Phengxay Deevanhxay

Simultaneous characterization of quaternary alkaloids, 8-oxoprotoberberine alkaloids, and a steroid compound in Coscinium fenestratum by liquid chromatography hybrid ion trap time-of-flight mass spectrometry

Simultaneous characterization of quaternary alkaloids, 8-oxoprotoberberine alkaloids, and a steroid compound in Coscinium fenestratum was successfully performed by liquid chromatography hybrid ion trap time-of-flight mass spectrometry (LC/IT-TOF MS). A total of 32 compounds, including 2 benzylisoquinoline alkaloids, 3 aporphine alkaloids, 12 quaternary protoberberine alkaloids, 10 8-oxoprotoberberine alkaloids, 3 tetrahydroprotoberberine alkaloids, and a steroid compound were simultaneously separated and characterized by matching the empirical molecular formulae with those published in literature and the multi-stage mass spectrometry (MS(n)) data obtained using structural information from IT, accurate mass measurement obtained from TOF MS, and HPLC separation. A total of 20 compounds, including 4 novel natural products were identified or tentatively identified for the first time from Coscinium fenestratum. In the positive-ion mode, 8-oxoprotoberberines produced [M+H](+) and [M+Na](+); the fragmentation of 8-oxodihydroprotoberberines produced [M+H-*CH(3)](+*), [M+H-*CH(3)-*CH(3)](+), and [M+H-*CH(3)-*CH(3)-CO](+), while 8-oxotetrahydroprotoberberines generated [M+H-*CH(3)](+*), [M+H-*CH(3)-*CH(3)](+), [M+H-*CH(3)-*H](+), and iminium ions from the cleavage of the protoberberine skeleton. The method can be applied for the analysis of 8-oxoberberine and other alkaloids in Coptis japonica, Phellodendron amurense, and other herbal medicines.

Liquid Water Visualization in Cathode Catalyst Layer of PEMFC by Soft X-ray Radiography

In proton exchange membrane fuel cells (PEMFCs), appropriate water management is essential in achieving a high cell performance over wide range of operating condition. The membrane requires sufficient humidification to fulfill its function as proton conductor. However, flooding at cathode side can hamper the transport of reactant and reduce the reactive area. Understanding liquid water transport in electrolyte membrane assemblies (MEA) is important to design an effective fuel cell. Several techniques have been developed for visualizing liquid water in MEA. However, the visualization of liquid water distribution in catalyst layer (CL) has not been reported due to the limit in spatial and temporal resolution of the available techniques. Recently, we developed soft X-ray radiography to visualized liquid water in PEMFC with high spatial and temporal resolution [1, 2]. In this study, we aim to investigate the water distribution in cathode CL. The effect of current density on the water distribution was studied by using soft-X ray radiography and AC impedance spectrometry. The visualization of the liquid water in an operating PEMFC was performed using laboratory-based soft X-ray microscope system (Tohken, TUX-3110FC). Mo-target was used for generating soft X-ray. The catalyst-coated membrane (CCM) was fabricated using a transfer printing method. The CL with Pt loading of 0.87 mg.cm was decaled on to the perfluorinated sulfonic acid membrane (Nafion® EC NRE 211, 25 μm-thickness) by hot pressing. A CCM with CL thickness of approximately 20 μm was made. An active area of the MEA was 0.10 cm (0.8 mm x 12 mm) and SIGRACET24BA (SGL Carbon) was used for both anode and cathode GDL. The channel width and depth were 1.0 and 0.5 mm, and the rib-to-channel ratio was 1. Hydrogen and oxygen were used as the fuel and oxidant at the flow rate of 100 std cm.min. Both anode and cathode inlet gas streams were humidified to 100% relative humidity. The cell was operated at room temperature. The Observation was performed in the rib area. The AC impedance measurements were executed at 120 s, 420 s, and 720 s after operating. The X-ray beam was adjusted to the center of CL in order to avoid the cone-beam effect in CL area. Soft Xray radiograph (a) and intensity from the selected area across the MEA under the rib area (b) are shown in Fig. 1. The intensity at the catalyst area was sufficient to evaluate the contrast caused by liquid water generated in the CL. Figure 2 shows the comparison of image obtained at the initial (OCV) condition and 600 s (integration time 32 s) after operating. There was no major change in case of without operating (0 A.cm), and operating at 0.2 A.cm. However, a drastic change was observed at 0.5 A.cm. The color in some area of catalyst layer changed from green to blue, indicating the accumulation of liquid water in CL. Figure 3 shows the intensity ratio of the selected area of the image at the initial condition to that of 600 s after operating. We observed the membrane swelling at the beginning of load. This made the cathode CL shifted to GDL side. Pixel shift to adjust the position of CL (3-4 pixels) and median filter operation were performed before calculation the intensity ratio. The intensity ratio increased in the CL toward the boundary of cathode CL and GDL, indicating water concentration gradient in CL. At the current density of 0.2 A.cm, liquid water was observed in the CL near GDL, while the CL near membrane tended to be dehydrated. When increasing the current density to 0.4 and 0.5 A.cm, the signal intensity ratio increased at the boundary of CL and membrane toward cathode GDL side. This result indicates a larger amount of liquid water accumulated in cathode CL compare to low current density. The signal intensity obtained by soft X-ray radiography shows correlation with the nyquist plot arc (data not shown). The arc at 0.2 A.cm was larger than that of 0.4 and 0.5 A.cm. This indicated the high charge transfer resistance of CL at 0.2 A.cm. The arc at 0.4, 0.5 A.cm became larger as operating time increased, indicating the limit oxygen diffusion to Pt site due to liquid water accumulation.

Performance Improvement in Redox Flow Battery With Flow-Through Channel Geometry

Redox Flow battery attracts much attention as one of the efficient rechargeable batteries because of its versatility for small and large scale energy storage. Although this battery has great potentials, further improvement on cell performance to achieve high current density is necessary for industrial implementation. In this study, we applied flow-through (interdigitated) channel geometry to a redox flow battery for enhancement of electrode utilization by advection transport. As a result, it is confirmed that the redox flow battery showed better performance by using interdigitated channels than ones with serpentine channels.Copyright