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- ItemNew insights into the structure of nanoporous carbons from NMR, Raman, and pair distribution function analysis(Washington D.C. : American Chemical Society, 2015) Forse, Alexander C.; Merlet, Céline; Allan, Phoebe K.; Humphreys, Elizabeth K.; Griffin, John M.; Aslan, Mesut; Zeiger, Marco; Presser, Volker; Gogotsi, Yury; Grey, Clare P.The structural characterization of nanoporous carbons is a challenging task as they generally lack long-range order and can exhibit diverse local structures. Such characterization represents an important step toward understanding and improving the properties and functionality of porous carbons, yet few experimental techniques have been developed for this purpose. Here we demonstrate the application of nuclear magnetic resonance (NMR) spectroscopy and pair distribution function (PDF) analysis as new tools to probe the local structures of porous carbons, alongside more conventional Raman spectroscopy. Together, the PDFs and the Raman spectra allow the local chemical bonding to be probed, with the bonding becoming more ordered for carbide-derived carbons (CDCs) synthesized at higher temperatures. The ring currents induced in the NMR experiment (and thus the observed NMR chemical shifts for adsorbed species) are strongly dependent on the size of the aromatic carbon domains. We exploit this property and use computer simulations to show that the carbon domain size increases with the temperature used in the carbon synthesis. The techniques developed here are applicable to a wide range of porous carbons and offer new insights into the structures of CDCs (conventional and vacuum-annealed) and coconut shell-derived activated carbons.
- ItemInterlaboratory study assessing the analysis of supercapacitor electrochemistry data(New York, NY [u.a.] : Elsevier, 2023) Gittins, Jamie W.; Chen, Yuan; Arnold, Stefanie; Augustyn, Veronica; Balducci, Andrea; Brousse, Thierry; Frackowiak, Elzbieta; Gómez-Romero, Pedro; Kanwade, Archana; Köps, Lukas; Jha, Plawan Kumar; Lyu, Dongxun; Meo, Michele; Pandey, Deepak; Pang, Le; Presser, Volker; Rapisarda, Mario; Rueda-García, Daniel; Saeed, Saeed; Shirage, Parasharam M.; Ślesiński, Adam; Soavi, Francesca; Thomas, Jayan; Titirici, Maria-Magdalena; Wang, Hongxia; Xu, Zhen; Yu, Aiping; Zhang, Maiwen; Forse, Alexander C.Supercapacitors are fast-charging energy storage devices of great importance for developing robust and climate-friendly energy infrastructures for the future. Research in this field has seen rapid growth in recent years, therefore consistent reporting practices must be implemented to enable reliable comparison of device performance. Although several studies have highlighted the best practices for analysing and reporting data from such energy storage devices, there is yet to be an empirical study investigating whether researchers in the field are correctly implementing these recommendations, and which assesses the variation in reporting between different laboratories. Here we address this deficit by carrying out the first interlaboratory study of the analysis of supercapacitor electrochemistry data. We find that the use of incorrect formulae and researchers having different interpretations of key terminologies are major causes of variability in data reporting. Furthermore we highlight the more significant variation in reported results for electrochemical profiles showing non-ideal capacitive behaviour. From the insights gained through this study, we make additional recommendations to the community to help ensure consistent reporting of performance metrics moving forward.
- ItemNuclear magnetic resonance study of ion adsorption on microporous carbide-derived carbon(Cambridge : Royal Society of Chemistry, 2013) Presser, Volker; Forse, Alexander C.; Griffin, John M.; Wang, Hao; Trease, Nicole M.; Gogotsi, Yuri; Simon, Patrice; Grey, Clare P.A detailed understanding of ion adsorption within porous carbon is key to the design and improvement of electric double-layer capacitors, more commonly known as supercapacitors. In this work nuclear magnetic resonance (NMR) spectroscopy is used to study ion adsorption in porous carbide-derived carbons. These predominantly microporous materials have a tuneable pore size which enables a systematic study of the effect of pore size on ion adsorption. Multinuclear NMR experiments performed on the electrolyte anions and cations reveal two main environments inside the carbon. In-pore ions (observed at low frequencies) are adsorbed inside the pores, whilst ex-pore ions (observed at higher frequencies) are not adsorbed and are in large reservoirs of electrolyte between carbon particles. All our experiments were carried out in the absence of an applied electrical potential in order to assess the mechanisms related to ion adsorption without the contribution of electrosorption. Our results indicate similar adsorption behaviour for anions and cations. Furthermore, we probe the effect of sample orientation, which is shown to have a marked effect on the NMR spectra. Finally, we show that a 13C → 1H cross polarisation experiment enables magnetisation transfer from the carbon architecture to the adsorbed species, allowing selective observation of the adsorbed ions and confirming our spectral assignments.
- ItemRing current effects: Factors affecting the NMR chemical shift of molecules adsorbed on porous carbons(Washington D.C. : American Chemical Society, 2014) Forse, Alexander C.; Griffin, John M.; Presser, Volker; Gogotsi, Yury; Grey, Clare P.Nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to study the adsorption of molecules in porous carbons, a process which underpins applications ranging from electrochemical energy storage to water purification. Here we present density functional theory (DFT) calculations of the nucleus-independent chemical shift (NICS) near various sp2-hybridized carbon fragments to explore the structural factors that may affect the resonance frequencies observed for adsorbed species. The domain size of the delocalized electron system affects the calculated NICSs, with larger domains giving rise to larger chemical shieldings. In slit pores, overlap of the ring current effects from the pore walls is shown to increase the chemical shielding. Finally, curvature in the carbon sheets is shown to have a significant effect on the NICS. The trends observed are consistent with existing NMR results as well as new spectra presented for an electrolyte adsorbed on carbide-derived carbons prepared at different temperatures.