Laser Photoreduction of Graphene Aerogel Microfibers: Dynamic Electrical and Thermal Behaviors

Abstract

This work reports the dynamic behaviors of graphene aerogel (GA) microfibers during and after continuous wave (CW) laser photoreduction. The reduction results in one-order of magnitude increase in the electrical conductivity. The experimental results reveal the exact mechanisms of photoreduction as it occurs: immediate photochemical removal of oxygen functional groups causing a sharp decrease in electrical resistance and subsequent laser heating that facilitates thermal rearrangement of GO sheets towards more graphene-like domains. X-ray and Raman spectroscopy analysis confirm that photoreduction removes virtually all oxygen and nitrogen containing functional groups. Interestingly, a dynamic period immediately following the end of laser exposure shows a slow, gradual increase in electrical resistance, suggesting that a proportion of the electrical conductivity enhancement from photoreduction is not permanent. A two-part experiment monitoring the resistance changes in real-time before and after photoreduction is conducted to investigate this critical period. The thermal diffusivity evolution of the microfiber is tracked and shows an improvement of 277 % after all photoreduction experiments. A strong linear coherency between thermal diffusivity and electrical conductivity is also uncovered. This is the first known work to explore both the dynamic electrical and thermal evolution of a GO-based aerogel during and after photoreduction.

Function Graded Carbon Micro‐Structures for Powerless Photon Sensing with Intriguing µm‐Scale Position Sensitivity

“…[25,26] These functional groups, nevertheless, also degrade some of the exceptional electrical and thermal conductivity of graphene. [27] So, the reason that laser treatment induces more obvious structural changes in the GMF than the CMF is that it has more impurities and functional groups. The laser treatment will remove some of them by thermal effect and photon-induced bond breaking.…”

“…In other words, the laser power range used to get the photovoltage signal is only 1.8−13 mW, which is much lower than that of GMF. Since graphene aerogel has a much lower thermal conductivity, [27,31,32] under the same laser heating, it will have a much higher temperature rise; therefore, the voltage change is stronger. Based on Figure 5b, an abrupt change in photovoltage is seen after x = 1.4 mm where the laser-treated and un-treated regions are separated from each other.…”

Pulsed Current for Diameter-Controlled Carbon Nanotubes and Hybrid Carbon Nanostructures in Electrolysis of Captured Carbon Dioxide

“…Multiwalled carbon nanotubes (MWCNTs) are remarkable nanostructured materials with excellent electrical conductivity, high thermal conductivity, and exceptional mechanical properties . These properties, among others, make MWCNT attractive for a range of applications, including electronics, energy storage, and biological systems. , However, the diameter of a nanotube has a major impact on both its mechanical and electrical characteristics, , with small-diameter MWCNTs (<30 nm) being the most valuable for many of these applications, but with the challenge of smaller MWCNTs involving more precise and difficult synthesis methods. − In this regard, a large number of efforts have been made using different CNT synthesis methods, such as chemical vapor deposition, − to control properties of MWCNTs using different catalysts, − temperatures, and reaction gas mixtures . One difficulty of conventional methods in influencing diameters and properties of nanotubes is the impact of secondary gas reactions that can occur, which complicate a simple picture between the carbon flux into the reactor and the MWCNT yield coming out. , Additionally, scaling these traditional methods involves large capital equipment, complex secondary chemistries, and hence higher cost than other conventional carbons, limiting applications for carbon nanotubes. , …”

“…Multiwalled carbon nanotubes (MWCNTs) are remarkable nanostructured materials with excellent electrical conductivity, 1 high thermal conductivity, 2 and exceptional mechanical properties. 3 These properties, among others, make MWCNT attractive for a range of applications, including electronics, 4 energy storage, 5 and biological systems. 6,7 However, the diameter of a nanotube has a major impact on both its mechanical and electrical characteristics, 5,8 with small-diameter MWCNTs (<30 nm) being the most valuable for many of these applications, but with the challenge of smaller MWCNTs involving more precise and difficult synthesis methods.…”

Thermal Transport in Extremely Confined Metallic Nanostructures: TET Characterization

“…The TET technique is an effective and accurate method (the total uncertainty for thermal diffusivity is 6%) for evaluating the thermal diffusivity of one-dimensional solid materials (including metals and dielectric materials), such as single-walled carbon nanotube bundles [ 45 ], graphene materials [ 46 , 47 , 48 , 49 ], silkworm silks, [ 50 ] silver nanowire network, [ 51 ] freestanding micrometer-thick poly films [ 52 ], carbon fibers [ 53 , 54 ], etc. In this review, we will focus primarily on the characterization of thermal transport in extremely confined metallic nanostructures using the TET and differential TET technique.…”