Optimal design and operational tests of a high-temperature PEM fuel cell for a combined heat and power unit

Abstract

Development of new materials for polymer electrolyte membranes has allowed increasing the operational temperature of PEM fuel cell stacks above 120C. The present paper summarizes the main results obtained in a research devoted to the design, fabrication and operational tests performed on a high-temperature PEMFC prototype. A 5-cell stack has been assembled with commercial Celtec P-1000 hightemperature MEAs from BASF Fuel Cells, but the rest of elements and processes have been developed at LIFTEC research facilities. The main innovations of the present study are related to the design of the stack, and to the manufacturing and operation procedures. The novelties in the design include the flowfield geometry for both anode and cathode plates, the way in which reactant gases are supplied to the flowfield, the concept of block that eases the assembly and maintenance processes, and the heating strategy for a very fast start-up. The changes introduced to the assembly, closing and conditioning procedures are extensively described and discussed in the manuscript and contribute to the improvement in the stack performance. Results obtained in the preliminary operational tests performed are very promising, and it is expected that the 30-cells HT-PEMFC stack will deliver an electric power 2.3 times larger than the one initially predicted. A well known highly efficient technology to generate electricity and thermal energy from a single fuel source is co-generation, also known as CHP (combined heat and power). This approach can also be used in a decentralized way, improving energy efficiency, security in energy supply, and reduction of CO 2 emissions. The EU and National Governments encourage the use of micro-combined heat and power systems (µ-CHP), in order to meet international and domestic targets on carbon emissions. For example, it is expected that by 2050 µ-CHP systems could provide 30-40% of the UK electricity needs [6]. To achieve this goal, the UK Government has lowered VAT from 17.5% to 5% for households that install µ-CHP systems, and has increased the planned reduction of carbon emissions for households up to 60% by 2050. In the same way, the Dutch Government is promoting similar initiatives and made public funding available to companies developing mass-market CHP systems [7]. µ-CHPs are especially interesting for small family houses (SFH) and medium family houses (MFH), small buildings and small and medium scale enterprises (SME) due to the very low noise and vibration levels. As both electricity and thermal energy demands fluctuate seasonally and hourly in residential buildings, it is necessary to take into account operational strategies for the variations in load demands. Then, it is necessary to develop a rational method of determining the size of the systems, as well as the operational strategies throughout the year [8].As the minimum required temperature in buildings may vary between 40C and 80C, an output temperature close to 100C is a convenient value for a µ-CHP system.In this context, fuel cell...

Analysis of the performance of a passive hybrid powerplant to power a lightweight unmanned aerial vehicle for a high altitude mission

“…The operating temperature ranges from 120°C to 180°C, and no humidification for the reactant gases is needed. A detailed description of the characteristics of these MEAs can be consulted in [25,26]. In order to work at a low current density, what can enlarge its lifetime, it is formed by 50 cells with monopolar plates manufactured in graphite (1.5 mm thick for the anode plates…”

Design and manufacture of a high-temperature PEMFC and its cooling system to power a lightweight UAV for a high altitude mission

“…Following the excellent results obtained in previous studies, hydrogen and oxygen are supplied to the flowfield geometries from the back side of the plates [25]. To this end, a lowered step has been manufactured in the back side that communicates the main gas manifolds with a thin slit that connects to the inlet section of the channels of the flow-…”

“…For this reason, they are vacuum packed in factory inside individual metallic vapor barrier bags. In order to achieve the very low humidity environment required by these MEAs, the assembly zone was isolated from the rest of the room by using a commercial plastic greenhouse [25]. To decrease the relative humidity inside the greenhouse, two pipes connected to the main air pressure line were strategically placed just over the assembly table and the hydraulic press.…”

Experimental determination of the heat transfer coefficient for the optimal design of the cooling system of a PEM fuel cell placed inside the fuselage of an UAV

“…Compared to graphite elements, the use of metallic plates improves the heat transfer process and simplifies the cooling system. The sealing and reactant gas supply systems will be similar to those in a 2.5 kW HT-PEMFC stack designed as a CHP-unit [45]. Finally very light endplates will be used to close the stack, manufactured in a high-temperature resistant plastic.…”