In-pore exchange and diffusion of carbonate solvent mixtures in nanoporous carbon

Alam, Todd M.; Popp, Thomas M. Osborn

doi:10.1016/j.cplett.2016.06.014

Cited by 9 publications

(12 citation statements)

References 45 publications

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“…This is consistent with a recent NMR study of solvents in a nanoporous carbon, 35 and helps to explain why we observe greater reductions of effective diffusion upon confinement than in MD simulations where much smaller observation times were studied. 23 PFG NMR experiments provide additional dynamic information about the exchange (or swapping) of ions between in-and ex-pore environments (Figure 2d).…”

supporting

confidence: 79%

“…MD simulations have also shown that (de)solvation of in-pore ions with acetonitrile takes place as quickly as ~1 ps, 23 and a recent study of dimethyl carbonate showed a relatively modest reduction of effective diffusion (by a factor of ~ 0.2) upon confinement in a nanoporous carbon. 35 Overall, the slower diffusing ions move through a highly dynamic solvent medium in the nanopores.…”

mentioning

confidence: 99%

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Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

et al. 2017

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Ionic transport inside porous carbon electrodes underpins the storage of energy in supercapacitors and the rate at which they can charge and discharge, yet few studies have elucidated the materials properties that influence ion dynamics. Here we use in situ pulsed field gradient NMR spectroscopy to measure ionic diffusion in supercapacitors directly. We find that confinement in the nanoporous electrode structures decreases the effective self-diffusion coefficients of ions by over two orders of magnitude compared to neat electrolyte, and in-pore diffusion is modulated by changes in ion populations at the electrode-electrolyte interface during charging.Electrolyte concentration and carbon pore size distributions also affect in-pore diffusion and the movement of ions in and out of the nanopores. In light of our findings we propose that controlling the charging mechanism may allow the tuning of the energy and power performances of supercapacitors for a range of different applications.As renewable energy and green technologies such as electric vehicles become prevalent, we must develop new ways to store and release energy on a range of timescales. Rechargeable batteries are ideal for timescales of minutes or hours (electric cars, portable electronic devices, grid storage etc.), while supercapacitors are more promising for second or sub-second timescales and are increasingly being used for transport applications where rapid charging and discharging are required. The superior power handling and cycle lifetime of supercapacitors comes at the expense of energy density, with recent materials-driven research aiming to address this issue by fine-tuning the nanoporous structure of the carbon electrodes, 1,2 and by using ionic liquid electrolytes that are stable at higher voltages. 3,4 Both approaches have afforded some increases in energy density, though not without sacrificing power density. The delicate balance between energy and power density must be understood if supercapacitors are to be used in a wide range of applications.Fundamental studies based on spectroscopic, 5-14 and theoretical, 15-18 methods have recently revealed the complex nature of charging in supercapacitors. Prior to charging, the electrode pores contain a large number of electrolyte ions, 15,19,20 and as a result charge storage is generally more complex than simple counter-ion adsorption (counter-ions are defined as having charge opposite to the electrode in which they are located). [5][6][7]15 A range of different charging mechanisms can operate

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confidence: 79%

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confidence: 99%

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

et al. 2017

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“…If the moiety is situated close enough to these domains, the electronic effect is to shift the nuclei response upfield of TMS. This type of unusual interaction has been best documented for molecules adsorbed on porous carbon [90–93]. The other unusual feature is the simplicity of the 1 H spectra of SSVCT‐02 and ‐05 when the corresponding 13 C spectra are as complicated as the other samples.…”

Section: Discussionmentioning

confidence: 85%

LX‐17 Thermal Decomposition‐Characterization of Solid Residues from Cook‐Off in a Small‐Scale Vessel Under Confinement

