Jiuli Chang

Nitrogen-Doped Porous Carbons As Electrode Materials for High-Performance Supercapacitor and Dye-Sensitized Solar Cell.

Activated N-doped porous carbons (a-NCs) were synthesized by pyrolysis and alkali activation of graphene incorporated melamine formaldehyde resin (MF). The moderate N doping levels, mesopores rich porous texture, and incorporation of graphene enable the applications of a-NCs in surface and conductivity dependent electrode materials for supercapacitor and dye-sensitized solar cell (DSSC). Under optimal activation temperature of 700 °C, the afforded sample, labeled as a-NC700, possesses a specific surface area of 1302 m2 g(-1), a N fraction of 4.5%, and a modest graphitization. When used as a supercapacitor electrode, a-NC700 offers a high specific capacitance of 296 F g(-1) at a current density of 1 A g(-1), an acceptable rate capability, and a high cycling stability in 1 M H2SO4 electrolyte. As a result, a-NC700 supercapacitor delivers energy densities of 5.0-3.5 Wh kg(-1) under power densities of 83-1609 W kg(-1). Moreover, a-NC700 also demonstrates high electrocatalytic activity for I3- reduction. When employed as a counter electrode (CE) of DSSC, a power conversion efficiency (PCE) of 6.9% is achieved, which is comparable to that of the Pt CE based counterpart (7.1%). The excellent capacitive and photovoltaic performances highlight the potential of a-NCs in sustainable energy devices.

Application of hierarchical TiO2 spheres as scattering layer for enhanced photovoltaic performance in dye sensitized solar cell

Hierarchical TiO2 spheres (HTSs) composed of thin nanosheets with a high ratio of exposed (001) facets were prepared by solvothermal reaction of titanium precursor under the mediation of HF and glacial acetic acid (HAc). The size of the spheres and the density of primary nanosheets could be effectively tuned by simply adjusting HAc dosage. The as-prepared HTSs were highly crystallized and demonstrated high BET surface area, but decreased apparently after calcination due to the collapse or fusion of the primary nanosheets. The calcinated HTSs were further applied as scattering layers in photoanodes of dye sensitized solar cells (DSSCs). Compared with the monolayered nanospindle (NS) photoanode with similar thickness, the bilayered photoanodes with the HTSs as scattering layers offered dramatically higher photocurrent density (Jsc) and therefore higher energy conversion efficiency (η). Due to the highest scattering effect and the lowest charge transfer resistance (Rct) at TiO2–dye–electrolyte interface, the DSSC with H2 (synthesized with HAc volume of 2 mL) as scattering layer offered η of 7.72%, which is 42% higher than that based on the monolayered NS photoanode.

Hierarchical ZnO aggregates assembled by orderly aligned nanorods for dye-sensitized solar cells

Hierarchical ZnO aggregates assembled by orderly aligned nanorods were prepared via a facile solvothermal method using diethylene glycol as solvent and zinc acetate dehydrate as precursor. Time dependent trails evidenced that the formation of the hierarchical aggregates experienced a multistep self-assembly process. Moreover, it was found that the reaction medium plays an important role in the assembling process and the diameter of the product could be tuned by simply altering the precursor dosage. The hierarchical product was further applied as scattering layer in bi-layered dye-sensitized solar cell (DSSC), and a high conversion efficiency of 5.2% was demonstrated, indicating a substantial improvement compared with the nanoparticle cell of 2.7%. Based on the optical and electrochemical investigations, the high conversion efficiency was mainly ascribed to the unique hierarchical structure of the ZnO aggregates. The rough surface of the nanorod subunits could enhance the dye loading capacity and the aggregates with micrometer sized diameter could improve the scattering effect. Moreover, the orderly aligned nanorods could minimize the grain boundaries, suppress the surface recombination and provide a direct pathway for fast electron transport, which therefore enhance the collection efficiency of the photoelectrons.

