Dynamic hydrogen reference electrode

Ktxver A, Vogel I, Vielstich W (1994) Distinct performance evaluation of a direct methanol SPE fuel cell. A new method using a dynamic hydrogen reference electrode. 

The impedance spectra of the DMFC cathode electrodes are obtained by subtracting the anode impedance from the total cell impedance. The cell impedance, ZDMFC, was obtained from normal operation of the DMFC (i.e., the cathode side was fed with air or 02 and the anode side was fed with methanol solution). The anode impedance was measured by supplying H2 to the cathode compartment, which was used as a dynamic hydrogen reference electrode. Since the impedance of the H2 electrode is negligible, the measured impedance is considered to be the anode impedance, Zanode. The cathode impedance is therefore... 

The electrochemical cell consists of a Teflon block with three interconnected cylindrical wells (See Fig. 2.2). The counter electrode is a polycrystalline nickel disk (12.54 mm diameter) cast in Kel-F and then press fitted into an orifice bored on the Teflon block. The dynamic hydrogen reference electrode, is formed by inserting a platinum wire into... 

The reference electrode used in this experiment, as already mentioned, was a dynamic hydrogen reference electrode consisting... 

Lauritzen, M., He, P., Young, A.P., Knights, S., Colbow, V., and Beattie, P. (2007) Study of fuel corrosion processes using dynamic hydrogen reference electrode./. New Mater. Bectrochem. Syst.,... 

Lauritzen, M.V., P. He, A. Young, et al. 2007. Study of fuel cell corrosion processes using dynamic hydrogen reference electrodes. ]. New Mat. Electrochem. Sys. 10 143-145. 

Lauritzen M V, He P, Young A P, Knights S, Colbow V and Beattie P (2007), Study of Fuel Cell Corrosion Processes Using Dynamic Hydrogen Reference Electrodes , Journal of New Materials for Electrochemical Systems, 10, 143-145. 

Fig. 7. Cell employed for measurements of ORR kinetics at the platinum micrpelectrode/recast ionomer interface [9]. (a) Side view (b) cross.section of cathode. W-working electrode, A-anode, R-dynamic hydrogen reference (DHE), and C-counter electrode for hydrogen electrode in DHE. (Reprinted by permission of the Electrochemical Society).

For isolating the overpotential of the working electrode, it is common practice to admit hydrogen to the counter-electrode (the anode in a PEMFC the cathode in a direct methanol fuel cell, DMFC) and create a so-called dynamic reference electrode. Furthermore, the overpotential comprises losses associated with sluggish electrochemical kinetics, as well as a concentration polarization related to hindered mass transport ... 

Hydrogen electrode — A gas electrode where purified hydrogen gas is dissolved, usually in an aqueous solution, in which an inert electrode, preferably a - platinized platinum (- platinum black, -> electrode materials) electrode is inserted. The hydrogen electrode is of exceptional importance in electrochemistry because the -> standard hydrogen electrode (SHE) provides by convention a reference potential for all half reactions and thus the thermodynamic reference point for all energy calculations. An alternative form is the -> dynamic hydrogen electrode (DHE). 

In general, the reference electrode should be (1) a reversible electrode that obeys the Nemst equation, (2) stable, and (3) able to respond quickly to changes in environmental conditions [63], The most commonly used reference electrodes for measuring the AC impedance spectra for fuel cells are the DHE (dynamic hydrogen electrode) and the RHE (reversible hydrogen electrode) [64, 65],... 

W designates the cathode ( working ) electrode, A, the anode, and R and C designate the dynamic hydrogen and the counterelectrode, respectively, for the DHE (dynamic hydrogen electrode) reference. 

The cell voltage Ucell is defined as the potential difference between the cathode and the anode. It is usually measured during fuel-ceU operation. The potential difference between the electrode and the electrolyte, which is caUed the anode or cathode potential in the following, is responsible for the electrochemical reaction occurring within the catalyst layers but cannot be measured directly. In the further text, we use electrolyte and membrane as equivalent expressions. While the electrode potential can be sensed from the bipolar plates, it is not feasible to sense the membrane potential directly, since each measurement equipment forms an interface between the membrane and the metal contact Two methods for the installation of a reference electrode within the ceU have been discussed in the Hterature, namely the reverse hydrogen electrode (RHE) [18] and the dynamic hydrogen electrode (DHE). In addition to ceU internal methods, a conventional... 

Figure 20.2 Dynamic hydrogen electrode (DHE) as reference electrode in sandwich configuration and edge configuration.

The second option is to incorporate a reference electrode, as shown in Figure 11.4. A small electrode separate from the anode is bonded onto the membrane. Pure hydrogen is fed to this reference electrode so that it behaves like a dynamic hydrogen electrode (DHE) the potential of which is 0 V. The voltage measured between the anode or the cathode and this reference electrode is the Va or the Vc. Such a cell design enables the measurement of the individual Va and Vc in a single experiment, and thus it is very useful. 

The effectiveness of EIS can be greatly enhanced with the use of a reference electrode, which has a stable potential at the time of measurement [3]. A suitable reference electrode allows discernment of the different electrode losses from the overall cell response, resulting in a more appropriate equivalent circuit. Ideally, the collective responses of the anode and cathode will add to the full cell resistance. Because the use of a stable reference electrode in many fuel cell systems is difficult, one common way to examine fuel cell behavior is the use of a dynamic hydrogen electrode (DHE). In this case, one of the electrodes is used as the DHE, with hydrogen flow at this location. It is assumed that the losses associated with the DHE are minor, and all polarizations measured can be attributed to the other electrode. This approach can be dubious and is not appropriate when there are phenomena at the DHE that can affect losses, such as anode dryout in a PEFC. Note that the DHE does not have to be the actual anode in the fuel cell but can be used at either electrode to examine the polarization of the opposing electrode. For example, a DHE can be used at the cathode of a DMFC to examine the polarization behavior of the anode in the DMFC. In this case, of course, the reaction does not galvanically proceed in the desired direction, and external power from a galvanostal/potentiostat system must be applied to drive the reaction in the desired direction. 

The most convenient and reliable electrical biasing method for use with a hydrated SPE cell has been shown to be a three electrode potentiostatic circuit which maintains the sensing electrode at a predetermined potential vs. a stable reference (1 >3.>j0e The most reversible reference is a Pt/Hp, H+, static or dynamic. In practical instruments, however, good accuracy and convenience are achieved using a large surface area platinoid metal black/air (Op). All work reported in this study utilized the air reference which has a potential of approximately +1.05 V vs. a standard hydrogen electrode (SHE). For convenience, all potentials reported are vs. the SHE ... 

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