Organic radical polymers for batteries represent some of the fastest-charging redox active materials available. Electron transport and charge storage must be accompanied by ion transport and doping ...for charge neutrality, but the nature of this process in organic radical polymers is not well understood. This is difficult to intuitively predict because the pendant radical group distinguishes organic radical polymers from conjugated, charged or polar polymers. Here we show for the first time a quantitative view of in situ ion transport and doping in organic radical polymers during the redox process. Two modes dominate: doping by lithium ion expulsion and doping by anion uptake. The dominance of one mode over the other is controlled by anion type, electrolyte concentration and timescale. These results apply in any scenario in which electrolyte is in contact with a non-conjugated redox active polymer and present a means of quantifying doping effects.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
For over a century, the phase behavior of bulk fluids has been described as PVT (pressure–volume–temperature) three-dimensional properties, but it has become increasingly clear that the liquid–vapor ...phase behavior in confined geometries is significantly altered from the bulk. Efforts have been devoted to accessing confined phase transitions using sorption, molecular simulations, and theoretical methods. However, a comprehensive picture of PVT relationships for confined hydrocarbons remains uncertain. Herein, we introduce d (confining pore diameter) as a fourth dimension, and we present PVT-d behavior of confined fluids in nanopores. For the first time, a T–d phase diagram is presented for n-hexane, n-octane, and n-decane under multiple confinement scales (37.9, 14.8, 9.8, 6.0, 4.1, 3.3, and 2.2 nm cylindrical pore diameter) using experimental differential scanning calorimetry and PVT-d equation of state theory at atmospheric pressure. As pore diameter decreases from 37.9 to 4.1 nm, the bubble point increases by as much as 15 K above bulk, until we observe behavior consistent with a supercritical state, pointing to confinement-induced supercriticality. Remarkably, experimental and theoretical findings overlap very well, showing that this approach effectively captures the phase boundaries between the liquid, vapor, and supercritical fluid regions. The model and completed EOS are additionally extended to calculation of isothermal capillary adsorption, and its validity is discussed.
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IJS, KILJ, NUK, PNG, UL, UM
Structural energy and power systems offer both mechanical and electrochemical performance in a single multifunctional platform. These are of growing interest because they potentially offer reduction ...in mass and/or volume for aircraft, satellites, and ground transportation. To this end, flexible graphene-based supercapacitors have attracted much attention due to their extraordinary mechanical and electrical properties, yet they suffer from poor strength. This problem may be exacerbated with the inclusion of functional guest materials, often yielding strengths of <15 MPa. Here, we show that graphene paper supercapacitor electrodes containing aramid nanofibers as guest materials exhibit extraordinarily high tensile strength (100.6 MPa) and excellent electrochemical stability. This is achieved by extensive hydrogen bonding and π–π interactions between the graphene sheets and aramid nanofibers. The trade-off between capacitance and mechanical properties is evaluated as a function of aramid nanofiber loading, where it is shown that these electrodes exhibit multifunctionality superior to that of other graphene-based supercapacitors, nearly rivaling those of graphene-based pseudocapacitors. We anticipate these composite electrodes to be a starting point for structural energy and power systems that harness the mechanical properties of aramid nanofibers.
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IJS, KILJ, NUK, PNG, UL, UM
Macromolecular radicals, radical polymers, and polyradicals bear unique functionalities derived from their pendant radical groups. The increasing need for organic functional materials is driving the ...growth in research interest in macromolecular radicals for batteries, electronics, memory, and imaging. This Viewpoint summarizes the current state-of-knowledge regarding the macromolecular nitroxide radicals’ redox mechanism, conductivity, chain conformation, controlled polymerization, network structure, conjugated forms, and applications. The nitroxide radical group is the focus because it is the most widely studied. Although most literature focuses upon applications, an emerging body of work is highlighting the fundamental physicochemical properties of macromolecular radicals. To this end, this Viewpoint recommends areas of opportunity in fundamental studies and best practices in reporting.
