Polymer electrolyte membrane power plants

The key achievements at Ballard (Wilkinson 1998)15 are low Pt loading (1 mg cm-2) in 50-kW fuel cell power plants, and that of a power-to-weight ratio of 1 kW/kg. The development of the solid polymer electrolyte membrane was by no means in a final state in the late 1990s. The quality of the membrane controls the highest current density at which the cell is viable. There are open areas, too, with regard to the composition (as apart from the loading and particle size) of the catalyst a PtRu alloy... 

At present, polymer electrolyte membrane fuel cells and power plants based on such fuel cells are produced on commercial scale by a number of companies in many countries. As a rule, the standard battery version of the 1990s is used in these batteries, though in certain cases different ways of eliminating water and regulating the water balance (water management) have been adopted. 

At present, apart from the United States, polymer electrolyte membrane fuel cells and power plants on their basis are developed in many other countries including China, France, Germany, South Korea, and the United Kingdom, and so on. The major part of the power plants delivered in 2006 (about 60%) was for power supply to portable equipment. The second place (about 26%) was taken by small stationary power plants for uninterruptible power supply. 

As power supply for a variety of portable devices is one of the more important future applications of polymer electrolyte membrane fuel cells, great efforts are made at present to reduce the dimensions and weight, and to even miniaturize both the fuel-cell stack and all auxiliary equipment needed for a power plant. 

Figures for the time required for a smooth operation of polymer electrolyte membrane fuel cells (and other fuel cells used in the same applications) are given variously as 2000-3000 h for the power plants in portable devices, as up to 3000 h over a period of 5-6 years for the power plants in electric cars, and as 5-10 years for stationary power plants. Much time will, of course, be required to collect statistical data for the potential lifetime of different kinds of fuel cells. Research efforts, therefore, concentrate on finding the reasons for the gradual decline of performance indicators and for premature failure of fuel cells. In recent years, many studies have been conducted in this area.

A detailed cost analysis for a polymer electrolyte membrane fuel cell power plant of 5 kW was provided in 2006 by Kamarudin et al. According to their data, the total cost of such a plant will be about 1200 of which 500 is for the actual fuel-cell stack and 700 for the auxiliary equipment (pumps, heat exchangers, etc.). The cost of the fuel-cell stack is derived from the components as 55 /kW for the membranes, 52 /kW for the platinum, 128 /kW for the electrodes, and 148 /kW for the bipolar plates. 

The polymer electrolyte membrane (PEM) electrolysis operates at temperatures of 30-100 °C. The electrodes have platinum as a catalyst. A few industrial companies undertake strong efforts to develop this kind of electrolysis. To date, the efficiency of alkaline electrolysis has not been reached. It is expected that PEM electrolysis is suitable to build plants for small power units as well. 

Mohanapriya et al. investigated a new class of biocomposite polymer electrolyte membranes comprised of chitosan (CS) and certain plant hormones such as 3-indole acetic acid (lAA), 4-chlorophenoxy acetic acid (CAA), and 1-naphthalene acetic acid (NAA) for application in DMFCs. The permeability of the membranes to both water and methanol was studied employing MRI and volume-localized NMR spectroscopy using a two-compartment permeability ceU. A DMFC fabricated using CS-IAA composite membrane, operating with 2 mol dm aqueous methanol and air at 70 °C, delivers a peak power density of 25 mW cm at a load current density of 150 mA cm [194]. 

Major areas of application are in the field of aqueous electrochemistry. The most important application for perfluorinated ionomers is as a membrane separator in chloralkali cells.86 They are also used in reclamation of heavy metals from plant effluents and in regeneration of the streams in the plating and metals industry.85 The resins containing sulfonic acid groups have been used as powerful acid catalysts.87 Perfluorinated ionomers are widely used in worldwide development efforts in the held of fuel cells mainly for automotive applications as PEFC (polymer electrolyte fuel cells).88-93 The subject of fluorinated ionomers is discussed in much more detail in Reference 85. 

The solar-hydrogen power plant design shown in Figure 4.1 (gatefold) assumes that the RFCs will use liquid electrolytes. This is just an assumption based on the fact that on this large-scale proton-emitting solid membrane designs are not yet available. If the RFC becomes reality and its development is completed by the time this plant is built, it is possible that the liquid electrolyte will be replaced by a solid polymer. 

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