Electro-potential reaction?

There are two competing reactions in NiMH cells:

• Ni(OH){2} + OH- => NiOOH + H{2}O + e- (300mV):: desirable charge reaction
• 4OH- => O{2} + 2H{2}O + 4e- (-204mV) :: undesirable O2 generation, deep discharge reaction

What I remember from chemistry class is the electrons comes with an electromotive force, a voltage, that is needed for each reaction. I suspect the second reaction has a slightly higher voltage requirement BUT I have been too long away from the classroom.

Would anyone know how to calculate or lookup the electromotive force needed for each reaction?

Thanks,
Bob Wilson