Montakan Suksomboon

High-performance supercapacitors based on silver nanoparticle–polyaniline–graphene nanocomposites coated on flexible carbon fiber paper

For practical use of supercapacitors, new electrode materials are needed with high ionic adsorption capacity at the solid–liquid interface, fast and reversible surface redox reaction, and fast charge transfer. In the current study, we produce a new hybrid material of electrochemical double layer capacitive graphene, pseudocapacitive polyaniline (PANI) and highly conductive silver nanoparticles (AgNPs). The nanocomposite of AgNP–PANI–graphene in a weight ratio of 0.1 : 1 : 1, coated on flexible carbon fiber paper (CFP), exhibits high specific capacitance and capacity retention. At an applied current density of 1.5 A g−1, the maximum specific capacitance of AgNP–PANI–graphene/CFP is 828 F g−1, which is about 4.0-, 2.2-, 1.6-, and 1.5-fold higher than those of graphene/CFP, PANI/CFP, AgNP–PANI/CFP, and PANI–graphene/CFP, respectively. The capacity retention of AgNP–PANI–graphene/CFP after a charge–discharge test having 3000 cycles is 97.5% of the original specific capacitance. This was 4.4, 12.9, 14.5, and 23.5% more stable than PANI–graphene/CFP, graphene/CFP, AgNP–PANI/CFP, and PANI/CFP, respectively. An 0.8′′ × 6′′ all-solid-state supercapacitor device composed of AgNP–PANI–graphene/CFP exhibited a specific capacitance of 142 F g−1 measured at an applied current density of 1.5 A g−1 and a wide working potential of 6.2 V after consecutive charge–discharge tests over a 16.40 h period. This fully charged supercapacitor could power a 3 V motor for 7.30 min.

Effect of alkaline electrolytes on the charge storage capacity and morphology of porous layered double cobalt hydroxide-coated graphene supercapacitor electrodes

Although alpha-cobalt hydroxide (α-Co(OH)2) with a layered double hydroxide (LDH) structure has been widely used as a supercapacitor electrode, the effect of an alkaline electrolyte on the charge storage performance of the α-Co(OH)2 has not yet been investigated. In this work, α-Co(OH)2 was electrodeposited on reduced graphene oxide-coated carbon fiber paper (rGO/CFP) using chronoamperometry at −0.5 V vs. Ag/AgCl. The effect of alkaline aqueous electrolytes on the performance of the α-Co(OH)2/rGO/CFP electrodes was then investigated by means of scanning and transmission electron microscopies, X-ray photoelectron and absorption spectroscopies, and electrochemical techniques. It was found that the concentrated alkaline electrolytes (i.e., 3–6 M [OH−]) can strip off and/or deform the porous structure of the α-Co(OH)2 deposited on rGO/CFP leading to poor charge storage capacity. 1 M [OH−] was found to be a suitable electrolyte concentration providing high specific capacitance (1096 F g−1 at 1.8 A g−1) without the deformation of the porous α-Co(OH)2 structure after testing. Morphological and electrochemical analyses of the α-Co(OH)2/rGO/CFP electrodes suggest that the effect of the alkaline electrolyte concentration plays a major role on the charge storage performance of α-Co(OH)2-based supercapacitors.