| The energy crisis and environmental pollution have stimulated significant research into new, efficient and sustainable energy sources to compensate and even replace traditional ones. The polymer electrolyte membranefuel cell(PEMFC) has been considered as promising green energy device due to its high energy conservation efficiency, the possibility of using regenerative fuels, low or zero levels of noxious emissions of environmental pollutants, a low operating temperature and a relatively quick start-up. PEMFC can be divided into two kinds of systems, according to the media(proton or hydroxyl ion transport) the PEMFC operated. Recently, the growing interest in the application of alkaline membrane fuel cells(AMFCs) is principally motivated by the prospective use of cheap, easy to start, and relatively abundant non-precious metal catalystsThe energy crisis and environmental pollution have stimulated significant research into new, efficient and sustainable energy sources to compensate and even replace traditional ones. The polymer electrolyte membranefuel cell(PEMFC) has been considered as promising green energy device due to its high energy conservation efficiency, the possibility of using regenerative fuels, low or zero levels of noxious emissions of environmental pollutants, a low operating temperature and a relatively quick start-up. PEMFC can be divided into two kinds of systems, according to the media(proton or hydroxyl ion transport) the PEMFC operated. Recently, the growing interest in the application of alkaline membrane fuel cells(AMFCs) is principally motivated by the prospective use of cheap, easy to start, and relatively abundant non-precious metal catalystsThe main points are summarized as follows:(1) Under H2/O2 the maximumpeak power densityof the cell madeby Pt/C loading of 0.5 mg cm-2 is 21.3 m W cm-2, which is much larger than that for Pt/C loading of 0.3 mg cm-2(18 m W cm-2). However, the cell performance made by Pt/C loading of 0.4 mg cm-2 is only 0.5 m W cm-2 lower than that for Pt/C loading of mg cm-2.The complexity of the MEA preparation and the other influence factors(such as the catalyst ink, spraying technology, hot-press temperature and pressure) may lead to these differences between the different catalyst loadings.This indicates that when the Pt/C loading reached 0.4 mg cm-2, the reaction rate of HOR has reached maximum. It can be seen thatthe N-S-MPCwith a loading of 3 mg cm-2 in this workcan give an initialcell performance with a peak power density of 21.7 m W cm-2, which is the highest value in all tested catalyst loading samples. In addition, it can be observed that the power density increases with the increasedcatalyst loading until 3 mg cm-2, then began to decrease when the catalyst was further increased. For the research, we further measure the effect of the catalyst layer thickness on the cell performances. The power density was observed to increase with the thickness of catalyst layer. However, thevalue(power density)growth leveled off when the thickness of the catalyst layer is increased so much, for example, larger than 90μm. This is due to the fact that the reaction zone waslimited by mass transfer. The increase of the power density withincreasing the thickness of the catalyst layer is largely due to theincrease of the total area of triple phase boundaries, at which ORR occurs. On the other hand, the decrease in power densitywhen catalyst layer was thicker than 90μm was due to the increaseof diffusion resistance of the reactants. Thinner catalyst layer wasfavorable for gas transport. Hence, an increase in the thickness of catalyst layerraised the local hydroxyl ionconcentration which was in favor of the process of ORR, thus resulted in an increase in the power density.(2) The maximum power density was found that the MEA using 30μL produced a maximum power density of 20.8 m W cm-2, which was the highest value among all the prepared MEAs.This indicates thatthat bonding layer hasa great influence on MEA performances.It is believed that a bonding layer can increase the interfacial adhesion and improve the interfacial stability between membranes and electrodes. The bonding layer also hasthe function of the ion channel and gas permeability. With thebonding layerloading increase, the ion channelincreases and the ionic conductivity was accelerated,leading to a decrease in the interfacial resistance. when the bonding layer loading increased from 20μL to 30μL, the power density increased 3.2 m W cm-2.However, lower performance was observed in the bonding layer of 40μL and 50μL, with power densities of 15.3 m W cm-2 and 11.4 m W cm-2, respectively. This may be due to the fact that the bonding layer loading has been increasedto the limit, where theion channels blocked and oxygen permeability significantly, thus leading to the poor power density.As a consequence, the thin bonding layer cannot only increases the interfacial adhesion, but alsoenhances the performance.(3) Nitrogen and sulfur co-doped mesoporous carbon(N-S-MPC) catalyst in acidic and alkaline fuel cell has good catalytic activity.(4) Effect of ionomer content on the single cell performance. When the ratio of 3:1, the sample showed the best performance for power generation, the peak power density is: 21.7 m W cm-2. Alkaline ionomer in catalytic layer not only connect the surface of the material, but also as a binder for catalyst particles bonded together to maintain long time operation of the fuel cell.(5) Fuel cell operation condition of MEA were studied.Operating temperature of the fuel cell also has a great influence on the performance of the fuel cell. Temperature of 50 ℃ when showing the power of(35.1 m W cm-2) and Pt/C power(37.7 m W cm-2).Fuel cell performance is improved the rise of temperature. On the one hand, the rise of temperature, reactant carry more water vapor in MEA, reduces the mass transfer resistance, thus reaction current. On the other hand, temperature also helps remove the introduction of the impurities in the process(6) The other two non-noble metal catalysts of preliminary research shows that the non-noble metal catalysts on the catalytic performance there is obvious low compare with Pt/C catalyst.But because of its economy and sources, they still have a certain competitivene... |
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