Investigating graphene/conducting polymer hybrid layered composites as pseudocapacitors: Interplay of heterogeneous electron transfer, electric double layers and mechanical stability

Hybrid electrochemical electrodes consisting of supercapacitive graphene nanosheets and pseudocapacitive conducting polymers such as polypyrrole (PPy) and polyaniline (PAni) are constructed layer-by-layer (LbL) via in-situ electropolymerization followed by electrochemical reduction of graphene oxide (ErGO) forming (PPy/ErGO)n=1 and (PAni/ErGO)n=1 bilayers, with subsequent multilayers up to n = 5. We investigated structural, physical and electrochemical properties and the hybrids prepared using this Scheme 1 showed excellent electro-chemo-mechanical stability and enhanced electrochemical performance attributed to appropriate polymer chain conformations and covalently tailored and chemically bridged interface-promoted synergistic effects. From cyclic voltammograms, we determined gravimetric specific capacitance (Cs) at scan rate 10 mV/s and at a discharge current density of 1.0 A g−1 that ranged 300-560 F g−1 outperforming other hybrid supercapacitors and capacity retention of ∼90% over 1000 cycles at a specific current density of 1.5 A g−1. From electrochemical impedance spectroscopy data fitting and circuit simulations we determined various equivalent circuit parameters including low frequency (Clf) and interfacial capacitance, charge transfer and solution resistance that helped to calculate gravimetric power and energy densities. We also prepared PAni/rGO multilayer pseudocapacitors by varying rGO weight loading by electrostatic LbL assembly (Scheme 2) and compared their electrochemical properties with those of Scheme 1. The findings reveal the significance of electro-processing and electrodeposition and clearly elucidate the role of engineered interfaces in enhancement of interfacial properties i.e. heterogeneous electron transfer, diffusion coefficient, mechanical strength and electrical double layer in Scheme 1 graphene-polymer hybrids.