Portable fuel cells operation

The net result of these polarizations is that fuel cells generally operate between 0.5 and 0.9 V DC. Fuel cell performance can be increased by increasing cell temperature and reactant partial pressure. However, for small or portable fuel cells, operation at ambient conditions is usually a requirement, particularly when the fuel cell is to be used as a replacement for batteries. 

In addition to these smaller applications, fuel cells can be used in portable generators, such as those used to provide electricity for portable equipment. Thousands of portable fuel cell systems have been developed and operated worldwide, ranging from 1 watt to 1.5 kilowatts in power. The two primary technologies for portable applications are polymer electrolyte membrane (PEM) and direct methanol fuel cell (DMFC) designs. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

The 1 kW Portable fuel cell generator is a fully automated power system that converts hydrogen fuel and oxygen from the air directly into D. C. electricity. Water is the only by-product of the reaction. This fuel cell generator that operates at low pressures provides reliable, clean, quiet and efficient power. It is small enough to be carried to where ever power is needed. The BallardF 1 kWfuel cell generator provides DC electricity when used directly and AC electricity when used in conjunction with... 

This picture shows the Ballartf 100-Watt portable fuel cell system. The " ambient fuel cells systems that operate at low pressures provide reliable, clean, quiet, and efficient power. They are small and rugged enough to be carried or transported to wherever power is needed The words in italics were supplied by Ballard Power Systems Inc. 

Thus it is a technical challenge that a system with portable fuel cell remains within allowable operating temperatures. 

There have recently been some indications, particularly from Japan, that portable fuel cells for use in laptop computers, cell phones, and other small devices may appear on the market in the near future. However, even if such fuel cells become available, the area does not appear to offer many employment opportunities for Texas community and technical college graduates. Since these fuel cells will imdoubtedly be discarded after use, there will be no jobs related to their installation, maintenance, or operation, and it does not appear that any manufacturing facilities wiU be located in Texas. 

Farhad and Hamdullahpur (2010) propose a novel portable fuel cell plant fueled by ammonia. In this plant a solid-oxide fuel cell (SOFC) stack consisting of anode-supported planar cells with an Ni-YSZ anode, YSZ electrolyte, and YSZ-LSM cathode is used to generate electric power. An ammonia cylinder with a capacity of 0.8 L is sufficient to sustain full-load operation of the portable system for 9 hours and 34 minutes. Computer simulation of this system predicts that for a 100-W portable device operating at a voltage of 25.6 V (a single-cell voltage of 0.73 V), an energy efficiency of 41.1% and a fuel utilization ratio of 80% are attainable. 

DMFC offers a low-cost, portable, reliable fuel cell operating at moderate temperatures not exceeding 100°C and under one atmospheric pressure. It uses dissolved fuels, such as CH3OH, which are fairly inexpensive and available without any restriction. A dissolved fuel cell contains a mixture of the usual alkaline aqueous electrolyte and a soluble cheap fuel. The electrodes must show different specific catalyst activities to produce voltage. The cell must contain a highly... 

The 50-Watt and 100-Watt portable fuel cell systems, illustrated in Fig. 43.11, are designed for military field use. The figure shows the units operating and reeharging batteries of military radios in the field. 

Each appheation requires a different fuel supply system and operating temperature for the required power density. In addition, their target costs will be different For example, automobile fuel cells should aim to reduce the cost of the current fuel cell system by hundreds of times to compete with mature internal combustion engines, and portable fuel cells can compete economically with current Uthium ion batteries. 

The portable device can be used at a low temperature, less than 60°C, although automobile or stationary fuel cells operate at above 70 or 80°C. The durability requirements are also different Therefore, we must systematically design a different polymer electrolyte membrane for each application. In most cases, a new polymer electrolyte is made and then the fuel cell performance is tested. However, we are proposing a systematic design methodology for the membrane to suit each application. 

Some of the user-specific requirements for portable applications are as follows quick tum-on and -off capability, responsive to dynamic variation in power needs of the device, compact, lightweight, and suitable for operation over a wide range of ambient temperature and humidity conditions. Additionally, portable fuel cells are expected to operate safely, providing power without exposing users to hazardous or unpleasant emissions, high temperature, and low noise. 

Example 2.4 Stoichiometry and Utilization Consider a portable 20 cm active area fuel cell operating steadily at 0.75 V, 0.6 A/cm. The fuel utilization efficiency is 50%, and the cathode stoichiometry is 2.3. The fuel ceU is expected to run for three days before being recharged. The cathode operates on ambient air, and the anode runs off of compressed hydrogen gas. 

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