Reynolds

Muetterties

Nelson

et al. 2021

Propellants Explo Pyrotec

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Concerns surround whether insensitive (or any) energetic materials are more dangerous to handle when exposed to abnormal thermal environments. This study characterizes the residual material remaining after LX‐17 (92.5 % 1,3,5‐triamino 2,4,6‐trinitro benzene (TATB) and 7.5 % Kel‐F) is exposed to various thermal environments in a sealed small‐scale vessel cook‐off test reactor (heated at 0.1 to 100 °C/min until the reactor opened at 3000 psi (20.7 MPa)). Previous work has shown no additional sensitivity of these residues as evaluated by small‐scale safety analysis, but characterization on the molecular scale indicates the TATB is transformed to more reactive compounds as well as the residue could be precursors to toxic gases. The solids and chars were characterized by various analytical methods. Heat‐flow measurements indicated exothermic release is due to a mixture of residual TATB and related decomposition products (which may be more energetic). The N/C and O/N ratios indicated a material much more degraded than TATB. Primarily, the solids were a network of amorphous C inter‐dispersed with N and O. Types of bonding include C−C, C−N, N−H, N−C, N=C, N≡C, C−O=, and −OH. Solvent extracts of the solids showed TATB decomposition intermediates benzo‐furazans and benzo‐furoxans, substituted TATB (mono‐nitroso, hydroxyl, and chlorinated) along with several unidentified smaller molecules. These results indicate thermal treatment produces an amorphous carbon residue with heteroatoms incorporated through differing functionality, varying depending upon the thermal severity of exposure. These structures also could further decompose producing toxic light gases (such as cyanide).

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“…In a later study, Alam & Osborn Popp applied the NMR method to a porous carbon soaked with a carbonate solvent. [52] They compared the NMR-derived pore size distribution to that obtained by a secondary method -classical density functional theory analysis of nitrogen and argon adsorption isotherms (a state-of-the-art approach).…”

Section: Quantifying Carbon Pore Size Distributions From Ring Current Shiftsmentioning

confidence: 99%

“…In a later study, Alam & Osborn Popp applied the NMR method to a porous carbon soaked with a carbonate solvent. [51] Importantly they compared the NMR-derived pore size distribution to that obtained by a secondary method -classical density functional theory analysis of nitrogen and argon adsorption isotherms (a state-of-the-art approach). The two pore size distributions showed some clear differences, with a unimodal pore size distribution obtained with the NMR method, and a bimodal pore size distribution obtained via the gas sorption method.…”

Section: Quantifying Carbon Pore Size Distributions From Ring Current...mentioning

confidence: 99%

NMR studies of adsorption and diffusion in porous carbonaceous materials

Forse

Merlet

Grey

et al. 2021

Progress in Nuclear Magnetic Resonance Spectroscopy

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Porous carbonaceous materials have many important industrial applications including energy storage, water purification, and adsorption of volatile organic compounds. Most of their applications rely upon the adsorption of molecules or ions within the interior pore volume of the carbon particles.Understanding the behaviour and properties of adsorbate species on the molecular level is therefore key for optimising porous carbon materials, but this is very challenging owing to the complexity of the disordered carbon structure and the presence of multiple phases in the system. In recent years, NMR spectroscopy has emerged as one of the few experimental techniques that can resolve adsorbed species from those outside the pore network. Adsorbed, or "in-pore" species are shielded with respect to their free (or "ex-pore") counterparts. This shielding effect arises primarily due to ring currents in the carbon structure in the presence of a magnetic field, such that the observed chemical shift differences upon adsorption are independent of the observed nucleus to a first approximation.Theoretical modelling has played an important role in rationalising and explaining these experimental observations. Together, experiments and simulations have enabled a large amount of information to be gained on the adsorption and diffusion of adsorbed species, as well as on the structural and magnetic properties of the porous carbon adsorbent. Here, we review the methodological developments and applications of NMR spectroscopy and related modelling in this field, and provide perspectives on possible future applications and research directions.

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In-pore exchange and diffusion of carbonate solvent mixtures in nanoporous carbon

Cited by 9 publications

References 45 publications

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

LX‐17 Thermal Decomposition‐Characterization of Solid Residues from Cook‐Off in a Small‐Scale Vessel Under Confinement

NMR studies of adsorption and diffusion in porous carbonaceous materials

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