Effects of hot pressing conditions on the performance of Nafion membranes coated by ink-jet printing of Pt/MWCNTs electrocatalyst for PEMFCs

In our previous work, a hydrothermal method was employed to prepare Pt/MWCNTs nanocomposites with 20 wt.% Pt, a low mean Pt nanoparticles size (2.8 nm) and a specific surface area of 99 m² g⁻¹. In this work, the membrane electrode assemblies (MEAs) with hydrothermally synthesized Pt/MWCNTs nanocatalysts were fabricated by catalyst-coated membrane (CCM) method. For this purpose, a commercial HP inkjet printer was used to deposit Pt/MWCNTs ink (as catalyst ink) directly on to the substrate (Nafion membrane or decal substrate) with a loading of 0.2 mg cm⁻² Pt for both the anode and cathode. The effects of hot-pressing conditions on the performance of MEAs were investigated through Taguchi design of experiments method using temperature (100 and 130 °C), pressure (800 and 1000 psi) and time (3 and 5 min) as effective experimental parameters. The compression ratios of MEAs were determined by testing the thicknesses before and after hot-pressing process. The performance of MEAs was characterized by the polarization curves and cyclic voltammetry (CV) and the surface morphologies of the electrodes were observed by scanning electron microscopy (SEM). The results showed that the most appropriate hot-pressing conditions were 800 psi, 100 °C, and 3 min. Electrochemical analysis and physical property examination revealed that the MEA fabricated by CCM method has a better performance compared to the one prepared by conventional decal transfer (DT) method.     

Direct liquid-feed fuel cells: Thermodynamic and environmental concerns

The present paper briefly reviews the different direct liquid-feed fuel cells that have been regarded through the open literature. It especially focuses on thermodynamic-energetic data and toxicological–ecological hazards of the chemicals used as liquid fuels. The analysis of those two databases shows that borohydride, ethanol and 2-propanol would be the most adequate liquid fuels for the polymer electrolyte membrane fuel cell-type systems, even if they are inferior to hydrogen. All the fuels and also all the by-products stem from their decomposition are more or less harmful towards health and environment. More particularly, hydrazine should be avoided because it and its by-product are very dangerous. It is to note that the present paper does not intend to review and to compare the performances of those fuel cells because of great differences in the efforts devoted to each of them.     

Optimizing polymer electrolyte membrane thickness to maximize fuel cell vehicle range

Automotive hydrogen polymer electrolyte membrane (PEM) fuel cell systems require periodic purges to remove nitrogen and water from the anode. Purging increases system performance by limiting anode hydrogen dilution, but reduces hydrogen utilization. State of the art fuel cell membrane electrode assemblies utilize thin ionomer membranes in an effort to increase performance and reduce cost. Thinner membranes also increase the required anode purge rates due to the increased transport of inert gases. A model was developed to examine the relationship between membrane thickness and vehicle range which takes into account anode purge rate. The model includes changes in efficiency and hydrogen utilization as a function of PEM thickness for a variety of operating conditions. The model predicts that an optimal membrane thickness which maximizes vehicle range exists, but this thickness is highly dependent on other system conditions. The results of this study can be extended to help optimize stack development and balance of plant design.     

Hydrothermal synthesis of Pt/MWCNTs nanocomposite electrocatalysts for proton exchange membrane fuel cell systems

A hydrothermal method for preparation of size-controlled Pt nanoparticles dispersed highly on multiwalled carbon nanotubes (Pt/MWCNTs) has been studied to optimize the effective parameters (temperature, time, pH and stirring rate) using Taguchi method. The synthesized Pt/MWCNTs nanocomposite samples were characterized through X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray fluorescence (XRF) analyses to identify mean Pt nanoparticles size and Pt content. The analysis of the primary experimental data and demonstration of the main effect trend of each parameter showed that a reaction temperature of about 140 °C, a reaction period of 5 h, a slightly basic reaction pH (∼9) and a stirring rate of 500 rpm are the optimum process conditions which give a low mean Pt nanoparticles size (2.8 nm) and a high Pt content (19.4 wt.%) simultaneously. Cyclic voltammetry (CV) analysis showed that under optimum conditions the synthesized sample gives a specific surface area of 99 m² g⁻¹. Obtaining the polarization curves for the two fabricated membrane electrode assemblies (MEAs) using the optimized catalyst and a commercial Pt/C catalyst (10 wt.%, Aldrich) with Pt loading of 0.4 mg cm⁻² demonstrated that the catalyst prepared under optimum conditions shows a considerably better performance.     

