Zero-CO2 emission and low-crossover 'rechargeable' PEM fuel cells using cyclohexane as an organic hydrogen reservoir

High performance (open circuit voltage = 920 mV, maximum power density = 14-15 mW cm(-2)) of the PEM fuel cell was achieved by using cyclohexane as a fuel with zero-CO2 emission and lower-crossover through PEM than with a methanol-based fuel cell.     

Cogeneration of cyclohexylamine and electrical power using PEM fuel cell reactor

Cogeneration of cyclohexylamine (CHA) and electrical power using a PEM fuel cell reactor were performed by the selective reduction of nitrobenzene (NB). The maximum power density was 1.5 mW cm⁻² at a current density of 15 mA cm⁻² during cogeneration with the reduction of NB in ethanol. The current density varied from 1.6 to 24 mA cm⁻² with the change of external load. A selectivity of 57.3% to CHA, and a selectivity of 28.2% to aniline (AN), with 8.2% conversion of NB were obtained when the hydrogen flow rate was 20 ml min⁻¹ at 70 °C for 2 h. Effects of Pt catalyst loading and NB concentration on the behavior of cogeneration were also studied.     

Direct borohydride fuel cell performance using hydroxide-conducting polymeric nanocomposite electrolytes

Solid electrolyte membranes based on alkali-doped polyvinyl alcohol (PVA) and PVA/carbon nanotubes (PVA/CNTs) are used in direct borohydride fuel cells (DBFCs). As 0.05 wt % of CNT is incorporated into the PVA matrix, the polymer crystallinity is decreased from 42.4% to 38.0% and the fractional free volume increases from 2.48% to 3.53%. The KOH-doped PVA/CNT exhibits the highest ionic conductivity of 0.0805 S cm⁻¹, because of the increased polymer free volume (which promotes vehicular OH⁻ transport) and the presence of CNT (which serves as the conducting microchannels). Sodium borohydride (NaBH₄) in NaOH solution and potassium borohydride (KBH₄) in KOH mixture are fed into the cells. The power density of the KBH₄-based DBFC is almost twice that of the NaBH₄-based DBFC (184 vs. 92 mW cm⁻²) due to less KBH₄ permeability through the films, higher conductivity of the KOH-doped PVA composites than those in the sodium counterpart, and probably higher electro-catalytic kinetics. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1779–1789, 2013     

The current voltage plot of PEM fuel cell with long feed channels

The formula for voltage loss on the cathode side of the polymer electrolyte membrane fuel cell (PEMFC) is derived, taking into account oxygen consumption in the feed channel. Limiting current density due to the oxygen exhaustion along the channel is obtained. Theory predictions are in line with experiments that were performed to test the theory. The results reveal new reserves for the optimization of the cell performance. They also show new in situ electroanalytical options: the study of electrochemical reaction in the catalyst layer via the cell voltage–current plots and via detecting of the feed gas consumption or local current distribution along channel.     

Mechanical endurance of polymer electrolyte membrane and PEM fuel cell durability

The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006     

Electrochemical H/D isotope effects in PEM fuel cell

An electrochemical H/D separation system consisting of electrolyzer and PEM fuel cell has been proposed. Isotope separation could be important as a part of the energy saving process in an energy-hydrogen-energy cycle. Any transfer of energy into hydrogen or vice versa induces change of the H/D isotope ratio, which can be considered, as a method to produce heavy water as by-product. In this way, the separation efficiency can contribute to the overall efficiency of the cycle.     

Anti-flooding cathode catalyst layer for high performance PEM fuel cell

Water management in cathode catalyst layer (CCL) plays an important role in the PEM fuel cell operation. A novel anti-flooding CCL is developed with the addition of oxygen permeable and hydrophobic dimethyl silicone oil (DSO) into the catalyst layer (CL) to improve the water balance and oxygen transport within the cathode. With the addition of 0.5 mg cm^?2 DSO in the CCL, the ability of water management has been enhanced greatly compared to that with a normal cathode. Electrochemical impedance spectroscopy has been employed to characterize the electrochemical behavior of the single fuel cell. The results show that the increased hydrophobicity of the CCL by DSO modification effectively expels water out of the voids of CCL. In addition, DSO in the CCL enhances oxygen accessibility to the CCL, thus improving the performance of the PEM fuel cell significantly.     

A TiO2-nanotube-array-based photocatalytic fuel cell using refractory organic compounds as substrates for electricity generation

A TiO(2)-nanotube-array-based photocatalytic fuel cell system was established for generation of electricity from various refractory organic compounds and simultaneous wastewater treatment. The present system can respond to visible light and produce obviously enhanced cell performance when a narrow band-gap semiconductor (i.e. Cu(2)O and CdS) was combined with TiO(2) nanotubes.     

