Assembly of Pt Nanoparticles on Graphitized Carbon Nanofibers as Hierarchically Structured Electrodes

Abstract

Carbon-based nanofibers decorated with metallic nanoparticles (NPs) as hierarchically structured electrodes offer significant opportunities for use in low-temperature fuel cells, electrolyzers, flow and air batteries, and electrochemical sensors. We present a facile and scalable method for preparing nanostructured electrodes composed of Pt NPs on graphitized carbon nanofibers. Electrospinning directly addresses the issues related to large-scale production of Pt-based fuel cell electrocatalysts. Through precursors containing polyacrylonitrile and Pt salt electrospinning along with an annealing protocol, we obtain approximately 180 nm thick graphitized nanofibers decorated with approximately 5 nm Pt NPs. By in situ annealing scanning transmission electron microscopy, we qualitatively resolve and quantitatively analyze the unique dynamics of Pt NP formation and movement. Interestingly, by very efficient thermal-induced segregation of all Pt from the inside to the surface of the nanofibers, we increase overall Pt utilization as electrocatalysis is a surface phenomenon. The obtained nanomaterials are also investigated by spatially resolved Raman spectroscopy, highlighting the higher structural order in nanofibers upon doping with Pt precursors. The rationalization of the observed phenomena of segregation and ordering mechanisms in complex carbon-based nanostructured systems is critically important for the effective utilization of all metal-containing catalysts, such as electrochemical oxygen reduction reactions, among many other applications.

Versatile Graphitized Carbon Nanofibers in Energy Applications

“…This is due to their favorable properties such as surface area, low density, and superior electrical as well as electronic conductivities and tunable structure, along with thermal, mechanical, and chemical stabilities of carbon-based electrodes 41−43 and their conductive natures 44 support metal/metal oxides in EESDs. 43,45,46 Of the many such materials, CNFs (1D nanostructure) have garnered special attention since these are the allotropes of carbon constituting a fibrous structure having diameters less than 1 μm with a high aspect ratio (over a few hundreds). 47 Originally, CNFs were thought of as a nuisance popular carbon filament, particularly in petrochemical and nuclear industries, formed during catalytic conversion of gases (CO x ).…”

“…The normal CNFs can be treated by various graphitization routes to attain "graphitized or graphitic CNFs" ,and this is elaborated in further sections. 43 The conductivities of CNFs are strongly related to the degree of graphitization. 54,55 A strong graphitic order is necessary to realize the full potential of CNFs as it is required for higher elastic modulus, besides conductivity (thermal and electrical).…”

“…71 The major steps to prepare graphitized CNFs include stabilization of precursor fiber and subsequent carbonization. 43,74,75 Structural stabilization of CNFs via thermal or chemical methods helps to improve the characteristics of CNFs. Thermal stabilization of CNFs at temperatures lower than carbonization temperatures is advantageous for preventing premature structure collapse and undue decomposition apart from mass loss.…”

“…Additionally, Figure 5g and j demonstrate decent Pt−C contact through the embedment that is advantageous for an efficacious electrical coupling along with the augmented stability of the composite. 43 Moreover, the major drawback of electrospun CNFs is that these are formed via superposing CNFs in space by a mere physical connection which is why the electron conduction path is a single CNF blocking the electron transmission in the other direction. Thereby, the construction of a high-speed electron transport network is pivotal for the enhanced energy storage performance of CNFs.…”

“…Carbon-based materials such as carbon black, activated carbon, hierarchical porous carbon, carbon nanotubes (CNTs), nanosheets, and nanofibers (CNFs) have emerged to be the exciting electrode materials in EESDs for over many years. This is due to their favorable properties such as surface area, low density, and superior electrical as well as electronic conductivities and tunable structure, along with thermal, mechanical, and chemical stabilities of carbon-based electrodes − and their conductive natures as fillers to support metal/metal oxides in EESDs. ,, Of the many such materials, CNFs (1D nanostructure) have garnered special attention since these are the allotropes of carbon constituting a fibrous structure having diameters less than 1 μm with a high aspect ratio (over a few hundreds) …”