Introducing non-conjugated ionic spacer in metallo-supramolecular polymer: Generation of nanofibers for high-performance electrochromic supercapacitor

Abstract

The use of indicative electrochromic (EC) supercapatteries is gaining significant attention for their ability to indicate their charging and discharging status through optical color changes and their high energy and power densities, making them a promising renewable alternative energy source. In this study, we performed molecular engineering to prepare a non-conjugated pyridinium cation-containing bisterpyridine ligand (TpyNTpy) and its metallo-supramolecular polymer (MSP), Fe-TpyNTpy. The MSP was thoroughly characterized through spectroscopic, morphological, and structural studies, revealing a homogeneous nanofiber morphology with good thermal stability. The gel-state EC devices, fabricated using Fe-TpyNTpy as the active layer, demonstrated EC color changes from purple to dirty white, with a large optical contrast of 47% at 570 nm, fast coloration (1.5 s) and bleaching (2.4 s) times, high coloration efficiency of 312.8 cm2C-1, longer optical memory, and extremely high EC cycle stability. Incorporating nonconjugated and ionic ligands helped address the opposite electrochemical behaviors, such as EC fastness and optical memory. The Fe-TpyNTpy film showed good supercapacitive properties in solution electrolytes, and the energy storage behavior was correlated with EC transmittance/color change. The energy storage properties were evaluated by preparing a hybrid ESD. The Fe-TpyNTpy and Prussian blue containing hybrid ESD exhibited an improved volumetric capacitance of 73 ± 2F/cm3 with low iR drop, high energy storage capacity (energy density 61 mWh/cm3 at a power density of 8.5 W/cm3), and 95% retention of initial volumetric capacitance after 10,000 charge–discharge cycles. The hybrid ESD can illuminate a single LED, demonstrating the practical applicability of the ESD.