This is a very interesting and good question. Direct Measurement could be quite challenging, if you mean "Electronic distance". DFT simulations would be certainly helpful.

Pt and Pd have different atomic diameters. These would make some extents of misfit between Pt and Pd crystals and also distort their d band center. This could change the catalytic effect of Pt. It  just only gets a local data through HRTEM to view the interface between them.

Could you achieve the atomic-scale resolution by HRTEM? If so, you should enable to directly measure the interfacial distance from HRTEM images. Is that true? Again, DTF simulation will very helpful as well,

Well, Thanks for your suggestion. We can directly view the interface by tilting crystal orientation in HRTEM and clearly see Pd and Pt face to face contact together.  This just shows a nano-scale region of coherent boundary.  May be I need to approach this point in another view, such as DTF simulation which related to the Pt synergistic effect.