We note that the electrode surface is relatively rough, which is the result of the electrode polishing by grinding paper. 3D SEM reconstruction shows roughness around 1 µm, while EDX analysis revealed under 2 at. % of Rh on the surface, with an additional ~4 at. % of oxygen (Figure and). These results agree with the previous EDX measurements on smooth Rh-modified Ni-poly . In the same work, XPS measurements revealed between 12.5 and 60 at. % of Rh, as the modification is restricted to the surface layer, at least half of it coming from the metallic Rh phase. For 45 seconds of exchange, we were previously able to observe Rh nanoparticles on the surface, but the overall amount of Rh was very small, so XRD was not able to detect the Rh phase even upon prolonged exchange on Ni foam electrode .