PEM Unit Research Articles

Development and assessment of a novel multigeneration plant combined with a supercritical CO2 cycle for multiple products

Multigenerational energy conversion plants are one of the most promising solutions for tackling environmental challenges and making efficient use of energy sources. In this regard, a newly designed multigeneration plant integrated with a methane-based Brayton cycle, a steam Rankine cycle, a supercritical CO2-based Brayton cycle, a multi-effect desalination process, a PEM unit, a domestic water heater process, and two thermoelectric generators is integrated, proposed and analyzed. The thermodynamic and environmental assessments of the developed paper are conducted and examined with energy and exergy efficiencies as well as CO2 emission rate. Similarly, a parametric study is executed and reported, by the way, to define the impact of the various significant factors on the developed plant's efficiency. In the end, the CO2 emission rate is determined and compared according to different energy conversion plants. In light of the analysis results, the net power, hydrogen, and freshwater production capacities of the reference study are calculated to be 1336 kW, 0.002004 kgs−1, and 0.954 kgs−1, respectively. Additionally, it is found that the developed study's energetic and exergetic performances are 55.76% and 52.17%. According to emission analysis results, the multigeneration system emits 272.2 kg/MWh less CO2 emissions than the single energy conversion system.

On the combined Brayton-Kalina cycle with PEM hydrogen production: An exergoeconomic analysis and multi-objective optimization with LINMAP decision maker

Energy recovery and hydrogen production are essential in the current energy horizon of the globe. Applying the waste thermal energy and producing clean fuels in the power-generating cycles by keeping a sustainable view are the main goals of the current study. A combined Brayton-Kalina cycle accompanied by a PEM hydrogen production unit is studied using thermodynamic, exergetic, and economic evaluations. An external source is applied to supply the required heat for the closed Brayton cycle and the waste thermal energy is fed into the Kalina cycle. The Brayton cycle destructs more exergy than the Kalina cycle, respectively by the sharing value of 58% and 40%. The Brayton cycle shows the highest investment cost rate and the Kalina sets in the next rank. The PEM unit needs about 1% share of the total investment cost rate. A multi-objective optimization using NSGA-II algorithm is conducted to find the best operating conditions, considering the energy and exergy efficiency as well as investment cost rate function, as the objectives. The optimization makes an increase of 6% and 3% respectively in the total energy and exergy efficiency compared to the base working conditions, while it raises the investment cost rate by about 15%.

Performance analysis of an on-site hydrogen facility for fuel cell trains

Fuel cell technologies and hydrogen can represent a potential and powerful enabler for replacing traditional diesel vehicles, especially in railways. In this train of thought, the present paper aims to investigate a fuel cell hybrid powertrain for a regional route. The main powertrain components are numerically modeled and the railway operations are simulated. The results achieved, in terms of power demand, efficiency and hydrogen consumption, are discussed and they are useful for properly sizing the refueling system. As a matter of fact, the train will be fueled with compressed hydrogen, produced on-site at a hydrogen central depot, where a hydrogen refueling station is thought to be installed. The hydrogen generation unit is considered to be a PEM unit, operating at 353 K and 20 bar. The produced hydrogen is then compressed by mean of a volumetric compressor and then stored in hydrogen tank type II, at 350 bar. The dispensing scheduling is based on the daily hydrogen demand required by the fuel cell-based train route, according to the railway timetable. The system is indeed investigated from a technical point of view, proving the integration of such systems to represent a clean, sustainable, and flexible option.

Performance of unit PEM fuel cells with a leaf-vein-simulating flow field-patterned bipolar plate

This study was conducted to investigate the performance of 25-cm2-unit polymer electrolyte fuel cells, the bipolar plate of which has a flow field that simulates leaf veins. The test flow fields were serpentine, parallel, and net leaf flow fields mimicking ginkgo and dicotyledonous leaves. The maximum power density for the ginkgo flow field was 7% lower than that for the serpentine flow field, and 40% higher than that for the parallel flow field under normal operating conditions. However, the air-feeding power required by the ginkgo was only 3% of that required by the serpentine. The usable power density for the ginkgo flow field was the highest among all flow fields. Additionally, the water-removal capability of the ginkgo flow field was superior to that of the parallel and net leaf flow fields, but inferior to that of the serpentine flow field. Furthermore, the amount of water remaining in the flow field channels was found to be correlated to the length of the unit channel. Therefore, the ginkgo pattern can be considered to be an optimal flow field design for the fuel cell.