Quantum mechanical interpretation and analysis of perovskite material based single layer fuel cells (SLFCs)

Fossil fuels are unable to meet the current energy demands and polluting the environment with the emission of harmful gases. Therefore, clean energy technology is need of the modern era. One of the energy conversion devices is fuel cell which utilized fuel from renewable sources and convert into electricity in an efficient and clean way. However, for commercialization of this technology high operating temperature, degradation of electrodes and manufacture cost is the key challenges in conventional three layer fuel cell. Significant improvements have been made to reduce the cost and operating temperature by selecting suitable materials. Therefore, single layer fuel cell (SLFC) has been got much attention due to simple geometry. The mechanism inside the SLFC is still mystery which has been explained in this paper using quantum mechanical parameters like band gap and effect of particle size on charge transportation.In this research work, nanocomposite materials for single layer fuel cell have been synthesized by chemical routes. The x-ray diffraction shows the cubic perovskite structure with average crystallite size in the range of 23–37 nm. The particle size and surface area is found to be 23 nm and 86.42 m² g^?1, respectively. Raman spectrum of LBSCF-SDC shows a red shift compared to LBSCF and band gap of the composition 3LBSCF-7SDC is found to be 2.51 eV. Moreover, the conductivity of the sample 3LBSCF-7SDC has been found to be 0.02 Scm^?1 at 750 °C. The quantum mechanical effects governing the working of single layer fuel cells are observed by different analyses. Photon confinement and Fano-Interactions phenomena resulted in a red shift using Raman analysis technique. The red shift in Raman spectrum is referred to a photon confined in a single layer fuel cell system. These effects are studied in single layer fuel cell for the first time with no previous analyses done in this newly field.     

A novel approach on the determination of the minimal operating efficiency of a PEM fuel cell

In this article, a novel mathematical approach is proposed to determine the minimal proton exchange membrane fuel cell efficiency below which it is not recommended to operate the fuel cell. The objective of this proposal is to minimize the annual fuel cost and the electricity cost of a proton exchange membrane (PEM) fuel cell since both terms are efficiency dependent. A new concept developed in this article might be used as a valuable mathematical tool to determine the minimal efficiency required to operate a fuel cell in a reasonable fashion in order to make the fuel cell system technically and economically feasible. Two dimensionless mathematical criteria J₁ and J₂ were proposed for the annual fuel cost and electricity cost, respectively. A minimum fuel cell efficiency of was obtained with J₁ and J₂ values of 2.7 and 0.026, respectively.     

Life time test in direct borohydride fuel cell system

The electric performances of direct borohydride fuel cells (DBFCs) are evaluated in terms of power density and life time with respect to the NaBH₄ concentration. A DBFC constituted of an anionic membrane, a 0.6 mg_Pt cm⁻² anode and a commercial non-platinum based cathode led to performances as high as 200 mW cm⁻² at room temperature and with natural convection of air. Electrochemical life time test at 0.55 mA cm⁻² with a 5 M NaBH₄/1 M NaOH solution shows a voltage diminution of 1 mV h⁻¹ and a drastic drop of performances after 250 h. The life time is twice longer with 2 M NaBH₄/1 M NaOH solution (450 h) and the voltage decrease is 0.5 mV h⁻¹. Analyses of the components after life time tests indicate that voltage loss is mainly due to the degradation of the cathode performance. Crystallisation of carbonate and borate is observed at the cathode side, although the anionic membrane displays low permeability to borohydride.     

