Mesoscopic behaviour of multi-layered graphene: the meaning of supercapacitance revisited

GUTIERREZ, FABIANA A.; BUENO, PAULO R.; RIVAS, GUSTAVO A.; BEDATTY FERNANDES, FLAVIO C.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2017 vol. 19 p. 6792 - 6806

1463-9076

The electronic density of states and its contribution to the capacitance of graphene compounds (oxidized and reduced)were investigated using an electrochemical impedance-derived capacitance spectroscopic approach. It is clearlydemonstrated that graphene oxide, which is known to exhibit semiconductor electronic characteristics, has little influenceon the magnitude of the measured capacitance. Moreover, when graphene oxide is electrochemically reduced tographene, the capacitance increases dramatically by about three orders of magnitude (from microfaradays tomillifaradays). This increased capacitive effect has been interpreted as being directly associated with the electrochemicalnon-faradaic (super- or ultracapacitive) characteristics of the interface (i.e. associated with its electroactive area, forinstance). The results obtained and interpretation made in this work demonstrate that the magnitude of the measuredcapacitance is a consequence of an electrochemical capacitive phenomenon (mesoscopic in essence; thus, the associatedcapacitance is equivalently termed mesoscopic capacitance) that energetically contains, in series, both electrostatic(geometrical) and quantum effects, thus being essentially different from those exclusively related to the amount ofexisting interfacial sites for ions (i.e. beyond those associated with pure double-layer capacitive effects). Conceptually, it isproposed that the mesoscopic capacitance of reduced graphene can be explained mainly through quantum chemicaleffects, ultimately following first-principles quantum mechanics supported on density functional theory, wherein thedensity of states is central.