Structure-activity relationship of surfactant for preparing DMFC anodic catalyst

Three kinds of surfactants as stabilizer were applied to the preparation of electrocatalysts for direct methanol fuel cell (DMFC). The catalysts have been characterized by examining their catalytic activities, morphologies and particle sizes by means of cyclic voltammetry, chronoamperometry, X-ray diffraction and transmission electron microscopy (TEM). It is found that the surfactants with different structures have a significantly influence on the catalyst shape and activity. The catalysts prepared with non-ionic surfactants as the stabilizer show higher activity for direct oxidation of methanol. The structure-activity relationship (SAR) analysis has been explored and the effect of hydrophile-lipophile balance (HLB value) has also been discussed.

Determination of ionic resistance and optimal composition in the anodic catalyst layers of DMFC using AC impedance

In the present study, a method based on transmission-line mode for a porous electrode was used to measure the ionic resistance of the anode catalyst layer under in situ fuel cell operation condition. The influence of Nafion content and catalyst loading in the anode catalyst layer on the methanol electro-oxidation and direct methanol fuel cell (DMFC) performance based on unsupported Pt-Ru black was investigated by using the AC impedance method. The optimal Nafion content was found to be 15 wt% at 75 degrees C. The optimal Pt-Ru loading is related to the operating temperature, for example, about 2.0 mg/cm(2) for 75-90 degrees C, 3.0 mg/cm2 for 50 degrees C. Over these values, the cell performance decreased due to the increases in ohmic and mass transfer resistances. It was found that the peak power density obtained was 217 mW/cm(2) with optimal catalyst and Nafion loading at 75 degrees C using oxygen. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Carbon-supported Pd–Ir catalyst as anodic catalyst in direct formic acid fuel cell

It was reported for the first time that the electrocatalytic activity of the Carbon-supported Pd-Ir (Pd-Ir/C) catalyst with the suitable atomic ratio of Pd and Ir for the oxidation of formic acid in the direct formic acid fuel cell (DFAFC) is better than that of the Carbon-supported Pd (Pd/C) catalyst, although Ir has no electrocatalytic activity for the oxidation of formic acid. The potential of the anodic peak of formic acid at the Pd-Ir/C catalyst electrode with the atomic ratio of Pd and Ir = 5:1 is 50 mV more negative than that and the peak current density is 13% higher than that at the Pd/C catalyst electrode.

Study of carbon-supported Au catalyst as the cathodic catalyst in a direct formic acid fuel cell prepared using a polyvinyl alcohol protection method

In this paper, it is reported for the first time that a carbon-supported Au (Au/C) catalyst for the cathodic catalyst in a direct formic acid fuel cell (DFAFC) was prepared using a polyvinyl alcohol (PVA) protection method. The results indicated that for oxygen reduction, the electrocatalytic activity of the Au/C catalyst prepared with the PVA protection method is much better than that of a Au/C catalyst prepared with the pre-precipitation method. This is due to the small average size and low relative crystallinity of the An particles in the Au/C catalyst prepared by the PVA protection method, compared to that of the Au/C catalyst prepared by the pre-precipitation method, illustrating that the average size and the relative crystallinity of the ALL particles has an effect on the electrocatalytic activity of the Au/C catalyst for oxygen reduction. In addition, because An has no electrocatalytic activity for the oxidation of formic acid, the Au/C catalyst possesses a high formic acid tolerance. After the electrocatalytic activity of the Au/C catalyst for the oxygen reduction is improved, it is suitable to be used as the cathodic catalyst in DFAFC.

Highly conductive, methanol resistant fuel cell membranes fabricated by layer-by-layer self-assembly of inorganic heteropolyacid

Layer-by-layer (LBL) self-assembly is a simple and elegant method of constructing organic-inorganic composite thin films from environmentally benign aqueous solutions. In this paper, we utilize this method to develop proton-exchange membranes for fuel cells. The multilayer film is constructed onto the surface of sulfonated poly(arylene ether ketone) (SPAEK-COOH) membrane by LBL self-assembly of polycation chitosan (CTS) and negatively charged inorganic particle phosphotungstic acid (VIA). The highly conductive inorganic nanoparticles ensure SPAEK-COOH-(CTS/PTA)(n) membranes to maintain high proton conductivity values up to 0.086 S cm(-1) at 25 degrees C and 0.24S cm(-1) at 80 degrees C, which are superior than previous LBL assembled electrolyte systems.

Controllable synthesis of pd nanocatalysts for direct formic acid fuel cell (DFAFC) application: From pd hollow nanospheres to pd nanoparticles

The controllable synthesis of nanosized carbon-supported Pd catalysts through a surface replacement reaction (SRR) method is reported in this paper. Depending on the synthesis conditions the Pd can be formed on Co nanoparticles surface in hollow nanospheres or nanoparticles structures. Citrate anion acts as a stabilizer for the nanostructures, and protonation of the third carboxyl anion and hence the nanostructure and size of the resulting catalysts are controlled via the pH of the synthesis solution. Pd hollow nanospheres, containing smaller Pd nanoparticles, supported on carbon are formed under the condition of pH 9 reaction solution. Meanwhile, highly dispersed carbon-supported Pd nanoparticles can be formed with higher pH (pH >= 10). All catalysts prepared through the SRR method show enhanced activities for the HCOOH electro-oxidation reaction compared to catalysts reduced by NaBH4.

