Electrochemically active area

Because this design has relatively low power density, recent work has focused on a monolithic SOFC, since this could have faster cell chemistry kinetics. The very high temperatures do, however, present sealing and cracking problems between the electrochemically active area and the gas manifolds. 

Generally, the absolute magnitude of Q is not as important as the ratio leak rate to the total flow rate Qieaf/QtotJ. The leakage rate given by Equation (5.4) is the volume flow rate at the temperature and pressure of the leakage flow, and must be corrected to standard conditions for comparison with reactant feed rates. The total required flow rate of fuel or air to the stack is proportional to the stack current, which increases with the electrochemically active area and is inversely proportional to the cell area specific resistance (R"). 

The local clamping pressure on the MEA can be much higher than the nominal clamping pressure. The ribs of flow channels on the flow plate reduce the effective contact area with the MEA. In a cross-flow arrangement, the contact area is only 25% of the electrochemical active area of the MEA. Figure 2 shows a checker board pattern formed on a pressure sensitive film inserted into a single cell assembly. The pattern shows the non-uniformity of the clamping pressure distribution on the active area of the MEA. 

Detailed investigation of ORR kinetics under subzero temperature showed that the fundamental ORR kinetic mechanism remains unchanged over a wide temperature range down to -40°C. The low-temperature CV detected the loss of cathode catalyst electrochemical active area during cold start, part of which was recovered at room temperature, while others were not recovered until higher temperature ( 70°C) operation. 

The pore/solid phase is further distinguished as transport and dead phase. The basic idea is that a pore phase unit cell surrounded by solid phase-only cells does not take part in species transport and hence in the electrochemical reaction and can, therefore, be treated as a dead pore and similarly for the electrolyte phase.25 The interface between the transport pore and the transport electrolyte phases is referred to as the electrochemically active area (ECA) and the ratio of ECA and the nominal CL cross-sectional area provides the ECA-ratio . It is be noted that in this chapter, ECA is normalized with the apparent electrode area and therefore differs from the definition in terms of the electrochemically active area per Pt loading reported elsewhere in the literature. 

The detrimental consequence of liquid water on the CL voltage loss primarily comes from the impeded oxygen transport and reduced electrochemically active area as explained above which can be described by the electrochemical kinetics in terms of the reaction current density,/, through the Tafel equation.27... 

Fig. 11.12 Electrochemical activity (area-specific activity) normalized by the surface area of Pt for the most active alloys. The Pt surface area was determined electrochemically using the hydrogen adsorption integral of each catalyst.

Inorganic NPs exhibit higher surface to volume ratios than their bulk counterparts. Thus, electrochemical interfaces modified with inorganic NPs will provide a higher electrochemically active area and therefore lead to higher detection sensitivity. 

Miniaturized working electrodes offer a possibility to cope with these difficulties Owing to their much larger electrochemically active areas, macroscopic counterelectrodes lead to voltage drops which are often negligible compared to the overpotential of a microelectrode. A reference electrode is therefore not necessary to get rid of the influence of the counter-electrode. As an example of an electrochemical... 

Although the current performance of SOFC anodes is still far from satisfactory, they are mainly being studied solely in terms of the electrochemically active area, the electric conductivity, thermal expansion, stability and reactivity with the solid electrolyte. It is... 

Overpotential loss is inversely proportional to the electrochemically active area. Thus, a composite anode with three phases is preferred, i.e., ceramic (ionic conduction), metallic (electronic conduction) and pore (gas diffusion) phases mixed together to expand the electrochemically active area to a three-dimensional anode volume. ... 

The chemical diffusivity of lithium ions 0 + in the transition metal oxides and graphite is taken as 10 10 cm s [13, 97-100] on the basis of scanning electron microscopy (SEM) inspections, the average radius R is estimated to be 1-10 pm. The electrochemically active area A a is calculated from the radius R, and the theoretical density of the particles considered assuming that A a is identical to the total surface area of the electrode comprised of the spherical particles. 

Scanning electrochemical microscopy (SECM), which has an intermediate resolution between that of conventional lithography and AFM/STM, is useful for mapping the electrochemically active areas of electronically conductive patterns of the films [38] it also can be used for the special mode of coating of the surface of metallic electrodes with ECP films by electroless deposition [39]. 

They have extended the kinetic study of lithium intercalation to such transition metal oxides as Lii.gNi02," " " Lii.8Mn204," " Li +s[Ti5/3Li,/3]04," 205, and carbonaceous materials. In these works, they have reported that the theoretical CTs, based upon the cell-impedance control concept, matched quantitatively those experimentally measured all the anomalous features of the experimental transients were readily interpreted in the cell-impedance controlled transients with such simplified parameters as electrochemical active area, dimensionality of the diffusion path, cell impedance, etc. 

Ana is the electrochemical active area of the electrode Du is the chemical diffusivity of lithium L is the thickness of the electrode, and c and represent the final and initial equilibrium concentration of lithium in the electrode, respectively. 

As mentioned in Section V.2, in this review the electrochemical active area Aea was overestimated and the chemical diffusivity of... 

The electrochemically active area is located as a ring around the tip. It has been used in SECM measurements an AFM picture was simultaneously obtained. 

During polarization of the electrode, PbS04 crystals are deposited on the metal surface. Since lead sulfate is a dielectric, the above electrochemical process stops in the areas covered by PbS04 crystal deposit. Thus, the only electrochemically active area is the metal surface... 

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