Naoto Todoroki

Dealloying of Nitrogen-Introduced Pt–Co Alloy Nanoparticles: Preferential Core–Shell Formation with Enhanced Activity for Oxygen Reduction Reaction

Voltammetric dealloying is a typical method to synthesize Pt-shell/less-noble metal (M) alloy core nanoparticles (NPs) toward the oxygen reduction reaction (ORR). The pristine nanostructures of the Pt–M alloy NPs should determine the ORR activity of the dealloyed NPs. In this study, we investigated the voltammetric dealloying behavior of the Pt–Co and nitrogen-introduced Pt–Co alloy NPs generated by synchronous arc-plasma deposition of Pt and Co. The results showed that the dealloying behavior is sensitive to cobalt nitride in the pristine NPs, leading to the preferential generation of a Pt-rich shell/Pt–Co alloy core architecture having enhanced ORR activity.

Electrochemical Reduction of CO2 on Ni- and Pt-Epitaxially Grown Cu(111) Surfaces

The electroreduction of CO2 on well-defined M/Cu(111) (M = Ni and Pt) bimetallic surface systems fabricated using molecular beam epitaxy was studied. The total faradic efficiency for CO2 reduction using one-monolayer (ML)-thick Pt epitaxially grown on a Cu(111) substrate (1-ML Pt/Cu(111)) was nearly the same as that for clean Pt(111). In contrast, the 1-ML-thick Ni/Cu(111) system exhibited increased selectivity for CH4 production compared with that of clean Ni(111), which may stem from the geometric tensile strain induced by the underlying Cu(111) substrate. Notably, bimetallic surfaces consisting of 0.1-ML-thick Ni or Pt grown on Cu(111) exhibited significantly different reduction behaviors compared with those of Cu because of the presence of the a small amount of epitaxially grown metal. For the 0.1-ML-thick Ni/Cu(111) system, the total faradaic efficiency for CO2 reduction and the production rate for CO were enhanced compared with those for clean Cu(111), whereas the production of CH4 decreased. In contrast, the total faradaic efficiency was significantly suppressed for the 0.1-ML-thick Pt/Cu(111) bimetallic substrate, with only a very small amount of CH4 production. The difference in the catalytic properties is attributed to the difference in the adsorption energies for CO, which is an intermediate in the electrochemical production of CH4 and C2H4.

Ultrahigh Vacuum Synthesis of Strain-Controlled Model Pt(111)-Shell Layers: Surface Strain and Oxygen Reduction Reaction Activity

In this study, we perform ultrahigh vacuum (UHV) and arc-plasma synthesis of strain-controlled Pt(111) model shells on Pt-Co(111) layers with various atomic ratios of Pt/Co and an oxygen reduction reaction (ORR) activity enhancement trend against the surface strain induced by lattice mismatch between the Pt shell and Pt-Co alloy-core interface structures was observed. The results showed that the Pt(111)-shell with 2.0% compressive surface strain vs intrinsic Pt(111) lattice gave rise to a maximum activity enhancement, ca. 13-fold higher activity than that of clean Pt(111). This study clearly demonstrates that the UHV-synthesized, strain-controlled Pt shells furnish useful surface templates for electrocatalysis.