**4. Effect of the electrode shape and future trends**

The importance of electrode shape on the behavior of the electrochemical cell has been recognized for a long time. For instance, the inaccuracies caused by the geometry of the electrode are discussed in detail in Section 6 of the Levich work (Levich, 1942).

Fig. 15. Koutecky-Levich plot of data reported by Unguresan & Gligor (Unguresan & Gligor, 2009) for a concentration of NADH of 1.6 m*M.*

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Fig. 16. Fitting of the experimental data reported by Unguresan & Gligor (Unguresan & Gligor, 2009) for a concentration of NADH of 1.6 m*M* by using Equation (21).

By analyzing the results of biphasic three-dimensional numerical simulations of an electrochemical cell with a cylindrical electrode, several authors found that the submerged electrode side wall along with its right angle shape induces that the liquid velocities in the vicinity of the electrode active face were lower than that predicted with the ideal model (Gonzalez, et al., 2011; Real-Ramirez, et al., 2010). To obtain a liquid velocities field as close as possible to the ideal one, those authors suggest using electrodes with rounded border shape.

The cylindrical electrodes are the ones mostly used for the characterization of electrochemical reactions. However, some authors still using bell-shaped electrodes. According to the authors of this chapter, the results of numerical simulations suggest that this type of electrodes may have a better performance than the cylindrical electrodes. Therefore, it is strongly recommended to conduct numerical simulations to characterize the hydrodynamics of an electrochemical cell with a bell-shaped electrode.
