Capacitive electronic metal-support interactions: Outer surface charging of supported catalyst particles

Abstract

Electronic metal-support interactions (EMSI) in catalysis are commonly rationalized in terms of an electron transfer between support material and supported metal catalyst particles. This general perspective, however, cannot fully explain experimentally observed EMSI for metallic nanoparticulate catalysts, because the strong charge screening of metals should locally confine effects of direct electronic interaction with the support to the catalystsupport interface (CSI), which, apart from the perimeter, is largely inaccessible for catalysis reactants. The concept of capacitive EMSI is proposed here for catalyst particles at the nanometer scale, where electronic equilibration results in a long-range charging of the catalytically active outer surface (CAOS) bypassing the expected strong metallic charge screening, which is confirmed and quantified by electrostatic and density functional theory simulations revealing a strong dependence on the coverage of the support surface with catalyst particles. This long-range charge transfer leads to a shift of the local work function at the CAOS. In order to describe the catalytic consequences, an amendment of d-band theory in terms of 'd-band + work function' is proposed. Furthermore, the charging of remote catalytic sites at the CAOS scales with the relative dielectric constant of the surrounding medium, and it is concluded that EMSI can have surprisingly strong influence especially in the presence of a strongly polarizable dielectric.

The effect of SnO2(110) supports on the geometrical and electronic properties of platinum nanoparticles

“…Similarly, the effect of Nb dopant showed to decrease the work function of SnO 2 . However, compared to SnO 2-δ , the influence was not as considerable; hence, there is a possibility that on the Nb-doped SnO 2 may also exist a certain percentage of V [41]. Additionally, our results can also be used to explain the suppressed charge transfer from Pt-nanoparticles to reduced CeO 2 compared to the stoichiometric CeO 2 [42].…”

“…Only in the case of oxidized SnO 2 , decreasing the Pt loading led to lower ORR activity, which was attributed to stronger adsorption of oxygenated species [40]. It was shown that electronic metal-support interactions can affect the charge of the catalytically active outer surface of nanoparticles [41]. This long-range charge transfer scales with the work function difference between the support and the catalyst [41] and is also size-dependent [42].…”

“…It was shown that electronic metal-support interactions can affect the charge of the catalytically active outer surface of nanoparticles [41]. This long-range charge transfer scales with the work function difference between the support and the catalyst [41] and is also size-dependent [42]. However, theoretically, the charge transferred between the support and Pt-nanoparticles was quantified [42][43][44][45][46][47].…”

“…The effect of the charge transfer based on the work function difference between the SnO 2 supports, and Ptnanoparticles is scarce. One example is the effect of the work function difference of Sb-doped SnO 2 , Sb-doped SO 2-δ , and Pt 55 on the charge transfer [41]. To the best of our knowledge, the size dependence of the charge transfer between Pt-nanoparticles and SnO 2 supports was not carried out, and the activity of the Pt/SnO 2 systems based on the interaction with oxygenated species and its effect on the ORR as a result of the charge transfer has not been discussed.…”

Electronic metal-support interactions in vacuum vs. electrolyte

“…It is, therefore, valid to ask if the overall work function (and consequently the pzc) would also be framed by the work functions of the support and catalyst nanoparticle more generally. The overall work function of similar heterosystems has been shown theoretically 7 and experimentally 8 to fall in-between the work functions of the support and nanoparticle, giving us reason to believe that this relationship holds qualitatively more generally.…”