Understanding the mechanism of carbonization and KOH activation of polyaniline leading to enhanced electrosorption performance

Capacitive deionization (CDI) emerged as a new water desalination technology in which ions are removed from brackish water by being attracted and stored in two polarized electrodes. The electrode material plays a very important role affecting other fundamental parameters such as the salt adsorption capacity (SAC), conductivity, desalination kinetics, and energy consumption. Typically, the CDI electrodes are carbon-based materials, fulfilling requirements such as high specific surface area (SSA), chemical stability, and conductivity. Here, we make a comprehensive study of the variables involved in the polyaniline activated carbons (PAC) preparation. A new mechanism is proposed to explain how the carbonization/activation conditions have influence on textural properties (SSA and pore volume) of PAC. We found that carbonization at temperatures ≤600 °C are mandatory to provide more KOH-reactive carbon intermediates due to their turbostratic structure. After activation at 850 °C, remarkable pore volume (2.30 cm³/g) and SSA (∼3600 m²/g) were achieved, which has direct influence on promoting high electrode capacitance (213 F/g), SAC (22.2 mg/g), and charge efficiency (81%). This SAC is among the highest values reported for CDI desalination using carbon electrodes. This work enlightens the mechanism to achieve high performance activated carbons providing a promising electrode material for CDI desalination.