ORR viability of alumina-supported platinum nanocluster: exploring oxidation behaviour by DFT

While alumina-supported platinum particles are versatile for several oxidation reactions, their viability as ORR catalysts has not been explored to date. Therefore, to assess the prospects of alumina-supported platinum nanoclusters in ORRs, a systematic DFT study has been carried out to explore the oxidation behavior of a Pt_n@Al₂O₃ (n = 1-7, 10) cluster. The results are compared with the oxidation behavior of the corresponding gas phase platinum cluster and that of an extended Pt(111) slab. Both supported and unsupported clusters activate adsorbed oxygen molecules and energetically favor dissociative chemisorption of oxygen, leading to stable oxide formation with Pt-O-Pt linkages. However, the influence of the alumina substrate downshifts the d-band centre of the platinum cluster, which not only reduces the reaction enthalpy of oxidation by 8-10%, but also elongates the Pt-O bond of the oxide product by 3-8%. These observations indicate that removal of oxide will be relatively easier for supported clusters than for unsupported clusters. Cluster binding is found to sustain during oxidation, as oxidation of the platinum host cluster results in reduction of the distance between the cluster and support surface. While the gas phase Pt₁₀ cluster does not show any similarity to the oxidation behavior shown by THE Pt(111) slab, the Pt₁₀@Al₂O₃ cluster reveals close resemblance. Both the Pt(111) slab and Pt₁₀@Al₂O₃ cluster form similar oxide products, having tri-coordinated oxygen with comparable Pt-O bond distances. The observed resemblance has been attributed to the similarity in the electronic structure and d-band centre position of the platinum surface and alumina-supported Pt₁₀ cluster. Whilst this similar oxidation behaviour of the Pt₁₀@Al₂O₃ cluster endorses its viability as an ORR catalyst, further modulation of this catalyst is desirable to improve its potential.