  Supercapacitors (S-C) are short-term energy storage elements that find many
applications, e.g., electronic charging devices and suppressors of power
fluctuations in grids that are interfaced with sustainable sources. The
capacitance of an ordinary capacitor increases when dispersing metallic
colloids in its dielectric. A similar strategy for S-C means a deployment of
nano-scale metal colloids (in our case, Au nano particles, or AuNPs) at the
very narrow interface between an electrolyte and the porous electrode (here,
active-carbon film on a grafoil current collector). This is achieved by making
the ligand that is coating the AuNPs negatively charged. We demonstrated a very
large specific capacitance increase with a minute addition of functionalized
AuNPs to the slurry. For example, C-V data at a scan rate of 20 mV/s indicated
a specific capacitance amplification by a factor of 10 when 30 micro-g of AuNPs
were incorporated with 200 mg of active carbon while using a 1 M Na2SO4
electrolyte and a 5% cellulose acetate butyrate as a binder. We make the case
that the adhesion of the AuNPs to the surface of the electrode was strong: upon
replacing the electrolyte, from 1 M Na2SO4 to 1 M KOH and retaining the same
set of electrodes, the enhancement capacitance factor decreased as compared to
1 M Na2SO4 electrolyte but remained large, ~3, as determined by C-V traces at
the same scan rate of 20 mV/s.
