Interaction energy of an hydroxide ion with a Pd surface

I need to estimate the interaction energy of a hydroxide ion with a palladium surface of $-0.6$V in water.


I know that the electric field of a charge $e$ is
$$
E = \frac{1}{4\pi\epsilon}\frac{e}{r^2}
$$


where $r$ is the distance and $\epsilon$ is the dielectric constant.


Also, I know that for an infinity charged plane the electric field is
$$
E=\frac{\sigma}{2\epsilon}
$$


where $\sigma$ is the surface charge density. I have the area of the surface, $A=0.125$ cm$^2$. But I wonder how can I calculate this interaction energy.


