A π-conjugated imine-rich organic material with exceptional pseudocapacitive properties for high-performance electrochemical desalination

Abstract

Capacitive deionization (CDI) holds immense potential for desalinating brackish and saline water. While organic materials have shown promise as electrode materials, their limited redox-active sites and low electron mobility present obstacles to their widespread use in CDI devices. Herein, a novel imine-rich organic compound, named HHAL, has been successfully synthesized using a one-step fused-ring condensation reaction. The HHAL molecule features a π-conjugated framework that enables substantial redox activity and superior electron mobility, as demonstrated by its exceptionally low HOMO-LUMO gap of ~1.93 eV. Additionally, the inclusion of abundant imine-based active sites within the HHAL molecule enhances Na⁺ capture, resulting in a large specific capacitance of 359 F g⁻¹ in NaCl aqueous solution. The mechanism of Na⁺ electrosorption and the related kinetic processes have been extensively studied through a combination of electrochemical measurements, in-situ characterization, and theoretical calculations. As a result, a hybrid CDI device incorporating the HHAL electrode has been crafted, showcasing an impressive desalination capacity of 78 mg g⁻¹, a swift average desalination rate of 2.6 mg g⁻¹ min⁻¹, and reliable regeneration performance, retaining approximately 98 % efficiency after 50 cycles. Therefore, these findings underscore the significant potential of this CDI device for high-efficiency desalination applications.