Relative maximum power density

In order to extend the fuel cell performance analysis to a wider range of Nafion-based membranes the maximum power density (MPD) and the relative maximum power density (RMPD), defined as the ratio between the maximum power density of the Nafion composite and the maximum power density for the cell using pure Nafion pure will be used. Although the literature data for MPD is more abundant than for methanol crossover current, only works reporting a reasonable power density over the corresponding temperature range have been included in Table 6.3,... 

Benicewicz s group also prepared a modified PPA process for PA-doped PFCB-PBI membrane (Figure 5.7) preparation. In the modified PPA process, polymerization of PFCB-PBI takes place at 140 C. To control the concentration of final polymer, a fixed amount of PA was added at the end of the reaction, then the temperature was increased to 200 C for 24 h. Hydrolysis of PPA to PA took place under controlled conditions (25 C and relative humidity of 55% for 24 h), and at the same time, membranes were formed [37]. At room temperature, proton conductivity of the PFCB-PBI membrane was 0.01 S/cm, and at 140 C, it was 0.12 S/cm without humidification. Although PA doping levels ( 50 PA/RU) were higher, its proton conductivity was lower compared to the other PBI membranes prepared by the PPA process (para-PBl, -0.20 S/cm, -40 PA/RU at 140 C) [13]. The maximum power densities of fuel cells with PA-doped PFCB-PBI membranes were 0.21 W/cm (H2/O2) and 0.15W/cm (H2/air) at 140 C. It was lower compared to para-PBl membranes prepared by the PPA process (maximum power density reached 0.9W/cm at approximately 2.0A/cm, 160 C, atmospheric pressure, H2/O2) [37]. 

The relatively higher concentration of proton carriers results in more efficient proton transfer through separators and higher power density [3]. Kim et al. reported higher maximum power density for AEM (610 mW m ) than by the Nafion (514mWm ) and CEM (480mWm ) [84]. The power density was further increased to 728 mW m with AEM cathode and 200 mM PBS in a tubular MFC [90]. 

Similarly, Bae et al. [60] compared the propylsulfonated and butylsul-fonated PBIs, shown in Fig. 9, in conductivity and fuel cell tests. In conductivity tests, the butylsulfonated-PBI exhibited a higher conductivity ( 3 X 10 S cm 90 °C, 100% RH) than propylsulfonated-PBI ( 10 S cm , 90 °C, 100% RH) and was able to maintain acceptable conductivities up to 160 °C. The propylsulfonated-PBI had relatively low overall conductivity, perhaps because of the rigidity of the shorter alkyl spacer. Fuel cell performance (ambient pressure, H2/O2) of the butylsulfonated-PBI was moderate compared to Nation systems. Under testing conditions of 80 °C and 100% RH, at a current density of 0.20 A cm , the voltage was 0.45 V. The maximum power density of 200 mW cm was achieved at 0.7 A cm and 0.3 V. 

Accdg to Ref 14, p 68 Ref 26a, p 5-21, " the total work capacity of an explosive is a fun ction of the total available heat liberated at the instant of detonation, but its power is determined by the rate at which the heat energy is liberated. In the past, measurement was made of the maximum pressure developed by detonation and this was considered an expression of the work function of the explosive. However, such tests were made with explosive charges having relatively low loading density values and it was then necessary to calculate by extrapolation the pressure produced by an explosive in its own volume... 

If the (averaged) power density of the laser was below about 30 pW pm no transition of a-S to p-S could he induced. Then, a-S was observable up to 15 GPa, the maximum pressure in the experiments, even if the laser fight was of relatively high energy (488 nm) [205]. 

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