Nanoarchitectonics of mesoporous carbon spheres by tuning the weight ratio of PEG-PCL block copolymer as template and phenol as carbon source towards supercapacitor applications

Fabrication of mesoporous carbon (MC) spheres is described, for the first time, upon tuning the weight ratio of poly(ethylene glycol)-poly(ε-caprolactone) to phenol as 1:1 and 1:4.3 via hydrothermal assisted carbonization approach. Field emission scanning electron microscope analysis suggested that morphologies of the MC with a 1:1 weight ratio (MC-1) are identified as spherical and monodisperse, whereas the MC containing a 1:4.3 weight ratio (MC-2) showed spherical morphology with polydisperse size distribution. Nitrogen adsorption-desorption isotherm investigations revealed that MC-1 illustrated a type IV configuration with H3 hysteresis loops, whereas the co-existence of type-III and type-VI isotherms is found for MC-2. The higher surface area, large pore volume, and pore radius of MC-1 compared to MC-2 suggest that MC-2 may have a more densely packed structure due to its high phenol content. The specific capacitance of as high as 87 Fg⁻¹ and 58 Fg⁻¹ are found, respectively, from the cyclic voltammetric and galvanostatic charge-discharge studies upon using MC-1 as electrodes in two-electrode configuration. The solution resistance and charge transfer resistance (R_ct) of MC spheres that estimated by electrochemical impedance spectroscopy are considerably smaller than those of already reported MC films. The small value of R_ct of MC spheres compared to that of films is attributed to a three-dimensional interconnected structure in the spherical geometry that facilitates faster charge transfer over films. Ragone plot analysis revealed that the highest energy density of 7.2 W h kg⁻¹ and the highest power density of 886 W kg⁻¹ is accomplished.