Reversible potential of a cell

When we consider a whole cell inserted into an electrical circnit, the half redox reactions are no longer balanced, becanse the electrons and ionic species are exchanged between one electrode and the other. The electrodes are no longer at 

2 The electrode with zero potential is the Normal Hydrogen Electrode (NHE). Experimentally, we choose an electrode for which we know the relative voltage in comparison to the NHE, tabulated for all temperatures. 

Hereinafter, so as to use identical equations to describe accumulators in charge or discharge mode, fuel cells or electrolyzers, we define the reversible potential, in standard conditions, of a cell, if it were at equiUbrium and lossless, as being the difference between the highest electrode potential E (positive eleetiode) and the lowest electrode potential E (negative electrode) [1.11] [TUR08]. 

The conditions of operation may well be different from standard conditions. The potential of the cell thus obeys the Nemst equation. The reversible potential of the cell is therefore calculated as follows  

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