Effect of the formulation of the electrode on the pore texture and electrochemical performance of the manganese dioxide-based electrode for application in a hybrid electrochemical capacitor†
A composite electrode based on manganese dioxide, a binder (poly(tetrafluoroethylene), PTFE) and a carbon additive were characterized by scanning electron microscopy, nitrogen gas adsorption and electrochemistry. Two different carbon additive materials were investigated: acetylene black and a high surface area carbon black (Black Pearls 2000). It was found that the addition of the PTFE binder does not block access to the porous network of MnO2 and the two carbon powders. Unlike Black Pearls that affect the pore texture, acetylene black appears to slightly adversely affect the mesoporous surface, presumably because of its larger particle size. The electrochemical utilization of MnO2 is similar whether acetylene black or Black Pearls 2000 is used as a carbon additive. This suggests that the porosity of the latter, which could provide a pool of ionic species, does not appear to play a significant role as demonstrated by similar specific capacitance at a slow scan rate. On the other hand, the highest conductivity of acetylene black leads to slightly higher specific capacitance at higher scan rate. Finally, it is shown that using a high surface carbon support with MnO2 can cancel the effect of the larger potential window of electroactivity of MnO2 because of its smaller electrochemical potential stability range.