Study of electro-mechanical properties of manganese-based nanocomposites for supercapacitors

The Electric Double Layer (EDL) supercapacitors can have extremely high-power densities, incomparable cycle life, s tability, a nd r eliability, a s a r esult t hey are a lready u sed in uninterruptible power systems (UPS), memory back-up systems and even in the emergency doors of A irbus A 380. Graphene-based e lectrodes w ith ap propriate d efects ( encapsulated metal or metal oxide nanocomposite) and optimized alignment display enhanced capacitive behavior and can provide good cycling performance of energy storage material. Graphene is a mo no-atomic layer o f S p hybridized car bon with ho neycomb l attice structure. W hen engineered with m etal oxides, they s how high e lectrochemical d ouble l ayer cap acitance through synergistic effect. MnO2 has been investigated extensively as a suitable material for high-performance electrochemical c apacitor due t o it s low-cost, r ich r edox behavior a nd good environmental compatibility. In this work, the potential for rGO-MnO2 nanocomposite to be used as supercapacitor material has been examined in detail, both experimentally and via molecular d ynamics simulation. To ex amine t he p erformance o f t he nanocomposite experimentally, Cyclic V oltammetry a nd G alvanostatic C harging D ischarging e xperiment (Chronopotentiometry) have b een p erformed at s everal s can r ates an d s everal cu rrent densities, respectively. For act ive mass o f 0.000405g and potential window of -100 – 800 mV, s pecific cap acitance o f 2 61 F/g has been obtained from G alvanostatic C harging Discharging, which is moderately good enough to use in a supercapacitor. In depth analysis using molecular d ynamic ( MD) simulation method h as p erformed t o u nderstand t he atomistic configuration of existing rGO-MnO2 structure and to improve the nanocomposite electrode structure for better performance. Our study suggests an improved design of rGOMnO2 nanocomposite e lectrode by adding nano slit-pore in a p articular way which can be called ‘ nano s lit-pore’ model. U sing this model electric p otential as a result specific capacitance shows higher values than typical planer model. This is because adding slit-pore in the electrode surface increases the ion-electrode interaction as a result more solvent and electrolyte ions clustered near electrode surface and provides higher capacitance values. Our results clearly indicate that slit-pore in nanoscale creates opportunity to use the potential o f graphene sheet edges to improve the capacitance. Upon charging, the structure of the EDL exhibits a g reater r esponse near t he ed ges d ue t o t he p referential accu mulation o f e xcess charge c arriers t oward the edges. And a lso t he r GO-MnO2 sheets incorporate its potential which is c alculated t hrough experiment and s howed qualitatively through s imulation. Summation o f t hese t wo effects increases the specific capacitance o f e lectric double layer supercapacitor an d w e p roposed the model as ‘nano s lit-pore’ mo del. Findings from t his study will enable us to enhance the energy storage capability of rGO-MnO2 nanocomposite EDL supercapacitor.