Doubt from electrochemistry

The question asks about the max amount of electrical energy that can be obtained from one mile of Ni2O3?
Now what I think: max obtainable work =Delta G=-nFE
should I use E(cell)=1.27 or E=0.40?
@ Shwetanshu_2018

It should be the overall cell reaction (1.27) since for something to generate emf we need both cathode and anode ( if we need any electricity at least). Electricity means flow of charges.