TY - JOUR

T1 - In Situ NMR Spectroscopy of Supercapacitors

T2 - Insight into the Charge Storage Mechanism

AU - Wang, Hao

AU - Forse, Alexander C.

AU - Griffin, John M.

AU - Trease, Nicole M.

AU - Trognko, Lone

AU - Taberna, Pierre-Louis

AU - Simon, Patrice

AU - Grey, Clare P.

PY - 2013/12/18

Y1 - 2013/12/18

N2 - Electrochemical capacitors, commonly known as supercapacitors, are important energy storage devices with high power capabilities and long cycle lives. Here we report the development and application of in situ nuclear magnetic resonance (NMR) methodologies to study changes at the electrode-electrolyte interface in working devices as they charge and discharge. For a supercapacitor comprising activated carbon electrodes and an organic electrolyte, NMR experiments carried out at different charge states allow quantification of the number of charge storing species and show that there are at least two distinct charge storage regimes. At cell voltages below 0.75 V, electrolyte anions are increasingly desorbed from the carbon micropores at the negative electrode, while at the positive electrode there is little change in the number of anions that are adsorbed as the voltage is increased. However, above a cell voltage of 0.75 V, dramatic increases in the amount of adsorbed anions in the positive electrode are observed while anions continue to be desorbed at the negative electrode. NMR experiments with simultaneous cyclic voltammetry show that supercapacitor charging causes marked changes to the local environments of charge storing species, with periodic changes of their chemical shift observed. NMR calculations on a model carbon fragment show that the addition and removal of electrons from a delocalized system should lead to considerable increases in the nucleus-independent chemical shift of nearby species, in agreement with our experimental observations.

AB - Electrochemical capacitors, commonly known as supercapacitors, are important energy storage devices with high power capabilities and long cycle lives. Here we report the development and application of in situ nuclear magnetic resonance (NMR) methodologies to study changes at the electrode-electrolyte interface in working devices as they charge and discharge. For a supercapacitor comprising activated carbon electrodes and an organic electrolyte, NMR experiments carried out at different charge states allow quantification of the number of charge storing species and show that there are at least two distinct charge storage regimes. At cell voltages below 0.75 V, electrolyte anions are increasingly desorbed from the carbon micropores at the negative electrode, while at the positive electrode there is little change in the number of anions that are adsorbed as the voltage is increased. However, above a cell voltage of 0.75 V, dramatic increases in the amount of adsorbed anions in the positive electrode are observed while anions continue to be desorbed at the negative electrode. NMR experiments with simultaneous cyclic voltammetry show that supercapacitor charging causes marked changes to the local environments of charge storing species, with periodic changes of their chemical shift observed. NMR calculations on a model carbon fragment show that the addition and removal of electrons from a delocalized system should lead to considerable increases in the nucleus-independent chemical shift of nearby species, in agreement with our experimental observations.

KW - SOLID-STATE NMR

KW - DOUBLE-LAYER CAPACITORS

KW - NUCLEAR-MAGNETIC-RESONANCE

KW - REVERSIBLE LITHIUM INSERTION

KW - QUARTZ-CRYSTAL MICROBALANCE

KW - INDEPENDENT CHEMICAL-SHIFTS

KW - ORIENTED MEMBRANE SAMPLES

KW - POROUS CARBON ELECTRODES

KW - CARBIDE-DERIVED CARBONS

KW - ACTIVATED CARBON

U2 - 10.1021/ja410287s

DO - 10.1021/ja410287s

M3 - Journal article

VL - 135

SP - 18968

EP - 18980

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 50

ER -