Porphyrin-Regulated Heterostructured Hydrogel Ionic Diode with a High Rectification Ratio and Output Voltage

Nanochannel ionic diodes require extremely complex and expensive fabrication processes. Polyelectrolyte ionic diodes attracted widespread attention among ionic rectification systems due to their simplicity of development and the ability to break the size limits of the nanochannel. However, enhancement of their rectification ratio is still in the exploratory stage. In this study, chitosan (CS) hydrogels and sodium polyacrylate (PAAs) hydrogels were prepared as the substrates for the heterostructured ionic diodes. 5,10,15,20-Tetrakis(4-aminophenyl)-21H,23H-porphyrin (TAPP) was selected to regulate the rectification ratio of ionic diodes. By adding 0.05 wt % TAPP to the CS hydrogel, the rectification ratio of the ionic diode can be increased to 10, which is 4 times larger than that of the undoped ionic diode. In contrast, the rectification ratio of the ionic diodes with TAPP added in the PAAs hydrogel decreases to 2. In addition, the ionic diode composed of the TAPP-doped CS hydrogel and PAAs hydrogel has the characteristics of a high open-circuit voltage. The open-circuit voltage of the 10 mm × 10 mm × 4 mm heterojunction hydrogel reached 370 mV. The ionic diodes can be used as a self-powered power supply device.