Direct identification of the charge state in a single platinum nanoparticle on titanium oxide

• Published in: Science (American Association for the Advancement of Science) 2022-10, Vol.378 (6616), p.202-206
• Main Authors: Aso, Ryotaro, Hojo, Hajime, Takahashi, Yoshio, Akashi, Tetsuya, Midoh, Yoshihiro, Ichihashi, Fumiaki, Nakajima, Hiroshi, Tamaoka, Takehiro, Yubuta, Kunio, Nakanishi, Hiroshi, Einaga, Hisahiro, Tanigaki, Toshiaki, Shinada, Hiroyuki, Murakami, Yasukazu
• Format: Article
• Language: English
• Subjects: Anomalies; Charging; Holography; Lattice strain; Metal oxides; Nanoparticles; Photoelectric emission; Platinum; Scanning probe microscopy; Spectroscopy; Titanium dioxide; Titanium oxide; Titanium oxides
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.abq5868

A goal in the characterization of supported metal catalysts is to achieve particle-by-particle analysis of the charge state strongly correlated with the catalytic activity. Here, we demonstrate the direct identification of the charge state of individual platinum nanoparticles (NPs) supported on titanium dioxide using ultrahigh sensitivity and precision electron holography. Sophisticated phase-shift analysis for the part of the NPs protruding into the vacuum visualized slight potential changes around individual platinum NPs. The analysis revealed the number (only one to six electrons) and sense (positive or negative) of the charge per platinum NP. The underlying mechanism of platinum charging is explained by the work function differences between platinum and titanium dioxide (depending on the orientation relationship and lattice distortion) and by first-principles calculations in terms of the charge transfer processes. Charging of metal nanoparticles supported on metal oxides can occur during catalytic reactions and can be measured as an average charge with x-ray photoemission spectroscopy or as anomalies in surface potential with scanning probe microscopy. Aso et al . used ultra-high-precision electron holography to directly identify the charge state of single platinum nanoparticles supported on a titanium dioxide crystal (see the Perspective by Gao and Terasaki). A phase-shift analysis visualized slight changes that resulted from charging around the parts of the platinum nanoparticle that extended out from the surface into the vacuum. A platinum nanoparticle could gain or lose one to six electron charges depending on the nanoparticle structure (lattice strain) or its orientation on the titanium dioxide support. —PDS Phase-shift analysis on the vacuum-protruding region of nanoparticles visualized slight positive and negative charging.