We are preparing different pore size with a different thickness on the gold substrate. As the thickness of the porous structure is increasing the current density is decreasing but in oxygen diffusion current is increasing. here, I am attaching my graph. Here, I don’t understand, if the active surface area is increasing with respect to the thickness of the pore size then why the current density is decreasing w.r.t. thickness.

Please suggest me, how I can improve current density or oxygen digfusion.