Fuel Cell Designs

If fuel cells could be used in transportation vehicles, it could have a major impact on worldwide consumption of petroleum. Major improvements that are needed for this to happen include increasing the efficiency of fuel cells, increasing their power density, reducing their manufacturing cost, and developing fuel cell designs capable of rapid start-up. 

Strobel R, Oszcipok M, Fasil M, Rohland B, Jorissen L, Garche J. 2002. The compression of hydrogen in an electrochemical cell based on a PE fuel cell design. J Power Sources 105 208-215. 

Contrary to traditional fuel cells, biocatalytic fuel cells are in principle very simple in design [1], Fuel cells are usually made of two half-cell electrodes, the anode and cathode, separated by an electrolyte and a membrane that should avoid mixing of the fuel and oxidant at both electrodes, while allowing the diffusion of ions to/from the electrodes. The electrodes and membrane assembly needs to be sealed and mounted in a case from which plumbing allows the fuel and oxidant delivery to the anode and cathode, respectively, and exhaustion of the reaction products. In contrast, the simplicity of the biocatalytic fuel cell design rests on the specificity of the catalyst brought upon by the use of enzymes. 

Fuel cell technology continues to advance with materials research. The catalyst material has been one of the major expenses in fuel cell design. An anode with about 40% less catalyst has been developed at Forsc-hungszentrum Julich GmbH in Julich, Germany. It has a bipolar plate with areas of different catalytic activity levels. The anode substrate has one phase that does not act as catalyst to methane-vapor reforming reactions, and another phase where it acts as a catalyst. 

One effort, being run in collaboration with the Army Research Office, has demonstrated a prototype fuel cell designed to replace in many applications a popular military standard battery. The target application is the Army s BA-5590 primary (i.e., use-once-and-dispose) lithium battery. The Army purchases approximately 350,000 of these batteries every year at a cost of approximately 100 per battery, including almost 30 per battery for disposal. Fuel cells, on the... 

Reasonable performance is exhibited by alkaline cells operated at low temperatures (room temperature up to about 70°C). This is because the conductivity of KOH solutions is relatively high at low temperatures. For instance an alkaline fuel cell designed to operate at 70°C will reduce to only half power level when its operating temperature is reduced to room temperature (20). 

Figure 6-11 IIR/DIR Operating Concept, Molten Carbonate Fuel Cell Design (42)...

Figure 8-1 Solid Oxide Fuel Cell Designs at the Cathode...

Australia Ceramic Fuel Cells Limited was demonstrated a 5 kWe laboratory prototype fuel cell system in 1997. Their system has thin sheet steel components as interconnects in a planer fuel cell design. They are currently scaling up to a 25 kWe pre-commercial stack module. 

Mehta, V, and Cooper, J. S. Review and analysis of PEM fuel cell design and manufacturing. Journal of Power Sources 2003 114 32-53. 

The need for different and novel materials as possible DLs has increased substantially in the last few years—especially with the development of new and more complex fuel cell designs. Lurthermore, the interest in small-scale fuel cells to be used as battery replacements in portable electronic devices such as PDAs, laptops, cell phones, music players, etc. has pushed the research for irmovative, inexpensive, and efficient fuel cells further [72,73]. Therefore, it is not surprising that most of the recent new DL materials are being used in micro fuel cells. 

The competition between different plate materials or plates has become more severe in recent years this is beneficial for fuel cell design and allows manufacturing companies to make a better choice. The major competition is focused on polymer-based composite plates and metal plates. As qualitatively shown in Table 5.4, each material has its advantages and shortcomings. To this end, it is difficult and also too early to make a judgment on which of these two plate materials is better. In addition, as mentioned at the beginning of this chapter, with different market applications, the fuel cells. 

For typical fuel-cell designs, mass transport through the fuel-cell sandwich occurs mainly by diffusion. The simplest way to describe diffusion is by Pick s law ... 

The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs that increase cell life without decreasing performance. 

The use of chlorine in a fuel cell system for space power applications has been suggested [100]. The CI2/H2 system is based on a proton-exchange membrane fuel cell design and is shown to give superior power and energy density when compared to conventional systems. 

Imaginative fuel-cell designs must be coupled with this materials effort. 

The ultimate goal of any diagnostic technique is to improve the design of PEM fuel cells to achieve the desired performance, durability, reliability, and cost. Thus far most species distribution research has focused on technique development and verification. A summary of the previously presented techniques is shown in Table 1. However, as the techniques continue to mature, they are providing increasing insight into improved fuel cell designs. 

Neutron imaging Two-dimensional H20 (liquid) Relatively high resolution technique, real-time data, applicable to typical fuel cell designs Need a powerful neutron source, very difficult to separate anode/cathode effects... 

Figure 10. Schematic of the segmented fuel cell design using printed circuit board (PCB) technology (with kind permission from Springer Science+Business Media 1 9 Fig. 1).

In this section we examine the primary transient phenomena that are of interest to SOFC analysis, and provide the fundamental model equations for each one. Examples for the use of these models are given in later sections. While the focus is on reduced-order models (lumped and one-dimensional), depending on the needs of the fuel cell designer, this may, or may not be justifiable. Each fuel cell model developer needs to ensure that the solution approach taken will provide the information needed for the problem at hand. For the goal of calculating overall cell performance, however, it is often that one-dimensional methods such as outlined below will be viable. 

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