Stress-activated pyrolytic carbon nanofibers for electrochemical platforms

Abstract

Carbon's electrochemistry depends on its type and microstructure, and how these affect the electrode's electronic density of states. We demonstrate how pyrolysis of electro-mechanically stressed Polyacrylonitrile (PAN) nanofibers, infused with carbon nanotubes, will result in a unique graphitic electrode, which possesses enhanced and multifaceted electrochemical behavior. As corroborated by materials characterization, the microstructure of the stress-activated pyrolytic carbon (SAPC) characteristically contains a high proportion of disorders in the forms of edge planes and embedded heterogeneous nitrogen atoms. These disorders introduce a range of energy states near the Fermi level, yielding enhanced kinetics in the as-synthesized SAPC electrodes. A comprehensive electrochemical study of the SAPC electrode in surface sensitive ([Fe(CN) 6 ] 3-/4-), surface insensitive ([IrCl 6 ] 2-/3-), and adsorption sensitive (dopamine) redox probes demonstrates 5e14-fold increases in its heterogeneous electron transfer rate compared to regular PAN-based carbon electrodes. The fast kinetics of SAPC electrodes in adsorption sensitive analytes translates into its capability for simultaneous detection of dopamine, uric acid, and ascorbic acid. The results point to a new class of pyrolytic carbon electrodes with an attractive electrocatalytic capacity, geared toward electrochemical sensing platforms.

Distinct Roles of Tensile and Compressive Stresses in Graphitizing and Properties of Carbon Nanofibers

“…First, we prepared solutions of PAN precursors that are infused with carbon nanotubes [ 4 , 10 ]. Then, the carbon precursors solution is electrospun into polymer nanofibers mats in a process that is described in detail in our previous reports [ 4 , 10 , 11 , 12 , 13 ]. The electrohydrodynamic forces inherent in the electrospinning process, combined with induced shear fields on the boundary layers of CNTs, unwind the polymer chains and carry out the first stage of molecular alignment in the synthesis process [ 6 , 7 , 14 ].…”

“…Upon electrospinning, some of the polymer nanofiber mats are mechanically rolled and treated under approximately 5.88 MPa compressive stress, while another portion of polymer fibers are treated with a tensile load of 52 kPa. The mechanical stresses augment the alignment of the molecular chains and forge the scaffold of the final carbon structure by confining the polymer chains during the formative cross-linking process in stabilization [ 1 , 2 , 3 , 4 , 10 , 11 , 12 ]. Both groups of fiber precursors were stabilized in air at 280 °C and then pyrolyzed under identical conditions at 1000 °C.…”

“…We attributed the presence of these atoms to the low temperature of our pyrolysis step, typically carried out at 900–1000 °C, which is far lower than current industry standards (typically 1500–3000 °C). This is advantageous from different aspects; first, fabricating graphitic carbon at a lower pyrolysis temperature is remarkably more cost-effective; second, the presence of functional heterogeneities (such as pyridinic nitrogen) will positively contribute to the electrochemical performance of carbon nanofibers [ 12 , 17 , 18 , 19 ].…”

Electrospun Mats Based on PVA/NaDDBS/CNx Nanocomposite for Electrochemical Sensing

“…A sufficiently high voltage is applied to a liquid to initiate electrospinning, which begins to accumulate charge, forming droplets until it reaches a conical form known as a Taylor cone. The size of the fiber depends on the distance between the collector plate and the Taylor cone, the voltage, and the viscosity of the liquid [8].…”

Fabrication of patterned graphitized carbon wires using low voltage near-field electrospinning, pyrolysis, electrodeposition, and chemical vapor deposition

“…Graphitized carbon has become a preferred material for numerous applications because of its superior physicochemical properties, such as mechanical strength 1,2 , electrochemical activity [3][4][5] , and exceptional thermal and electrical conductivities 6 . More specifically, carbon-based micro/nanopatterns are important for developing electrochemical sensors 7 , transparent conductors 8 , flexible electronics 9 , photonic crystals 10 , and supercapacitors 11 .…”