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Direct observation of the CO_(2) formation and C–H consumption of carbon electrode in an aqueous neutral electrolyte supercapacitor by in-situ FTIR and Raman

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Journal of Energy Chemistry 2022年第8期31卷 488-496,I0013页

作者： Murilo M.Amaral Victor Y.Yukuhiro Rafael Vicentini Alfredo C.Peterlevitz Leonardo M.Da Silva Pablo Fernandez Hudson Zanin Advanced Energy Storage Division State University of Campinas13083-852Av.Albert Einsten 400CampinasSPBrazil Chemistry Institute State University of Campinas13083-970Josue de Castro StreetCampinasSPBrazil Department of Chemistry Laboratory of Fundamental and Applied ElectrochemistryFederal University of Jequitinhonha and Mucuri’s ValleyRodovia MGT 367km 5835000Alto da Jacuba39100-000DiamantinaMGBrazil Center for Innovation on New Energies University of Campinas13083-841 CampinasSão PauloBrazil

Electrical double-layer capacitors(EDLCs)consist of energy storage devices that present high-power and moderate energy density.The electrolyte and electrode physicochemical properties are crucial for improving their overall energy storage capabilities.Therefore,the stability of the EDLCs’materials is the primary focus of this study.Since energy storage depends on the specific capacitance,and also on the square of the maximum capacitive cell voltage(UMCV).Thus,electrodes with high specific surface area(SSA)and electrolytes with excellent electrochemical stability are commonly reported in the literature.Aqueous electrolytes are safer and green devices compared to other organic-based solutions.On the other hand,their UMCVis reduced compared to other electrolytes(e.g.,organic-based and ionic liquids).In this sense,spanning the UMCVfor aqueous-based electrolytes is a’hot topic’research.Unfortunately,the lack of protocols to establish reliable UMCVvalues has culminated in the publishing of several conflicting results.Herein,we confirm that multiwalled carbon nanotubes(MWCNTs)housed in cells degrade and produce CO_(2) under abusive polarisation conditions.It is probed by employing electrochemical techniques,in-situ FTIR and in-situ Raman spectroscopies.From these considerations,the current study uses spectro-electrochemical techniques to support the correct determination of the electrode and electrolyte stability conditions as a function of the operating electrochemical parameters.

关键词： Electrode and electrolyte stabilities In-situ FTIR CO_(2)formation Carbon degradation Supercapacitor Aqueous electrolytes Carbon nanotubes

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Boosting energy-storage capability in carbon-based supercapacitors using low-temperature water-in-salt electrolytes

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Journal of Energy Chemistry 2022年第7期31卷 521-530,I0013页

作者： Joao Pedro A.Santos Manuel J.Pinzón érick A.Santos Rafael Vicentini Cesar J.B.Pagan Leonardo M.Da Silva Hudson Zanin Brazilian Renewable Energies Center for Innovation on New EnergiesSchool of Electrical and Computer EngineeringUniversity of CampinasSao Paulo 13083-852Brazil Department of Semiconductors Instruments and PhotonicsSchool of Electrical and Computer EngineeringUniversity of CampinasSao Paulo 13083-852Brazil Laboratory of Fundamental and Applied Electrochemistry Department of ChemistryFederal University of Jequitinhonha e Mucuri’s ValleyMinas Gerais 39100-000Brazil

Supercapacitors(SCs) are high-power energy storage devices with ultra-fast charge/discharge properties.SCs using concentrated aqueous-based electrolytes can work at low temperatures due to their intrinsic properties, such as higher freezing point depression(FPD) and robustness. Besides the traditional organic-and aqueous-based(salt-in-water) electrolytes used in SCs, water-in-salt(WISE) sodium perchlorate electrolytes offer high FPD, non-flammability, and low-toxicity conditions, allowing the fabrication of safer, environmentally friendly, and more robust devices. For the first time, this work reports a comprehensive study regarding WISE system’s charge-storage capabilities and physicochemical properties under low-temperature conditions(T < 0 ℃) using mesoporous carbon-based electrodes. The effect of temperature reduction on the electrolyte viscosity and electrical properties was investigated using different techniques and the in-situ(or operando) Raman spectroscopy under dynamic polarization conditions.The cell voltage, equivalent series resistance, and specific capacitance were investigated as a function of the temperature. The cell voltage(U) increased ~ 50%, while the specific capacitance decreased ~20%when the temperature was reduced from 25 ℃ to -10 ℃. As a result, the maximum specific energy(E = CU^(2)/2) increased ~ 100%. Therefore, low-temperature WISEs are promising candidates to improve the energy-storage characteristics in SCs.

关键词： Carbon supercapacitors Water-in-salt electrolytes Low-temperature charge-storage Specific energy improvement at low temperatures

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Best practices for electrochemical characterization of supercapacitors

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Journal of Energy Chemistry 2023年第5期80卷 265-283,I0007页

作者： João Pedro Aguiar dos Santos Fernando Cesar Rufino Joǎo IYutaka Ota Rodolfo CFernandes Rafael Vicentini Cesar JBPagan Leonardo Morais Da Silva Hudson Zanin Brazilian Renewable Energies Center for Innovation on New EnergiesSchool of Electrical and Computer EngineeringUniversity of CampinasSP 13083-852Brazil School of Electrical and Computer Engineering University of CampinasSP 13083-852Brazil Department of Chemistry Laboratory of Fundamental and Applied ElectrochemistryFederal University of Jequitinhonha e Mucuri's ValleyRodovia MGT 367km 5835000Alto da Jacuba39100-000 DiamantinaMGBrazil

We discuss here essential aspects of the experimental supercapacitors characterization by a series of well-known electrochemical methods.We are motivated by a considerable number of publications that misreport procedures and results.Authors often conceal or neglect essential information about the electrochemical analytical apparatus used and its configuration.The lack of such information may lead researchers,especially inexperienced ones,to misunderstand the procedures and results.Eventually,the misled electrochemical equipment configuration favors misinterpretation of data and low reproducibility rates.This paper aims to highlight these issues and clarify them.We explain fundamental concepts of some electrochemical analytical methods,such as cyclic voltammetry,galvanostatic charge-discharge,single potential step chronoamperometry,and electrochemical impedance spectroscopy,focusing on the supercapacitor field.Distinct configurations of electrical parameters are presented and discussed to highlight the effects of incorrect setup and uncover misleading results.We discuss how the electrochemical setup and data analyses matter in reliable data results for the supercapacitor.

