Despite intense, long-term interest in organic semiconductors from both an applied and fundamental perspective, key aspects of the electronic properties of these materials remain poorly defined. A particularly challenging problem is the molecular nature of positive charge carriers, that is, holes or oxidized species in organics. Here, the unique ability of single-molecule spectroelectrochemistry (SMS-EC) to unravel complex electrochemical process in heterogeneous media is used to study the oxidation of nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole). A reversible hole-injection charging process has been observed that occurs primarily by initial injection of shallow (untrapped) holes, but soon after the injection, a small fraction of the holes becomes deeply trapped. Good agreement between experimental data and simulations strongly supports the presence of deep traps in the studied nanoparticles and highlights the ability of SMS-EC to study energetics and dynamics of deep traps in organic materials at the nanoscale.
We report the electrochemical characterization and the observation of excimer emission from a series of 9-naphthylanthracene-based dimer- and trimer-bridged high steric hindrance aromatic groups during photoluminescence (PL) measurements in the solid state and in solution electrogenerated chemiluminescence (ECL) measurements. Cyclic voltammetry of 4,4'-bis(9-(1-naphthyl)anthracen-10-yl)biphenyl (4A) and 1,3,5-tris(9-(1-naphthyl)anthracen-10-yl)benzene (4C) showed two or three reversible, closely spaced one-electron transfers on oxidation in dichloromethane. The ECL emission spectra of 4A and 4C resulting from the annihilation reaction in benzonitrile showed two bands: one at the same wavelength as the PL peak in the solution state, and a broad band at longer wavelength. With a coreactant, such as peroxydisulfate, ECL spectra showed a single peak that was less broad in shape. PL measurement in the solid state and measurement of representative time traces of PL intensity, lifetimes, and picosecond time-correlated single-photon counting confirmed excimer emission at long wavelength. A reprecipitation method was used to prepare well-dispersed organic nanoparticles (NPs) of 4A in both aqueous and acetonitrile solutions. The smallest stable size of NPs produced was ~15 ± 6 nm, as analyzed by transmission electron microscopy. These organic NPs produced stable and weak ECL emission from the annihilation reaction in both aqueous and MeCN solutions. With a coreactant, such as peroxydisulfate, the ECL signal on reduction was sufficiently strong to obtain an ECL spectrum.
Hierarchical Ru- and RuO2-foams show excellent cyclability and good oxygen efficiency when used as catalyst cathode material for lithium–oxygen batteries.
Lithium-sulfur (Li-S) batteries have advantages in terms of their high specific capacity, natural abundance, and low cost of elementary sulfur on the basis of the multielectron conversion reactions in organic electrolytes. Despite their potential as next-generation batteries, Li-S batteries are still limited by critical challenges such as redox shuttling and the parasitic reaction of polysulfides arising from intrinsic electrochemistry as well as a low electrical conductivity of sulfur and the insolubility of Li 2 S associated with the materials' properties. The unique redox electrochemistry of sulfur in aqueous electrolytes, which is completely different from that in organic electrolytes, provides a rational strategy to resolve the aforementioned problems by the design of new materials and cell constructions. Furthermore, this system enables to achieve significant benefits of aqueous systems in terms of safety, chemical tractability, environmental friendliness, low cost, and high ionic conductivity. Here, at first materials and cell constructions for aqueous Li-S batteries are reviewed, covering the fundamental electrochemistry of sulfur in aqueous electrolytes, the advances in the host materials and aqueous electrolytes, and the cell design of flow-type aqueous Li-S batteries. Additionally, the current impediments and perspectives into the future direction of this field are provided.of 1675 mAh g −1 , natural abundance, and low cost of sulfur cathode. [1] On a basis of the multielectron conversion reaction in organic electrolytes, Li-S batteries can achieve the theoretical energy density of 2567 Wh kg −1 , which is by far higher than 387 Wh kg −1 of LIBs using graphite/ LiCoO 2 . [2] Despite these advantages, Li-S batteries still face some challenges associated with intrinsic redox electrochemistry such as redox shuttling and parasitic reaction of polysulfides as well as materials' properties such as low electrical conductivity (10 −30 S cm −1 ) of sulfur and insolubility of Li 2 S, [3] which is discussed in detail in Section 2. In order to overcome these bottlenecks, most researches mainly focused on developing new host and electrolyte materials, interlayers, separators, additives, and other issues related to organic-based systems. [4] A "gamechanging strategy" is to design materials and cell constructions in different electrolyte solutions, so-called aqueous electrolytes. Along with environmental benign feature of aqueous electrolyte, aqueous rechargeable battery system has significant advantages over organic counterparts in terms of the avoidance of the safety issue of flammable organic electrolytes, the rigorous manufacturing conditions, and the high costs of the electrolyte solvent and salts. However, the energy density of aqueous rechargeable battery system is lowered due to the limited potential window of the aqueous electrolyte by the water decomposition at 1.23 V versus Standard Hydrogen Electrode (SHE), which is much narrower than that of the organic electrolyte. Thermodynamic stability of aqueous ele...
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