Question: what is the formula for standard electrode potential?
Answer: This is the standard electrode potential for the reaction Ni2+(aq) + 2e− → Ni(s). Because we are asked for the potential for the oxidation of Ni to Ni2+ under standard conditions, we must reverse the sign of E°cathode. Thus E° = −(−0.28 V) = 0.28 V for the oxidation.