Dissolved fuel cells

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 electrocatalytic oxidation of methanol has been widely investigated for exploitation in the so-called direct methanol fuel cell (DMFC). The most likely type of DMFC to be commercialized in the near future seems to be the polymer electrolyte membrane DMFC using proton exchange membrane, a special form of low-temperature fuel cell based on PEM technology. In this cell, methanol (a liquid fuel available at low cost, easily handled, stored, and transported) is dissolved in an acid electrolyte and burned directly by air to carbon dioxide. The prominence of the DMFCs with respect to safety, simple device fabrication, and low cost has rendered them promising candidates for applications ranging from portable power sources to secondary cells for prospective electric vehicles. Notwithstanding, DMFCs were... 

Electrolyte dissolved fuel alkaline fuel cells, 12 216 Electrolytes AFC, 12 215 aqueous, 9 591-593 batteries, 3 415-418 in continuous saponification, 22 738 defined, 3 409... 

Electrolytes are ubiquitous and indispensable in all electrochemical devices, and their basic function is independent of the much diversified chemistries and applications of these devices. In this sense, the role of electrolytes in electrolytic cells, capacitors, fuel cells, or batteries would remain the same to serve as the medium for the transfer of charges, which are in the form of ions, between a pair of electrodes. The vast majority of the electrolytes are electrolytic solution-types that consist of salts (also called electrolyte solutes ) dissolved in solvents, either water (aqueous) or organic molecules (nonaqueous), and are in a liquid state in the service-temperature range. [Although nonaqueous has been used overwhelmingly in the literature, aprotic would be a more precise term. Either anhydrous ammonia or ethanol qualifies as a nonaqueous solvent but is unstable with lithium because of the active protons. Nevertheless, this review will conform to the convention and use nonaqueous in place of aprotic .]... 

A schematic of a typical fuel-cell catalyst layer is shown in Figure 9, where the electrochemical reactions occur at the two-phase interface between the electrocatalyst (in the electronically conducting phase) and the electrolyte (i.e., membrane). Although a three-phase interface between gas, electrolyte, and electrocatalyst has been proposed as the reaction site, it is now not believed to be as plausible as the two-phase interface, with the gas species dissolved in the electrolyte. This idea is backed up by various experimental evidence, such as microscopy, and a detailed description is beyond the scope of this review. Experimental evidence also supports the picture in Figure 9 of an agglomerate-type structure where the electrocatalyst is supported on a carbon clump and is covered by a thin layer of membrane. Sometimes a layer of liquid water is assumed to exist on top of the membrane layer, and this is discussed in section 4.4.6. Figure 9 is an idealized picture, and... 

It is usual to operate an aqueous-medium fuel cell under pressure at temperatures well in excess of the normal boiling point, as this gives higher reactant activities and lower kinetic barriers (overpotential and reactant diffusion rates). An alternative to reliance on catalytic reduction of overpotential is use of molten salt or solid electrolytes that can operate at much higher temperatures than can be reached with aqueous cells. The ultimate limitations of any fuel cell are the thermal and electrochemical stabilities of the electrode materials. Metals tend to dissolve in the electrolyte or to form electrically insulating oxide layers on the anode. Platinum is a good choice for aqueous acidic media, but it is expensive and subject to poisoning. 

What happens electrochemically when this contact occurs It is clear that an electrochemical cell is formed. One can see that it will be a kind of fuel cell. The Fe wire will tend to dissolve anodically (Fe —> Fe + 2e) and the 02 will tend to be reduced cathodically on the Hg (Oz + 4H+ + 4e —t 2HzO). 

Because of its significance to fuel cell technology and air-depolarized batteries, the cathodic reduction of oxygen dissolved in aqueous electrolytes has been the subject of numerous mechanistic studies. They had been reviewed repeatedly (103-111), and today the mechanistic details are well... 

With a Pt/metal ratio from 1 1 to 5 1, V, Hf, Zr, Nb, and Ta had been tried. All these metals are nonnoble and are expected to be dissolved in phosphoric acid in the fuel cell under operation conditions. The initially used binary alloys are indeed not stable enough, and the catalyst loses its enhanced catalytic activity during several thousand hours of operation. Recently it was detected and claimed that tertiary and quarternary alloys that contain chromium are remarkably much more stable than the binary alloys, so that the aim of 40,000 hr of operation, which is the usually assumed lifetime for phosphoric acid fuel cells, can be achieved. 

The combustion of coal and oil to make electricity produces S02, which reaches the atmosphere and is the primary cause of acid rain. Dissolved S02 could instead be used to make electricity in a fuel cell process ... 

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