800nm fiber Bragg Grating sensing interrogation system using TFBG and CCD array

An 800nm band fiber Bragg grating sensing interrogation system using TFBG as the core wavelength division component is presented. A charge coupled device (CCD) linear array is put on the focal plane of the lens to detect the light. TFBG is used to tap light out of the fiber core to fiber cladding. The sensing wavelength is 795 to 830nm, with accuracy of 20pm and scan speed 100Hz. Using FBG sensor, we achieve the temperature sensitivity as 1.8°C and strain sensitivity as 18με

Development of nanoscale catalysts for direct liquid-fed fuel cell applications

Direct liquid-fed fuel cell is a promising power device for applications, such as consumer electronic products. Formic acid and ethanol are considered to be good candidates as the fuels. Among the major technical hurdles in direct formic acid fuel cell (DFAFC) and direct ethanol fuel cell (DEFC), low activities of electrocatalysts are known to be one of the key factors that affect the performance of fuel cell systems. This thesis focuses on development of highly active catalysts for both formic acid and ethanol oxidation as well as on investigation of the reaction mechanisms. This work starts with development of robust protocols for synthesis of Pd and Pd based binary catalyst. Without using “explicit” protective reagent, Pd nanoparticles with a controlled size ranging from 3.9 to 7.5 nm were produced. In addition, based on the idea of reaction engineering control, a novel protocol that enables the production of both alloy and non-alloy Pd-Au binary catalysts were developed. This strategy was demonstrated to be applicable for synthesis of other binary alloy catalyst, i.e., Pd-Rh. Interesting electrochemical properties of the as prepared Pd and Pd based binary (PdAu, PdRh) nanoparticles for formic acid oxidation were observed. Other than synthesizing binary catalyst, this approach ensured the production of well distributed Rh/C. Improved activity of Rh/C compared with conventional Pd/C for ethanol oxidation in alkaline medium was found. Electrochemical impedance spectroscopy (EIS) was utilized for investigation of the reaction mechanisms. Our impedance study on formic acid oxidation suggest that unlike that on Pt/C, formic acid oxidation on Pd/C mainly follows the dehydrogenation pathway without generation of poisonous species, i.e. COads. Moreover, distinct impedance behaviors of ethanol oxidation on Rh/C and Pd/C suggest that ethanol oxidation on these two catalysts could follow different reaction pathways, which could be the reason for the observed higher activity of Rh/C compared with Pd/C. The development of the highly active nanocatalysts is believed to contribute to the improvement of the performance of fuel cell systems, while the study on the reaction mechanism provides better understanding and potential opportunities for the advancement of the fuel cell technologies

Highly active rhodium/carbon nanocatalysts for ethanol oxidation in alkaline medium

We report the synthesis and electrochemical characterization of rhodium/carbon (Rh/C) and palladium-rhodium/carbon (Pd-Rh/C) nanocatalysts for ethanol oxidation. Our results, for the first time. demonstrated that in an alkaline environment. Rh/C shows a much higher catalytic activity at low potential range than that of Pd-Rh/C and Pd/C. Intermediate species are produced during the oxidation process on Rh/C, as revealed by the complex impedance spectra (e.g., pseudo-inductive loop) at low potential range (i.e., -0.5 to -0.3 V). Adsorbed oxygen species, which are generated at high potentials, block active surface sires of Rh/C, resulting in the negative polarization resistance. (C) 2011 Elsevier B.V. All rights reserved

A first-principles study of CO oxidation by surface oxygen on Pt-incorporated perovskite catalyst (CaPtxTi1-xO3)

In the present work, we investigated the structural and catalytic properties of a prototype system Pt-doped CaTiO3 by means of first principles calculations. We paid particular attention to the aggregation and penetration of Pt on different surfaces of CaTiO3, and subsequent CO oxidation by surface oxygen atoms on Pt-doped CaTiO3. Our calculations indicate that CO oxidation can potentially take place when Pt is doped on the first layer of CaTiO3(001). The activation barriers are calculated to be 0.20-0.45 eV. The possibly induced O vacancy on the surface will produce a magnetic behavior by breaking the spin density symmetry due to one Pt-O bond cleavage. Our study is expected to provide an insight into the catalytic behavior of Pt ions in Pt-doped perovskite toward the oxidation of exhaust gas

Optimization of a thermoelectric cooler-based system for atmospheric water production in terms of temperature of condensing surface

