Porphyrin-Based Covalent Organic Polymer Wrapped MWCNT Electrodes under Moderate Salt Concentration for Super-Stable Aqueous Sodium-Ion Intercalated Sustainable Supercapacitor

To rival commercial organic electrolytes, it is important to focus on safe, cheap aqueous electrolytes with lower salt concentration (≈5.0 m) and a wider electrochemical stable potential window (ESPW). This study reports the facile synthesis of porphyrin-based covalent organic polymers (PTZ-COP, CBZ-COP, and TPA-COP) through a one-pot aromatic electrophilic polycondensation reaction between pyrrole and monomeric aldehydes (PTZ-CHO, CBZ-CHO and TPA-CHO). To enhance conductivity, these covalent organic polymers (COPs) were noncovalently wrapped on multiwall carbon nanotubes (MWCNTs), forming MWCNT@PTZ-COP, MWCNT@CBZ-COP and MWCNT@TPA-COP. Among all, phenothiazine-based COPs wrapped on MWCNT viz. MWCNT@PTZ-COP stands out, exhibiting notable surface area and redox-active moieties with high heteroatom (N, S) contents in the framework. These properties contribute to its superior performance in the form of an electrochemical double-layer capacitor (EDLC) and pseudocapacitor. In the three-electrode, the MWCNT@PTZ-COP achieves a wider ESPW of 2.2 V, demonstrates a remarkable specific capacitance of 292.7 F g^-1 along with an energy density 196.8 Wh kg^-1 and power density of 752 W kg^-1, at a current density of 0.7 A g^-1 in 5 m NaClO₄. As-designed symmetric supercapacitor cell of MWCNT@PTZ-COP demonstrates an impressive specific capacitance of 55.5 F g^-1 and energy density 37.3 Wh kg^-1, respectively. Additionally, it exhibits a high areal capacitance of 46.4 mF cm^-2 in 5 m NaClO₄. Moreover, it exhibits outstanding 100% capacitance retention after running 20 000 GCD cycles at 3.2 A g^-1. This system demonstrates the highest cell voltage for a porphyrin-based COPs aqueous symmetric supercapacitor with a high energy density and stability.