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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In this work, using an in-house made Loschmidt diffusion cell, we measure the effective coefficient of dry gas (O 2 -N 2 ) diffusion in cathode catalyst layers of PEM fuel cells at 25 • C and 1 atmosphere. The thicknesses of the catalyst layers under investigation are from 6 to 29 m. Each catalyst layer is deposited on an Al 2 O 3 membrane substrate by an automated spray coater. Diffusion signal processing procedure is developed to deduce the effective diffusion coefficient, which is found to be (1.47 ± 0.05) × 10 −7 m 2 s −1 for the catalyst layers. Porosity and pore size distribution of the catalyst layers are also measured using Hg porosimetry. The diffusion resistance of the interface between the catalyst layer and the substrate is found to be negligible. The experimental results show that the O 2 -N 2 diffusion in the catalyst layers is dominated by the Knudsen effect. Crown

High value utilization of renewable biomass materials is of great significance to the sustainable development of human beings. For example, because biomass contains large amounts of carbon, they are ideal candidates for the preparation of carbon nanotube fibers. However, continuous preparation of such fibers using biomass as carbon source remains a huge challenge due to the complex chemical structure of the precursors. Here, we realize continuous preparation of high-performance carbon nanotube fibers from lignin by solvent dispersion, high-temperature pyrolysis, catalytic synthesis, and assembly. The fibers exhibit a tensile strength of 1.33 GPa and an electrical conductivity of 1.19 × 105 S m−1, superior to that of most biomass-derived carbon materials to date. More importantly, we achieve continuous production rate of 120 m h−1. Our preparation method is extendable to other biomass materials and will greatly promote the high value application of biomass in a wide range of fields.

We consider the time dependence of the absorption coefficient due to the photoinduced chemical reaction (PCR) and species diffusion to calculate the temperature rise in the thermal-lens (TL) effect. The TL signal at the detector plane is also calculated. This theoretical approach removes the restriction that the PCR time constant is much greater than the characteristic TL time constant, which was assumed in a previously published model. Hydrocarbon fuel and aqueous Cr(VI) samples are investigated, and quantitative experimental results for the thermal, optical, and PCR properties are obtained. While similar results were obtained for the Cr(VI) solution using the previous and present models, the relative difference between the PCR time constants extracted from the same experimental data for a hydrocarbon fuel sample is found to be more than 220%. This demonstrates the significant difference of the two models.

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In the present work, we use an open-photoacoustic-cell ͑OPC͒ operating at high frequency to measure thermal properties of two-layer system samples. Photothermal deflection technique is also employed to measure the samples. The effective thermal diffusivity measured using the OPC method is interpreted using the concept of effective thermal resistance for a series two-layer system. The results show the reliability of the photoacoustic method for a complete thermal characterization of the samples. In addition, by varying the sample effective thickness, the thermal diffusivity and conductivity of each layer are precisely determined. The effective thermal diffusivity, thermal conductivity, and specific heat of a porous catalyst layer ͑thickness varying from 13 to 53 m͒ deposited on an aluminum foil ͑53 m in thickness͒ were thus measured and found to be ͑3.7Ϯ 0.3͒ ϫ 10 −3 cm 2 / s, ͑7.5Ϯ 0.7͒ ϫ 10 −3 W / cm K, and ͑1.6Ϯ 0.2͒ J / gK, respectively.