关键词： Supercapacitor Electrochemical instrumentation Electrochemical methods Electrochemistry

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Ion dynamics into different pore size distributions in supercapacitors under compression

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Journal of Energy Chemistry 2023年第5期80卷 110-119,I0004页

作者： João Pedro Aguiar dos Santos Cesar J.B.Pagan Rafael Vicentini Reinaldo F.Teófilo Renato Beraldo Leonardo M.Da Silva Hudson Zanin Brazilian Renewable Energies Center for Innovation on New EnergiesSchool of Electrical and Computer EngineeringUniversity of CampinasAv.Albert Einstein 40CampinasSP13083-852Brazil School of Electrical and Computer Engineering University of CampinasSP 13083-852Brazil Multivariate Chemical Data Analysis Laboratory Department of ChemistryUniversidade Federal de Viçosa36570-900 ViçosaMGBrazil Department of Chemistry Laboratory of Fundamental and Applied ElectrochemistryFederal University of Jequitinhonha and Mucuri's ValleyRodovia MGT 367km 5835000 Alto da Jacuba39100-000DiamantinaMGBrazil

Compressing supercapacitor(SCs)electrode is essential for improving the energy storage characteristics and minimizing ions’distance travel,faradaic reactions,and overall ohmic resistance.Studies comprising the ion dynamics in SC electrodes under compression are still rare.So,the ionic dynamics of five aqueous electrolytes in electrodes under compression were studied in this work for tracking electrochemical and structural changes under mechanical stress.A superionic state is formed when the electrode is compressed until the micropores match the dimensions with the electrolyte’s hydrated ion sizes,which increases the capacitance.If excessive compression is applied,the accessible pore regions decrease,and the capacitance drops.Hence,as the studied hydrated ions have different dimensions,the match between ion/pore sizes differs.To the LiOH and NaClO4electrolytes,increasing the pressure from 60 to 120 and 100 PSI raised the capacitance from 13.5 to 35.2 F g^(-1)and 30.9 to 39.0 F g^(-1),respectively.So,the KOH electrolyte with the lowest and LiCl with the biggest combination of hydrated ion size have their point of maximum capacitance(39.5 and 36.7F g^(-1))achieved at 140 and 80 PSI,respectively.To LiCl and KCl electrolytes,overcompression causes a drop in capacitance higher than 23%.

关键词： Mechanic compression Pore size distribution lon dynamics Activated carbon Supercapacitors

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Raman probing carbon&aqueous electrolytes interfaces and molecular dynamics simulations towards understanding electrochemical properties under polarization conditions in supercapacitors

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Journal of Energy Chemistry 2021年第9期30卷 279-292页

作者： Rafael Vicentini Leonardo M.Da Silva Débora V.Franco Willian G.Nunes Juliane Fiates Gustavo Doubek Luís F.M.Franco Renato G.Freitas Cristiano Fantini Hudson Zanin Advanced Energy Storage Division Carbon Sci-Tech LabsUniversity of CampinasAv Albert Einstein 400CampinasSP 13083-852Brazil Department of Chemistry Federal University of Jequitinhonha and Mucuri’s ValleyRodovia MGT 367km 5835000Alto da Jacuba39.100-000 DiamantinaMGBrazil Advanced Energy Storage Division Center for Innovation on New EnergiesLaboratory of Advanced BatteriesSchool of Chemical EngineeringUniversity of Campinas(UNICAMP)CampinasSP 13083-852Brazil Department of Chemistry Federal University of Mato GrossoICET-UFMT78060-900 CuiabáMTBrazil Departamento de Física ICExUniversidade Federal de Minas GeraisBelo HorizonteMG 31270-901Brazil

Raman probing of carbon electrode and electrolyte under dynamic conditions is performed here using different aqueous electrolytes to elucidate the fundamental events occurring in electrochemical supercapacitor during charge–discharge processes.The areal capacitance ranges from 1.54 to 2.31μF cm^(-2)μm and it is determined using different techniques.These findings indicate that the Helmholtz capacitance governs the overall charge-storage process instead of the space charge(quantum)capacitance commonly verified for HOPG electrodes in the range of~3 to 7μF cm^(-2).Molecular dynamics simulations are employed to elucidate the origin of the reversible Raman spectral changes during the charge–discharge processes.A correlation is verified between the reversible Raman shift and the surface excesses of the different ionic species.A theoretical framework is presented to relate the effect of the applied potential on the Raman shift and its correlation with the surface ionic charge.It is proposed that the Raman shift is governed by the interaction of solvated cations with graphite promoted by polarization conditions.It is the first time that a comparative study on different aqueous electrolyte p H and cation ion size has been performed tracking the Raman spectra change under dynamic polarization conditions and contrasting with comprehensive electrochemistry and dynamic molecular simulations studies.This study shines lights onto the charge-storage mechanism with evidence of Kohn anomaly reduction in the carbon electrode during the reversible adsorption/desorption and insertion/extraction of ionic species.

关键词： Defect reorganization in graphite Surface excess of charge Operando Raman studies Electrical double-layer capacitors

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