@inproceedings{62814, abstract = {{Porous carbons are prominent electrode materials in energy storage applications such as supercapacitors. However, rational materials development is hampered by difficulties in interpreting electrochemical impedance spectra (EIS) and drawing conclusions about promising aspects of device improvement. Here, we characterized electrodes consisting of activated carbon with polyacrylic acid binder in four different concentrations of sulfuric acid, using cyclic voltammetry and electrochemical impedance spectroscopy. Both datasets were evaluated with simple equivalent circuits and comparatively analyzed. Conductivity of the electrolyte was independently measured. Cyclic voltammograms (CV) show larger resistance and capacitance at low scan rates. Resistances obtained from EIS are in good agreement with those obtained by cyclic voltammograms particularly at high scan rates. The comparison against specific electrolyte resistance can reveal whether resistances within the solid electrode architecture or resistances within the electrolyte, partially confined by pores, are the dominant cause of increased resistance at low scan rate. Comparison between CV and EIS points to the main electrode capacitance being described by a constant phase element (CPE) used to fit the low-frequency region of EIS.}}, author = {{Reinke, Sebastian and Khamitsevich, Vera and Linnemann, Julia}}, booktitle = {{2024 International Workshop on Impedance Spectroscopy (IWIS)}}, keywords = {{electrochemical impedance spectroscopy, distorted cyclic voltammograms, supercapacitors, carbon}}, publisher = {{IEEE}}, title = {{{Complementary Analysis of Cyclic Voltammograms and Impedance Spectra of Porous Carbon Electrodes}}}, doi = {{10.1109/iwis63047.2024.10847115}}, year = {{2025}}, } @article{63950, abstract = {{Sodium-ion batteries are at the forefront of new, sustainable energy systems required for the global energy transition. 23Na in situ solid-state nuclear magnetic resonance spectroscopy is capable of unraveling structures in working electrochemical cells during the charging and discharging processes. To evaluate its suitability for long-term studies, local sodium environments in sodium/sodium ion cells based on silicon carbonitride and hard carbon materials are tracked for up to 49 cycles (228.5?h). The formation of dendrites as well as the decay of a secondary metallic sodium species is observed, and local structures are analyzed up to the point of capacity degradation and cell failure. Initial points of cell breakdown are reflected in the NMR data by characteristic changes in signal intensities, whereas the degradation of the cells is reflected by a cease to periodic signal intensity fluctuations. Meanwhile, ex situ 23Na NMR spectra of the deactivated cells reveal a complex range of environments for sodium ions.}}, author = {{Egert, Sonja and Remesh, Renuka and Jusdi, Agatha Clarissa and Sugawara, Yushi and Schutjajew, Konstantin and Oschatz, Martin and Buntkowsky, Gerd and Gutmann, Torsten}}, journal = {{Batteries & Supercaps}}, keywords = {{solid-state nmr, hard carbon, in-situ, SiCN, sodium ion batteries}}, number = {{n/a}}, pages = {{e202500516}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Long-Term Cycling Stability of Sodium/Sodium Ion Cells Probed by In Situ Solid-State NMR Spectroscopy}}}, doi = {{10.1002/batt.202500516}}, volume = {{n/a}}, year = {{2025}}, } @inproceedings{62812, abstract = {{Attributing features of electrochemical impedance spectra to electrochemical phenomena is both crucial and frequently ambiguous. To elucidate the origin of the ohmic part of the spectrum, activated carbon electrodes were prepared with different contents of polyacrylic acid as binder. Their impedance spectra and cyclic voltammograms were recorded using sulfuric acid of five different concentrations as the electrolyte. To distinguish electrolyte resistance and resistances related to the activated carbon layer of the electrode, the specific electrolyte conductivity was independently measured and compared against the ohmic part of the electrochemical impedance spectra (EIS). The capacitive cyclic voltammograms show larger resistive contributions with higher scan rate and lower electrolyte conductivity. Comparing the ohmic part of the EIS to the specific resistance of the electrolyte, a linear function with no statistically significant offset was found. The ohmic part of the EIS, thus, reflects the electrolyte resistance, not that of the carbon electrode.