Chemical and mechanical stability of EPDM in a PEM fuel cell environment

Proton exchange membrane (PEM) fuel cell stack requires elastomeric gaskets in each cell to keep the reactant gases within their respective regions. Long-term durability of the fuel cell stacks depends heavily on the functionality of the elastomeric gasket material. Chemical and mechanical stability of the elastomeric material is of great concern to the overall performance of the fuel cell stacks. The degradation of a commercially available gasket material, ethylene-propylene-diene monomer (EPDM), was investigated in a simulated PEM fuel cell environment in this work. One solution and two temperatures, based on actual fuel cell operation, were used in this study. Optical microscopy was used to show the topographical changes on the sample surface. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the gasket material before and after exposure to the simulated PEM fuel cell environment over time. Atomic absorption spectrometry was used to identify the leachants in the soaking solution from the elastomeric material. Microindentation test and dynamic mechanical analysis (DMA) were conducted to assess the change of mechanical properties of the samples exposed to the environment. The atomic absorption spectrometer analysis shows that silicon and calcium were leached from the material into the soaking solution. The ATR-FTIR results indicate that the chemical changes were not apparent. The microindentation test and DMA results reveal that mechanical properties were not changed significantly.     

In situ observations of water production and distribution in an operating H2/O2 PEM fuel cell assembly using 1H NMR microscopy

Proton NMR imaging was used to investigate in situ the distribution of water in a polymer electrolyte membrane fuel cell operating on H2 and O2. In a single experiment, water was monitored in the gas flow channels, the membrane electrode assembly, and in the membrane surrounding the catalysts. Radial gradient diffusion removes water from the catalysts into the surrounding membrane. This research demonstrates the strength of 1H NMR microscopy as an aid for designing fuel cells to optimize water management.     

Direct ethanol oxidation fuel cell with anionite membrane and alkaline electrolyte

A number of cathode catalysts were synthesized from nitrogen-containing organic complexes on XC-72R carbon black for an alkaline electrolyte. The catalysts were studied by the rotating disc electrode (RDE) technique. The polyacrilonitrile (PAN), phthalocyanine (Pc), and cobalt tetra(methoxyphenyl)porphyrin (CoTMPP) systems showed the highest activity. The slope of the oxygen polarization curves in the first region in 1 M KOH was 35–40 mV; this corresponds to concentration polarization in an alkaline solution in the O₂-HO₂⁻ system. A cyclic voltammetry study demonstrated that the catalytic systems with the highest corrosion stability were Pc + Co + Fe/XC-72R and CoTMPP/XC-72R pyropolymer. The activity of the catalysts decreased by 20–25% compared with the initial current densities on average. An ethanol-oxygen fuel cell with a Fumasep FAA anionite membrane and nonplatinum catalysts was tested. The maximum power density was 32 mW/cm² at 40°C. The stability test of the fuel cell showed that the materials used for the membrane-electrode assembly allowed more than 100 h of continuous operation with constant working characteristics.     

生物柴油-柴油混合燃料的理化及排放特性研究

对生物柴油-柴油混合燃料的表面张力、运动黏度、抗磨性、氧化稳定性以及碳烟排放等特性进行了测试和研究.结果表明,生物柴油-柴油混合燃料的表面张力随生物柴油含量的增加呈抛物线趋势变化,并随温度升高呈幂函数曲线下降.生物柴油的磨斑直径小于柴油,最大卡咬极限压力大于柴油.生物柴油的质量分数为40％-70％,混合燃料的氧化稳定性...     

Electrochemical noise diagnostics of PEM fuel cell stack for micro-cogeneration application

Journal of Solid State Electrochemistry - Electrochemical noise (EN) generated by a 3500 W PEM fuel cell stack (50 cells) has been measured during micro-cogeneration durability tests. The...     

Contact resistance between gas diffusion layer and catalyst layer of PEM fuel cell

In this study, the electrical contact resistance between gas diffusion layer (GDL) and catalyst layer (CL) on an electrolyte membrane was experimentally evaluated as a function of compression. The contact resistances between the GDL and CL decreased nonlinearly as the GDL thickness decreased due to the compression pressure. The values of the contact resistance between the GDL and CL were found to be more than one order of magnitude larger than the contact resistance between the GDL and graphite, and even comparable to the ionic resistance of the membrane. Because of the large value and variation in contact resistance between the GDL and CL, severe current distribution may be created inside the cell. The results reported here should be highly useful in providing a more accurate picture of the transport phenomena in a fuel cell.     

Structural defects and the electronic structure of zirconium hydrides: x-ray emission spectra and quantum chemical calculations

X-ray emission spectroscopy and the Green function LMTO band method was used to study the effect of structural defects in the hydrogen sublattice on the electronic structure and chemical bonding in ZrH₂.Institute of Metal Physics, Urals Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 70–74, November–December, 1989.     

