posted on 2022-01-14, 18:35authored byLászló Szabó, Xingtao Xu, Koichiro Uto, Joel Henzie, Yusuke Yamauchi, Izumi Ichinose, Mitsuhiro Ebara
Carbon nanoarchitectures
derived from biobased building blocks
are potential sustainable alternatives to electrode materials generated
with petroleum-derived resources. We aim at developing a fundamental
understanding on the connection between the structure and electrochemical
performance of porous carbon nanofiber (PCNF) architectures from the
polysaccharide chitosan as a biobased building block. We fabricated
a range of PCNF architectures from the chitosan carbon precursor and
tailored their structure by varying the amount and molecular weight
of the sacrificial pore-forming polymer poly(ethylene oxide). The
morphology (high-resolution scanning electron microscopy), carbon
structure (X-ray diffraction, transmission electron microscopy), pore
network (N2 gas adsorption, small-angle X-ray scattering),
and surface/bulk composition (X-ray photoelectron spectroscopy, energy-dispersive
X-ray spectroscopy) were studied in detail together with a comprehensive
electrochemical analysis on the fabricated electrodes. In supercapacitor
devices, the best-performing freestanding electrode had (1) a high
accessible surface area (as,BET ≈
700 m2 g–1) and hierarchical pore network
(micro- and mesopores) providing a fast ion diffusion process, high
specific capacitance, and rate capability, (2) surface chemistry allowing
a high Coulombic efficiency by avoiding parasitic Faradaic side reactions,
and (3) a unique turbostratic carbon nanostructure leading to low
charge transfer resistance while keeping good electrical conductivity.
This electrode exhibited good stability over 2000 cycles (at 2 A g–1) with high capacitance retention (>80%) and charge
efficiency (>90%). In the capacitive deionization (CDI) device,
our
electrode demonstrated an ultrahigh salt adsorption capacity of 23.6
mg g–1, which is among the state-of-the-art values
reported for a biobased carbon. A high charge efficiency (85%) was
achieved during the CDI process using low-cost materials, in contrast
to similarly performing devices fabricated with expensive ion exchange
membranes or petroleum-based carbon precursors. Our results demonstrate
that inexpensive chitosan-based materials can be readily transformed
in one carbonization step without any aggressive activating chemicals
into tailor-made hierarchically ordered state-of-the-art carbon materials
for charge storage devices.