Keggin-Type Vanadotungstate Nanocluster-Anchored Polypyrrole Nanotubes for Enhanced Capacitance Performances

Polypyrrole
nanotubes (PNTs) have excellent electrical conductivity,
a high specific surface area (SSA), and certain mechanical strength
and are good substrate materials for composite polyoxometalates. In
this work, Keggin-type vanadotungstate (AgVW12) was uniformly
dispersed on PNTs to yield a binary composite AgVW12@PNTs
by the solvothermal method. This composite demonstrated a higher specific
capacitance (Cs of 1115.7 F g–1 at 2 A g–1), a better rate performance (Cs of 719.7 F g–1 at 15 A g–1), smaller electrochemical impedance, and longer cycle
life than PNTs and AgVW12. The eminent electrochemical
performance can be ascribed to the reversible multielectron transfer
capability of AgVW12, the excellent electrical conductivity
of PNTs, and the structural features of hollow PNTs and the porous
AgVW12. Kinetic calculations suggest that the pseudocapacitance
contribution accounts for half of the charge storage process at 80
mV s–1, and this contribution increases with higher
sweep rates. The AgVW12@PNTs-CC//AC-CC device displays
a higher energy density of 43.28 W h kg–1 at a power
density of 3250 W kg–1 and a long cycle life (91.45%
capacitance retention after 10,000 cycles). These results surpass
most reported ASC devices. The findings indicate that the anchoring
of POMs on conductive polymers with structural advantages can overcome
their own shortcomings and maximize their superior redox properties.