The extraction of water from the atmosphere is considered as a potential solution to alleviate the problem of water shortages. Therefore, it is crucial to improving the efficiency of water production from atmosphere. In this work, the effect of temperature of the condensing surface below 0 °C on the water productivity of thermoelectric water generator (TWG) has been studied for the first time. The experimental results indicate that the average water productivity increases with the decrease of the condensing fin surface temperature and there is a maximum increase of 186 % in the average water productivity of TWG when the temperature of condensing fin surface decreases from 5 °C to −10 °C, which is due to the increased temperature difference and the enhanced thermal conductivity of the ice layer. When the form of condensation on the surface of condensing fins is changed from condensing to frosting, the water productivity is increased by 22.1 % at maximum, which can be attributed to the higher thermal conductivity of ice than water. The effect of the sampling time on average water productivity of TWG has also been studied. With the increase of sampling time (0.5 h–3.5 h), the average water productivity of the device gradually decreases by 30.3 %. And the highest average productivity of TWG has been observed at a sampling time of 0.5 h. In addition, the effects of flow rate of water in water block heat exchanger, air flow rate of the cooling fan, voltage of TEC on water productivity are experimentally investigated as well. This study provides a strong theoretical foundation for enhancing the water productivity from humid air

y Nonprecious Nanoalloys Embedded in N-Enriched Mesoporous Carbons Derived from a Dual-MOF as Highly Active Catalyst towards Oxygen Reduction Reaction

In this work, we reported the synthesis of a novel electro-catalyst composed of Fe and Co bimetallic nanoalloys embedded in N-enriched carbon framework (FeCo@NC) for oxygen reduction reaction. The FeCo@NC was synthesized through pyrolyzing a dual metal-organic framework (MOF) under argon atmosphere. This FeCo@NC electrocatalyst showed remarkable performance towards ORR with a high half-wave potential of 0.827 V versus reversible hydrogen potential (RHE), which was comparable to the state-of-the-art commercial Pt/C catalyst. The enhanced activity could be ascribed to the large specific surface area, the abundant active sites and the synergistic effect of bimetallic alloy

Enhanced selective CO2 adsorption on polyamine/MIL-101(Cr) composites

The global climate change induced by greenhouse gases has stimulated active research for developing efficient strategies to mitigate CO2 emission. In the present study, we prepared a series of polyamine/ metal-organic framework (MOF) composites as highly selective CO2 adsorbents from a CO2/N-2 mixture, which is relevant to CO2 capture in flue gas. We show that loading polyethyleneimine (PEI) into MIL101( Cr) frameworks can significantly enhance the selective CO2 adsorption capacity at low pressure and ambient temperature. Further, the comparative study reveals that both the particle size of the MOF and the molecular-weight of PEI play an important role in the CO2 capture ability. Regarding the particle size, smaller MIL-101(Cr) particles can facilitate the loading of PEI into the inner pores and result in lower surface area/pore volume. Thus, the resulting PEI/MIL-101(Cr) composites possess lower CO2 adsorption capacity, but are compensated by higher selectivity of CO2 over N-2. On the other hand, lower molecular-weight linear PEI could readily diffuse into the inner pores and effectively block the N-2 adsorption. As a result, the as-prepared A-PEI-300 sample in this work exhibits an excellent CO2 uptake of 3.6 mmol g(-1) and ultrahigh CO2/N-2 selectivity at 0.15 bar and 25 degrees C. In contrast, the higher molecular-weight branched PEI is advantageous at elevated temperature, since the composites can retain high CO2 adsorption capacity owing to the large amount of primary amine groups. Overall, polyamine/MOF composites are shown to be good candidate adsorbents for CO2 capture from flue gas. To achieve the optimal CO2 capture ability, comprehensive optimization of the polyamine and MOF structures should be performed

Scalable production of few-layer niobium disulfide nanosheets via electrochemical exfoliation for energy-efficient hydrogen evolution reaction

Two-dimensional (2D) niobium disulfide (NbS2) materials feature unique physical and chemical properties leading to highly promising energy conversion applications. Herein, we developed a robust synthesis technique consisting of electrochemical exfoliation under alternating currents and subsequent liquid-phase exfoliation to prepare highly uniform few-layer NbS2 nanosheets. The obtained few-layer NbS2 material has a 2D nanosheet structure with an ultrathin thickness of ∼3 nm and a lateral size of ∼2 μm. Benefiting from their unique 2D structure and highly exposed active sites, the few-layer NbS2 nanosheets drop-casted on carbon paper exhibited excellent catalytic activity for the hydrogen evolution reaction (HER) in acid with an overpotential of 90 mV at a current density of 10 mA cm–2 and a low Tafel slope of 83 mV dec–1, which are superior to those reported for other NbS2-based HER electrocatalysts. Furthermore, few-layer NbS2 nanosheets are effective as bifunctional electrocatalysts for hydrogen production by overall water splitting, where the urea and hydrazine oxidation reactions replace the oxygen evolution reaction