Engineering topics
Dewey, Oliver S.
Publications and source records attributed to Dewey, Oliver S..
A semi-continuous process for co-production of CO 2 -free hydrogen and carbon nanotubes via methane pyrolysis
Heterogeneous catalytic pyrolysis of hydrocarbons to produce CO 2 -free hydrogen and high-quality solid carbon have historically been stymied by issues related to catalyst deactivation by carbon formed during pyrolysis on the catalyst surface. In addition, a system that demonstrates sustained performance in terms of high conversion, high H 2 yield, and high quality of produced carbon has remained elusive. Here, we propose and demonstrate a semi-continuous methane pyrolysis process to H 2 and carbon nanotubes (CNTs) consisting of repeated pyrolysis and in situ (i.e., within the reactor) CNT dislodging by vigorous steam/argon fluidization. With this process, we demonstrate 10 process cycles with high H 2 yield from CH 4 and CNT dislodging in a fluidized-bed reactor with an Fe/q-Al 2 O 3 catalyst synthesized by an easily scalable incipient wetness impregnation process. We also identify and present opportunities for future catalyst and process development.
Versatile acid solvents for pristine carbon nanotube assembly
Chlorosulfonic acid and oleum are ideal solvents for enabling the transformation of disordered carbon nanotubes (CNTs) into precise and highly functional morphologies. Currently, processing these solvents using extrusion techniques presents complications due to chemical compatibility, which constrain equipment and substrate material options. Here, we present a novel acid solvent system based on methanesulfonic or p-toluenesulfonic acids with low corrosivity, which form true solutions of CNTs at concentrations as high as 10 g/liter (≈0.7 volume %). The versatility of this solvent system is demonstrated by drop-in application to conventional manufacturing processes such as slot die coating, solution spinning continuous fibers, and 3D printing aerogels. Through continuous slot coating, we achieve state-of-the-art optoelectronic performance (83.6 %T and 14 ohm/sq) at industrially relevant production speeds. This work establishes practical and efficient means for scalable processing of CNT into advanced materials with properties suitable for a wide range of applications.
Macroscopic weavable fibers of carbon nanotubes with giant thermoelectric power factor
Low-dimensional materials have recently attracted much interest as thermoelectric materials because of their charge carrier confinement leading to thermoelectric performance enhancement. Carbon nanotubes are promising candidates because of their one-dimensionality in addition to their unique advantages such as flexibility and light weight. However, preserving the large power factor of individual carbon nanotubes in macroscopic assemblies has been challenging, primarily due to poor sample morphology and a lack of proper Fermi energy tuning. Here, we report an ultrahigh value of power factor (14± 5 mW m -1 K -2 ) for macroscopic weavable fibers of aligned carbon nanotubes with ultrahigh electrical and thermal conductivity. The observed giant power factor originates from the ultrahigh electrical conductivity achieved through excellent sample morphology, combined with an enhanced Seebeck coefficient through Fermi energy tuning. We fabricate a textile thermoelectric generator based on these carbon nanotube fibers, which demonstrates high thermoelectric performance, weavability, and scalability. The giant power factor we observe make these fibers strong candidates for the emerging field of thermoelectric active cooling, which requires a large thermoelectric power factor and a large thermal conductivity at the same time.
Perovskite-Carbon Nanotube Light-Emitting Fibers
Active fibers with electro-optic functionalities are promising building blocks for the emerging and rapidly growing field of fiber and textile electronics. Yet, there remains significant challenges that require improved understanding of the principles of active fiber assembly to enable the development of fiber-shaped devices characterized by having a small diameter, being lightweight, and having high mechanical strength. To this end, the current frameworks are insufficient, and new designs and fabrication approaches are essential to accommodate this unconventional form factor. Here, we present a first demonstration of a pathway that effectively integrates the foundational components meeting such requirements, with the use of a flexible and robust conductive core carbon nanotube fiber and an organic–inorganic emissive composite layer as the two critical elements. We introduce an active fiber design that can be realized through an all solution-processed approach. In conclusion, we have implemented this technique to demonstrate a three- layered light-emitting fiber with a coaxially coated design.