Anatase TiO2 nanocrystals enclosed by well-defined crystal facets and their application in dye-sensitized solar cell

Anatase TiO2 nanocrystals enclosed by well-defined {101} and {001} crystal facets were prepared via a facile hydrothermal method using H+ exchanged potassium titanate nanowires (H-KTNWs) as precursors. The size and shape of the nanocrystals could be tuned by simply altering the precursor dosage and the NH4F concentration. The photovoltaic tests show that with decreasing of particles size, the dye-sensitized solar cell (DSSC) exhibits lower open circuit voltage (Voc) and fill factor (FF) due to the increased grain boundaries. However, because of the high short circuit current density (Jsc) stemming from the enhanced dye loading capacity, the power conversion efficiency (PCE) was promoted. Moreover, the shape effect on the DSSC performance was evaluated by comparing the nanocrystals with similar surface area but different shapes. The cell derived from truncated octahedrons exposing ∼25% {001} facets shows a ∼10% PCE improvement compared with the cell derived from octahedrons exposing ∼94% {101} facets. Based on the optical and recombination dynamic tests, the enhanced Jsc, Voc and FF could be ascribed to the enhancement in light scattering effect and suppressed electron recombination, which may result from the improved connectivity of the adjacent nanoparticles because it is energetically favourable for the truncated octahedrons to be linked together by the high energy {001} facets.

Hierarchical titania mesoporous sphere/graphene composite, synthesis and application as photoanode in dye sensitized solar cells

Hierarchical TiO(2) mesoporous sphere/graphene composites (HTMS/Gs) were prepared by incorporation proper amounts of graphene oxide (GO) into the reaction system toward hierarchical TiO(2) mesoporous spheres (HTMSs). The HTMS/Gs inherit the merits of high specific surface area derived from both HTMS and graphene, as well as the well conductivity of graphene. Power conversion efficiencies (PCEs) of dye sensitized solar cells (DSSCs) using HTMS/Gs as photoanode materials were also investigated. The graphene content in HTMS/G exhibited great influence on PCE. Lower graphene content in HTMS/G showed superior dye adsorption capacity, lower charge recombination and thus higher photocurrent density over bare HTMS. However, excessive graphene promoted the recombination of photo-generated electrons, which deteriorated the PCE. Due to the high dye adsorption capacity and the prolonged electron recombination lifetime, the HTMS/G contains 5.68 wt.% graphene, denoted as HTMS/G(5.68), boosted up the short circuit current density (J(sc)) to 16.17 mA/cm(2), and a PCE of 7.19% was achieved, which is 21.8% higher than that of bare HTMS.

Electrochemical energy storage and adsorptive dye removal of Platanus fruit-derived porous carbon

Activated Platanus fruit carbon (a-PFC) was synthesized by pyrolytic carbonization and alkali activation treatment of an easily available biomass, Platanus fruit (PF). Carbonization yielded a Platanus fruit carbon (PFC) sample with a partially graphitized phase, and the following KOH activation created a highly porous texture containing a large fraction of micropores, and therefore a high specific surface area. Both of these factors are beneficial for surface-related applications such as electrode materials for electrochemical capacitors and adsorbents for the removal of organic dyes. A supercapacitor based on a-PFC3, which was synthesized with a KOH : PFC activation ratio of 3, offers a high gravimetric capacitance of 216 F g−1 at 1 A g−1, a high rate performance and an excellent cycling stability, highlighting the potential of a-PFC3 in electrochemical energy storage. Its high specific surface area also makes a-PFC3 an efficient adsorbent for the removal of methylene blue (MB) from aqueous solution.

