Media 1: Controllable directive radiation of a circularly polarized dipole above planar metal surface

Originally published in Optics Express on 16 December 2013 (oe-21-25-30327

Stabilizing CuPd Nanoparticles via CuPd Coupling to WO_2.72 Nanorods in Electrochemical Oxidation of Formic Acid

Stabilizing a 3d-transition metal component M from an MPd alloy structure in an acidic environment is key to the enhancement of MPd catalysis for various reactions. Here we demonstrate a strategy to stabilize Cu in 5 nm CuPd nanoparticles (NPs) by coupling the CuPd NPs with perovskite-type WO_2.72 nanorods (NRs). The CuPd NPs are prepared by controlled diffusion of Cu into Pd NPs, and the coupled CuPd/WO_2.72 are synthesized by growing WO_2.72 NRs in the presence of CuPd NPs. The CuPd/WO_2.72 can stabilize Cu in 0.1 M HClO₄ solution and, as a result, they show Cu, Pd composition dependent activity for the electrochemical oxidation of formic acid in 0.1 M HClO₄ + 0.1 M HCOOH. Among three different CuPd/WO_2.72 studied, the Cu₄₈Pd₅₂/WO_2.72 is the most efficient catalyst, with its mass activity reaching 2086 mA/mg_Pd in a broad potential range of 0.40 to 0.80 V (vs RHE) and staying at this value after the 12 h chronoamperometry test at 0.40 V. The synthesis can be extended to obtain other MPd/WO_2.72 (M = Fe, Co, Ni), making it possible to study MPd-WO_2.72 interactions and MPd stabilization on enhancing MPd catalysis for various chemical reactions

Polyvinylpyrrolidone-Coated Cubic Hollow Nanocages of PdPt₃ and PdIr₃ as Highly Efficient Self-Cascade Uricase/Peroxidase Mimics

Uricase-catalyzed uric acid (UA) degradation has been applied for hyperuricemia therapy, but this medication is limited by H2O2 accumulation, which can cause oxidative stress of cells, resulting in many other health issues. Herein, we report a robust cubic hollow nanocage (HNC) system based on polyvinylpyrrolidone-coated PdPt3 and PdIr3 to serve as highly efficient self-cascade uricase/peroxidase mimics to achieve the desired dual catalysis for both UA degradation and H2O2 elimination. These HNCs have hollow cubic shape with average wall thickness of 1.5 nm, providing desired synergy to enhance catalyst’s activity and stability. Density functional theory calculations suggest the PdIr3 HNC surface tend to promote OH*/O* desorption for better peroxidase-like catalysis, while the PdPt3 HNC surface accelerates the UA oxidation by facilitating O2-to-H2O2 conversion. The dual catalysis power demonstrated by these HNCs in cell studies suggests their great potential as a new type of nanozyme for treating hyperuricemia

Tuning Sn-Catalysis for Electrochemical Reduction of CO₂ to CO via the Core/Shell Cu/SnO₂ Structure

Tin (Sn) is known to be a good catalyst for electrochemical reduction of CO₂ to formate in 0.5 M KHCO₃. But when a thin layer of SnO₂ is coated over Cu nanoparticles, the reduction becomes Sn-thickness dependent: the thicker (1.8 nm) shell shows Sn-like activity to generate formate whereas the thinner (0.8 nm) shell is selective to the formation of CO with the conversion Faradaic efficiency (FE) reaching 93% at −0.7 V (vs reversible hydrogen electrode (RHE)). Theoretical calculations suggest that the 0.8 nm SnO₂ shell likely alloys with trace of Cu, causing the SnO₂ lattice to be uniaxially compressed and favors the production of CO over formate. The report demonstrates a new strategy to tune NP catalyst selectivity for the electrochemical reduction of CO₂ via the tunable core/shell structure

A New Core/Shell NiAu/Au Nanoparticle Catalyst with Pt-like Activity for Hydrogen Evolution Reaction

We report a general approach to NiAu alloy nanoparticles (NPs) by co-reduction of Ni­(acac)₂ (acac = acetylacetonate) and HAuCl₄·3H₂O at 220 °C in the presence of oleylamine and oleic acid. Subject to potential cycling between 0.6 and 1.0 V (vs reversible hydrogen electrode) in 0.5 M H₂SO₄, the NiAu NPs are transformed into core/shell NiAu/Au NPs that show much enhanced catalysis for hydrogen evolution reaction (HER) with Pt-like activity and much robust durability. The first-principles calculations suggest that the high activity arises from the formation of Au sites with low coordination numbers around the shell. Our synthesis is not limited to NiAu but can be extended to FeAu and CoAu as well, providing a general approach to MAu/Au NPs as a class of new catalyst superior to Pt for water splitting and hydrogen generation

Fe Stabilization by Intermetallic L1₀‑FePt and Pt Catalysis Enhancement in L1₀‑FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1₀-MPt alloy nanoparticle (NP) structure and how to surround the L1₀-MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L1₀-FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Pt shell, especially the two atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO₄ solution (at both room temperature and 60 °C) and in the membrane electrode assembly (MEA) at 80 °C. The L1₀-FePt/Pt catalyst has a mass activity of 0.7 A/mg_Pt from the half-cell ORR test and shows no obvious mass activity loss after 30 000 potential cycles between 0.6 and 0.95 V at 80 °C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). We are extending the concept and preparing other L1₀-MPt/Pt NPs, such as L1₀-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications