Effects of Anode Flow Field Design on CO2 Bubble Behavior in μDMFC

Clogging of anode flow channels by CO2 bubbles is a vital problem for further performance improvements of the micro direct methanol fuel cell (μDMFC). In this paper, a new type anode structure using the concept of the non-equipotent serpentine flow field (NESFF) to solve this problem was designed, fabricated and tested. Experiments comparing the μDMFC with and without this type of anode flow field were implemented using a home-made test loop. Results show that the mean-value, amplitude and frequency of the inlet-to-outlet pressure drops in the NESFF is far lower than that in the traditional flow fields at high μDMFC output current. Furthermore, the sequential images of the CO2 bubbles as well as the μDMFC performance with different anode flow field pattern were also investigated, and the conclusions are in accordance with those derived from the pressure drop experiments. Results of this study indicate that the non-equipotent design of the μDMFC anode flow field can effectively mitigate the CO2 clogging in the flow channels, and hence lead to a significant promotion of the μDMFC performance

Synthesis and Properties of Ni-doped Goethite and Ni-doped Hematite Nanorods

Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate solutions with various Ni/(Ni+Fe) ratios (0, 5, 10, 20, 33 and 50 mol % Ni) by hydrothermal precipitation in a highly alkaline medium using the strong organic alkali, tetramethylammonium hydroxide (TMAH). Ni-doped hematite (α-Fe2O3) nanorods were obtained by calcination of Ni-doped goethite nanorods at 400 °C. The Ni 2+ -for-Fe 3+ substitution in goethite and hematite was confirmed by determination of the unit cell expansion (due to the difference in the ionic radii of Fe 3+ and Ni 2+ ) using XRPD and determination of the reduction of a hyperfine magnetic field (due to the difference in magnetic moments of Fe 3+ and Ni 2+ ) using Mössbauer spectroscopy. Single-phase goethite nanorods were found in samples containing 0 or 5 mol % Ni. A higher Ni content in the precipitation system (10 mol % or more) resulted in a higher Ni 2+ -for-Fe 3+ substitution in goethite, and larger Ni-doped goethite nanorods, though with the presence of low crystalline Ni-containing ferrihydrite and Ni ferrite (NiFe2O4) as additional phases. Significant changes in FT-IR and UV-Vis-NIR spectra of prepared samples were observed with increasing Ni content. Electrochemical measurements of samples showed a strong increase in oxygen evolution reaction (OER) electrocatalytic activity with increasing Ni content. © 2018 Croatian Chemical Society. All Rights Reserved

Flotation deinking of old newsprint using poly (Diallylmethylammonium chloride) as a single deinking agent

"July 2000.""Submitted to Progress in Paper Recycling.

Elucidation of oxygen reduction reaction pathway on carbon-supported manganese oxides

The oxygen reduction reaction (ORR) is a complex process. This is particularly the case for carbon-supported electrocatalysts in alkaline electrolytes, because carbon can catalyze the ORR via a two-electron transfer to generate hydroperoxide (HO2-), which subsequently undergoes either chemical decomposition to generate O-2 and OH- (HODR) or electrochemical reduction to OH- (HORR). In this study, we elucidated the ORR pathway on a series of carbon-supported manganese oxides, which have been extensively studied as electrocatalysts in alkaline electrolytes. A comparison of the turnover frequencies of the HODR and HORR showed that although an apparent four-electron transfer process was identified when the HO2- yield was measured using the rotating ring disk electrode technique, the real ORR pathway involved a two-electron transfer process to generate HO2-, with subsequent chemical decomposition of HO2. These results will help us to understand the intrinsic catalytic behavior of carbon-supported transition-metal oxides for the ORR in alkaline electrolytes. (C) 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

On-line alleviation of poisoning in direct methanol fuel cells with pulse potential strategy

Catalyst poisoning from the impurities in the industrial grade methanol is a major challenge for the large-scale application of direct methanol fuel cells in low cost. In this work, we systematically investigate the impurities influencing on cell performance, and confirm that the adsorption of carbonyl containing intermediate species derived from the partial electro-oxidation of the impurities is a crucial factor leading to performance degradation. Hence, an on-line alleviation strategy by intermittently applying pulse potential (reduction potential on the anode or oxidation potential on the cathode) is proposed. The applied potential will bring a reductive condition on the anode, which releases the active sites via the reduction of carbonyl containing species adsorbed on platinum-ruthenium electro-catalysts. Based on this strategy, the adsorption of carbonyl containing intermediate species are effectively suppressed, and the decay rate declines by nearly two orders of magnitude than that of a single cell under traditional operation, which paves a way for the practical application of direct methanol fuel cells with industrial grade methanol feed

Performance enhancement by optimizing the reformer for an internal reforming methanol fuel cell

Internal reforming methanol fuel cell (IRMFC) has potential applications in portable or stationary power supply system, but currently performance of the IRMFC is limited by the low hydrogen production of its reformer. In order to produce more hydrogen with less volume, in this paper a single channel serpentine packed bed reformer was designed, and its bed size was optimized by experiment and numerical simulation to enhance heat transfer and increase catalyst utilization. It was found that with the bed diameter from 5.8 mm down to 3.8 mm, the reformer temperature distribution was more uniform but the bed pressure drop increased a lot. Considering performance and pressure drop, the reformer of 5 mm was optimal, per milliliters of which could supply 9.8 mL/min hydrogen at 453 K, almost twice as much as that by A. Mendes et al with one-third of their catalyst loading. The reformer was quite stable, and less than 10% decline in methanol conversion was observed during the 100 hours period at 473 K. When incorporated into an IRMFC single cell, power density of the single cell reached 0.45-0.55 W/cm(2) at 453-473 K under CH3OH solution and air feed, the highest in existing reports. The main drawback has to do with low stability of the IRMFC single cell at high current density

An Experimental Method to Measure Flow Distribution in the Cathode of High-Temperature Polymer Electrolyte Membrane Fuel Cells Stack

The flow distribution in manifolds has an important influence on the performance and life of the stack, but currently the methods to measure the cathode flow distribution between cells in a high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) stack is scarce. Herein, an experimental method for measuring the cathode flow distribution between cells is developed, which converts the cathode flow (Q) signal into a signal of hydrogen limiting current (i(L)). By dimensional analysis and experimental verification, it is found that i(L) and Q have a linear relationship within a certain range. In the HT-PEMFC single cell, the method can be used to quickly evaluate and screen the cathode diffusion layer. When used in the HT-PEMFC stack, the effect of temperature is negligible, but it is necessary to ensure the same compression ratio of each cell, whereas the i(L) of each cell is tested simultaneously in the stack. In addition, the method is limited to measure flow distribution between cells in the stack because the i(L) value is averaged

Secondary current density distribution analysis of an aluminum-air cell

Secondary current density distributions in a parallel two-plane Al/air cell and a wedge shaped Al/air cell were analyzed. The parameters studied include the entrance effect, the activity of the cathode, the cell gap and the extension of the cathode. The entrance effect disappears at about a one to two cell gap from the entrance. The activity of the cathode has a large effect on the local current density. With increases in the cell gap, the average current density decreases, but the peak current density over the average current density increases. By extending the cathode below the anode, the high local current density can be reduced. In a wedge shaped Al/air cell, the planar portion of the anode enters the cell. As the anode is consumed, the top portion of the anode is consumed faster because of the decreased cell gap and increased reaction rate. The anode adapts to be parallel to the cathode in the cell. A FEMLAB (finite element method) package was used for all the calculations. © 2006 Elsevier B.V. All rights reserved