共查询到20条相似文献,搜索用时 15 毫秒
1.
The characterization of proton exchange membrane fuel cell electrodes is essential for understanding the electrode performance. In this paper, mercury intrusion porosimetry and the nitrogen adsorption method were used to measure pore size distributions and porosities (ϵ) of various electrodes, which were made with either platinum supported on amorphous carbon (Pt/VA) or platinum supported on graphitized carbon (Pt/VG), and had ionomer‐to‐carbon weight ratios (I/C) of 0.5, 1.0, and 1.5. The oxygen effective diffusivity ( ) in electrodes was measured as a function of relative humidity (RH) in an apparatus that was previously described [Z. Yu, R. N. Carter, J. Power Sources 195 (2010) 1079–1084]. The tortuosity of electrodes at the dry condition (80 °C and 0% RH) was then determined from the measured porosities and . For a given catalyst, as the I/C ratio increased, it was found that the electrode's mean pore size, porosity, and all decreased, but the tortuosity increased. For a given I/C ratio, the Pt/VA electrode exhibited larger mean pore size, larger porosity, larger , and smaller tortuosity compared with the Pt/VG electrode. The contrast between Pt/VA and Pt/VG electrodes with the same I/C ratio indicates different ionomer distribution on the catalyst surface. 相似文献
2.
Primary energy savings and CO2 reduction is one of the key motivations for the use of fuel cell systems in the energy sector. A benchmark of domestic cogeneration by PEMFC with existing large scale power production systems such as combined steam‐gas turbine cycle, clearly reveals that only fuel cell systems optimising overall energy efficiency (> 85%) and electrical efficiencies (> 35%) show significant primary energy savings, about 10%, compared with the best competing technology. In this context, fuel processing technology plays a dominant role. A comparison of autothermal and steam reforming concepts in a PEMFC system shows inherent advantages in terms of efficiency at low complexity for the latter. The main reason for this is that steam reforming allows for the straightforward and effective use of the anode‐off gas energy in the reformer burner. Consequently, practical electrical system efficiencies over 40% seem to be achievable, most likely by steam reformers. FLOX®‐steam reforming technology has reached a high state of maturity, offering diverse advantages including: compact design, stable anode off‐gas usage, high efficiency, as well as simple control behaviour. Scaling of the concept is straightforward and offers an opportunity for efficient adaptation to smaller (1 kW) and larger (50 kW) units. 相似文献
3.
C. Kunde R. Hanke‐Rauschenbach M. Mangold A. Kienle K. Sundmacher S. Wagner R. Hahn 《Fuel Cells》2010,10(6):949-959
This paper deals with the control of a miniaturised fuel cell system. A single air blower is used to control both heat and water management of the fuel cell. As the number of manipulated variables is smaller than the number of control variables, classical control algorithms are not applicable. To find a suitable controller, a system model is developed that shows the qualitatively same behaviour as the experimental setup. The dynamic behaviour of the model and the influence of the blower are studied by phase portraits. A control algorithm is then conceived by qualitative analysis of the phase portraits and tested in simulations. 相似文献
4.
W. J. Hall 《Fuel Cells》2014,14(6):945-953
High temperature polymer electrolyte membrane (HT‐PEM) fuel cells offer some advantages over their low temperature equivalent, but there have been relatively few reports into their use in vehicles. This paper describes the power train design and operation of a fleet of Microcab H2EV vehicles. The power train consisted of a HT‐PEM fuel cell coupled via a DC/DC convertor to a lithium iron phosphate traction battery, which was then connected to two Lynch motors. The integration and operation of all the major power train components is described. Also described here is the vehicle control unit that uses digital and analog communications to provide overall management of the vehicle. Details are given of all the safety systems designed into the vehicle. Some data describing the performance of the H2EV power‐train during typical drive cycles is presented, which shows that the system was functional. It is concluded that HT‐PEM fuel cell light vehicles are viable, but the heating and cooling time of the fuel cell needs to be significantly reduced. 相似文献
5.
