Cell EMF and Gibbs Energy

The maximum amount of work that a cell in its standard state can perform is given by:

W_max = –nFE⁰

The significance of –ve sign is that the work is done by the cell. Since the maximum amount of useful work which a system can perform is equal to decrease in Gibbs energy,

W_max = ΔG⁰ = –nFE⁰

If ΔG⁰ calculated is negative, then the cell reaction is spontaneous, otherwise not.