Prussian Blue and Carbon-Dot Hybrids for Enhanced Electrochromic Performance.

In this study, Prussian blue@Carbon-dot (PB@C-dot) hybrids have been developed by one-step hydrothermal method. The incorporation of C-dots into Prussian blue thin film as a way of improving its electrochromic performance was investigated. The structure of the PB@C-dot hybrid was characterized through X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The electrochromic properties showed that incorporation of 10 mL C-dots into the film showed higher optical contrast of 1.6 and superior coloration/bleaching response of 10 and 3 s. It is proposed that the C-dots component used in the construction of the PB@C-dot hybrid plays a key role to achieve superior electrochromic performance.

Assembly of Copper Phthalocyanine on TiO2 Nanorod Arrays as Co-catalyst for Enhanced Photoelectrochemical Water Splitting.

A photoelectrochemical device was achieved by interfacial self-assembly of macrocyclic π-conjugated copper phthalocyanine (CuPc) on surface of TiO2 nanorod arrays (NRs). The photocurrent density of the elegant TiO2@CuPc NRs photoanode reaches 2.40 mA/cm2 at 1.23 V vs. RHE under the illumination of 100 mW/cm2 from AM 1.5G sun simulator, which is 2.4 times higher than that of the pure TiO2. At the same time, the photoelectrochemical device constructed through this strategy has good stability and the photocurrent density remain almost no decline after 8 h of continuous operation. The Mott-Schottky and LSV curves demonstrate that CuPc act as a co-catalyst for water oxidation and a possible mechanism is proposed for water oxidation based on careful analysis of the detailed results. The holes from VB of TiO2 photogenerated by electrons exciting are consumed by a process in which Cu2+ is oxidized to Cu3+ and Cu4+, and then oxidize water to produce oxygen. CuPc species is considered to be a fast redox mediator to reduce the activation energy of water oxidation in and effectively promote charge separation.

Carbon/SnO2/carbon core/shell/shell hybrid nanofibers: tailored nanostructure for the anode of lithium ion batteries with high reversibility and rate capacity.

A carbon/SnO(2)/carbon core/shell/shell hybrid nanofibrous mat was successfully prepared via single-spinneret electrospinning followed by carbonization and hydrothermal treatment. The morphology and structure of carbon/SnO(2)/carbon hybrid nanofibers were characterized by field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, wide-angle X-ray diffraction and X-ray photoelectron spectroscopy, and their electrochemical properties were studied as an anode in lithium ion batteries (LIBs). It is shown that the designed hybrid nanofibrous mat exhibits excellent electrochemical properties, including high reversible capacity with high columbic efficiency and impressive rate capacity. The greatly enhanced electrochemical performance is mainly due to the morphological stability and reduced diffusion resistance, which are induced by both the carbon core and deposited carbon skin. Furthermore, the embedded and de-aggregated SnO(2) nanoparticles in the carbon phase, which are less than 10 nm in size, provide large numbers of reaction sites for lithium ions and ensure complete alloying with them.

High ionic conductivity P(VDF-TrFE)/PEO blended polymer electrolytes for solid electrochromic devices.

Solid polymer electrolytes with excellent ionic conductivity (above 10(-4) S cm(-1)), which result in high optical modulation for solid electrochromic (EC) devices are presented. The combination of a polar host matrix poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) and a solid plasticized of a low molecular weight poly(ethylene oxide) (PEO) (M(w)≤ 20,000) blended polymer electrolyte serves to enhance both the dissolution of lithium salt and the ionic transport. Calorimetric measurement shows a reduced crystallization due to a better intermixing of the polymers with small molecular weight PEO. Vibrational spectroscopy identifies the presence of free ions and ion pairs in the electrolytes with PEO of M(w)≤ 8000. The ionic dissolution is improved using PEO as a plasticizer when compared to liquid propylene carbonate, evidently shown in the transference number analysis. Ionic transport follows the Arrhenius equation with a low activation energy (0.16-0.2 eV), leading to high ionic conductivities. Solid electrochromic devices fabricated with the blended P(VDF-TrFE)/PEO electrolytes and polyaniline show good spectroelectrochemical performance in the visible (300-800 nm) and near-infrared (0.9-2.4 µm) regions with a modulation up to 60% and fast switching speed of below 20 seconds. The successful introduction of the solid polymer electrolytes with its best harnessed qualities helps to expedite the application of various electrochemical devices.

Water-processable polyaniline with covalently bonded single-walled carbon nanotubes: enhanced electrochromic properties and impedance analysis.

Hybrid electrochromic materials were readily synthesized via copolymerization of aniline with p-phenylenediamine-functionalized single-walled carbon nanotubes (SWCNTs) in the presence of poly(styrene sulfonate) (PSS) dopant in an aqueous medium. Polyaniline (PANI)-grafted SWCNTs are formed, and they are uniformly dispersed in the PANI/PSS matrix. Impedance analysis shows that the charge-transfer resistances of the hybrids at all states are reduced drastically with increasing SWCNT loading. With 0.8 wt % SWCNTs, the charge-transfer resistances of the hybrid at +1.5 and -1.5 V are only about 20% and 12% of those of PANI/PSS, respectively, which is due to the greatly increased redox reactivity given by the enhanced electron transport in the hybrid and further doping function of the SWCNTs. The remarkable increase in redox reactivity leads to much enhanced electrochromic contrast from 0.34 for PANI to 0.47 for PANI-SWCNT-0.8%.

Supercritical Carbon Dioxide-Treated Electrospun Poly(vinylidene fluoride) Nanofibrous Membranes: Morphology, Structures and Properties as an Ionic-Liquid Host.

A reverse-barrier technique is used to enable the treatment of electrospun poly(vinylidene fluoride) nanofibrous membranes with supercritical carbon dioxide. The treatment induces the formation of nanopores and extended-chain ß crystallites of small lateral dimensions in the nanofibers. It also creates interfiber junctions, resulting in a remarkable improvement in mechanical properties of the membranes. The treated membranes are able to retain their shape very well after loading with an ionic liquid (IL). The ionic conductivity of the IL-loaded membrane is very close to that of the neat IL.

Toward electrochromic device using solid electrolyte with polar polymer host.

Polymer electrolyte is an important component in many multilayer devices such as batteries, fuel cells, and electrochromic devices. The effects of polymer electrolyte solidification on the ionic movement and device performance are presented based on near-infrared (IR) (860-2500 nm) electrochromic (EC) devices using the conducting polymer polyaniline. EC devices using electrolyte with polar polymer host of P(VDF-TrFE) show stable and reversible light modulation up to 65% in gel state and 30% in solid state. This is significantly improved when compared to devices with solidified nonpolar polymer host which retains less than 10% light modulation. Electrochemical impedance combined with in situ light modulation measurement identifies various key characteristics exerted by the electrolyte states on device performance. Gel-state devices are affected by the amount of dissociated ions while ionic movement in the electrolyte bulk and through the electrolyte/EC material interface dictates the light modulation in semisolid devices. For solid-state devices, electronic leakage, ionic dissociation, and interaction with electrochrome molecules have been found to limit the operation.