Assessment of CO2 bubble generation influence on direct methanol fuel cell performance

Fuel cells fed directly by liquid methanol represent a class of suitable devices for supply portable small power applications. To become a market attractive technology some issues must be properly addressed and resolved. The presence of gaseous CO2 generated in the anode channels is the main issue as it can hinder the free surface of the Gas Diffusion Layer reducing the active area and the methanol flux through the porous media towards the catalyst layer. In this work the influence of gas phase fraction on the cell performance and the relationship with the operating parameters such as air flow rate, methanol-water solution flow rate and current density is investigated. The characterization of CO2 bubbles flow in the anode channel is carried out

Experimental measurement technique for the assessment of the fuel crossover diffusion coefficient in the membrane electrode assembly of a direct methanol fuel cell

Since the cross-over still seems to be the main issue of the direct methanol fuel cells, an experimental evaluation of the diffusive cross-over is performed. Even if the relationship of the rate through the membrane is the sum of the three terms of diffusive, osmotic and drag, the diffusive component is also present at open circuit lowering the Open Circuit Voltage of the single cell up to 50 % with respect to the Nernst potential. The goal of the research is to develop a direct measurement technique of the crossover that can provide the effective values of the parameters that characterize the membrane electrode assembly. The experimental set up consists in the pressure, flow and temperature control and acquisition using Labview. A sensitive analysis for three values of temperatures at 60°C, 65°C and 70°C is performed for first. Then, a small overpressure was generated in the cathode side by a valve located at the cathode outlet. A set of pressure were analysed for 0, 30 and 90 mbar of overpressure at the cathode. The tested fuel cell has a commercial Nafion 117 membrane and carbon paper gas diffusion layers 700 cm2 large. Preliminary results show that the differential concentration term seems to be significantly larger than the osmotic term. The diffusion coefficients are useful for fuel cell modelling and for the calibration of the operating conditions in the sensor less DMFC systems

Applications of Micro-CAES Systems: Energy and Economic Analysis☆

Abstract The present study concerns the development of a micro-CAES system for thermal and electrical energy storage for residential and non-residential users (shelter/remote users including), in order to reduce energy costs and increase the reliability of energy supply from renewable sources. The micro-CAES system allows you to store the electricity generated from renewable and conventional sources to pressure energy. Further thermal energy can be recovered from conversion process, stored and used for space heating or hot water. The micro-CAES allows you to reduce peak energy demand by utilities (peak shaving), decrease the size of the power generation devices (downsizing), reduce the power of the contract with the grid operator, size the system on the load curve power users in order to increase energy efficiency and economic sustainability reducing management costs with the advantage to reduce operating costs, use of non-toxic materials, zeroing of GHG emissions (zero emission). The innovative technology is based on high-efficiency energy storage process via storage of compressed air at high pressure, quasi-isothermal compression of a mixture air-liquid for heat storage and supply of electrical power constant during the expansion. The air-liquid mixture with excellent ratio between the phases allows you to obtain quasi-isothermal compression, with maximum compression efficiency and high thermal exchange, it enables to have a constant electrical power during the expansion, at a constant pressure during discharge. A dedicated software enables to manage the micro-CAES system to adapt its operation as a function of external conditions and user requirements. An energetic and economic analysis has been performed identifying the optimal size reference. The power supply system provides for the integration of small wind and photovoltaic with a storage system based on micro-CAES. The technological challenge is to be able to ensure a constant power level selected throughout the day

Energy and thermodynamical study of a small innovative compressed air energy storage system (micro-CAES)

There is a growing interest in the electrical energy storage system, due to the high penetration of the energy produced by renewable sources, the possibility of leveling the absorption peak of the electric network (peak shaving) and the advantage of separating the production phase from the exertion phase (time shift). Compressed air energy storage systems (CAES) are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, a result of the mathematical model created in a Matlab/Simulink® environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. This is something promising for the development of an experimental devic

Development of Improved Passive Configurations of DMFC with Reduced Contact Resistance

Abstract The Direct Methanol Fuel Cell (DMFC) represents today an appropriate solution for powering portable applications and small electronic devices, due to: 1) its compactness, 2) the high power density when compared with batteries and 3) the facility in transporting proper quantities of fuel (generally a liquid mixture of methanol and water). In order to further reduce the DMFCs size, passive configurations without external pumps and auxiliary devices are actively studied. Oxygen is supplied from the surrounding air while methanol-water solution is stored into a built-in tank in contact with the gas diffusion layer (GDL) that is constantly kept wet. Such configurations have a lower current density, roughly around 10÷30 mA/cm2, when compared with active configuration (40÷80 mA/cm2). It is then important to improve the baseline performance (power and efficiency) of such cells by optimizing all system components. Here we aim at reducing the effects of the contact resistance between GDL and current collectors by carrying out a sensitivity analysis on a number of relevant cells parameters such as:. assembly shape, gaskets, current collectors materials and open ratios. Analysis will be carried out at different molar concentrations (1 to 4 M) of the water-methanol solution used as fuel

Design and experimental set-up of hydrogen based microgrid: characterization of components and control system development

In this study, the implementation of a hydrogen microgrid is investigated, considering the integration of H2 production, storage, and energy conversion to feed a typical end-user. A remote control system has been realized through LabVIEW software, allowing to monitor real-time all the devices and analyze their performances. The integrated system is composed of a PEM electrolyzer (325 W), a storage system based on metal hydrides (two tanks, 54 g of hydrogen each, 1.08 wt%) and an energy converter (PEM Fuel Cell stack, 200 W). A programmable electronic load was used to set a power demand throughout the year, simulating an end-user. Data collected from each component of the micro-grid were used to characterize the energetic performance of the devices, focusing on the H2 production via electrolyzer, charging cycles of the H2 storage system, and energy conversion efficiency of the FC stack. Finally, the global efficiency of the microgrid is computed. Even though the system is realized in laboratory scale, this circumstance will not invalidate the significance of the configuration due to modularity of all the technologies that can be easily scaled up to realistic scales

Ship Docked in Port Emissions Assessment and Pollutant Reduction Systems by Means of Shore Power Electricity

Presentata a ECOS2007 e selezionata per pubblicazione su Energ