This presentation describes a process, involving electrospray of carbonaceous polymer sol on a current collector-substrate, followed by in situ curing, drying and carbonization. The electrospray process splits the precursor sol into fine droplets by Coulombic fission, prior to the deposition on the substrate. The pyrolysis of cured and dried gel film provides the active layer with enhanced internal surface area for the double layer capacitance, and lower resistance to charge transport. The choices of different methods and parameters e.g., sol composition, electrospray voltage, drying method, pyrolysis and pore activation protocols make possible the tuning of pore structure.

The carbonaceous precursor sol, considered in this work is resorcinol formaldehyde (RF). The sol-gel transition involves addition and polycondensation reactions respectively, where the latter step contributes to crosslinks. Upon pyrolysis, the crosslinks develop into micropores. RF gel can be prepared in either aqueous or organic solvent, and the choice of solvent may affect the morphology of the deposited film. Further, the method of solvent removal for the drying of cured RF gel film contributes to the mesopore formation in the carbon film. In particular, the simultaneous evaporation of organic solvent at the time of curing vis-à-vis the lyophilization of aqueous gel film can lead to distinctly different pore structure. The hierarchical structure with connected mesopores enables better access to the micropores. The presentation addresses these aspects using experimental measurements. The nitrogen adsorption-desorption experiment on bulk carbon powder showed the pore size distribution and specific surface area. The carbon powder is also analyzed here using XRD, FTIR, and Raman spectroscopy.

Carbon paper is used in this work as the current collector. Sufficient adhesion between the deposited film and the carbon paper enabled handling of the composite through curing, solvent removal, and carbonization steps without peel. The morphology of the film is studied under SEM, and the pore size is calculated using the image analysis software. The electrochemical performance of the electrode is studied in a symmetric cell using KCl and KOH respectively as electrolytes. The cyclic voltammetry, chronopotentiometry, and impedance spectroscopy are performed to estimate specific capacitance, electrolyte resistance at different extents of ion penetration into the pore. The retention of capacitance and coulombic efficiency after several charge-discharge cycles are reported here.