Electroactive area per unit volum

The electroactive area per unit volume /4s should be stated whenever possible (this is frequently and incorrectly called the the specific electrode area) ... 

One of the most useful figures of merit is the product of mass transport coefficient and electroactive area per unit volume. ... 

There are many variants for the mode of operation of a reactor, in addition to those discussed in Chapter 2, section 2.5, e.g. one strategy is to use a primary cell to extract the majority of metal from the process liquor, while a secondary cell performs the final stages of metal recovery (Fig. 7.1). In this fashion, the primary cell may involve a modest mass transport rate and operate with a small fractional conversion per pass. The secondary cell may scavenge metal effectively by virtue of, for example, a high electroactive area per unit volume. In some cases, metal leached as a concentrate from the secondary cell may be recycled to the primary one all the metal recovered might then be obtained as solid material. 

Packed bed electrode — A static three-dimensional - electrode consisting of a restrained bed of electronically conducting particles in continuous intimate contact. Packed Bed Electrodes (PBEs) present high electroactive area per unit electrode volume and moderately high -> mass transport characteristics (the limiting current at a PBE may exceed 100 times the one observed at a two-dimensional electrode of the same volume). 

The designation covers those electrodes displaying a very high surface area per unit volume, Ae, caused by no planarity. Usually, they also cause conditions of good turbulence at their interface with the electrolyte, enhancing the mass transfer process of the electroactive species towards the electrode surface. Both characteristics strongly improve the electrochemical reaction rate as expressed by the equation... 

Reaction engineering parameters. The achievement of a correct rate and selectivity of production requires control and uniformity of the potential and current distribution. In turn, very high rates will usually involve a uniformly high mass transport over the electrode, achieved by provision of the required hydrodynamics. The electroactive area per unit reactor volume may need to be high if the available current density is low and a compact design is required. Adequate heat transfer must be available between the reactor and its environment. 

Electroactive area per unit reactor volume Electroactive area per unit electrode volume Cost of a unit of electrical power Width of flow channel Concentration of species i Concentration of species i in the bulk solution Concentration of species i at the electrode surface... 

It has already been mentioned that three-dimensional, porous, electrodes offer particularly high values of the electroactive area per unit reactor volume whilst also giving a moderate increase in the mass transport coefficient The result is a significantly increased performance from a given volume of reactor, compared to two-dimensional electrode materials, due to the high value of fct s-This performance may be utilized in various ways including ... 

The space time yield is a measure of the rate of production per unit volume of reactor and is normally quoted in units such as mol dm h . The space time yield is proportional to the effective current through the cell per unit volume of reactor and hence on the current density (overpotential, concentration of electroactive species and the mass transport regime), current efficiency and the active surface area of electrode per unit volume. 

The objective of catalyst layer design is twofold from a materials scientist s perspective, the objective is to maximize the electrochemically active surface area (ECSA) per unit volume of the catalytic medium Secsa, by (i) catalyst dispersion in nanoparticle form or as an atomistically thin film and (ii) optimization of access to the catalyst surface for electroactive species consumed in surface reactions. From a fuel cell developers point of view, the objective is to optimize pivotal performance metrics like voltage efficiency, energy density, and power density (or specific power) under given cost constraints and lifetime requirements. These performance objectives are achievable by integration of a highly active and sufficiently stable catalyst into a structurally well-designed layer. 

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