Rajaram Narayanan

Dimensionality-Dependent Electrochemical Kinetics at the Single-Layer Graphene–Electrolyte Interface

The theories to describe the rate at which electrochemical reactions proceed, to date, do not consider explicitly the dimensionality or the discreteness and occupancy of the energy levels of the electrodes. We show experimentally that such quantum mechanical aspects are important for dimensionally confined nanostructured materials and yield unusual variation of the kinetic rate constants with applied voltage in single-layer graphene. The observed divergence from conventional electrokinetics was ascribed to the linear energy dispersion as well as a nonzero density of states at the Dirac point in the graphene. The obtained results justify the use of density of states-based rate constants and considerably add to Marcus-Hush-Chidsey kinetics.

The Modification of the Pore Characteristics of Activated Carbon, for Use in Electrical Double Layer Capacitors, through Plasma Processing

It was aimed to determine whether plasma processing could contribute to enhanced capacitance and energy density of activated carbon electrode based electrochemical capacitors, through the formation of additional surface charges. While an increase of up to 35% of the gravimetric capacitance, along with ~ 20% decrease in resistance, was obtained through optimal plasma processing, increased plasma exposure yielded a drastic reduction (/increase) in the capacitance (/resistance). It was also found that the capacitance and resistance modulation was a sensitive function of sample processing as well as electrochemical testing procedure. Considering the complexity of modeling realistic porous matrices, a metric to parameterize the reach of an electrolyte into the matrix has been posited.

The role of defects and dimensionality in influencing the charge, capacitance, and energy storage of graphene and 2D materials

Abstract The inevitable presence of defects in graphene and other two-dimensional (2D) materials influences the charge density and distribution along with the concomitant measured capacitance and the related energy density. We review, in this paper, the various manifestations of the capacitance including both the classical electrostatic (e.g. associated with double layer, space charge, chemical capacitances) and the quantum forms, as well as a few methodologies to tune the respective capacitances. The role of a proper determination of the surface area of 2D materials, considering the presence of defects, in determining the capacitance and the magnitude of the energy storage is also considered.