Quantum capacitance

About: Quantum capacitance is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 24165 citations.

Large Capacitance Enhancement Induced by Metal-Doping in Graphene-Based Supercapacitors: A First-Principles-Based Assessment

Abstract: Chemically doped graphene-based materials have recently been explored as a means to improve the performance of supercapacitors. In this work, we investigate the effects of 3d transition metals bound to vacancy sites in graphene with [BMIM][PF6] ionic liquid on the interfacial capacitance; these results are compared to the pristine graphene case with particular attention to the relative contributions of the quantum and electric double layer capacitances. Our study highlights that the presence of metal-vacancy complexes significantly increases the availability of electronic states near the charge neutrality point, thereby enhancing the quantum capacitance drastically. In addition, the use of metal-doped graphene electrodes is found to only marginally influence the microstructure and capacitance of the electric double layer. Our findings indicate that metal-doping of graphene-like electrodes can be a promising route toward increasing the interfacial capacitance of electrochemical double layer capacitors, pri...

Two-Dimensional Layered Metallic VSe2 /SWCNTs/rGO Based Ternary Hybrid Materials for High Performance Energy Storage Applications.

Abstract: In this work, the ternary hybrid structure VSe2 /SWCNTs/rGO is reported for supercapacitor applications. The ternary composite exhibits a high specific capacitance of 450 F g-1 in a symmetric cell configuration, with maximum energy density of 131.4 Wh kg-1 and power density of 27.49 kW kg-1 . The ternary hybrid also shows a cyclic stability of 91 % after 5000 cycles. Extensive density functional theory (DFT) simulations on the structure as well as on the electronic properties of the binary hybrid structure VSe2 /SWCNTs and the ternary hybrid structure VSe2 /SWCNTs/rGO have been carried out. Due to a synergic effect, there are enhanced density of states near the Fermi level and higher quantum capacitance for the hybrid ternary structure compared to VSe2 /SWCNTs, leading to higher energy and power density for VSe2 /SWCNTs/rGO, supporting our experimental observation. Computed diffusion energy barrier of electrolyte ions (K+ ) predicts that ions move faster in the ternary structure, providing higher charge storage performance.

The intrinsic volumetric capacitance of conducting polymers: pseudo-capacitors or double-layer supercapacitors?

Abstract: The capacitance of conducting polymers represents one of the most important material parameters that in many cases determines the device and material performances. Despite a vast number of experimental studies, the theoretical understanding of the origin of the capacitance in conducting polymers remains unsatisfactory and appears even controversial. Here, we present a theoretical method, based on first principle capacitance calculations using density functional theory (DFT), and apply it to calculate the volumetric capacitance of two archetypical conducting polymers: poly(3,4-ethylene dioxythiophene) (PEDOT) and polypyrrole (PPy). Our aim is to achieve a quantitate description of the volumetric capacitance and to provide a qualitative understanding of its nature at the atomistic level. We find that the volumetric capacitance of PEDOT and PPy is ≈100 F cm−3 and ≈300 F cm−3, respectively, which is within the range of the corresponding reported experimental results. We demonstrate that the capacitance of conducting polymers originates from charges stored in atomistic Stern layers formed by counterions and doped polymeric chains. The Stern layers have a purely electrostatic origin, since the counterions do not form any bonds with the atoms of the polymeric chains, and no charge transfer between the counterions and conducting polymer takes place. This classifies the conducting polymers as double-layer supercapacitors rather than pseudo-capacitors. Further, we analyze contributions to the total capacitance originating from the classical capacitance CC and the quantum capacitance CQ, respectively, and find that the latter provides a dominant contribution. The method of calculations of the capacitance developed in the present paper is rather general and opens up the way for engineering and optimizing the capacitive response of the conducting polymers.

Role of quantum capacitance in coupled low-dimensional electron systems

Abstract: We have investigated the charging behavior of a layer of self-assembled InAs quantum dots placed in close vicinity to a two-dimensional electron gas (2DEG). As the gate bias is changed, the number of electrons in each system is altered simultaneously. Based on the quantum capacitance of the involved layers we develop a general model to determine the charging state of coupled low-dimensional systems from capacitance-voltage (CV) spectroscopy. The model is then applied to the special case of a layer of self-assembled quantum dots coupled to a 2DEG. As a complementary method, we have employed Hall voltage measurements. We find that the measurement of the two-dimensional carrier density through lateral transport provides a direct insight into the vertical charging process of the quantum dot system. Six individual charging peaks related to the occupation of the $s$ and $p$ shells of the dots can be resolved. In agreement with results from CV spectroscopy, Coulomb blockade and quantization energies can be extracted. Moreover, the Hall measurement offers a higher peak-to-valley ratio and a better estimate for the number of simultaneously charged dots than the capacitance data.