Carbon single cell performances

Liu et al. prepared carbon-supported zirconium oxynitride (ZrO jNy/C) by ammonolysis of carbon-supported zirconia (Zr02/C) at 950°C [81]. The onset potential of the TxO ylC for the ORR was 0.7 V vs. RHE, and the four-electron pathway for the ORR was achieved on the surface of the ZrO cN3,/C. The maximum power density of the single cell using the ZrO N C as a cathode at 80°C was 50 mW cm, which was much lower than that of a single ceU using commercial Pt/C as a cathode. The enhancement of the catalytic activity is required to obtain a superior single cell performance. 

In PEMFCs, Ralph et al. [86] tested a Ballard Mark V single cell with two different DLs a carbon cloth (Zoltek PWB-3) and a carbon fiber paper (Toray TGP-090) all the other operating conditions stayed the same for bofh cases. It was observed that the carbon cloth demonstrated a distinct advantage over the CFP at high current densities (>600 mA/cm ), while at low current densities both DLs performed similarly. If was claimed fhaf this was because the CC material enhanced mass transport properties and improved the water management within the cell due to its porosity and hydrophobicity. 

Figure 6.15. Influence of GDL pore-former content on cell performance of a H2/02 single cell (0) 0 mg/cm2, (o) 3 mg/cm2, ( ) 5 mg/cm2, (A) 7 mg/cm2, and (V) 10 mg/cm2 pore-former loading 5 mg/cm2 carbon loading in the GDL and 0.4 mg Pt/cm2 in the catalyst layer [15]. (Reprinted from Journal of Power Sources, 108(1-2), Kong CS, Kim DY, Lee HK, Shul YG, Lee TH. Influence of pore-size distribution of diffusion layer on mass-transport problems of proton exchange membrane fuel cells, 185-91, 2002, with permission from Elsevier and the authors.)...

Figure 3.51. Single PEM fuel cell performance. Current-voltage relationship (open symbols) and implied power density (filled symbols), are shown for different operational temperatures in the range of 45-90°C, for a cell with a catalyst layer with incorporated PTFE (polytetrafluoroethene) to reduce water flooding, a low loading of a carbon-supported Pt catalyst layer (120 pg Pt cm ) and finally Nation intrusions. (From Z. Qi and A. Kaufman (2003). Low Pt loading high performance cathodes for PEM fuel cells. /. Power Sources 113,37-43. Used with permission from Elsevier.)...

It is worth noting that the remarkable effect described for the carbon support porosity on the metal utilization factor and hence on the specific electrocat-alytic activity in methanol electrooxidation was only observed when the catalysts were incorporated in ME As and measured in a single cell. The measurements performed for thin catalytic layers in a conventional electrochemical cell with liquid electrolyte provided similar specific catalytic activities for Pt-Ru/C samples with similar metal dispersions but different BET surface areas of carbon supports [223]. The conclusions drawn from measurements performed in liquid electrolytes are thus not always directly transferable to PEM fuel cells, where catalytic particles are in contact with a solid electrolyte. Discrepancies between the measurements performed with liquid and solid electrolytes may arise from (1) different utilization factors (higher utilization factors are usually expected in the former case), (2) different solubilities and diffusion coefficients, and (3) different electrode structures. Thus, to access the influence of carbon support porosity... 

Amperometric detectors are easily miniaturized with preservation of performance, since their operation is based on reactions at the electrode surface. Using a single carbon fiber or microelectrode as a working electrode allows detector cells of very small volume and in-column detectors to be constructed for use in open tubular and packed capillary column liquid chromatography [189-192]. These microcolumn separation techniques combined with amperometric detection are exploited for the quantitative analysis of volume-limited samples such as the contents of single cells [193,194]. 

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