Methanol crossover effect

The electrocatalytic oxygen reduction in DMFC systems requires the development of highly selective electrodes in the presence of methanol. Present electrolyte membranes based on Nafion 117 are permeable to methanol (crossover effect), which depolarizes the platinum cathode [81,82]. For this reason, our strategy, some years ago, was to produce electrocatalytic materials from the thermal decomposition of some neutral transition-metal carbonyl compounds in the presence... 

V. A. Paganin, E. Sitta, T. Iwasita, and W. Vielstich. Methanol crossover effect on the cathode potential of a direct PEM fuel cell. J. Appl. Electrochem., 35 1239-1243, 2005. 

Metal-free nitrogen and phosphorus dual-doped, electrocatalytically active, functionalized nanocarbon (FNC) and photoluminescent carbon nanodots (PCNDs) were simnltaneonsly synthesized using a facile one pot microwave-assisted process (Prasad et al., 2013). In addition to the electrocatalytic activity, FNC also shows attractive properties as a metal-free oxygen reduction catalyst and it is resistant to methanol crossover effects in alkaline media The 5-10 nm PCNDs, exhibiting blue fluorescence nnder UV exposure were successfiilly used for bioimagrug apphca-tions. 

For DMFC systems, Pt cathodes are also used as the catalyst of choice however, given Pt s ability to reduce oxygen and oxidize methanol, this lack of selectivity makes them sensitive to methanol crossover from anode to cathode via the membrane. This methanol crossover can have a depolarizing effect on cathode performance, reducing overall cathode activity. To combat this, an extensive effort has been made to identify and develop selective oxygen/reduction catalysts unaffected by MeOH crossover. 

The reactions are just like the ones that produce polystyrene. First, a molecule of methyl methacrylate reacts with a polystyryl anion to form a methyl methacrylate anion (crossover). Then the methyl methacrylate block grows in a series of propagation steps, followed by the addition of methanol to effect termination as before. We can draw the structure for the block copolymer, named poly styrene-6/oe -methyl methacrylate) as is shown here. 

M.K. Ravikumar and A.K. Shula, Effect of methanol crossover in a liquid-feed polymer-electrolyte direct methanol fuel cell, J. Electrochem. Soc., 1996, 143, 2601-2606. 

Methanol crossover is one of the major obstacles to prevent DMFC from commercialization. This effect, which is caused by diffusion of methanol through the membrane, reduces the cell efficiency. Competing with the oxygen reduction reaction on the cathode side, methanol adsorbs on the surface of Pt and is oxidized to CO2. The main poisoning species formed during the chemisorption and oxidation of methanol is carbon monoxide... 

As evident from the i-E response, the 1.0 M solution of methanol delivered better performance at low current densities compared with all concentrations of TMM studied at 90 C. However, at very high current densities (>750 mA/cm ) the 0.5 and 1.0 M solutions of TMM shows improved performance with respect to methanol. This type of behavior was observed at a number of different ceil operating temperatures. When the effect of TMM concentration upon cell performance was investigated, it was observed that at low current densities the solutions of low fuel concentration showed less polarization, whereas at higher current densities solutions of higher concentrations showed better performance. This trend in performance is due to fuel crossover effects which dominate at low... 

As illustrated in Figs. 1.107 and 1.108, high fuel efficiencies in operating 2 X 2 -size fuel cells equipped with PSSA-PVDF membranes are obtainable, especially at lower temperatures, due to the decreased methanol crossover obsen/ed. The fuel efficiency was determined for all samples at a number of different operating temperatures and ail displayed decreasing fuel efficiency with an increase in temperature, as shown in Fig. 1.107. This effect can be attributed solely to the amount of fuel crossover occurring as a function of... 

The operating efficiency of direct methanol fuel cells is greatly lowered because of methanol crossover. This effect leads to unproductive methanol consumption and to a marked decrease in working voltage, caused by the action of methanol on the oxygen electrode potential. So far, only two options can be seen to lessen or completely... 

Du CY, Zhao TS, Yang WW (2007) Effect of methanol crossover on the cathode behavior of a DMFC a half-cell investigation. Electrochim Acta 52 5266-5271... 

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