Zhigang Qi

Open circuit voltage and methanol crossover in DMFCs

It is difficult to definitely measure the open circuit voltage (OCV) of a direct methanol fuel cell (DMFC). For example, after a cell is changed from a loaded state to a no load, open circuit state, the voltage increases quickly and reaches a peak value in seconds. Some might use this peak voltage as the OCV. However, the voltage starts to decline quite rapidly following the peak, and it takes several minutes to become stabilized at a lower value. This stabilized, lower voltage should be used as the OCV. Another unique and interesting phenomenon is the rapid cell voltage increase following an initial instant decline when a load is applied to a DMFC. This increase is believed to be due to diminishing of excess methanol that accumulates at the cathode side during the open circuit period. The effects of air flow rate, methanol concentration and cell temperature on the OCV, methanol crossover and cell performance were also studied.

Enhancement of PEM fuel cell performance by steaming or boiling the electrode

Treatment of electrodes or catalyst-coated membranes with steam or boiling water for as short as 10 min dramatically increased their performance when tested in proton exchange membrane (PEM) fuel cells afterwards. The treatment was found to be effective for numerous electrodes consisting of various types of carbon-supported Pt catalysts with different Pt loadings. It is proposed that the treatment increases the number of active sites or regions in the catalyst layer which leads to an enhanced catalyst utilization.

Effect of CO in the anode fuel on the performance of PEM fuel cell cathode

Even trace amounts of CO in the fuel for a proton-exchange membrane fuel cell (PEMFC) could poison not only the anode, which is directly exposed to the fuel, but also the cathode, which is separated from the fuel by a proton-exchange membrane; and the performance decline of the cathode is sometimes more than that of the anode. Adsorption of CO on the cathode catalyst has been detected electrochemically, and this indicates that CO can pass through the membrane to reach the cathode. To reduce such a poisoning effect, fuel cell operation conditions (e.g. level of membrane humidification, gas pressure difference between cathode and anode), membrane and catalyst layer structures, and CO-tolerant cathode catalysts should be further explored.

Modification of carbon supported catalysts to improve performance in gas diffusion electrodes

The effect of surface oxidation of the carbon support of Pt catalysts with nitric acid has been investigated. Oxidation of the support before deposition of the Pt leads to a decrease in the Pt particle size, as reported by others, and enhanced performance for oxygen reduction in gas diffusion electrodes. Oxidation of the support after Pt deposition produces an even greater enhancement in performance, which we have attributed to enhanced proton conductivity in the catalyst layer. It is speculated that hydrophilic carboxylic acid groups produced by surface oxidation enhance wetting of the catalyst layer.

Electronically Conducting Proton Exchange Polymers as Catalyst Supports for Proton Exchange Membrane Fuel Cells. Electrocatalysis of Oxygen Reduction, Hydrogen Oxidation, and Methanol Oxidation

A variety of supported catalysts were prepared by the chemical deposition of Pt and Pt‐Ru particles on chemically prepared poly (3,4‐ethylenedioxythiophene)/poly (styrene‐4‐sulfonate) (PEDOT/PSS) and PEDOT/polyvinylsulfate (PVS) composites. The polymer particles were designed to provide a porous, proton‐conducting and electron‐conducting catalyst support for use in fuel cells. These polymer‐supported catalysts were characterized by electron microscopy, impedance spectroscopy, cyclic voltammetry, and conductivity measurements. Their catalytic activities toward hydrogen and methanol oxidation and oxygen reduction were evaluated in proton exchange membrane fuel‐cell‐type gas diffusion electrodes. Activities for oxygen reduction comparable to that obtained with a commercial carbon‐supported catalyst were observed, whereas those for hydrogen and methanol oxidation were significantly inferior, although still high for prototype catalysts.

Activation of low temperature PEM fuel cells

Proton-exchange membrane (PEM) fuel cells intended to be operated at ambient conditions for portable applications are first activated by being exposed at elevated temperature and pressure. The performance of the resulting fuel cells, especially those whose electrodes are of low catalyst loadings made using supported catalysts, improve dramatically. The activation procedure is effective, quick and easy to perform.

Characteristics of Polypyrrole/Nafion Composite Membranes in a Direct Methanol Fuel Cell

Commercial perfluorosulphonic acid membranes (Nafion) have been impregnated with polypyrrole by in situ polymerization to decrease the crossover of methanol in direct methanol fuel cells (DMFCs). Modified membranes produced by polymerization of the pyrrole with hydrogen peroxide and iron(III) have been evaluated in a DMFC. Both methods produce membranes that can provide enhanced cell performance, although membranes produced with iron(III) as the oxidizing agent for the polymerization require additional treatments to restore their conductivity and promote bonding to the electrodes. Performance gains result from substantial reductions of the cathode overpotential, while anode overpotentials increase due to the lower conductivities of the modified membranes. Part of the beneficial effect at the cathode appears to be due to lower water crossover from the anode to the cathode.

Quick and effective activation of proton-exchange membrane fuel cells

It was found that operating a proton-exchange membrane fuel cell at elevated temperature and pressure could largely activate it. When the fuel cell was tested again at ambient conditions, its performance was much higher than that before the activation procedure was performed. Without the activation, the fuel cell could probably never achieve the enhanced performance if only a traditional break-in procedure was performed. The activation procedure normally did not need to exceed 2 h, and it was applicable to all the catalysts, electrodes, catalyst-coated membranes (CCMs), and membrane-electrode assemblies studied.

Low Temperature Direct 2-Propanol Fuel Cells

2-Propanol exhibits a substantially higher cell voltage than methanol in a direct liquid fuel cell at a current density less than ca. 100mA/cm 2 . Although the performance increases with cell temperature, the cell can deliver 690 mV at a current density of 20 mA/cm 2 at room temperature. These features could make 2-propanol an attractive fuel for portable power applications.

Effect of oxygen storage materials on the performance of proton-exchange membrane fuel cells

Abstract Oxygen storage materials with a chemical composition of Ce 0.8 Zr 0.2 O 2 and V 2 O 5 , were prepared and incorporated into the cathode catalyst layer of proton-exchange membrane fuel cells, respectively. The presence of Ce 0.8 Zr 0.2 O 2 slightly enhanced the performance of the fuel cell, but the incorporation of V 2 O 5 largely decreased the fuel cell performance.