Electrode active surface area

In the quest to improve fuel cell performance, the concept of fuel cell reactions requiring a three-phase interface was first proposed by Grove. In his initial experiment, he noticed that the reaction sped up when the three-phase area was large. In 1923, Schmid [7] developed the first gas diffusion electrode, which significantly increased the electrode active surface area and revolutionized fuel cell electrodes. The electrode contained a coarse-pore graphite gas-side layer and a fine porous platinum electrolyte layer. 

The effectiveness of a porous electrode over a plane surface electrode is given by the product of the active surface area S in cm /mL and the penetration depth Tp of the reaction process into the porous electrode. 

A third way to increase both the active surface area and the number of oxygenated species at the electrode surface is to prepare alloy particles or deposits and then to dissolve the non-noble metal component. This technique, which is similar to that used to prepare Raney-type catalysts, yields very high surface area electrodes and hence some improvements in the electrocatalytic activities compared with those of pure platinum. However, it is always difficult to be sure whether the mechanism of enhancment of the activities is due to this effect or the possible presence of remaining traces of the dissolved metal. Results with PtyCr and PtSFe were encouraging, although the effect of iron is still under discussion. From studies in a recent work on the behavior of R-Fe particles for methanol electrooxidation, it was concluded that the electrocatalytic effect is due to the Fe alloyed to platinum. ... 

In this section, we demonstrate the real ORR activities (apparent rate constant per real active surface area, fe pp) and P(H202) at bulk Pt and nanosized Pt catalysts dispersed on carbon black (Pt/CB) with dp,= 1.6 + 0.4, 2.6 + 0.7, and 4.8 1.0 nm in the practical temperature range 30-110 °C [Yano et al., 2006b]. The use of a channel flow double-electrode (CFDE) cell allowed us to evaluate fe pp and P(H202) precisely. 

The so-called indicator electrodes must be considered as microelectrodes, which means that the active surface area is very small compared with the volume of the analyte solution as a consequence, the electrode processes cannot perceptibly alter the analyte concentration during analysis in either non-faradaic potentiometry or faradaic voltammetry. 

Assume that current is passed either through the total nucleus surface area or through part thereof, such as the edge of a two-dimensional nucleus of monoatomic thickness. The transition of the ion Mz+ to the metallic state obeys the equation for an irreversible electrode reaction, i.e. Eqs (5.2.12), (5.2.23) and (5.2.37). The effect of transport processes is neglected. The current density at time t thus depends on the number of nuclei and their active surface area. If there is a large number of nuclei, then the dependence of their number on time can be considered to be a continuous function. For the overall current density at time t we have... 

Similarly, in the development of solid oxide fuel cells (SOFCs), it is well recognized that the microstructures of the component layers of the fuel cells have a tremendous influence on the properties of the components and on the performance of the fuel cells, beyond the influence of the component material compositions alone. For example, large electrochemically active surface areas are required to obtain a high performance from fuel cell electrodes, while a dense, defect-free electrolyte layer is needed to achieve high efficiency of fuel utilization and to prevent crossover and combustion of fuel. 

To facilitate a demonstration of the advantages of the 3-D architecture, we quantitatively compare metrics related to performance (e.g.. areal energy capacity, active surface area) of a conventional 2-D parallel-plate design with the 3-D interdigitated array cell (Figure 3). We assume a thin-film 2-D battery that comprises a 1-cm -area anode and cathode, each 22.5-/thick electrolyte. The total volume of electrodes and separator is 5 x 10 cm (the cell housing is ignored for simplicity, but is expected to be a comparable... 

The particulate nature of the trapped metal results in each growing crystal of metal becoming a microelectrode that enlarges the active surface area of the electrode. Thus the deposition rate is maintained as concentration of metals in solution declines. 

Detector Characteristics. The applied potential that produced the largest analytical signal was 0.56 V versus SCE. The decrease in analytical signal at potentials more positive than 0.56 V suggested a decrease in the active surface area of the electrode due to competitive solvent oxidation at the active sites. 

In this case, it is likely that electron transfer is sluggish through the A1 oxide film on the pure A1 electrode, and this limits the rate at which the ORR can be sustained. The high ORR rate on the Cu-bearing materials was attributed to corrosion and surface roughening that increased the area capable of supporting the ORR. In the case of the intermetallic compound, dealloying may also have contributed to the increase in active surface area. 

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