Controlled Microwave-Assisted Synthesis of Covalent Organic Frameworks Opens the Way Toward More Suitable Porous Supercapacitor Electrodes

Seeking efficient materials is still the key process for achieving high-performance electrical double-layer capacitor-type supercapacitors. In the present work, the synthesis of a well-known covalent organic framework, COF-5, was revisited and optimized by a microwave irradiation-assisted solvothermal approach. The highest Brunauer–Emmett–Teller specific surface area ever of 2600 m2 g–1 was achieved for this material along with a reaction yield of >90% with a reduced reaction time. This study provides further evidence on the real convenience of using microwave irradiation as an alternative route for efficiently synthesizing covalent organic framework-based materials. Indeed, the electrical conductivity increases by 4 orders of magnitude up to 2.35 × 10–2 S cm–1. Furthermore, the synthesized COF-5 was evaluated as-prepared or together with conducting additives as active electrode materials for supercapacitor applications. Accordingly, a specific capacitance of 100 F g–1 at 2 mV s–1 was obtained after the activation process. Importantly, the better organization of the structure of the COF strongly enhances its stability over a potential range of 1.3 V at 100 mV s–1 for 100 000 cycles in aqueous electrolytes

Processable Star-Shaped Molecules with Triphenylamine Core as Hole-Transporting Materials: Experimental and Theoretical Approach

In this study we report on the characterization of five star-shaped π-conjugated molecules by means of UV–vis absorption spectroscopy and electrochemical cyclic voltammetry. These molecules, with triphenylamine (TPA) core bearing one thienothiophene moiety and a different number of thiophene ones, are designed as hole-transporting materials for dye-sensitized solar cell (DSSC) applications. Theoretical calculations employing the B3LYP functional are also carried out in order to understand the structure–property relationships. UV–vis absorption measurements and time-dependent density functional theory (TDDFT) calculations show the presence of intense UV–vis bands for all compounds. These bands are dominated by two degenerate π–π* excitations mostly involving the HOMO → LUMO and HOMO → LUMO+1 transitions. Electrochemical cyclic voltammetry and DFT calculations show the HOMO (LUMO) energy levels increasing (decreasing) with the number of conjugated heterocyclic rings in these molecules. The HOMO energies have been found to vary between −5.38 and −5.13 eV thus showing good positioning with respect to the Fermi level of gold electrode (DSSC applications). The calculated internal reorganization energies (λ_i) suggest for these materials promising hole-transport properties. The analysis of the space extension of the HOMO orbitals as a function of the number of conjugated rings in these molecules gives useful information on their design