Carbon weight loss

Comparison of BET surface area and cumulative carbon weight loss following corrosion at 1.2 V versus RHE, 1 M H2SO4, 80°C, 24 h for a range of carbon blacks. (Reprinted from S. C. Ball et al.. Journal of Power Sources, 171,18. Copyright 2007 with permission of Elsevier.)... 

Figure 3. Carbon corrosion rate versus carbon weight loss for both conventional and graphitized KB-supported Pt catalysts. The carbon corrosion rate (in units of A/g( ) is based on the measured CO2 concentration at the exit of a 50 cnr cell using a GC, assuming 4e /( (T molecule. The carbon weight loss is obtained by integrating the measured CO2 evolution rate over time. The cell is operating on neat H2/N2 (95 °C, 80% RIIjn, and 120 kPaa, s) with potential held at 1.2 Volts versus RHE.

Figure 18.9. Carbon weight loss vs. time for two different catalysts at both 0.9 V and 1.2 V and 80 °C (100% RH, 120 kPa,bs) [47]. (Reproduced by permission of ECS—The Electrochemieal Society, from Mathias ME, Makharia R, Gasteiger HA, Conley JJ, Fnller TJ, Gittelman CJ, et al. Two fuel cell cars in every garage )...

Carbon Weight loss [%] T = 100 min Weight loss [%] T = 800 min BET surface area [m /g] Carbon type... 

It was demonstrated that idle and OCV operation resulted in a 2-5% carbon weight loss after 2000 h of continuous operation while shutdown/startup cycle exhibited a 5-10% weight loss at the end of cell operation. Fuel starvation corroded carbon support quickly since greater than 25% carbon weight loss was observed during the first 100 h of cell operation. 

Fig. 1 COj concentration (solid symbols) and accumulative carbon weight loss (open symbols, integrated from the CO flux at the exit of the working electrode) as a function of time over a commercial conventional-carbon-supported membrane electrode assembly (MEA). The N -fed working electrode (50 cm min" ) was held at a potential of 1.2 V versus the H -fed counter/reference electrode (200 cm min" ) at 95°C and 80% inlet relative humidity (RHj i j). RHE reversible hydrogen electrode...

F 6 Cell voltage loss versus carbon weight loss measured at 0.8 A cm" with H /air (2 2 stoichiometric flows) at 80°C, 175kPa(abs), and 50%/50% RH. The inset shows the carbon weight loss versus time at 1.2 V (vs. RHE), 95°C, and 80% RH. KB Ketjenblack, Gr-KB Graphitized Ketjenblack, Gr-Vulcan Graphitized Vulcan XC-72C. (Reproduced with permission of Yu et aL (2006a), The Electrochemictd Society)... 

Within the 5,500 operational hours of automotive PEMFC systems, the stack could sit for a long time at idle condition, i.e., when no power is supplied to the propulsion system, and the only power drawn from the fuel cell stack is that required to support the fuel cell system andllaries (e.g., cooling pumps). This results in cathode potentials of approximately 0.90V (Mathias et al. 2005). This idle time could total over several thousand hours depending on the particular usage profile. The stack could also be at open circuit voltage (OCV) condition, where no current is drawn from the stack and the eathode potential increases to approximately 0.95 V. This can occur just before fuel ceU system shutdown, immediately after startup, as weU as in the case of battery/fuel ceU hybrid systems in which the battery provides the electrical load under low power or idle conditions. The accumulated time at OCV condition for 38,500 start/stop cycles could be over lOOh (38,500 cycles x 10 s per cycle). Figure 8 shows the predicted carbon weight loss as a function of time at these two potentials, based on the carbon corrosion... 

Fig. 8 Predicted carbon weight loss versus time at 0.90 V (idle conditions) and 0.95 V (open circuit voltage, OCV, conditions) for a commercial conventional-carbon-supported MEA at 80°C...

Fig. 10 Carbon corrosion rate versus cycle time open symbols) of a commercial conventional-carbon-supported MEA under an accelerated test condition cycles between 0.6 and 0.9 V (40 cycles per hour) at 80% RH. j and 80°C. The solid symbols are for carbon weight loss versus time, projected out to 5,500h...

Fig. 13 Allowable accumulated time resulting in 30% carbon weight loss in the anode during global starvation for a 50 wt% catalyst at a platinum and carbon loading of 0.2 mg...

As we discussed in the previous section (see Fig. 6), the cell voltage typically loses approximately 50mV at 0.8 A cm at 11 2% carbon weight loss for a variety of graphitized... 

Fig. 18 Integrated carbon weight loss (integrated from COj concentration at the erdt of the working electrode) of approximately 50wt% platinum catalysts supported on various carbon blacks as a function of time at 95°C, 1.2 V (vs. RHE), and 80%...

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