Highly Efficient\nAqueous Symmetric Redox Electrochemical\nCapacitor Based on UiO-66-NH<sub>2</sub>–Polyaniline Composite\nPowering Yellow LEDs

Metal–organic frameworks (MOFs) have garnered\nconsiderable\nattention as supercapacitor electrode materials due to their large\nspecific surface area and adjustable pore structure, but they are\npractically limited by poor conductivity. To address this limitation,\nin this study, the MOF, UiO-66-NH<sub>2</sub>, is modified with a\nconducting polymer, polyaniline (PANI), through <i>in situ</i> polymerization. In the composite, the MOF unit enriches the PANI\npolymers with a large number of electroactive centers, facilitating\nthe electron transfer process. Among the as-synthesized composites,\nUP0.1 exhibited best electrochemical performance with a high specific\ncapacitance of 462.2 F g<sup>–1</sup> at a specific current\nof 1 A g<sup>–1</sup> in a 2 M KOH electrolyte. Introducing\nthe redox-active substance K<sub>4</sub>[Fe(CN)<sub>6</sub>] into\nKOH resulted in reduced diffusion and charge transfer resistances,\nleading to an enhanced specific capacitance value of 859.5 F g<sup>–1</sup> at the same current. The as-fabricated aqueous symmetric\nsupercapacitor device can be operated up to 1.4 V without any oxygen\nevolution reaction, exhibiting a high specific capacitance of 252.3\nF g<sup>–1</sup>, which is equivalent to the areal capacitance\nof 1.3 F cm<sup>–2</sup> at a specific current of 0.8 A g<sup>–1</sup>. The device achieved a high specific energy of 68.7\nW h kg<sup>–1</sup> at a high specific power of 2.24 kW kg<sup>–1</sup>, along with good electrochemical stability. Two devices\nconnected in series were used to demonstrate the practical application\nusing yellow LEDs, paving the way toward the futuristic production\nof energy storage electronics.