Estimation of MEA parameters and prediction of PEM fuel cells electrical performances using numerical modelling

In this paper, a coupled model of transfer phenomena within Proton Exchange Membrane Fuel Cell (PEMFC) developed from Stefan-Maxwell (in the diffusion and active layers), Butler-Volmer (in the active layer), and water mass transport (in the electrolyte membrane) equations is presented. This modeling allows interpreting experimental results, prediction of PEMFC electrical performances and guiding perspective investigations on optimization of PEMFC. The model helps the research of dominating sensitivity parameters, as well as the estimation of some badly known MEA (Membrane Electrode Assembly) parameters using fuel cell tests.     

有机溶剂对PEM燃料电池CCM结构和性能的影响

采用直接喷涂法将催化剂涂覆在质子交换膜上形成CCM(catalyst coated membrane),CCM与碳纸扩散层组成膜电极用于质子交换膜燃料电池.制备CCM的混合液由质量分数20%的Pt/C催化剂、质量分数5%的Nafion溶液、有机溶剂和水组成.不同的有机溶剂(乙醇、异丙醇和叔丁醇)、有机溶剂的含量、溶剂的...     

Determination of polymer electrolyte membrane (PEM) degradation products in fuel cell water using electrospray ionization tandem mass spectrometry

Within the scope of research of membrane degradation phenomena during fuel cell operation a reliable analytical procedure for the extraction, detection and quantification of possible membrane oxidation products has been developed. These oxidation products originate from the attack of hydroxyl or peroxyl radicals on the membrane polymer. Such radicals are formed in situ (during fuel cell operation) or ex situ (Fenton test as oxidative stress simulation). The analysis of membrane oxidation products was carried out by electrospray ionization tandem mass spectrometry. Five potential membrane oxidation products (4‐hydroxybenzoic acid (4‐HBA), 4‐hydroxybenzaldehyde (4‐HBAD), 4,4‐biphenol (4,4‐BP), 4‐hydroxybenzenesulfonate (4‐HBS), and 4,4‐sulfonylbiphenol (4,4‐SBP)) were selected based on the molecular structure of the sulfonated polyarylether membrane used. In conjunction with the development of a multiple reaction monitoring (MRM) method, the ionization and fragmentation of the selected compounds were investigated. For 4,4‐BP a molecular ion (M^+?) was observed in the positive ionization mode and used for MRM method development. Reproducible extraction of the model compounds was achieved using a mixed‐mode sorbent material with both weak anion‐exchange and reversed‐phase retention properties. By using the developed analytical procedure, the identities of two membrane degradation products (4‐HBA and 4‐HBAD) were determined in situ and ex situ. In addition to the investigation of membrane degradation phenomena, the combination of extraction on a mixed‐mode sorbent material and tandem mass spectrometric detection is attractive for the analysis of aromatic sulfonic acids, phenolic acids and phenols. Copyright © 2010 John Wiley & Sons, Ltd.     

Computational analysis of heat transfer in a PEM fuel cell with metal foam as a flow field

Journal of Thermal Analysis and Calorimetry - Thermal management of proton-exchange membrane (PEM) fuel cell has an important effect on the overall cell performance. In this paper, metal foams as...     

Molecular oxygen reduction in PEM fuel cell conditions: ToF-SIMS analysis of co-based electrocatalysts

A series of Co-based electrocatalysts for oxygen reduction in acid media has been prepared using two different Co precursors: cobalt acetate (CoAc) and a cobalt porphyrin (CoTMPP). These catalysts have been analyzed by ToF-SIMS to obtain information on the number and the structure of catalytic active sites in these materials. The results are compared with the results of a similar analysis already performed on a series of Fe-based electrocatalysts (J. Phys. Chem. B 2002, 106, 8705) also prepared with two different Fe precursors: iron acetate (FeAc) and an iron porphyrin (ClFeTMPP). The interpretation of ToF-SIMS data for Fe-based catalysts allowed us to conclude that whatever the Fe precursor was, the same catalytic sites (FeN2/C and FeN4/C, with their respective dominant ToF-SIMS signatures: FeN2C4+ and FeN4C8+ ions) were found. The comparison of the ToF-SIMS data with the activity of those catalysts led to the conclusion that the FeN2C catalytic site was more active than FeN4/C. When the same procedure is applied to ToF-SIMS data measured for Co-based catalysts, the following conclusions are drawn: (i) as for Fe precursors, both Co precursors also give similar results; (ii) as for Fe-based catalysts, the same four families of MetalNxCy+ ions, with 1, 2, 3, and 4 nitrogen atoms, are also found in the spectra of Co-based catalysts, but there is no dominant CoNxCy+ ion signature; (iii) only CoN4/C can be ascertained on the basis of ToF-SIMS measurements. There is no strong support from ToF-SIMS measurements for (or against) the existence of CoN2/C in Co-based catalysts as there is for FeN2/C in Fe-based catalysts; (iv) contrary to Fe-based catalysts, all catalytic sites (if there are any besides CoN4/C) are about equally active in Co-based electrocatalysts.