This is as expected, since for like charges (q1q2 > 0),
electrostatic force is repulsive and a positive amount of work is needed to
be done against this force to bring the charges from infinity to a finite
distance apart For unlike charges (q1 q2 < 0), the electrostatic force is
attractive In that case, a positive amount of work is needed against this
force to take the charges from the given location to infinity In other words,
a negative amount of work is needed for the reverse path (from infinity to
the present locations), so the potential energy is negative