T. S. K. Raunija R. K. Gautam V. M. Bhradwaj N. Nandikesan M. Shaneeth S. C. Sharma A. Verma 《Fuel Cells》2016,16(6):801-809
The objective of the present work is to develop carbon/carbon (C/C) composite bipolar plate at low cost with rapid processing time by a novel process. Carbon/carbon composite was developed using exfoliated carbon fiber reinforcement, isroaniso as primary matrix precursor, and resole type phenolic resin as secondary matrix precursor. Randomly oriented hybrid carbon fiber (T‐800 and P‐75) reinforced hybrid carbon matrix composite was fabricated. The slicing and channel forming were carried out using simple and conventional machines. The competency of the material was investigated by characterizing and analyzing density, scanning electron miscroscopy (SEM), compressive strength, compressive modulus, flexural strength, tensile strength, impact strength, hardness, electrical conductivity, thermal conductivity, coefficient of thermal expansion, permeability, and corrosion current. The C/C composite bipolar plate with exfoliated carbon fibers offered bulk density 1.75 g cm−3, tensile strength 45 MPa, flexural strength 98 MPa, compressive strength 205 MPa, electrical conductivity 190 (through‐plane) and 595 S cm−1 (in‐plane), and thermal conductivity 24 (through‐plane) and 51 W m−1 K−1 (in‐plane). Further, single cell test was performed to evaluate the effectiveness of the C/C composite bipolar plate in the PEM fuel cell and the performance was compared with the commercial graphite bipolar plate at different operating temperatures. 相似文献
6.
An analysis of three‐dimensional computational fluid dynamics (CFD) is conducted to investigate the coupled cooling process involved in fluid flow and heat transfer between the solid plate and the coolant flow for optimization of the cooling design of a fuel cell stack. A conception of IUT (Index of Uniform Temperature) across the entire area is presented to evaluate the degree of uniform temperature profile across the cooling plates. Six cooling modes, including three serpentine‐type modes and another three parallel‐type modes, are presented and analyzed for optimization of the cooling mode of fuel cells. The prediction finds that the cooling effect of serpentine‐type cooling modes could be better than that of parallel‐type cooling modes. 相似文献
7.
The effects of inhomogeneous compression of gas diffusion layers (GDLs) on local transport phenomena within a polymer electrolyte membrane (PEM) fuel cell were studied theoretically. The inhomogeneous compression induced by the rib/channel structure of the flow field plate causes partial deformation of the GDLs and significantly affects component parameters. The results suggest that inhomogeneous compression does not significantly affect the polarisation behaviour or gas–phase mass transport. However, the effect of inhomogeneous compression on the current density distribution is evident. Local current density under the channel was substantially smaller than that under the rib when inhomogeneous compression was taken into account, while the current density distribution was fairly uniform for the model which excluded the effect of inhomogeneous compression. This is caused by the changes in the selective current path, which is determined by the combination of conductivities of components and contact resistance between them. Despite the highly uneven current distribution and variation in material parametres as a function of GDL thickness, the temperature profile was relatively even over the active area for both the modelled cases, contrary to predictions in previous studies. However, an abnormally high current density significantly accelerates deterioration of the membrane and is critical in terms of cell durability. Therefore, fuel cells should be carefully designed to minimise the harmful effects of inhomogeneous compression. 相似文献
8.
A model fuel cell with a single transparent straight flow channel and segmented anode was constructed to measure the direct correlation of liquid water movement with the local currents along the flow channel. Water drops emerge through the largest pores of the GDL with the size of the droplets that emerge on the surface determined by the size of the pore and its location under the gas flow channel or under the land. Gravity, surface tension, and the shearing force from the gas flow control the movement of liquid in the gas flow channel. By creating a single large diameter pore in the GDL, liquid water flow emergent from the GDL was forced to be in specific locations along the length of the channel and either under the land or under the channel. The effects of gravity were amplified when the large pore was under the channel, but diminished with the large pore under the land. Current fluctuations were minimised when the dominant water transport from the GDL pore was near the cathode outlet. The results show that it is possible to engineer the water distribution in PEM fuel cells by modifying the pore sizes in the GDL. 相似文献
9.
In this paper an approach for the dynamic modelling of polymer electrolyte membrane fuel cells is presented. A mathematical formulation based on empirical equations is discussed and several features, exhibiting dynamic phenomena, are investigated. A generalized steady state fuel cell model is extended for the development of a method for dynamic electrochemical analysis. Energy balance and reactant flow dynamics are also explained through physical and empirical relationships. A well‐researched system (Ballard MK5‐E stack based PGS‐105B system) is considered in order to understand the operation of a practical fuel cell unit. Matlab‐SIMULINKTM has been used in simulating the models. The proposed method appears to be relatively simple and consequently requires less computation time. Simulation results are compared with available experimental findings and a good match has been observed. 相似文献
10.
Our study explores the use of porous carbon as anode catalyst support to improve borohydride utilization in a direct borohydride fuel cell. Pt catalysts supported by carbon aerogel (CA) and macroporous carbon (MPC) are synthesized by template method. The pores in porous carbon materials catch hydrogen bubbles to regulate the contact of anolyte with catalytic sites, and this leads to the depression of hydrogen evolution during BH4− electrooxidation. However, the hydrogen bubbles in the pores simultaneously deteriorate charge carrier transport and thus increase anode polarization. The CA‐supported Pt catalyst improves the coulombic efficiency of BH4− electrooxidation. However, the MPC‐supported Pt catalyst performed better than the CA‐supported Pt catalyst. MPC also has a good pore distribution, which improves the coulombic efficiency of BH4− electrooxidation without decreasing anode performance. 相似文献
11.
Steady state and dynamic simulations are performed in order to compare the models. Considering the external response of FC system integrated in the tramway hybrid system, both reduced models show similar results with an important reduction of computation time with respect to the complete model. However, the reduced model 1 shows better results than the reduced model 2 when representing the internal behaviour of FC system, so that this model is considered the most appropriate for propulsion system applications. 相似文献
12.
In this paper, a parametric study of a combined proton exchange membrane (PEM) fuel cell and triple‐effect absorption cooling system (TEACS) is undertaken to investigate the effect of different operating conditions and system parameters on the COPs, efficiency of the fuel cell and the integrated system's overall utilisation factor. It is found that the fuel cell efficiency increases from 40% to 44.5% as the operating temperature of the fuel cell increases. However, as the fuel cell's temperature and current density increase, the COPs decrease from 2.4 to 0.9 as a result of the increase in the energy output of the fuel cell ranging from 7.4 to 10.7 kW. The efficiency of the fuel cell decreases from 41% to 32% with an increase in both fuel cell's current density and membrane thickness. The overall utilisation factor of the integrated system decreases from 84% to 35% with an increase in the current density and molar flow rate. Finally, this study reveals that the present integrated PEM fuel cell unit with a TEACS can be considered as an attractive and environmentally benign option for cogeneration purposes in sustainable buildings. 相似文献
13.
In this work, the fluid dynamics within a membrane‐less microchannel fuel cell is analyzed computationally. The membrane‐less design is a result of the laminar nature of the fluid flow at small Reynolds numbers, restricting the fuel and oxidant to the vicinity of the corresponding electrodes, without the need of a proton exchange membrane (PEM). However, the performance of such cells is limited by the slow diffusive mass transport near the electrodes, with a large fraction of the reactants leaving the channel without coming in contact with the catalytic surfaces, and thus not being used. We mitigate this problem through the introduction of channel surface modification consisting of angled grooves designed to create convective flows that direct the reactants toward the active surfaces. The grooved structures are optimized for maximum fuel utilization. Operation of this type of cells at Péclet numbers close to 2,500 leads to a performance doubling compared with unmodified cells. Moreover, this increase in efficiency is accompanied by a more uniform distribution of the current across the electrodes, reducing the possibility of hot spots being developed. 相似文献
14.
The effect of potential on the corrosion behavior of uncoated stainless steel SS316L as bipolar plate material in proton exchange membrane (PEM) fuel cell cathode environment is studied. Electrochemical methods, X‐ray photoelectron spectroscopy, scanning electron microscope are employed to characterize the corrosion behavior of SS316L at different polarization potentials in PEM fuel cell cathode environment. The results show that the corrosion current density of SS316L increases with the increase of polarization potential significantly. When the potential is higher than 0.7 V versus SCE, severe corrosion occurs on SS316L. The work also shed light on the corrosion mechanisms of SS316L at different potential in the PEM fuel cell cathode environment. 相似文献
15.
16.
