Conductive Carbon Nanoparticles Research Articles

Interplay between Nitrogen Concentration, Structure, Morphology, and Electrochemical Performance of PdCoNi “Core–Shell” Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

AbstractThis report describes the electrochemical behavior of a family of “core‐shell” electrocatalysts consisting of a carbon nitride (CN) “shell” matrix and a “core” of conducting carbon nanoparticles (NPs). The CN “shell” matrix embeds PdCoNi alloy NPs and covers homogeneously the carbon “core”. The chemical composition of the materials is determined by inductively‐coupled plasma atomic emission spectroscopy (ICP‐AES) and microanalysis; the structure is studied by powder X‐ray diffraction (powder XRD); the morphology is investigated by high‐resolution transmission electron microscopy (HR‐TEM). The surface activity and structure are probed by CO stripping. The oxygen reduction reaction (ORR) kinetics, reaction mechanism, and tolerance towards contamination from chloride anions are evaluated by cyclic voltammetry with the thin‐film rotating ring‐disk electrode (CV‐TF‐RRDE) method. The effect of N concentration in the matrix (which forms “coordination nests” for the Pd‐based alloy NPs bearing the active sites) on the ORR performance of the electrocatalysts is described. Results show that N atoms: 1) influence the evolution of the structure of the materials during the preparation processes, and 2) interact with alloy NPs, affecting the bifunctional and electronic ORR mechanisms of active sites and the adsorption/desorption processes of oxygen molecules and contaminants. Finally, the best PdCoNi electrocatalyst shows a higher surface activity in the ORR at 0.9 V vs. RHE with respect to the Pt‐based reference (388 μA cmPd‐2 vs. 153 μA cmPt‐2).

Hollow carbon microparticles prepared from spray-dried particles of lignin aqueous solution

An approach for manufacturing hollow carbon microparticles of various morphologies has been developed. The approach includes spray drying of an aqueous solution of lignin and inorganic compounds to prepare composite microparticles, followed by heat treatment, washing, and drying. The morphology of the carbon microparticles is greatly affected by the inorganic compound used and the added fraction of the inorganic compound to lignin, although the kind of lignin and its molecular weight have little effect on the morphology. The weight yield of carbon microparticles to the original lignin content is about 40%. Typical morphologies of carbon microparticles are (1) very thin and flexible spherical hollow carbon microparticles prepared by addition of lithium carbonate, and (2) hollow and porous carbon microparticles obtained by using sodium metasilicate in which carbon beads of about 10 nm are connected in a highly branched structure. Spherical hollow carbon microparticles with a bulk density of 0.015 g cm−3 are so flexible that their original spherical form is mostly recovered when returned to atmospheric pressure after compression at 100 MPa. The hollow and porous carbon microparticles obtained by heating at 1000 °C exhibit superior electrical conductivity compared with commercial conductive carbon nanoparticles, acetylene black and Ketjenblack. [TANSO 2013 (No. 259) 248–54.]

Broadband Dielectric Relaxation Spectroscopy in Polymer Nanocomposites

AbstractSummary: Dielectric spectroscopy in the frequency domain and thermally stimulated depolarization currents techniques, covering together a broad frequency range (10−4–109 Hz), were employed to investigate molecular dynamics in relation to structure and morphology in polymeric nanocomposites. Several systems were investigated, three of them with the same epoxy resin matrix and different inclusions (modified smectite clay, conducting carbon nanoparticles and diamond nanoparticles) and two with silica nanofiller (styrene‐butadiene rubber/silica and polyimide/silica nanocomposites). Special attention was paid to the investigation of segmental dynamics associated with the glass transition of the polymer matrix, in combination also with differential scanning calorimetry measurements. Effects of nanoparticles on local (secondary) relaxations and on the overall dielectric behavior were, however, also investigated. Several interesting results were obtained and discussed for each of the particular systems. Two opposite effects seem to be common to the nanocomposites studied and dominate their behavior: (1) immobilization/reduction of mobility of a fraction of the chains at the interface to the inorganic nanoparticles, due to chemical or physical bonds with the particles, and (2) loosened molecular packing of the chains, due to tethering and geometrical confinement, resulting in an increase of free volume and of molecular mobility.

