Supercapacitor electrodes based on electropolymerized protoporphyrins

Abstract

The delocalized π-electrons on the tetrapyrrole ring allow efficient electron transport properties of porphyrins so that they can serve as electrode materials in energy storage devices. We demonstrate a pair of natural chlorophyll-related protoporphyrins, namely protoporphyrin IX (Por) and Mn (III) protoporphyrin IX chloride (MnPor), as the precursors to prepare polyporphyrin (PolyPor and PolyMnPor) films through the electrochemical coupling of the vinyl groups on the porphyrin macrocycles. The extension of the π-conjugated backbone lengthens the intramolecular channel of electrons and allows the electron transporting in higher speed, leading to an excellent electrochemical performance. Under 100 cyclic voltammogram cycles of polymerization, single-layered PolyPor gives capacitance of 93 F g−1, whereas laminar structure PolyMnPor provides significantly higher capacitance of up to 135 F g−1 with an expanded potential window. The well-aligned layer structure effectively accelerating the diffusion of electrolyte ions and enabling more accessible two-dimensional nanochannels furtherly promotes the electrochemical performance. Besides, we also optimize PolyMnPor synthesis condition; larger mass loading and higher capacitance of 250 F/g are achieved. These remarkable results demonstrate polyprotoporphyrins are promising and potential candidates as organic electrode materials. This study could direct future development of cost-effective energy storage devices based on naturally abundant biomaterials.