Carbonized Cellulose Nanofibril with Individualized Fibrous Morphology: toward Multifunctional Applications in Polycaprolactone Conductive Composites.

Drying cellulose nanofibril (CNF) from aqueous suspensions often leads to aggregated fibril morphology, negatively affecting its performance in ensuing applications. In this work, we introduced a new solvent drying approach to acquire dry CNF from aqueous suspensions and subsequently pyrolyzed the CNF precursor to obtain carbonized CNF (CCNF) without loss of its fibrous morphology. The fibrous CCNF was dispersed homogeneously in polycaprolactone (PCL) thermoplastic resin, greatly enhancing PCL composite tensile performance. After being further mixed with carbon black (CB), the CCNF helped to minimize CB aggregation due to formation of interconnected three-dimensional (3D) structures. The CCNF/CB/PCL composite exhibited superior electrical conductivity ascribed to electrons transporting more efficiently among CB aggregates. The composite is also suitable for applications such as 3D printed electromagnetic interference (EMI) shielding and deformation sensing. Specifically, the 3D printed EMI shielding composite efficiently absorbed EM radiation in the frequency range of 4-26 GHz, and the 3D printed deformation sensor exhibited excellent sensitivity, durability, and flexibility in monitoring mechanical distortions. Herein, this study sheds light on the development of multifunctional conductive composites embedded with fibrous CCNF from sustainable resources.

Nitrogen-doped fullerene as a potential catalyst for hydrogen fuel cells.

We examine the possibility of nitrogen-doped C60 fullerene (N-C60) as a cathode catalyst for hydrogen fuel cells. We use first-principles spin-polarized density functional theory calculations to simulate the electrocatalytic reactions on N-C60. The first-principles results show that an O2 molecule can be adsorbed and partially reduced on the N-C complex sites (Pauling sites) of N-C60 without any activation barrier. Through a direct pathway, the partially reduced O2 can further react with H(+) and additional electrons and complete the water formation reaction (WFR) with no activation energy barrier. In the indirect pathway, reduced O2 reacts with H(+) and additional electrons to form H2O molecules through a transition state (TS) with a small activation barrier (0.22-0.37 eV). From an intermediate state to a TS, H(+) can obtain a kinetic energy of ∼0.95-3.68 eV, due to the Coulomb electric interaction, and easily overcome the activation energy barrier during the WFR. The full catalytic reaction cycles can be completed energetically, and N-C60 fullerene recovers to its original structure for the next catalytic reaction cycle. N-C60 fullerene is a potential cathode catalyst for hydrogen fuel cells.

Colossal positive Seebeck coefficient and low thermal conductivity in reduced TiO(2).

Reduced (oxygen deficient) single crystal TiO(2) exhibits a very large positive Seebeck coefficient S at low temperature. S as large as 60 000 µV K(-1) was observed near 10 K for the least reduced sample, which gives a thermoelectric power factor of 170 µW K(-2) cm(-1). This value is about four times higher than the power factor of Bi(2)Te(3)-based materials near room temperature. As the temperature increases the Seebeck coefficient becomes negative. The magnitude of the room temperature Seebeck coefficient, thermal conductivity and electrical resistivity decrease with the reduction of the samples. The thermal conductivity is as low as 0.83 W K(-1) m(-1) for the heavily reduced sample at 390 K due to phonon scattering by defect planes. The colossal Seebeck coefficient found in the materials is discussed in terms of the phonon drag of the holes.