Cordellia Sita

An outstanding effect of graphite in nano-MgH2–TiH2 on hydrogen storage performance

TiH2-modified MgH2 was prepared by high energy reactive ball milling (HRBM) of Mg and Ti in hydrogen and showed high weight H storage capacity and fast hydrogenation/dehydrogenation kinetics. However, a decrease in the reversible H storage capacity on cycling at high temperatures takes place and is a major obstacle for its use in hydrogen and heat storage applications. Reversible hydrogen absorption/desorption cycling of the materials requires use of the working temperature ≥330 °C and results in a partial step-by-step loss of the recoverable hydrogen storage capacity, with less significant changes in the rates of hydrogenation/dehydrogenation. After hydrogen desorption at 330–350 °C, hydrogen absorption can proceed at much lower temperatures, down to 24 °C. However, a significant decay in the reversible hydrogen capacity takes place with increasing number of cycles. The observed deterioration is caused by cycling-induced drastic morphological changes in the studied composite material leading to a segregation of TiH2 particles in the cycled samples instead of their initial homogeneous distribution. However, the introduction of 5 wt% of graphite into the MgH2–TiH2 composite system prepared by HRBM leads to an outstanding improvement of the hydrogen storage performance. Indeed, hydrogen absorption and desorption characteristics remain stable through 100 hydrogen absorption/desorption cycles and are related to an effect of the added graphite. The TEM study showed that carbon is uniformly distributed between the MgH2 grains covering segregated TiH2, preventing the grain growth and thus keeping the reversible storage capacity and the rates of hydrogen charge and discharge unchanged. Modelling of the kinetics of hydrogen absorption and desorption in the Mg–Ti and Mg–Ti–C composites showed that the reaction mechanisms significantly change depending on the presence or absence of graphite, the number of absorption–desorption cycles and the operating temperature.

PEMFC for aeronautic applications: A review on the durability aspects

Abstract Proton exchange membrane fuel cells (PEMFC) not only offer more efficient electrical energy conversion, relative to on-ground/backup turbines but generate by-products useful in aircraft such as heat for ice prevention, deoxygenated air for fire retardation and drinkable water for use on-board. Consequently, several projects (e.g. DLR-H2 Antares and RAPID2000) have successfully tested PEMFC-powered auxiliary unit (APU) for manned/unmanned aircraft. Despite the progress from flying PEMFC-powered small aircraft with 20 kW power output as high as 1 000 m at 100 km/h to 33 kW at 2 558 m, 176 km/h [1, 2, 3], durability and reliability remain key challenges. This review reports on the inadequate understanding of behaviour of PEMFC under aeronautic conditions and the lack of predictive methods conducive for aircraft that provide real-time information on the State of Health of PEMFCs. Highlights: The main research findings are – To minimize performance loss due to high altitude and inclination by adjusting cathode stoichiometric ratio. – To improve quality of oxygen-depleted air by controlling operating temperature and stoichiometric ratio. – Need to devise real time prediction methods conducive for determining PEMFC SoH in aircraft.

Advances in HT-PEMFC MEAs

PEM (polymer electrolyte membrane) technology has been used in low-temperature fuel cells and high-temperature fuel cells, as well as water electrolyzers, for many years. Such electrochemical devices are of great interest and importance in the establishment of the so-called Hydrogen Economy . Advancement in polybenzimidazole (PBI)-based high-temperature proton exchange membrane fuel cells (HT-PEMFCs), specifically for stationary applications, has been achieved through systematic optimization of its components. Membrane electrode assembly (MEA) is the heart of an HT-PEMFC, and the fabrication of MEA is a key step for “real” HT-PEMFC applications. A series of studies on developing high-performance MEAs for PBI or ABPBI-based high-temperature fuel cells (120–180°C) are presented in this chapter. Some critical points and perspectives on developing high-performance MEAs are also summarized.

HT-PEMFC Modeling and Design

Modeling and simulation studies of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are important in order to better understand the operational behavior of the fuel cell and its performance and lifetime. These models play important roles in the understanding and prediction of HT-PEMFC performance and durability by analyzing various crucial parameters such as species concentrations, local current densities, temperature gradients, and pressure distributions within the fuel cell. These fuel cell modeling studies are often performed at the single cell level or stack level based on specific requirements and it may be either steady-state or dynamic using isothermal or nonisothermal models. The details of the modeling and simulation studies of HT-PEMFC at fuel cell level and stack level models including thermal management and electrochemical models are discussed in this chapter.

Catalysts for High-Temperature Polymer Electrolyte Membrane Fuel Cells

Increasing the temperature of polymer electrolyte membrane fuel cells (PEMFCs) implies advantages and disadvantages in terms of material cost, performance, and degradation. Platinum (Pt) is the best catalytic material for high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) electrodes, owing to the possibility it affords of minimizing CO poisoning with temperature enhancement. Nevertheless, it involves an increase in overall cost, mainly due to the larger platinum loadings used (when compared to Pt loadings for low-temperature polymer electrolyte membrane fuel cells). On the other hand, cathodic electrocatalysts still require that the kinetics of the sluggish oxygen reduction reaction be improved. Another disadvantage associated with the use of anodic and cathodic electrocatalysts is the corrosion of both carbon supports and catalytic nanoparticles, which is promoted by the increase in temperature. In this section, the most important factors affecting the performance of these materials are described and a brief description of the state of the art in the design and use of new materials in HT-PEMFCs is presented.

Stationary HT-PEMFC-Based Systems—Combined Heat and Power Generation

A combined heat and power (CHP) system for energy generation is the most suitable stationary application for fuel cells. High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC)-based fuel cell CHP (FC-CHP) systems, owing to their high operating temperatures, have simpler layouts for auxiliary devices and can operate on reformate with relatively high CO content. The most suitable application of HT-PEMFC technology is in systems where utilization of heat is essential. This makes HT-PEMFC perfect for FC-CHP applications in which electrical energy and heat are produced in a cogenerated manner, enhancing the total efficiency of the overall system. Currently a few HT-PEMFC-based FC-CHP systems are being deployed worldwide and the results of preliminary validation are promising for the technology’s potential commercialization in the near future.