Fluorescent carbon quantum dots, capacitance and catalysis active porous carbon microspheres from beer

Fluorescent nitrogen containing carbon quantum dots (NCQDs) and porous carbon microspheres (PCMs) were simultaneously synthesized by a facile hydrothermal method using beer as precursor. The afforded NCQDs in supernatant exhibited strong blue fluorescence in aqueous solution and dry state under UV light excitation, showing the huge potential as fluorescent dye. The PCMs in sediment showed great potential in supercapacitor electrode and catalyst for certain reaction. After ZnCl2 activation at 900 °C, the obtained highly porous a-PCM900 (denoted according to activation temperature) offered a high specific capacitance of 273.2 F g−1 at 1 A g−1, excellent rate capability and cycling stability when employed as supercapacitor electrode. Moreover, a-PCM900 could also serve as efficient non-noble metal catalyst for reduction conversion of 4-nitrophenol to 4-aminophenol by NaBH4 with high activity and well reusability.

Solvothermal synthesis of antimony sulfide dendrites for electrochemical detection of dopamine

Sb2S3 dendrites composed of 1-dimensional rods were prepared by a facile solvothermal reaction. The dosage of the poly(acrylic acid) (PAA) morphology-controlling reagent and the reaction temperature are key factors determining the final morphology of the product. Temporal experiments revealed that the formation of Sb2S3 dendrites experienced successive stages including precipitate reaction, crystallization and tip splitting. The as-prepared Sb2S3 dendrites were further employed as sensing material for electrochemical detection of dopamine (DA). A cyclic voltammogram (CV) showed that an Sb2S3 dendrite modified electrode enables the selective electro-oxidation of DA in the presence of ascorbic acid (AA). The constructed biosensor demonstrated a linear response range of 0.125-160 μM and a detection limit of 0.1 μM, which suggests that the Sb2S3 dendrites are promising sensing materials in the electrochemical analysis of DA.

Micelles directed preparation of ternary cobalt hydroxide carbonate-nickel hydroxide-reduced graphene oxide composite porous nanowire arrays with superior faradic capacitance performance

Electrode material is the key component of a supercapacitor, the highly accessible surface area, efficient electrons/ions migration channels, robust structural stability and redox activity of electrode material are pivotal prerequisites for harvesting optimal capacitive performance. Herein, a ternary cobalt hydroxide carbonate-nickle hydroxide-reduced graphene oxide composite (CN-rGO) with porous nanowire arrays architecture was deposited onto Ni foam substrate through confined hydrothermal reaction directed by surfactant micelles. The as-prepared CN-rGO nanowire arrays exhibit mesoporous texture with high specific surface area, which allows sufficient soaking of electrolyte with short diffusion path length. Additionally, the vertically aligned nanowires with incorporation of reduced graphene oxide offer efficient channels for migration of electrons generated by faradic components. Both features enable the sufficient faradic reactions and charge storage of the CN-rGO electrode. Under optimal Co:Ni feeding molar ratio of 7:3, the battery typed faradic CN-rGO electrode offers superior specific capacitance (2442 F g-1 at 1 A g-1), good rate capability (65% capacitance retaining ratio within 1-20 A g-1) and cycling stability (70% maintaining ratio after 2000 charge-discharge cycles). When used as faradic electrode of hybrid supercapacitor (HSC), balanced energy density (42.9-26.2 Wh kg-1), power density (393-3519 W kg-1) and cycleability (80% initial capacitance maintaining ratio undergoes 5000 charge-discharge cycles) can be delivered simultaneously, highlighting the potential of the micelles directed CN-rGO nanowire arrays electrode in efficient energy storage device.

4,4,5,5-Tetra­methyl-2-(4-pyridinio)-2-imidazoline-1-oxyl-3-oxide perchlorate

The crystal structure of the title compound, C12H17N3O2 +·ClO4 −, consists of 4,4,5,5-tetramethyl-2-(4-pyridinio)imidazoline-1-oxyl-3-oxide radical cations and perchlorate anions. Both the cation and the Cl atom of the anion are located on the same twofold rotation axis, and the crystal structure shows the average structure for the radical cation. The five-membered ring assumes a half-chair conformation. The cation links with the anion via N—H⋯O hydrogen bonding.