Insight into pseudocapacitive and electrical double-layer capacitive behaviors in polyaniline-based supercapacitors

A facile method is developed to prepare polyaniline (PANI)-based supercapacitors with pseudocapacitive and electrical double-layer capacitive behaviors by modulating carbon nanotube (CNT) paper hydrophilicity. When hydrophobic CNT paper is used as the current collector for PANI electrodeposition, a thin PANI is grown at the surface of the CNT paper firstly and then this PANI layer acts as a seeding layer for the following PANI deposition and finally a continuous and uniform PANI film forms at the surface of the paper. When hydrophilic CNT paper works as the current collector, PANI prefers to grow along the CNT texture due to good wettability of CNT with the electroplating solution. The above different growth kinetics causes that the PANI composition on the hydrophobic CNT paper is quite different from that on the hydrophilic CNT paper and the former has much higher -NH-/-N = ratio than the latter. The amine nitrogen is active to make reversible redox reactions with the electrolyte, resulting in the pseudocapacitive behavior of the supercapacitor with PANI on the hydrophobic CNT paper as the electrodes. On the contrary, the PANI on the hydrophilic paper has lower -NH-/-N = ratio and larger surface area with the electrolyte, and thus the corresponding supercapacitor shows electrical double-layer capacitive behavior. By rationally designing the PANI composition, the supercapacitors in this work exhibit comparable electrochemical performance to the reported ones focusing on constructing an elaborate and complex CNT/PANI architecture in terms of its high specific capacitance (∼ 1025.9 mF cm^-2) and long cycling life (∼ 92.0%, 5000 cycles).