Highly active, stable oxidized platinum clusters as electrocatalysts for the hydrogen evolution reaction

Abstract

In the present work, we synthesized and characterized an electrocatalyst consisting of sub-nanometric Pt clusters uniformly dispersed on a TiO₂ support. X-ray photoelectron spectra (XPS) and X-ray adsorption fine structure (XAFS) data demonstrate that these sub-nanometric Pt clusters are in a highly oxidized state and possess two localized Pt–O coordination structures. The Pt–O bonds between the oxidized Pt clusters and the TiO₂ give rise to a strong metal–support interaction (SMSI). When applied to the hydrogen evolution reaction (HER), this catalyst exhibits significantly enhanced catalytic activity (increased by a factor of up to 8.4) and enhanced stability compared with the state-of-the-art commercial Pt/C catalysts. Particularly, the additional XPS and XAFS characterizations of the catalyst after long-term electrolysis demonstrate the absence of metallic Pt species, confirming that the catalytic active site comes from the oxidized Pt clusters rather than from the the metallic Pt species. This improved performance is considered to be induced by the unique electronic structure of the oxidized Pt clusters and by the SMSI. Based on the results of density functional theory calculations, the 5d orbital of the oxidized Pt cluster atoms appears to hybridize with the H 1s orbital to form weak Pt–H valence bonds, leading to a ΔG (relative free energy) value of approximately zero eV for H* absorption. This effect explains the mechanism responsible for the excellent catalytic activity of these oxidized Pt clusters for the HER. This work therefore provides important insights into the role of oxidized Pt clusters as an HER electrocatalyst. The evident stabilization of the oxidized Pt clusters on TiO₂ supports via the charge-transfer mechanism provides a useful approach for improving the durability of electrocatalysts that may be applicable to other noble metal/support systems.