• Energy Research

One of the main problems in electrochemical hydrogen pumps is the transport of protons, water retention and hydrogen crossover through the membrane. Considering prospects for an electrochemical hydrogen compression system, in this work, membranes based on Sulfonated Poly (Ether-Ether Ketone) (SPEEK) were made and modified with Halloysite nanotubes (HNT) and Halloysite nanotubes impreg- nated with phosphotungstic acid (PWA/HNT30)15. These modified membranes were physicochemically characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found that the nanotubes were suc- cessfully incorporated by impregnating the heteropolyacid on the nanotubes. In addition, the membranes were characterized by swelling (area and volume) and WUp, obtaining a slight decrease in these values. In contrast, the proton conductivity was increased by 42% and 88% for the membranes impregnated with HNTs and (PWA/HNT30)15, respectively. Finally, the membranes were evaluated in a hydrogen pumping system, and lower energy consumption at j = 0.4 A cm-2 has been obtained.

Abstract An investigation of properties and operating parameters of a passive DMFC monopolar mini-stack, such as catalyst loading and methanol concentration, was carried out. From this analysis, it was derived that a proper Pt loading is necessary to achieve the best compromise between electrode thickness and number of catalytic sites for the anode and cathode reactions to occur at suitable rates. Methanol concentrations ranging from 1 M up to 10 M and an air-breathing operation mode were investigated. A maximum power of 225 mW was obtained at ambient conditions for a three-cell stack, with an active single cell area of 4 cm 2 , corresponding to a power density of about 20 mW cm −2 .

Transportation and portable applications already use hydrogen as fuel, but it is essential to use highly-efficient hydrogen storage methods to increase its usage in the future. The compressed form is the most utilized for transportation applications, but mechanical compressors have low efficiency when compressing low quantities of gas to high pressure. The most suitable device for hydrogen compression is the Electrochemical Hydrogen Compressor (EHC). It has the same structure as a Proton Exchange Membrane Fuel Cell (PEM-FC), but it works at very high-pressure ( 700 bar). The present work analyses the monopolar plate of an Electrochemical Hydrogen Compressor prone to hydrogen embrittlement. Irregular shape variations generate peaks of stress magnitude and triaxiality, further contributing to decreasing metal ductility at the local scale. The calculation of the stress field in such components is essential due to the possibility of failure due to the material embrittlement caused by hydrogen. The paper presents a conceptual design of an EHC operating at 700 bar and focuses on the shape and the mechanical stress of the end-plates to have conservative levels of the nominal stress states, which then are taken as the design parameter for providing adequate structural integrity and mechanical reliability to the component. The FEM analysis with Marc software—of MSC Software Corporation—identified the optimal end-plates configuration in circular plan view and active area. The plate, sized to have a deflection no greater than 0.1mm when the EHC works at 700 bar, should have the minimum thickness of 17 mm.

Two designs of flow fields/current collectors for a passive direct methanol fuel cell (DMFC) monopolar three-cell stack were investigated. The first one (A) consisted of two plastic plates covered by thin gold film current collectors in the area of electrodes with a distribution of holes through which methanol (from a reservoir) and air (from ambient) could diffuse into the electrodes. The second design (B) consisted of thin gold film deposited on the external borders of the fuel and oxidant apertures where the electrodes were placed in contact. A big central hole allowed a direct exposure of electrodes to ambient air (for the cathodes) and methanol solution (for the anodes). An investigation of the performance and discharge behaviour of the two designs was carried out. The advantages and disadvantages of each configuration were analysed. Similar performances in terms of maximum power were recorded; whereas, better mass transport characteristics were obtained with the design B. On the contrary, open circuit voltage (OCV) and stack voltage at low current were higher for the design A as a consequence of lower methanol cross-over. A longer discharge time (17 h) with a unique MeOH charge was recorded with design B at 250 mA compared to the design A (5 h). This was attributed to an easier CO2 removal from the anode and better mass transport properties.