Polymer electrolyte fuel cell systems are increasingly being used in applications requiring an inverter to convert the direct current (DC) output of the stack to an alternating current (AC). These inverters, and other time‐varying inputs to the stack such as the anode feed pressure, cause deviations from the average stack current, or ripple currents, which are undesirable for reasons of performance and durability. A dynamic fuel cell model has been developed and validated against experimental data for a 5 kW fuel cell stack, examining in detail the ripple current behaviour. It was shown that the ripple currents exceed the 2% maximum recommended value, and may lead to long‐term degradation of the fuel cell stack. 相似文献
17.
The cooling system of a high‐temperature PEM fuel cell with a nominal electric power of 1.5 kW for a combined heat and power unit (CHP) has been designed using a thermochemical model. The 1D model has been developed as a simple, predictive, and useful tool to evaluate, design, and optimize cooling systems of PEM fuel cells. As proved, it can also be used to analyze the influence of different operational and design parameters, such as the number and geometry of the channels, or the air flow rate, on the overall performance of the stack. To validate the model, predicted results have been compared with experimental measurements performed in a commercial 2 kW air‐forced open‐cathode stack. The model has then been applied to calculate the air flow required by the designed prototype stack as a function of the power output, as well as to analyze the influence of the cooling channels configuration (cross‐section geometry and number) on the heat management. Results have been used to select the optimum air‐fan cooling system, which is based on compact axial fans. 相似文献
18.
The characterization of the mechanical properties of fuel cell electrodes through the experimental techniques is a complex task due to the low thickness, constituents' heterogeneous composition, and fragile nature of the film. We present a preliminary investigation on the thermomechanical response of fuel cell catalyst layer (CL) obtained through the numerical experiment. Since the Nafion ionomer is one of the constituents' of the CL, a modified micromechanically motivated viscoplastic model is adopted to characterize the Nafion ionomer in terms of reduced density factor to account for the void content. The catalyst agglomerates are taken as inclusions in the ionomer matrix to form a composite unit which is used to plot the true stress–true strain response. Practicality of this work is tested by implementing the electrode layer as a separate component in the single fuel cell unit cell model. A remarkable difference in the magnitude of stress levels in the membrane is observed under thermal and hydrated conditions with the presence and absence of electrode layer in the simulation domain. The present work will assist in improved understanding of the localized stress distribution in the membrane, which is essential to understand its mechanical endurance. 相似文献
19.
Today there is a consensus regarding the potential of NaBH4 as a good candidate for hydrogen storage and release via hydrolysis reaction, especially for mobile, portable and niche applications. However as gone through in the present paper two main issues, which are the most investigated throughout the open literature, still avoid NaBH4 to be competitive. The first one is water handling. The second one is the catalytic material used to accelerate the hydrolysis reaction. Both issues are objects of great attentions as it can be noticed throughout the open literature. This review presents and discusses the various strategies which were considered until now by many studies to manage water and to improve catalysts performances (reactivity and durability). Published studies show real improvements and much more efforts might lead to significant overhangs. Nevertheless, the results show that we are still far from envisaging short‐term commercialisation. 相似文献
20.
This study is an evaluation of the effectiveness of the flexography printing process for manufacturing catalyst‐coated membranes (CCMs) for use in proton exchange membrane fuel cells (PEMFCs). Flexography is a maskless and continuous process that is used in large‐scale production with water‐based inks to reduce the cost of production of PEMFC components. Unfortunately, water has undesirable effects on the Nafion® membrane: water wets the membrane surface poorly and causes the membrane to bulge outwards significantly. Membrane printability was improved by pre‐treating membrane samples by water immersion for short periods (<2 min). This pre‐treatment was used to control the membrane deformation before printing to limit the impact of the ink transfer. Water and ink drop deposition experiments were performed to estimate the liquid‐air‐Nafion® apparent contact angle and the locally induced membrane deformation. Despite the short immersion times used in the tests, the immersion pre‐treatment appeared to induce structural modifications that enhanced both the membrane wettability and the dimensional stability. Flexography printability tests were performed on these treated membranes and showed that the dimensional instability of the Nafion® membrane was the critical parameter for limiting the ink transfer. The immersion pre‐treatment improved the printability of the Nafion® membranes, which were used to fabricate cathodes that were tested in an operational fuel cell. 相似文献