Conductive carbon nanoparticles hybrid PEO/P(VDF-HFP)/SiO 2 nanocomposite polymer electrolyte type dye sensitized solar cells

Conductive carbon nanoparticles were introduced into PEO/P(VDF-HFP)/SiO 2 nanocomposite polymer electrolyte for dye sensitized solar cells (DSSCs). The conductive mechanism is changed by adding different amount carbon nanoparticles: 2.5, 5, 7.5, and 15 wt.%. AC impedance measurements and DC voltage–current measurements were carried out to analyze the conductive mechanism of the composite polymer electrolyte (CPE in short). DSC thermograms also indicated the configuration change of the different carbon nanoparticles content modified CPE. Small amount of carbon nanoparticles modification improved the ionic conductivity and the solar to electric energy conversion efficiency of DSSC with 5 wt.% carbon nanoparticles modified CPE is improved to 4.27% compared with the original DSSC performance of 3.87%. Too much carbon nanoparticles content in CPE is unfavorable for the ionic conductivity and the electronic conductive path is formed in it. The efficiency of 15 wt.% carbon nanoparticles modified CPE type DSSC is decreased to 3.61%.

Carbon nanoparticle stabilised liquid|liquid micro-interfaces for electrochemically driven ion-transfer processes

Stabilised liquid|liquid interfaces between an organic 4-(3-phenylpropyl)-pyridine (PPP) phase and an aqueous electrolyte phase are obtained in the presence of suitable nanoparticles. The use of nanoparticulate stabilisers (ca. 30 nm diameter laponite or 9–18 nm diameter carbon) in “Pickering” emulsion systems allows stable organic microdroplets to be formed and these are readily deposited onto conventional tin-doped indium oxide (ITO) electrodes. In contrast to the electrically insulating laponite nanoparticles, conducting carbon nanoparticles are shown to effectively catalyse the simultaneous electron transfer and ion transfer process at triple phase boundary junctions. Anion transfer processes between the aqueous and organic phase are driven electrochemically at the extensive triple phase junction carbon nanoparticle|4-(3-phenylpropyl)-pyridine|aqueous electrolyte. The organic phase consists of a redox active reagent 5,10,15,20-tetraphenyl-21H,23H-porphinato manganese(III) (MnTPP +), 5,10,15,20-tetraphenyl-21H,23H-porphinato iron(III) (FeTPP +), or proto-porphyrinato-IX iron(III) (hemin) dissolved in 4-(3-phenylpropyl)-pyridine (PPP). The composition of the aqueous electrolyte phase determines the reversible potential for the Nernstian anion transfer process. The methodology is shown to be versatile and, in future, could be applied more generally in liquid|liquid electroanalysis.

Dielectric Studies of Segmental Dynamics in Epoxy Nanocomposites

Dielectric techniques were employed, along with differential scanning calorimetry (DSC), to investigate segmental dynamics associated with the glass transition in epoxy nanocomposites. Two epoxy network matrices were used, the first based on diglycidyl ether of Bisphenol A (DGEBA) and diethylenetriamine, and the second on DGEBA and poly(oxypropylene)diamine (Jeffamine D2000). In the first matrix, the inclusions were organically modified clays, diamond particles with a diameter of about 6 nm, and conductive carbon nanoparticles with a diameter of about 10 nm, whereas in the second, polyhedral oligomeric silsesquioxanes (POSS) were covalently attached to the chains as dangling blocks. In the nanocomposites of the first matrix, glassy at room temperature, segmental dynamics becomes slower and the glass transition temperature increases on addition of the filler. In the epoxy/POSS nanocomposites, rubbery at room temperature, dynamics is described by a two‐phase (layer) model: a fraction of the polymer is immobilized, obviously at interfaces with POSS, whereas the rest is slightly plasticized, compared to the pure matrix. In Commemoration of the Contributions of Professor Valery P. Privalko to Polymer Science.

Actuation of liquid crystal elastomers reprocessed with carbon nanoparticles

Liquid crystal elastomers are currently of great interest due to their large thermally stimulated changes in shape. Here the authors show that by using an existing network and conducting carbon nanoparticles dispersed in a solvent with high swelling capability, a surface integrated layer can be created. This layer allows the effective resistivity to be reduced from highly insulating to usable values for electrical actuation and withstands large changes in geometrical shape both in contraction and expansion. Utilizing a resistive “Joule” heating effect, the reprocessed system shows a 150% length change and can be cycled beyond 10kcycles.