Fuel cell measurements

Roth C, Martz N, Buhrmester T, Scherer J, Fuess H. 2002. In-situ XAFS fuel cell measurements of a carbon-supported Pt-Ru anode electrocatalyst in hydrogen and direct methanol operation. Phys Chem Chem Phys 4 3555-3557. 

G. J. M. Janssen and M. L. J. Overvelde. Water transport in the proton-exchange-membrane fuel cell Measurements of the effective drag coefficient. Journal of Power Sources 101 (2001) 117-125. 

Unfortunately, due to technical difficulties, reference electrodes have not been widely employed in fuel cell measurements. The primary cause is the geometric restriction imposed by the thin solid electrolyte (for example, a typical electrolyte thickness is about 50, um for a Nation 112 membrane). Additional factors such as the shape and position of the reference electrode must be taken into account in order to obtain reliable and meaningful results. In reality, the requirements for a reference electrode are less stringent than expected, since the main problem is the drift of the reference potential during measurement, which can result in large error due to the strong potential dependence of the impedance. 

Figure 6.5 shows the AC impedance spectra of the same fuel cells measured at different cathodic potentials. It is evident that as the overpotential increases, the diameter of the kinetic arc decreases due to the increasing kinetic rate. At low overpotential, the kinetics dominates and only the kinetic arc appears. At high overpotentials, the low-frequency region shows additional arcs, which are associated with mass-transport limitations across the gas diffusion layer and within the catalyst layer. 

The Pt-loading goals for the DOE 2008 program will be met if the half-cell performance of the new catalysts is matched in fuel cell measurements and the catalysts prove to be stable. 

This behavior correlates with an increase in the internal resistance of the fuel cell measured at 1 Khz as the cathode oxygen flow is increased. This could be due to a loss of water from the membrane into the dry gas stream. In addition, good performance was obtained even under conditions of extremely low oxygen flow (< 0.03 L min. ) as illustrated in Figure. 2. To ensure that the... 

Pt-Sn electrocatalysts have been considered as the most active binary catalyst for the EOR, and their superior performance has been confirmed in fuel cell measurements [89-91]. Sn promotes the EOR activity of Pt and works even better than Ru. Polyol method [92, 93] and Bonneman method [94,95] were employed to synthesize alloy Pt-Sn/C and Pt-SnO c/C catalysts, and Jiang et al. [68] claimed that the greater activity was from Pt-SnO c/C due to the presence of both sufficiently... 

Strik, D.P., Ter Heijne, A., Hamelers, H.V.M., et al., 2008. Feasihihty study on electrochemical impedance spectroscopy for microbial fuel cells measurement modes data validation. Meeting Abstracts. MA2008—01 243. 

Rotating Disk Electrode and Fuel-Cell Measurements... 

From the site density Sp and the kinetic current density Jr ( t 0.8 V), one can determine the turnover frequency TOF (0.8 V), which is given in Table 16.2 for both, RDE as well as fuel cell measurements (columns G and H). 

Fuel cell measurements excellently reflect the actual performance of a catalyst and its applicability. Besides the kinetic behavior, however, the mass transport properties (proton, electron, and oxygen transport as well as water removal) and the internal resistance affect the performance in fuel cells. Thus, it becomes difficult to estimate the kinetic properties of a catalyst just from FC measurements. Rotating (Ring) Disk Electrode (R(R)DE) measurements more precisely reflect the kinetic properties (ORR activity and selectivity). Therefore, in this work also, R(R)DE measurements were taken into account. A comparison of publications showed that measurement conditions (for PEM-FC and R(R)DE) often vary considerably from one laboratory to another, which hinders a direct comparison of the different materials [7, 114, 115, 160, 165, 166, 168-171, 173, 175, 177, 196-206]. In order to enable a better evaluation, F. Jaouen initiated a cross-laboratory comparison of FC and RDE measurements for various Me-N-C catalysts [160]. In Fig. 16.20, fuel cell measurements of these catalysts are shown. 

It must be noted that those kinetic parameters depend not only on the measurement conditions, such as temperature, but also on the structures of flie catalyst. Table 3.2 lists the exchange current density of the HOR as a function of temperature on the PtRu/C anode in a real PEM fuel cell, measured and simulated by Song et al. [8] and Zhang et al. [47]. 

The polarization curve is a portrait of a fuel cell. Measuring this curve is a routine procedure performed in numerous labs worldwide. However, modeling of the polarization curve is one of the biggest challenges for fuel cell theory. 

More and more simulation studies and experiments are focused on the relationship between current density and water flooding. Although the consequences vary with the properties of fuel cells, measuring methods, and model assumptions, they have a similar trend that current density results in water production as well as water removal in electrode. The water flood is dependent upon the combined influence of these two impacts. 

On preparation of a semi-interpenetrated electrolyte membrane (HBP-PA-co-HPB-Ac membrane), phase separation took place in the membrane. The resulting film is not suitable for fuel cell measurement. Therefore, fuel cell measurement was carried out using CL-HBP(L)-PA and the CL-HBP(H)-PA membranes. 

HBP-SA, HBP-SA-Ac, HBP-PA and HBP-PA-Ac polymers, interpenetrated electrolyte membrane HBP-SA-co-HBP-Ac, and the crosslmked membranes CL-HBP-SA and CL-HBP-PA showed the VTF-type temperature dependence. These polymers and membranes are thermally stable up to 260 °C, and they had suitable thermal stability as an electrolyte in the polymer electrolyte fuel cell operating under non-humidified conditions. Fuel cell measurement using a single membrane electrode assembly cell with crosslinked membranes CL-HBP-SA and CL-HBP-PA was successfully performed under non-humidified conditions, and polarization curves were observed. The concept of the proton conduction coupled with the polymer chain motion was proposed as one possible approach toward high temperature fuel cells. 

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