Voltage cycling

For convenience and simplicity, the electrochemical study of electrode materials is normally made in hthium/(electrode material) cells. For carbonaceous materials, a lithium/carbon cell is made to study electrochemical properties, such as capacity, voltage, cycling life, etc.. Lithium/carbon coin cells use metallic lithium foil as the anode and a particular carbonaceous material as the... 

Development for stationary applications is aimed at different specifications, but the materials development mainly coincides with that for transport applications. The operating life time for stationary fuel cells is, however, much longer than for use in cars, 40000 h or more versus 5000 h for passenger cars. Fuel cells in cars, though, will experience more voltage cycling as well as start-stop cycles. 

Fig. 14.10 Normalized ECA loss due to voltage cycling (0.5-1.0 V vs. RHE (solid) and 0.5-1.5 V vs. RHE (hollow) 50 mVs 1 scan rate) for Pt/MWCNT (square) and commercial Pt/Vulcan XC-72R (circle) (Reprinted with permission from [137] - 2010 Royal Society of Chemistry).

Fig. 14.16 ECA evolution (inset normalized ECA) for Pt supported on nitrogen-doped MC (square) and Pt supported on high surface area carbon black (circle). Operating conditions voltage cycling between 0.5 to 1.0 V vs. RHE, 50 mVs"1 scan rate, room temperature, 0.1 M HC104 (Reprinted with permission from [151] - 2012 Wiley).

Three general mechanisms have been proposed to explain the Pt ECA loss observed on steady-state and voltage cycling conditions ... 

Change in electrochemical area and oxygen reduction specific activity for Pt and PtCo cathodes during a 0.9-0.7 V voltage cycling as a function of log cycle number 900 mV, H2/O2 2/10 stoichiometry, 150 kPa j, 80°C. (S. C. Ball et al.. Electrochemical Society Transactions, 11, 1267 (2007). Reproduced by permission of The Electrochemical Society.)... 

After a few voltage cycles, the shape of the curve changes, and finally the zero curve", shown dotted in the figure, is obtained. The areas under the anodic and cathodic peaks are here equal and correspond to the transfer of one electron per TAA molecule. We assume that these reproducible peaks, whose position is independent of the pH of the electrolyte, are caused by a change in valency of the central cobalt atom. 

Three-Electrode Instruments for Polarography and Voltammetry In Fig. 5.45, if E connected to point a is a DC voltage source that generates a triangular voltage cycle, we can use the circuit of Fig. 5.45 for measurements in DC polarography as well as in linear sweep or cyclic voltammetry. An integrating circuit as in... 

Recent kinetic studies indicate that carbon corrosion can be significant under normal transient operation.56,57,60-62 The rate of voltage change, common in the automotive application, enhances cathode carbon-support corrosion.16 Hence, further model improvement shall be focused on finding the carbon corrosion kinetics associated with voltage cycling. Currently, the relationship between fuel cell performance decay and accumulated carbon-support loss is only empirical.22 More effort has to be made to incorporate mechanisms that can accurately quantify voltage decay with carbon-support loss.31,32... 

The commercial DLC must also fulfill its functional task in a wide range of conditions. For example, specifications define the superposition of the following working conditions a temperature domain defined between -40°C and 70°C, combined with a voltage cycling between 1.35 and 2.7 V, 50 G mechanical shocks, and a current intensity distribution between -0.2 and +0.2 A/F. 

Figure 8.20 (a) I-V characteristics on voltage cycling (left, off state right, on state) and (b) static I-V characteristic curves of a-GeSc2 (After Kotkata et al., 1994). 

PHASE - Part of an AC voltage cycle. Residential electrical service is 2-phase commercial facilities are usually 3-phase AC voltage. 

Semiconductor rectifiers contain at least two separate materials, a P-type and an N-type silicon semiconductor, joined together and held by conductors. With an alternating voltage across this combination, normally called a silicon diode, the electrons in the N-layer and the holes in the P-layer respond by moving in opposite directions. Figure 8.6 shows that during one half of the voltage cycle, the electrons and holes move toward the junction, and current flows. In the other half of the cycle, the electrons and holes move away from the junction, and current flow is impossible. 

Fig. 18.12 Stability measurement of various dealloyed PtCua and dealloyed PtCuCoa catalyst compared to pure Pt standard cathode catalysts in single fuel cell MEAs. The Pt-mass activities at 0.9 V are plotted before and after 30,000 voltage cycles (0.5-1.0 V, lOOmV s ). Cell conditions anode H2/cathode N2, 100 % relative humidity, 80 °C (reprint with permission from ref. [62])...

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