Nitrogen-Doped Carbon Nanocoil Array Integrated on Carbon Nanofiber Paper for Supercapacitor Electrodes

Integrating a nanostructured carbon array on a conductive substrate remains a challenging task that presently relies primarily on high-vacuum deposition technology. To overcome the problems associated with current vacuum techniques, we demonstrate the formation of an N-doped carbon array by pyrolysis of a polymer array that was electrochemically grown on carbon fiber paper. The resulting carbon array was investigated for use as a supercapacitor electrode. In-depth surface characterization results revealed that the microtextural properties, surface functionalities, and degree of nitrogen incorporated into the N-doped carbon array can be delicately controlled by manipulating carbonization temperatures. Furthermore, electrochemical measurements showed that subtle changes in these physical properties resulted in significant changes in the capacitive behavior of the N-doped carbon array. Pore structures and nitrogen/oxygen functional groups, which are favorable for charge storage, were formed at low carbonization temperatures. This result showed the importance of having a comprehensive understanding of how the surface characteristics of carbon affect its capacitive performance. When utilized as a substrate in a pseudocapacitive electrode material, the N-doped carbon array maximizes capacitive performance by simultaneously achieving high gravimetric and areal capacitances due to its large surface area and high electrical conductivity

Crystalline Matrix of Mesoporous TiO₂ Framework for Dye-Sensitized Solar Cell Application

In the present study, a well-ordered columnar porous TiO₂ matrix is designed via inverted triblock copolymers self-assembly and introduced as a photoanode for dye-sensitized solar cells (DSSCs). The inverted triblock copolymer, polystyrene-<i>b</i>-poly­(ethylene oxide)-<i>b</i>-polystyrene, with the hydrophobic polystyrene segments at both ends of a hydrophilic poly­(ethylene oxide) chain is synthesized by atom transfer radical polymerization. These reverse-featured triblock copolymers allow facile stacking to 3-dimensional (D) columnar porous matrix from 2-D porous film via hydrophobic–hydrophilic interaction. A 3-D matrix with well-ordered cylindrical pores is favorable to current flow by providing a direct electron pathway. DSSCs with a 3-D matrix of 2 μm thickness show an enhanced photocurrent density of 8.1 mA cm^–2 and higher photoconversion efficiency of 4.23% compared with those of TiO₂ nanoparticle photoelectrode under the illumination of 1 sun (AM 1.5 G 100 mW cm^–2). For the first time, we address that a 3-D metal oxide electrode with columnar pore is demonstrated via reverse-featured triblock copolymer and analyzed with relationships between their structural features and impedance spectroscopy for DSSCs

Electronic Optimization of Heteroleptic Ru(II) Bipyridine Complexes by Remote Substituents: Synthesis, Characterization, and Application to Dye-Sensitized Solar Cells

We prepared a series of new heteroleptic ruthenium(II) complexes, Ru(NCS)2LL′ (3a−3e), where L is 4,4′-di(hydroxycarbonyl)-2,2′-bipyridine and L′ is 4,4′-di(p-X-phenyl)-2,2′-pyridine (X = CN (a), F (b), H (c), OMe (d), and NMe2 (e)), in an attempt to explore the structure−activity relationships in their photophysical and electrochemical behavior and in their performance in dye-sensitized solar cells (DSSCs). When substituent X is changed from electron-donating NMe2 to electron-withdrawing CN, the absorption and emission maxima reveal systematic bathochromic shifts. The redox potentials of these dyes are also significantly influenced by X. The electronic properties of the dyes were theoretically analyzed using density functional theory calculations; the results show good correlations with the experimental results. The solar-cell performance of DSSCs based on dye-grafted nanocrystalline TiO2 using 3a−3e and standard N3 (bis[(4,4′-carboxy-2,2′-bipyridine)(thiocyanato)]ruthenium(II)) were compared, revealing substantial dependences on the dye structures, particularly on the remote substituent X. The 3d-based device showed the best performance: η = 8.30%, JSC = 16.0 mA·cm−2, VOC = 717 mV, and ff = 0.72. These values are better than N3-based device