}}, author = {{Reinke, Sebastian and Khamitsevich, Vera and Röth, Oliver and Linnemann, Julia}}, booktitle = {{2023 International Workshop on Impedance Spectroscopy (IWIS)}}, keywords = {{electrochemical impedance spectroscopy, supercapacitors, carbon}}, publisher = {{IEEE}}, title = {{{Assessment of the Physicochemical Meaning of the Ohmic Series Resistance Observed for High Frequencies in Electrochemical Impedance Spectra}}}, doi = {{10.1109/iwis61214.2023.10302764}}, year = {{2023}}, } @article{64045, abstract = {{Abstract In this work, we report on an improved cell assembly of cylindrical electrochemical cells for 23Na in-situ solid-state NMR (ssNMR) investigations. The cell set-up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. 23Na in-situ ssNMR monitors the sodiation/desodiation of a Na{\textbar}NaPF6{\textbar}HC cell (cell 1) over a period of 22?days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution 23Na ex-situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na{\textbar}NaPF6{\textbar}HC cell (cell 2) is sodiated for 11?days achieving a capacity of 220?mAh/g. 23Na ex-situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi-metallic sodium species next to ionic sodium species. This observation of quasi-metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material.}}, author = {{Šić, Edina and Schutjajew, Konstantin and Haagen, Ulrich and Breitzke, Hergen and Oschatz, Martin and Buntkowsky, Gerd and Gutmann, Torsten}}, issn = {{1864-5631}}, journal = {{Chemsuschem}}, keywords = {{solid-state nmr, hard carbon, electrochemical cells, in-situ characterization, sodium}}, pages = {{e202301300}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Electrochemical Sodium Storage in Hard Carbon Powder Electrodes Implemented in an Improved Cell Assembly: Insights from In-Situ and Ex-Situ Solid-State NMR}}}, doi = {{10.1002/cssc.202301300}}, volume = {{17}}, year = {{2023}}, } @article{21207, abstract = {{Simple thermal treatment of guanine at temperatures ranging from 600 to 700 °C leads to C1N1 condensates with unprecedented CO2/N2 selectivity when compared to other carbonaceous solid sorbents. Increasing the surface area of the CN condensates in the presence of ZnCl2 salt melts enhances the amount of CO2 adsorbed while preserving the high selectivity values and C1N1 structure. Results indicate that these new materials show a sorption mechanism a step closer to that of natural CO2 caption proteins and based on metal free structural cryptopores.}}, author = {{Kossmann, Janina and Piankova, Diana and V. Tarakina, Nadezda and Heske, Julian Joachim and Kühne, Thomas and Schmidt, Johannes and Antonietti, Markus and López-Salas, Nieves}}, issn = {{0008-6223}}, journal = {{Carbon}}, keywords = {{CN, Cryptopores, Carbon dioxide capture}}, pages = {{497--505}}, title = {{{Guanine condensates as covalent materials and the concept of cryptopores}}}, doi = {{https://doi.org/10.1016/j.carbon.2020.10.047}}, volume = {{172}}, year = {{2021}}, } @article{62804, abstract = {{We report on the facile synthesis of porous carbons based on a biopolymer lignin employing a two-step process which includes the activation by KOH in various amounts under an inert gas atmosphere. The resulting carbons are characterized with regard to their structural properties and their electrochemical performance as an active material in double-layer capacitors using for the first time an ionic liquid (EMIBF4) as the electrolyte for this type of carbon material to enhance storage ability. A capacitance of more than 200 F g–1 at 10 A g–1 is achieved for a carbon with a specific surface area of more than 1800 m2 g–1. One of the most crucial factors determining the electrochemical response of the active materials was found to be the strong surface functionalization by oxygen-containing groups. Furthermore, the sulfur content of the carbon precursor lignin does not result in a significant amount of sulfur-containing surface functionalities which might interact with the electrolyte.}}, author = {{Klose, Markus and Reinhold, Romy and Logsch, Florian and Wolke, Florian and Linnemann, Julia and Stoeck, Ulrich and Oswald, Steffen and Uhlemann, Martin and Balach, Juan and Markowski, Jens and Ay, Peter and Giebeler, Lars}}, issn = {{2168-0485}}, journal = {{ACS Sustainable Chemistry & Engineering}}, keywords = {{supercapacitor, carbon, pyrolysis, lignin}}, number = {{5}}, pages = {{4094--4102}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Softwood Lignin as a Sustainable Feedstock for Porous Carbons as Active Material for Supercapacitors Using an Ionic Liquid Electrolyte}}}, doi = {{10.1021/acssuschemeng.7b00058}}, volume = {{5}}, year = {{2017}}, }