Abstract
This study aimed to fabricate ionic diode or rectifier devices by asymmetrically attaching nanostructured ion-conducting materials and membranes on a polypropylene adhesive substrate with needle-drilled microholes. The ion-conducting membranes ensured ion selectivity, while the microhole substrate facilitated current rectification and ion concentration polarisation. This method of fabricating ionic diodes resulted in effective current rectification. This current rectification phenomenon has potential implications in sensing, desalination, and other applications.
This study developed a method for asymmetrically attaching sulfonated poly (phenylene oxide) (SPPO) to polypropylene adhesive tape to create a semi-permeable system for cation transport and current rectification. Characterisation using FTIR confirmed successful sulfonation, introducing -S=O groups for membrane stability and cation conduction. Zeta potential measurements showed a consistent negative charge across different electrolytes. Contact angle analysis indicated SPPO’s hydrophilic nature (62°), while polypropylene adhesive tape was more hydrophobic (101°). SEM revealed a smooth SPPO membrane with a thickness of 29 μm, and EDS confirmed its composition as carbon (76.2%), oxygen (16.5%), and sulfur (7.4%). Cation rectification depended on microhole diameter, electrolyte concentration, and electrolyte type, with competition between cation and proton transport.
The second section explored the use of polyacrylonitrile-chitosan (PAN-CS) in ionic diode fabrication, showing anionic selectivity and cationic diode behavior when attached asymmetrically to microholes in polypropylene adhesive tape. Characterisation techniques like FTIR, SEM, and zeta potential confirmed that PAN has a negative surface charge due to nitrile groups, while chitosan is positively charged at low pH due to amine groups. The PAN-CS composite exhibits switchable charge behavior with a point of zero charge (pzc) around pH 11.5. The membrane is highly hydrophilic with a contact angle of 0°, which enhances ion transport, and electrochemical tests demonstrated pH-responsive ionic diode behavior. Elemental analysis showed PAN composition with nitrile groups and chitosan-containing amine groups, making the PAN-CS membrane suitable for membrane-based applications.