Half-cell Metrics

No single half-cell (3-electrode) measurement can produce a valid device efliciency 

The most common example is the use of what appears to be the ABPE with an invalid voltage as per the following equation. 

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Based on the individual half-cell reaction potentials, the theoretical electrochemical potential offered by a single Zn/Br cell should be approximately 1.828 V. This value is the Nemstian potential under zero current flow. However, the presence of internal inefficiencies and various resistance contributions seen in practice are expected to result in slightly lower cell voltage values. Another important performance metric for Zn/Br systems is current density, which is the amount of current passing through a unit area of an electrode surface. The current density, in turn, has a direct influence on the electrode capacity (i.e. energy per unit area) as well as the operating efficiency of the overall system. 

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Equilibration of the redox protein is faster in the reflection cell, because the diffusional path length is only half the optical pathlength, which enables a rapid switching of the molecule between different redox states. Although direct electrochemistry is preferable, it turns out that redox cofactors are sometimes deeply buried in proteins and enzymes so that mediators are required to speed up the equilibration [4]. However, they can be kept at very low concentrations and thus do not interfere with the optical measurement. Under these conditions, ampero-metric, coulometric, or cyclovoltammetric experiments in combination with UVA IS/IR... 

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