it depends on the vapour pressure of the liquid
No, it is not possible if the body is of a fixed dimension and the charges are electrostatic. The potential of a body is directly proportional to the charge on it. If the body is experiencing decreasing potential, it is because charges are being transferred. The charge is changing to effect the change of potential. If a given electrostatic potential is assigned to a balloon, and charges are being transferred as air is let out of the balloon, it is possible to achieve a decrease of potential while maintaining a constant charge density on the surface of the balloon, but that's afield of the question. Charges must be transferred to effect any change in potential, so overall charge will change as potential changes in a body under consideration.
Electric current is the movement of electrons through a conductor.