Developing the processing stages of carbon fiber composite paper as efficient materials for energy conversion, storage, and conservation

Carbon is a wonder material and has served the mankind since the inception of civilization in a variety of ways. Among its different forms, carbon fibers are especially known for their conductivity and favorable strength to weight ratio. Here the development of PAN based carbon fibers embedded in a matrix material followed by pyrolysis to form a fibrous C/C composite has been discussed. The processing of carbon paper has been divided into four steps, with the product of each stage used separately for different energy applications. (1) Carbon fiber preform has been used as a filler to achieve high strength in bipolar plates for PEM Fuel cells (energy conversion). Flexural strength of nearly 80 MPa has been achieved as compared to 40 MPa of the commercially available Schunk plate, Germany. (2) Resin impregnated preform, i.e. the Green composite paper has been employed as an energy efficient heating element (energy conservation). This has been further fabricated as a room heater, which works at <200 W of power as compared to 1–2 kW ingested by the commercial heaters. (3) The Carbonized paper, worked well as a free standing anode for rechargeable Li-ion batteries (energy storage). It delivers a discharge capacity of 225 mAh/g @ 0.2C rate with excellent cycling performance (>500 cycles). The (4) Graphitized carbon paper has proved to be an excellent electrode (anode and cathode) backing material for PEM Fuel cell. 25% hike in the peak power density of unit PEM FC has been achieved while employing CNT incorporated NPL carbon paper as compared to while using Toray carbon paper of Japan and tested under similar conditions. This in turn is attributed to the unique properties acquired by the material with subsequent processing at each stage which has been discussed in detail.

Development of multiwalled carbon nanotubes platinum nanocomposite as efficient PEM fuel cell catalyst

Multiwalled carbon nanotubes platinum nanocomposite has been prepared via chemical route by reduction of Pt salt on MWCNTs in ethylene glycol solution while refluxing in Argon atmosphere. The effect of different pH media during the reduction process on their physical and electrochemical properties, as well as on their performance in unit PEM fuel cell has been studied and further compared with the reaction carried out while refluxing in air as already demonstrated by the authors. The I-V performance of unit PEM fuel cell shows a peak Power density of 156 mW cm−2 with catalyst prepared in alkaline medium, an increase of > 110 % as compared to 72 mW cm−2 obtained while employing catalyst prepared in acidic medium and tested under similar conditions. This is attributed not only to the small particle size of reduced Pt NPs, but also to its uniform distribution when reduction is carried out in alkaline medium. This has been further explained by detail reaction mechanism under alkaline conditions.

A PEM fuel cell with metal foam as flow distributor

In this work, we report our experimental results of the PEM fuel cell with metal foam as flow distributor. These experimental results show the characteristics of the PEM fuel cell with the metal foam as flow distributor and extend our understanding of the relation between cell performance and mass transport properties into a region of parameters that the conventional PEM unit cell cannot provide. The comparison in polarization curve is made between the PEM unit cell with different metal-foam properties and the PEM unit cell with graphite flow channel plate as flow distributor. The experimental results show that the PEM fuel cell with metal foam as flow distributor possesses some unique characteristics compared with the conventional PEM unit cell with flow channel plate as flow distributor. The unique characteristics are listed in this paper with our preliminary analysis. Due to the high porosity of metal-foam (as high as 95%) plus convective flow through the metal-foam, mass transport limitation phenomenon is not as pronounced as in the case of conventional PEM unit cell with flow channel plate as flow distributor. Another interesting phenomenon is that electrical conductivity of metal-foam plays a significant role in performance, which is seldom the case in the conventional PEM unit cell with flow channel plate as flow distributor. Although there are several technical challenges to be overcome for the current form of metal-foam to replace flow channel plates, the unique mass-transport properties of metal foam plus its light weight are very attractive.

Effects of flow field design on the performance of a PEM fuel cell with metal foam as the flow distributor

In this work, we report the improvements made on the PEM fuel cell with metal foam as the flow distributor. The comparison in polarization curve is made between the PEM unit cell with different metal foam flow field designs and the PEM unit cell with graphite bipolar plate as flow distributor. The experimental results show that after using improved metal foam flow field designs, the fuel cell's performance increases. Our results show that, in the PEM unit cell with single zone metal foam, the convection is weak at side corners. Dividing the metal foam into multiple regions and using multiple inlets effectively improves gas distribution. AC impedance measurement was also performed to study impedance characteristics. The Nyquist and Bode plots confirmed that Ohmic resistance, activation resistance, and mass transfer resistance of metal foam fuel cell are all smaller than that of conventional PEM unit cell.

The experimental validation of a simplified PEMFC simulation model for design and optimization purposes

Geometric design, including the internal structure and external shape, considerably affect the thermal, fluid and electrochemical characteristics of a polymer electrolyte membrane fuel cell (PEMFC), which determines the polarization curves as well as the thermal and net power responses. In order to predict the response of PEM fuel cells according to the variation of manufacturing materials physical properties, operating and design parameters, a reliable simulation model (and computationally fast) is necessary, which accounts for the power losses due to pressure drops in the gas channels. In this paper, a simplified and comprehensive PEMFC mathematical model introduced in previous studies is experimentally validated. Numerical results are obtained with the model for an existing set of ten commercial unit PEM fuel cells. The model accounts for pressure drops in the gas channels, and for temperature gradients with respect to space in the flow direction, and current increase that are investigated by direct infrared imaging, showing that even at low current operation such gradients are present in fuel cell operation, and therefore should be considered by a PEMFC model, since large coolant flow rates are limited due to induced high pressure drops in the cooling channels. The computed polarization and power curves are directly compared to the experimentally measured ones with good qualitative and quantitative agreement. The combination of accuracy and low computational time allow for the future utilization of the model as a reliable tool for PEMFC simulation, control, design and optimization purposes.

A novel polymeric electrolyte based on a copolymer containing self-assembled stearylate moiety for lithium-ion batteries

A novel polymeric electrolyte based on a self-assembled copolymer moiety has been prepared by a simple method of photo-induced radical polymerization of a mixture consisting of stearylmethacrylate (SMA) and poly(ethylene glycol)-monomethacrylate (PEM) that dissolves LiBF 4 as the electrolytic salt. The SMA moiety work as mechanically stable backbone and the PEM unit dissolving the salts serves as ion-conducting path in the polymeric composite. Solid-state NMR measurements indicated that the resulting polymer composite consists of PEM-rich and SMA-rich phases, each of which exists within several nanometers apart. The ionic conductivity of the polymer electrolyte with the composition of PEM/SMA = 7/3 (by mass ratio) was 2.8 × 10 −5 S cm −1 at 50 °C, which was significantly higher than that of the polymer electrolyte based on cross-linked PEM copolymer without SMA.

Constructal flow structure for a PEM fuel cell

This paper introduces a model and a structured procedure to optimize the internal structure (relative sizes, spacings) and external shape (aspect ratios) of a unit PEM fuel cell so that net power is maximized. The optimization of flow geometry is conducted for the smallest (elemental) level of a fuel cell stack, i.e., the unit PEM fuel cell, which is modeled as a unidirectional flow system. The polarization curve, total and net power, and efficiency are obtained as functions of temperature, pressure, geometry and operating parameters. The optimization is subjected to fixed total volume. There are two levels of optimization: (i) the internal structure, which basically accounts for the relative thicknesses of two reaction and diffusion layers and the membrane space, and (ii) the external shape, which accounts for the external aspect ratios of a square section plate that contains all unit PEM fuel cell components. The available volume is distributed optimally through the system so that the net power is maximized. Temperature and pressure gradients play important role, especially as the fuel and oxidant flow paths increase. Numerical results show that the optimized internal structure is “robust” with respect to changes in external shape. The optimized internal structure and external shape are a result of an optimal balance between electrical power output and pumping power required to supply fuel and oxidant to the fuel cell through the gas channels. Directions for future improvements at the PEM fuel cell stack level in flow architecture (constructal design) are discussed.