The effect of various electrolyte cations on electrochemical performance of polypyrrole/RGO based supercapacitors

In this work, polypyrrole/graphene doped by p-toluenesulfonic is prepared as an active material for supercapacitors, and its capacitance performance is investigated in various aqueous electrolytes including HCl, LiCl, NaCl, and KCl with a concentration of 3 M, respectively. A rising trend of capacitance is observed according to the cationic mobility (Li+ < Na+ < K+ < H+), which is due to its effect on the ionic conductivity, efficient ion/charge diffusion/exchange and relaxation time. On the other hand, long-term cycling stability is in the following order: KO < NaCl < LiCl < HCl, corresponding to the decreasing tendency of cation size (K+ > Na+ > Li+ > H+). The reason can be attributed to the fact that the insertion/de-insertion of large size cation brings a significant doping level decrease and an over-oxidation increase during the charging-discharging cycles. Hence, we not only obtain good capacitance performance (280.3 F g(-1) at 5 mV s(-1)), superior rate capability (225.8 F g(-1) at 500 mV s(-1)) and high cycling stability (92.0% capacitance retention after 10 000 cycles at 1 A g(-1)) by employing 3 M HCl as an electrolyte, but also reveal that the electrolyte cations have a significant effect on the supercapacitors' electrochemical performance.