CNR-ITAE is involved in projects related to hybrid electric fuel cell vehicles, in which different powertrain configurations (from FC full powertrain to range extender) have been evaluated, in terms of the energy flows and system components size. The principal aim is to develop fuel cell-battery hybrid powertrains to be used in vehicles designed for some niche markets. A traction battery pack, a starting battery pack, a fuel cell power module and the combination of a parallel fuel cell-battery hybrid system have been tested. In this latter configuration, the fuel cell is used as main power source for the powertrain, also providing battery charge. The battery has the role to provide peak power during the starts of the vehicle. The hybrid powertrain has shown a fast response even at extreme and impulsive loads and a wider range compared to a battery vehicle, without compromising the weight limitations on the vehicles.

The knowledge of the electrochemical processes inside a Fuel Cell (FC) is useful for improving FC diagnostics, and Electrochemical Impedance Spectroscopy (EIS) is one of the most used techniques for electrochemical characterization. This paper aims to propose the identification of a Fractional-Order Transfer Function (FOTF) able to represent the FC behavior in a set of working points. The model was identified by using a data-driven approach. Experimental data were obtained testing a Proton Exchange Membrane Fuel Cell (PEMFC) to measure the cell impedance. A genetic algorithm was firstly used to determine the sets of fractional-order impedance model parameters that best fit the input data in each analyzed working point. Then, a method was proposed to select a single set of parameters, which can represent the system behavior in all the considered working conditions. The comparison with an equivalent circuit model taken from the literature is reported, showing the advantages of the proposed approach.

CNR-ITAE is developing several hydrogen and fuel cell demonstration and research projects, each intended to be part of a larger strategy for hydrogen communities settling in small Sicilian islands. These projects involve vehicle design, hydrogen production from renewable energy sources and methane, as well as implementation strategies to develop a hydrogen and renewable energy economy. These zero emission lightweight vehicles feature regenerative braking and advanced power electronics to increase efficiency. Moreover, to achieve a very easy-to-use technology, a very simple interface between driver and the system is under development, including fault-recovery strategies and GPS positioning for car-rental fleets. Also marine applications have been included, with tests on PEFC applied on passenger ships and luxury yacht as power system for on-board loads. In marine application, it is under study also an electrolysis hydrogen generator system using seawater as hydrogen carrier. For stationary and automotive applications, the project includes a hydrogen refuelling station powered by renewable energy (wind or/and solar) and test on fuel processors fed with methane, in order to make the power generation self-sufficient, as well as to test the technology and increase public awareness toward clean energy sources. © 2008 International Association for Hydrogen Energy.

This work focused on the modelling of latent heat thermal energy storage systems. The mathematical modelling of a melting and solidification process has time-dependent boundary conditions because the interface between solid and liquid phases is a moving boundary. The heat transfer analysis needs the interface position over time to predict the temperature inside the liquid and the solid regions. This work started by solving the classical two-phase (one-dimensional) Stefan problem through a Matlab implementation of the analytical model. The same physical problem was numerically simulated using ANSYS FLUENT, and the good match of analytical and numerical results validated the numerical model, which was used for a more interesting problem: comparing three different latent heat TES configurations during the discharging process to evaluate the most efficient in terms of maximum average discharging power. The three axial heat conduction structures changed only for the fin shape (rectangular, trapezoidal and fractal), keeping constant the volume fractions of steel, aluminium and PCM to perform a proper comparison. Results showed that the trapezoidal fin profile performs better than the rectangular one, and the fractal fin profile geometry was revealed as the best for faster thermal exchange when the solidifying frontier moves away from the steel ring. In conclusion, the average discharging power for the three configurations was evaluated for a time corresponding to a reference value (10%) of the liquid fraction: the rectangular fin profile provided 950.8 W, the trapezoidal fin profile 979.4 W and the fractal fin profile 1136.6 W, confirming its higher performance compared with the other two geometries.