Emf tells us about the potential difference between the two terminals of a battery or some other source.
However, potential difference stands for a much broader meaning.
There can be a potential difference between any two points in an electric field.
Emf is a kind of potential difference. The word EMF is used only for batteries or voltage sources in circuits.
Consider an electric field in free space.
If potential at point A be
That has got nothing to do with batteries or energy sources in circuits.
In the case of circuits there can be a difference in electric potential between any two points. But, emf is only the potential difference between terminals of the battery.
Emf is just the kind of non-electrical energy that have tendency to produce a electro-chemical reaction for the sepration of charges inside the battery.
But electric potential may or may not be the potential difference b/w the electric field of any charge.
So according to this view we can say both are the different quantities.