I n our communication 1 , we have investigated Pt nanoparticles supported on high surface area carbons (Pt/C) and boron carbide composites (Pt/BC). We showed that purely electronic interactions between the nanoparticulate catalyst and its support have bearings on electrocatalytic activity for the oxygen reduction reaction in acidic media and catalyst stability. This has been achieved by interrogating the electronic states of the supported Pt catalysts in an electrochemical environment via X-ray absorption near edge structure (XANES), which showed a relatively more positive charge on Pt nanoparticles if supported on BC compared to very similar Pt nanoparticles supported on C. Similarity of the Pt nanoparticle size distribution and morphology was established by transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS), respectively, to exclude other factors contributing to the electrocatalytic characteristics.We also investigated the two catalysts ex situ under ultra-high vacuum (UHV) conditions by X-ray photoelectron spectroscopy (XPS), which has shown a shift to higher binding energies of the Pt 4f signal relative to the reference C 1s signal for the Pt/BC catalyst. Following the band filling argument put forward by Watanabe et al. 2 , we have tentatively interpreted this change with a relatively more negative charge of Pt supported on BC compared to Pt on C under UHV conditions. A fuller account of the reasoning is contained in the published reviewer file of our original communication.This led us to point out that the relative state of charge of the Pt nanoparticles on the two supports (i.e., more negative or more positive) appears different under potentiostatic control in aqueous electrolyte than under UHV conditions. In an attempt to rationalise this observation, we have argued that the overall work function of the heterogeneous electrode surfaces should be different for the Pt/C and Pt/BC systems, which leads to a shift of the potential of zero charge (pzc) 3 of the heterogeneous Pt/BC electrode surface relative to Pt/C. An additional positive charge has, therefore, to be accommodated by the Pt/BC electrode if held at the same potential, because it is further away from the pzc.Binninger addressed this minor point 4 . In an attempt to show that "no inversion of the relative charge transfer between support and Pt nanoparticle can be deduced", Binninger has put forward an electrostatic argument. He investigates the potential at which the nanoparticle electrolyte-facing, external surface has zero charge in the limit of infinitely strong screening (i.e., where the Debye length is much shorter than the catalyst particle size) in the electrolyte in detail and concludes that this potential is the same as is found for an extended Pt electrode under the same conditions. This result is unsurprising given that the assumption of infinite screening will quench all electrostatic interaction between nanoparticle and support through the electrolyte. Binninger then qualitatively expands his co...