeneous graphitic structures and amorphous carbons. 4 The small size of the graphitic domains cause a high density of edge sites, (particularly in the case of high BET (Brunauer-Emmett-Teller) surface area carbon supports), ...

The Key to High Performance Low Pt Loaded Electrodes

“…We hypothesize that this is due to achieving a more homogeneous ionomer coverage on the carbon support (Vulcan XC72) which we functionalized with amide/imide/lactam groups (-NH x ), which are known to ionically interact with the ionomer's sulfonic acid groups (-SO 3 H). 20,21 This hypothesis is consistent with a very recent conference report 22 and with our finding that the unassigned MEA voltage losses, i.e., after correction for the measured proton and oxygen transport resistances, are reduced to unprecedentedly low values in MEAs based on NH x -functionalized carbon supports.…”

Engineering Catalyst Layers for Next‐Generation Polymer Electrolyte Fuel Cells: A Review of Design, Materials, and Methods

“…Novel support materials such as metal oxides, graphene, or functionalized carbon supports have been widely proposed to promote aspects of the CL design, such as ionomer distribution and corrosion resistance. [ 74,178,324,186,225,253,319–323 ] The thickness and distribution of the Nafion film is dependent on the substrate surface composition and chemistry. [ 79,193,212 ] Hence, functionalization of the support material has the potential to alter ionomer distribution on the surface affecting the morphology of the resulting CL and improving electrode performance.…”

“…[ 64,70–73 ] It has also been reported that support durability and CL performance can significantly depend on the chemical composition of the support, as well as the degree and nature of its functionalization. [ 74–76 ] The support material does not just impact electrical conductivity and carbon corrosion, but also reactant mass transport and ionomer distribution, necessitating understanding of structure–performance relationships in the CL. [ 52,76–81 ] The morphology of the CL is usually defined by the structure of the support material and the manufacturing method, both of which play a role in shaping the morphology and therefore performance of the CL.…”

The Use of CeO2-TiO2 Nanocomposites as Enzyme Immobilization Platforms in Electrochemical Sensors

“…After the discovery of the unique physicochemical properties of nanomaterials, they have started to be used as catalysts in various applications to achieve improved performance in different applications ranging from energy and sensing to electronic materials (13)(14)(15)(16)(17). By the use of nanoparticles in electrochemical sensors, it became possible to construct electrochemical sensors with enhanced electrochemical performance due to their unique physical, chemical, and catalytic properties (18,19).…”