A nitrogen-doped electrocatalyst from metal-organic framework-carbon nanotube composite
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jia Lin and Zhonghua Zhu The University of Queensland, School of Chemical Engineering, Brisbane 4072, Australia
Hao Wangb) Center for Future Materials, University of Southern Queensland, Springfield Campus, Queensland 4300, Australia (Received 17 July 2017; accepted 29 September 2017)
Replacing precious and nondurable platinum-based catalysts by economical and commercially available materials is a key issue addressed in contemporary fuel cell technology. Carbon-based nanomaterials display great potential to improve fuel tolerance and reduce the cost and stress on metal scalability. However, their relatively low catalytic activity limits the development and application of these catalysts. In this study, we have synthesized a nitrogen-doped carbon electrocatalyst from metal–organic frameworks and carbon nanotube composites, taking advantage of the existing N in the organic linker in the MOFs with more N added through ammonia treatment. The morphology and composition of synthesized catalysts were characterized by SEM, TEM, XPS, and Raman. The derived catalyst exhibited superior catalytic activity than that of commercial Pt-based catalysts. The N enriched carbon catalyst with high surface area, a graphitic carbon skeleton, and a hierarchical porous structure facilitated the mass and charge transfer during electrolysis.
I. INTRODUCTION
As a sustainable and renewable clean energy source, fuel cells, which can generate electricity from fuels, have long been considered as a promising solution to the global energy crisis and environmental pollution caused by fossil fuels. The critical but sluggish oxygen reduction reaction (ORR) in conventional fuel cells limits the current density and cell voltages; therefore, the optimization of electrochemical catalytic performance toward the reduction of oxygen has attracted much attention from both industrial and academic researchers. On the other hand, the expensive and less earth-abundant preciousmetal catalysts (such as Pt/C catalysts) suffer from low tolerance to fuel crossover and the inherently poor efficiency of the ORR; therefore, the ongoing research is focused on the development of cost effective precious metal-free materials with unique electronic properties and high stability. Doped carbon materials have shown promising potentials in competitive activity and significantly enhanced fuel crossover tolerance as compared to commercial Pt/C catalysts.1 Contributing Editor: Chuan Zhao Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.416
Heteratoms doping in the carbon heterocyclic ring offers an effective route to enhance the electron-donor properties of the carbon matrix, improve the spin density and charge distribution of neighboring C atoms, and consequently enhance catalytic activity.2–6 N-doped carbons, such as nitrogen-doped carbon nanotubes or graphene, graphitic C3N4, pyrolytic carbon from polymer/biomass, have been extensively developed as promising ORR catalysts.4,5,7–9 Several key parameters
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