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IJS, KILJ, NUK, PNG, UL, UM
Colorimetric sensors, as a key branch of the application of photonic crystals (PCs), brings enthusiasm to scientists to do research. Here, simple mesoporous and structurally colored one-dimensional ...photonic crystals (1DPCs) constructed by alternating assembly of poly(acrylamide-N,N′-methylene bis(acrylamide)) (P(AM-MBA)) nanogels and TiO2 nanoparticles are reported as high-performance colorimetric humidity sensors. The sensors with bright colors display rapid response to relative humidity (RH) change and reach sensing balance in 0.5 s. By varying RH from 47.0% to 89.3%, stopband of a sensor changes from 426 to 668 nm, almost spanning the whole visible range. Meanwhile, visual sensing of RH possesses good reversibility and repeatability. Moreover, the sensors with delicate patterns are facilely fabricated by partial UV photodegradation of the polymer layers with nano TiO2 as catalyst. The delicate patterns and backgrounds show different colors and change color simultaneously and quickly by varying the ambient humidity. Accurate QR code pattern is also realized on the PC sensor; it is found successful reading of the data is only achieved by increasing RH to realize high color contrast between the code and background. Given their excellent properties, the porous hybrid PCs are promising as high-performance humidity sensors with potential display, decoration, information-storage, and encryption functions.
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IJS, KILJ, NUK, PNG, UL, UM
Metal pretreatments play a crucial role in the long-term performance of metals. Hexavalent chromium has been a state of the art metal pretreatment, but it is being phased out due to human health and ...environmental concerns. Therefore, the need for environmentally friendly pretreatment coatings has emerged. 2-D nanomaterials such as graphene have gained interest in this regard because of their ability to act as physical barriers to corrosion-causing agents, yet graphene's deposition is not always scalable or sustainable. Adding to the complexity, the corrosion inhibiting ability of 2-D graphene nanosheets has exhibited differing results in the past. Here, we present reduced graphene oxide-polyvinyl alcohol (PVA) nanocomposite coatings on branched polyethylenimine (B-PEI)-coated aluminum alloy 2024-T3, where B-PEI, acts as an adhesion promoting layer, realized by a high throughput airbrushing process of a graphene oxide-polymer ink followed by reduction. For the first time, a water-stable dispersion of reduced graphene oxide and polyvinyl alcohol (PVA) is prepared and quickly sprayed to yield a smooth pinhole-free coating, where reduced graphene oxide sheets act as bricks and PVA as mortar. It is shown that the coating is an exceptional oxygen barrier, similar in performance to SiO x . The reduced graphene oxide sheets may also provide an alternative electronic pathway that prevents electrons from reaching the cathodic site, thereby hindering the corrosion cycle. Coatings with varying compositions on aluminum alloy 2024-T3 were evaluated in 0.2 M NaCl solution for 30 days period. The alloy coated with 60 to 70 wt% reduced graphene oxide exhibited the best performance, with little to no corrosion. Coatings with higher or lower reduced graphene oxide content exhibited corrosion due to increased oxygen permeability and swelling, which may explain conflicting prior reports.
A hierarchically structured nitrogen-doped porous carbon is prepared from a nitrogen-containing isoreticular metal-organic framework (IRMOF-3) using a self-sacrificial templating method. IRMOF-3 ...itself provides the carbon and nitrogen content as well as the porous structure. For high carbonization temperatures (950 °C), the carbonized MOF required no further purification steps, thus eliminating the need for solvents or acid. Nitrogen content and surface area are easily controlled by the carbonization temperature. The nitrogen content decreases from 7 to 3.3 at % as carbonization temperature increases from 600 to 950 °C. There is a distinct trade-off between nitrogen content, porosity, and defects in the carbon structure. Carbonized IRMOFs are evaluated as supercapacitor electrodes. For a carbonization temperature of 950 °C, the nitrogen-doped porous carbon has an exceptionally high capacitance of 239 F g–1. In comparison, an analogous nitrogen-free carbon bears a low capacitance of 24 F g–1, demonstrating the importance of nitrogen dopants in the charge storage process. The route is scalable in that multi-gram quantities of nitrogen-doped porous carbons are easily produced.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
Ti
3
C
2
T
x
belongs to the family of MXenes, 2D materials with an attractive combination of functional properties suitable for applications such as batteries, supercapacitors, and strain ...sensors. However, the fabrication of devices and functional coatings based on Ti
3
C
2
T
x
remains challenging as they are prone to chemical degradation by their oxidation to TiO
2
. In this paper, we examine the oxidation of Ti
3
C
2
T
x
in air, liquid, and solid media via conductivity measurements to assess the shelf life of Ti
3
C
2
T
x
MXenes. The oxidation of Ti
3
C
2
T
x
was observed in all the media used in this study, but it is fastest in liquid media and slowest in solid media (including polymer matrices). We also show that the conventional indicators of MXene oxidation, such as changes in color and colloidal stability, are not always reliable. Finally, we demonstrate the acceleration of oxidation under exposure to UV light.
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