It is worth noting that the rationalization presented above does not take into account the change of the Fermi level of a metal nanoparticle as its size decreases. When the nanoparticle accepts an excess electron density of δ from an adsorbate (e.g., borohydride in the PNP reduction; δ ≈ 0.3), the nanoparticle's Fermi level EF is increased under an inverse relationship with the nanoparticle size [56]: ΔEF = 8EFδrϕ−1, where r is the atomic radius (r = 0.14 nm for Pt [39]). The increase of EF reduces the adsorption energy over the metal surface and thus improves reactivity. With ϕ = 2.8–4 nm as we have in our experiments, ΔEF/EF stabilizes in the range of 10–14%; therefore, the effect of Fermi-level increase is insignificant. For nanoparticles with a diameter of 1 nm [14] and [64], ΔEF/EF can be as large as 40%; therefore, the optimal composition may change as the size of nanoparticles varies.