A carbon-supported Pd-P catalyst as the anodic catalyst in a direct formic acid fuel cell

In this paper, it is reported for the first time that a carbon-supported Pd-P (Pd-P/C) catalyst for the anodic catalyst in the direct formic acid fuel cell (DFAFC) can be prepared. The Pd-P/C catalyst shows that its electrocatalytic activity and especially its stability for the oxidation of formic acid are much higher than that of a Pd/C catalyst. Therefore, the Pd-P/C catalyst may have practical applications in DFAFCs.

Modeling of a compact plate-fin reformer for methanol steam reforming in fuel cell systems

The characteristics of a compact plate-fin reformer (PFR) which integrates endothermic and exothermic reactions into one unit have been investigated by experiment as well as by numerical simulation. One reforming chamber was integrated with two vaporization chambers and two combustion chambers to constitute a single unit of PFR. In the PFR, which is based on a plate-fin beat exchanger, catalytic combustion of the reforming gas is used to simulate the fuel cell anode off gas (AOG) which supplies the necessary heat for the methanol steam reforming. Temperature distributions in all chambers and composition distribution in reforming chamber have been studied, and the effect of the ratio of H2O/CH3OH on the performance of the PFR has also been investigated. A model of the PFR was derived using a three-dimensional numerical model for a cross-current flow arrangement. Theoretical predictions of the temperature distributions in the PFR were in good agreement with experimental values. In addition, the numerical model was able to accurately predict the methanol conversion and the reformate composition in reforming chamber. © 2005 Elsevier B.V. All rights reserved.

Methanol steam reforming in a compact plate-fin reformer for fuel-cell systems

A compact plate-fin reformer (PFR) consisting of closely spaced plate-fins, in which endothermic and exothermic reactions take place in alternate chambers, has been studied. In the PFR, which was based on a plate-fin heat exchanger, catalytic combustion of the reforming gas, as a simulation of the fuel cell anode off gas (AOG), supplied the necessary heat for the reforming reaction. One reforming chamber, which was for hydrogen production, was integrated with two vaporization chambers and two combustion chambers to constitute a single unit of PFR. The PFR is very compact, easy to be placed and scaled up. The effect of the ratio of H2O/CH3OH on the performance of the PFR has been investigated, and temperature distributions in different chambers were studied. Besides, the stationary behavior of the PFR was also investigated. Heat transfer of the reformer was enhanced by internal plate-fins as well as by external catalytic combustion, which offer both high methanol conversion ratio and low CO concentration. In addition, the fully integrated reformer exhibited good test stability. Based on the PFR, a scale-up reformer was designed and operated continuously for 1000 h, with high methanol conversion ratio and low CO concentration. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

A comprehensive comparison of fuel options for fuel cell vehicles in China

Fuel cell vehicles (FCVs) offer the potential of ultra-low emissions combined with high efficiency. Proton exchange membrane (PEM) fuel cells being developed for vehicles require hydrogen as a fuel. Due to the various pathways of hydrogen generation, both onboard and off-board, the question about which fuel option is the most competitive for fuel cell vehicles is of great current interest. In this paper, a life-cycle assessment (LCA) model was made to conduct a comprehensive study of the energy, environmental, and economic (3E) impacts of FCVs from well to wheel (WTW). In view of the special energy structure of China and the timeframe, 10 vehicle/fuel systems are chosen as the study projects. The results show that methanol is the most suitable fuel to serve as the ideal hydrogen source for fuel cell vehicles in the timeframe and geographic regions of this study. On the other hand, gasoline and pure hydrogen can also play a role in short-term and regional applications, especially for local demonstrations of FCV fleets. (c) 2004 Elsevier B.V All rights reserved.

Development of electrocatalysts for direct alcohol fuel cells

In the present review, we summarize the recent progress in electrocatalysts for direct alcohol fuel cells, focussing on the research of electrocatalysts for both alcohol oxidation and oxygen reduction, which are crucial in the development of fuel cells. A modified EG (ethylene polyol) method to prepare well-dispersed nano-sized Pt-based electrocatalysts with high loadings is reported. By this method, a more active carbon supported PtRu catalyst for methanol oxidation reaction and a PtSn catalyst for ethanol oxidation reaction have been synthesized successfully. Furthermore, a methanol tolerant Pd-based catalyst for cathode oxygen reduction reaction has been developed. HRTEM and HR-EDS have been employed to characterize the microstructure and micro-components of the above electrocatalysts. Results show that the bimetallic electrocatalysts prepared by the modified EG method display uniform size and homogeneous components at nanometer scale.