T. K. Bose

Dynamic behavior of a PEM fuel cell stack for stationary applications

We discuss the behavior and performance of a proton exchange membrane fuel cell stack under fast load commutations. We present experimental results for the polarization curves, energy balance sheet, and time response of the fuel cells. Although load transients are present both in the voltage and current generated, it is found that the fuel cell system response is faster than 0.15 s to load commutations. The experimental results were also compared to the Amphlett et al. and Kim et al. models, which were found to describe the data well.

Low-pressure adsorption storage of hydrogen

Abstract The amount of gas that can be stored in an adsorption system is dictated by the nature of the adsorbent material and the operating conditions of the storage system, namely the storage pressure and temperature. This paper describes the impact of these factors on H2 storage. The discussion is based on measurements of hydrogen adsorption on commercially available and densified adsorbents. The measurements were carried out in the pressure range 1–80 atm and at different storage temperatures using a high-pressure volumetric method. The results show that the adsorption technique could provide a viable method for hydrogen storage.

Renewable energy systems based on hydrogen for remote applications

An integrated renewable energy (RE) system for powering remote communication stations and based on hydrogen is described. The system is based on the production of hydrogen by electrolysis whereby the electricity is generated by a 10 kW wind turbine (WT) and 1 kW photovoltaic (PV) array. When available, the excess power from the RE sources is used to produce and store hydrogen. When not enough energy is produced from the RE sources, the electricity is then regenerated from the stored hydrogen via a 5 kW proton exchange membrane fuel cell system. Overview results on the performances of the WT, PV, and fuel cells system are presented.

Hydrogen adsorption in carbon nanostructures

Abstract Hydrogen adsorption, (BET) specific surface area and X-ray diffraction (XRD) measurements have been performed on carbon nanofibers, intercalated and exfoliated carbon materials. Excess adsorption capacity was evaluated at equilibrium pressures and temperatures ranging from 0.1 to 10.5MPa and 77 to 295K, respectively. We find that at room temperature, carbon nanofibers can adsorb up to 0.7wt% at 10.5MPa. We observed that the presence of different nickel–copper ratios in the catalyst particles leads to change in crystalline structure and specific surface area. Furthermore, we noted that the latter can be increased by the addition of hydrogen in the organic gas during the synthesis of the nanofibers. Finally, we will discuss the hydrogen coverage per unit surface area which is substantially larger on nanostructures than on activated carbon.

Characterization of a Ballard MK5-E Proton Exchange Membrane Fuel Cell Stack

We present the results of an experimental investigation of the energy balance of a Ballard MK5-E proton exchange membrane fuel cell (PEMFC) stack. We have investigated the transient phenomena that occur during PEMFC stack warm-up, under load switching, and when the PEMFC stack is connected to a DC/AC inverter. A simple and convenient model describing the polarization curve as a function of the temperature is presented and validated by our experimental data. We also present experimental results on the increase PEMFC stack performance as a function of the current density for different oxygen concentrations of the oxidant gas.

Analytical model for predicting the performance of photovoltaic array coupled with a wind turbine in a stand-alone renewable energy system based on hydrogen

We present the results of an analysis of the performance of a photovoltaic array that complement the power output of a wind turbine generator in a stand-alone renewable energy system based on hydrogen production for long-term energy storage. The procedure for estimating hourly solar radiation, for a clear sunny day, from the daily average solar insolation is also given. The photovoltaic array power output and its effective contribution to the load as well as to the energy storage have been determined by using the solar radiation usability concept. The excess and deficit of electrical energy produced from the renewable energy sources, with respect to the load, govern the effective energy management of the system and dictate the operation of an electrolyser and a fuel cell generator. This performance analysis is necessary to determine the effective contribution from the photovoltaic array and the wind turbine generator and their contribution to the load as well as for energy storage.

Moisture effect on hydrogen storage properties of nanostructured MgH2–V–Ti composite

Abstract In this paper, we present our recent results on the effect of moisture during prolonged cycling on hydrogen storage properties of nanostructured MgH 2 hydride with V and Ti catalysts additions synthesized by ball milling. The hydrogen charge and discharge stability of the nanocomposite hydride has been tested at 300° C for up to 1000 cycles under hydrogen containing 101 ppm moisture. Between the first and the 500th or 1000th cycle, an increase of hydrogen storage capacity by about 5% is observed in dynamic and PCT measurements. This could be due to structural relaxations. While absorption kinetics remain fast, the results show a significant and systematic slow-down of the desorption rates by about a factor of two during cycling. The X-ray diffraction patterns of nanocomposite performed before and after 1000 cycles reveal that the peak shape for magnesium remains unchanged indicating that the crystal growth is negligible. This microstructural stability during cycling suggests that the decreasing desorption rate of the nanocrystalline magnesium-based composite is not induced by any internal structural modification. On the other hand, the presence of moisture in the hydrogen gas during cycling induces surface effects which most likely cause the decrease of the hydrogen discharge flow rate.

A sample translatory type insert for automated magnetocaloric effect measurements

This paper describes the development of an automated sample translatory type apparatus capable of measuring the magnetocaloric effect of potential magnetic refrigerants over the temperature range 10 to 325 K in applied fields of up to 9 T. A Quantum Design® Physical Property Measurement System has been used as the host platform. The emphasis of the design is on rapid and accurate automated measurements with field slew rates of 9 T per second. Measurement repeatabilities of ±30 mK have been achieved. Results are presented for the rare earth metals gadolinium, dysprosium and holmium, and a gadolinium-yttrium alloy.

Solubility of solids in supercritical fluids from the measurements of the dielectric constant: Application to CO2–naphthalene

A new method for the measurement of solid solubilities in supercritical fluids is described in detail. The method is based on the measurement of the dielectric constant of the saturated supercritical solution solvent–solute and that of the supercritical solvent as a function of pressure along different isotherms. Our method is simple, absolute, easy to use, and permits precise measurement of the solubility of solids in supercritical fluids. Solubilities of naphthalene in supercritical CO2 in the pressure range 12–30 MPa are reported along the isotherms 313.15, 318.15, and 323.15 K.

Gravimetric and volumetric approaches adapted for hydrogen sorption measurements with in situ conditioning on small sorbent samples

We present high sensitivity (0 to 1 bar, 295 K) gravimetric and volumetric hydrogen sorption measurement systems adapted for in situ sample conditioning at high temperature and high vacuum. These systems are designed especially for experiments on sorbents available in small masses (mg) and requiring thorough degassing prior to sorption measurements. Uncertainty analysis from instrumental specifications and hydrogen absorption measurements on palladium are presented. The gravimetric and volumetric systems yield cross-checkable results within about 0.05 wt % on samples weighing from (3 to 25) mg. Hydrogen storage capacities of single-walled carbon nanotubes measured at 1 bar and 295 K with both systems are presented.