Polyaniline-decorated porous carbons with engineered meso/macrochannels for high performance capacitive deionization

Abstract

Porous activated carbons (PACs) are widely used capacitive deionization (CDI) electrode materials because of their high specific surface area and low cost. However, the excessive co-ion expulsion and slow charge storage kinetics by electrical double layer (EDL) adsorption resulting from their rich microporous structures limit their ion removal capacities and rates. In this study, PACs with abundant built-in meso/macroporous channels were successfully synthesized using asphalt powder and KOH as precursors with the aid of tableting pressurization. The contents of meso/macroporous channels can be manipulated by adjusting the applied tableting pressure. The existence of these channels facilitated ion transport and enhanced EDL adsorption. To further enhance the CDI desalination capacity, polyaniline (PANI) was in situ grown on the PAC surface to form PAC/PANI composites to induce pseudocapacitive deionization. The introduced N functional groups enhanced hydrophilicity and promoted the faradaic reaction with Cl⁻. A synergy between EDL adsorption and pseudocapacitive deionization was observed by correlating the physiochemical properties of PAC/PANIs with CDI efficiencies. By fine-tuning the PANI loading amount, optimum synergism was achieved with the desalination capacity of 35.3 mg g⁻¹ at 1.2 V, which was 5.3-fold higher than desalination by single EDL adsorption. This study revealed the synergism between EDL adsorption and pseudocapacitive deionization in the CDI desalination process and proposed a new strategy for engineering PAC with maneuverable built-in meso/macroporous channels for enhanced CDI capacities.