千瓦级质子交换膜燃料电池电堆的实验研究

空泡率是汽液两相流动的基本参数之一,而已有过冷沸腾空泡率计算方法研究以高质量流速为主。且大量文献报道现有空泡率模型难以适用于低流速过冷沸腾工况。该文基于低流速过冷沸腾净蒸汽产生点(NVG)理论模型,进一步建立了计算过冷沸腾空泡率的分布拟合模型。在较宽广的压力、质量流速、热流密度和流道尺寸范围内将模型计算结果与现有空泡率实验数据进行了比较,低流速工况下该模型与实验数据符合良好,表明该模型可适用于低流速过冷沸腾工况。     

Simulation of FCV Fuel Consumption Using Stationary PEMFC

In the near future, the use of FCVs （fuel cell vehicles） is expected to help mitigate environmental problems such as exhaustion of fossil fuels and greenhouse gas emissions. Manufacturers publish an FCV＇s specific fuel consumption, but not its dynamic characteristics such as fuel consumption ratio and motor power ratio. Thus, it is difficult to reflect the dynamic characteristics of FCVs in lifecycle system evaluation. To solve this problem, we propose a fuel-consumption simulation method for FCVs using a 1.2 kW stationary PEMFC （proton exchange membrane fuel cell）. In this study, the specific fuel consumption under driving cycles such as the Japanese 10-15 and the JC08 modes are determined and compared with the FCV simulation results obtained using fuel consumption ratios derived from the stationary PEMFC. In the simulation, the specific fuel consumption was found to be 1.16 kg-H2/100-km for the base case under the Japanese 10-15 driving cycle.     

Ultra-low catalyst loading cathode electrode for anion-exchange membrane fuel cells

A new cathode architecture for anion-exchange membrane fuel cells (AEMFCs) is proposed and fabricated by direct deposition of palladium (Pd) particles onto the surface of the micro-porous layer (MPL) that is interfaced with a backing layer. The MPL is composed of carbon nanotubes while the backing layer is made of a carbon paper. The sputter-deposited electrode with a worm-like shape not only extends the electrochemical active surface area, but also facilitates the oxygen transport. This new cathode, albeit with a Pd loading as low as 0.035 mg cm⁻², enables the peak power density of an AEM direct ethanol fuel cell to be as high as 88 mW cm⁻² (at 60 °C), which is even higher than that using a conventional cathode with a 15-times higher Pd loading. The significance of the present work lies in the fact that the new sputter-deposited electrode is more suitable for fuel-electrolyte-fed fuel cells than the conventional electrode designed for proton-exchange membrane fuel cells (PEMFCs).     

A Nafion-based self-humidifying membrane with ordered dispersed Pt layer

A double-layer Nafion-based membrane consisting of a pure Nafion layer and an ordered dispersed Pt particles layer was investigated. The Pt particles were dispersed under the anode graphite ribs, which provide the sites for the recombination of the permeating _H2${\mathrm{H}}_2$ and _O2${\mathrm{O}}_2$ into water. The electrochemical performances of the ordered Pt particles dispersed membrane in proton exchange membrane fuel cell (PEMFC) were studied and compared with those of the common Pt particles dispersed membrane and the pure Nafion membrane. The results indicate that the ordered Pt dispersed membrane reduces the amount of Pt dosage than the common Pt dispersed membrane and improves the performance of PEMFC operated under dry conditions than the pure Nafion membrane as well.     

温度、压力和湿度对质子交换膜燃料电池性能的影响

以Nafion质子交换膜燃料电池(PEMFC)为对象,通过测量电池的电流—电压、电流—功率和电压—时间曲线,研究了温度、压力和湿度等条件对电池性能的影响,同时也考察了电池的能量转换效率及短期运行时的稳定性,得出了电池较佳的工作条件。实验和计算结果表明：在反应温度为72℃、H2和02压力分别为0．2MPa、进气湿度饱和时,电池最大输出功率可达0．7W．cm^-2;在0．3W.cm^-2～0．7W．cm^-2范围内电池能量转换效率为62％—34％;在大电流密度下电池仍能稳定工作。