SCIENtIFIC REPoRTS | 7: 16551 | DOI:10.1038/s41598-017-16424-z
Carbons by Stress-induced Routes
, Sunshine Holmberg
, Oscar Pilloni
, Laura Oropeza-Ramos
Graphitic carbons’ unique attributes have attracted worldwide interest towards their development
and application. Carbon pyrolysis is a widespread method for synthesizing carbon materials.
However, our understanding of the factors that cause dierences in graphitization of various
pyrolyzed carbon precursors is inadequate. We demonstrate how electro-mechanical aspects of the
synthesis process inuence molecular alignment in a polymer precursor to enhance its graphitization.
Electrohydrodynamic forces are applied via electrospinning to unwind and orient the molecular chains
of a non-graphitizing carbon precursor, polyacrylonitrile. Subsequently, exerting mechanical stresses
further enhances the molecular alignment of the polymer chains during the formative crosslinking
phase. The stabilized polymer precursor is then pyrolyzed at 1000 °C and characterized to evaluate its
graphitization. The nal carbon exhibits a uniformly graphitized structure, abundant in edge planes,
which translates into its electrochemical kinetics. The results highlight the signicance of physical
synthesis conditions in dening the structure and properties of pyrolytic carbons.
Our understanding of carbon, a deceptively simple element, has been challenged and evolved dramatically over
the last couple of decades. e discoveries of carbon nanotubes
have served to overturn our per-
ception of carbon materials structures and properties, and broadened our vision beyond the traditional diamond
and graphite allotropes. Consequently, these new carbon materials have prompted a signicant volume of de novo
experimental and theoretical research aimed at understanding their synthesis and application. A good portion of
these studies is concerned with establishing correlations between the synthesis method and the resulting micro-
structure. However, the synthesis-structure relationships in new carbon materials are still inconclusive despite
their widespread industrial use.
In this context, the nature of what makes a carbon precursor graphitizable or non-graphitizable has long
eluded researchers. In the original work by Rosalind Franklin
, it was proposed that non-graphitizable carbons
were nanoporous in nature with a tendency to form sp
bonds that inhibit the alignment of graphite planes
and thus graphitization, even at extremely high temperatures. However, as explained more recently by Harris
, graphite layers are capable of realigning themselves at high temperatures, even within a highly nanopo-
rous structure. Furthermore, diamond, which consists of sp
-hybridized carbon atoms, transforms into graphite
above 1700 °C and therefore sp
bonds alone cannot prevent graphitization. Harris instead proposed that stable
fullerenic features between the individual graphite layers are preventing the graphitization, and generating the
microstructure associated with non-graphitizing carbons
Several other studies have attributed the degree of graphitization in organic precursors to their physical and
chemical nature, thus declaring graphitizability an intrinsic property of a precursor
. Kipling et al. linked
the “non-graphitizing” quality of some precursors to the absence of an extended fusion phase in their carbon-
ization, when heated to 300–500 °C
. is fusion phase allows the carbon atoms to freely rearrange them-
selves into more thermodynamically stable graphitic planes. Instead, “non-graphitizing” precursors undergoes
crosslinking phase at those temperatures, which x the molecular structure and impede the formation of gra-
phitic planes. Despite this inherent limitation in “non-graphitizing” polymers, multiple studies have continued
to investigate alternative strategies, such as hot drawing of polymer bers, to induce graphitization in these
Department of Mechanical Engineering, California State University, Fresno, USA.
Department of Mechanical and
Aerospace Engineering, University of California, Irvine, USA.
Programa de Maestría y Doctorado en Ingeniería,
Universidad Nacional Autónoma de México, CDMX, Mexico.
Facultad de Ingeniería, Universidad Nacional
Autónoma de México, CDMX, Mexico. Correspondence and requests for materials should be addressed to M.M.
Received: 12 July 2017
Accepted: 12 November 2017
Published: xx xx xxxx