An electron moving in a direction opposite to the electric field experiences a force due to the electric field. The force on the electron is given by F = qE, where q is the charge on the electron and E is the electric field. The potential energy of the electron is given by U = qV, where V is the potential difference between the electron's initial and final positions. The potential energy of the electron is therefore decreased by an amount qV when it moves in a direction opposite to the electric field.