Fuel cell design for multiple applications

Application and performance requirements of fuel cells

In rare cases, fuel cells are required to meet specific key performance parameters, such as reliability, power output capacity and life. In this case, the battery designer will try to meet these key performance specifications, but rarely meet other performance requirements. Sometimes a specific application requires that fuel cells must meet these key performance requirements in harsh working environments.

  1. Application of fuel cell in battery

Fuel cells will be most useful for applications where reliability and continuous power output are critical. The battery company in Philadelphia is a pioneer in developing alkaline, low-temperature, H2-O2 batteries for this specific application. The company adopts microporous electrodes with high electrochemical activity, excellent mechanical strength and high conductivity. The electrodes used do not spontaneously ignite, so they can be exposed to the air without any damage. It has been proved that these batteries can operate at a current density of 2.5ma/cm ² When working continuously for more than 25000h, the current density is 70ma / cm ² The current density is 200 MA / cm for more than 6000h ² More than 4000 H.

These continuous working hours clearly demonstrate its high reliability and minimum maintenance requirements. As mentioned, both electrodes are made of porous nickel. The hydrogen electrode contains palladium silver catalyst, and the oxygen electrode contains silver nickel catalyst. A coaxial H2-O2 fuel cell has been designed, developed and tested for more than thousands of hours. This special fuel cell has shown more than 1kW / ft ² Power density, while reliability and electrical performance are not damaged.

  1. Hydrogen based double skeleton catalyst (DSK) electrode and double skeleton catalyst fuel cell working under harsh conditions

The fuel cell of DSK system can use solid electrolyte, such as high brittle nickel alloy. This nickel alloy was prepared by melting 50% aluminum and 50% nickel by mass. The remaining particles found in the metal powder consist of nickel with a large inner surface. Metal powders can be pressure sintered to form electrodes of appropriate shape and size. Such electrodes provide sufficient mechanical stability, excellent conductivity and significant thermal conductivity. In order to solve the sensitivity of poisoning, it is necessary to introduce a macro skeleton for mechanical support and conductive heat conduction. The micropores of the macroskeleton contain catalyst particles, which are bonded through a diffusion process to maintain catalytic activity. The alloy used here is composed of uniform aluminum grains with purity higher than 99.8% (by weight). The nickel anode is melted in a carbon crucible under the protective layer of calcium chloride (CaCl2) at a temperature higher than 1300 ℃. Fuel cells using hydrogen based DSK electrodes with fine porous coatings have the best performance in terms of current density and polarization voltage.

DSK based fuel cell with single layer DSK electrode. The performance of DSK based hydrox fuel cell with layer DSK electrode is a function of operating temperature. Polarization voltage and power density of oxygen and hydrogen electrodes (w / cm) ²)、 Current density (MA / cm) ²) The characteristics are strictly dependent on the operating temperature. The experimental test data of different designers show that the oxygen electrode has a limited polarization voltage even when the current is zero. The experimental data also show that the polarization can be reduced to 100mV at 85 ℃. The battery reaches a reversible potential of 1.23V. The conversion efficiency of the battery from chemical energy to electric energy can be measured by the product of voltage ratio and charging ratio. 92% of the total efficiency can be achieved even if the current density is zero. The voltage and efficiency decrease with the increase of current density. If the discharge voltage is maintained at 50% of the battery electromotive force, this specific battery design is exactly 0.65v, and it is possible to obtain the maximum output power from the battery. The voltage at this terminal, even when the maximum current density is 500mA / cm ² When, a 1mm thick electrolyte layer of potassium hydroxide is used, and an airtight electrode is used at the working temperature of 68 ° C, with a current density of about 250mA / cm ², The calculated power density is about 154mw / cm ²。 The preliminary calculation using the appropriate values of the included parameters shows that the specific battery assumes the weight of each electrode and 2G / cm of 1mm without any accessories ² The power weight ratio of potassium hydroxide (KOH) layer is about 77 MW / g.

Some key design aspects of fuel cells need to be highlighted. The fuel can be a mixed gas and the oxidant can be oxygen. Generally, fuel and oxidant electrodes are made of a typical catalytic porous nickel with a thickness of about 0.028in [1]. If the battery uses alkaline electrolyte, it should be kept at a thickness of 0.030 in and can withstand 100 Ib / in ² Or above the pressure difference in asbestos or similar porous grids. If high reliability and long continuous working time are the main design requirements, the battery stack and sufficient structural support for the module must be carefully considered. The H2-O2 fuel cell using DSK electrode and alkaline electrolyte provides the most effective and reliable electrochemical conversion with the lowest cost and complexity. The performance characteristics of h2-o2dsk battery with alkaline electrolyte at ambient temperature are summarized in table 3.3.

These results show that with the increase of current density, the terminal voltage decreases, but the power output level increases. At higher current density, the drop of terminal voltage is due to the resistance loss in the circuit.

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