Category Archives: Israel Journal of Chemistry

Single Entity Electrochemistry and Its Application to Nanomaterial Synthesis

Posted on 15 June 2022 by nJoon Ho Park, nHyokyum Ahn, nHyun S. Ahnn

Abstract

Single entity analysis is an important research topic in electrochemistry. Thus far, collisions of nanomaterials and subsequent interaction between electrodes and particles have been studied. Single entity electrochemistry exhibited inherent heterogeneity distinct from that of ensembles. By showing various current responses, single entity electrochemistry allows us to investigate the adsorbed chemical species on the electrode surface (dielectrics, hard nanoparticles, soft nanoparticles), enabling analysis of electrode-particle interaction at the nanoscale. Electrochemical analysis of soft nanoparticles enabled the detection of biological materials and was applied to the synthesis of nanoparticles to be used as electrocatalysts. It shows great promise as a synthetic method for various structures of nanoparticles by reducing metal ions volume confined emulsion nanodroplets.

High Yield Synthesis and Quadratic Nonlinearities of Gold Nanoprisms in Solution: the Role of Corner Sharpness

Posted on 2 June 2022 by

Abstract

Size and shape of noble metal nanoparticles have a major influence on their linear and second order nonlinear properties. Among these nanostructures, acentric objects are expected to display high quadratic nonlinear responses. In this work, a single – step growth of gold nanoprisms (GNPs) was achieved by seedless growth. Their second harmonic response has been investigated experimentally and theoretically with edge length ranging from 40 to 116 nm and for different curvature radii at corners. Their first hyperpolarizabilities β have been measured by Harmonic Light Scattering at 1064 nm. Their calculated and experimental β values are found to display, not only a linear dependence with the surface area as reported for other metallic nanoparticle shapes, but also a strong influence of their corner sharpness on the corresponding nonlinearities. Such high experimental and theoretical β values of GNPs are mainly assigned to the sharpness of tips.

Optical Resonances of Chiral Metastructures in the Mid‐infrared Spectral Range

Posted on 8 April 2022 by

Abstract

Metamaterials with localized surface plasmon resonances have been the subject of intense research for a wealth of applications ranging from active photonic devices to analytical sensing units that utilizes the local field enhancement to improve sensitivity and decrease acquisition time. Herein, we focus on the modelled properties of a series of spiral metastructures that present multiple chiral plasmon modes in the 1–10 μm mid-IR spectral range and that could be utilized to enhance vibrational circular dichroism measurements to further identify molecular, supramolecular and structural chirality centres. Finite-difference time-domain electromagnetic modelling was conducted to calculate the infrared spectra of the metastructures in response to a circularly polarized excitation. Several geometric parameters were altered to further tune the position of the resonances. In addition, the near-field distribution of the optical resonances was calculated providing a spatial snapshot of the chiral modes. Preliminary spiral structures were fabricated using electron beam lithography and their vibrational circular response was measured.

Design of Fe‐Nx/Tungsten Carbide for Efficient Electrocatalyst Oxygen Reduction in Acidic Media

Posted on 13 September 2021 by nQingxia Yang, nLijuan He, nChunyu Ke, nJiaqiang Zhong, nWeihua Yangn

Abstract

Improving the activity and stability of Fe/N/C catalyst in oxygen reduction reaction (ORR) is a huge challenge in the commercial application of polymer electrolyte membrane fuel cells (PEMFCs). In the past decade, there have been significant break-throughs in the performance of transition metal catalysts, but little progress has been made in their stability. Herein, a zinc-based zeolite imidazole framework (ZIF-8) and tungsten carbide engaged strategy was reported to prepare Fe/N/C catalyst. Particularly, physical vapor deposition (PVD) was used to trap tungsten carbide nanoparticles with particle size of less than 3 nm limited into the FeNC catalytic micropores to synthesis composite catalyst (WC@FeNC). Compared with original Fe/N/C cata-lysts, confined WC nanoparticles in Fe/N/C porous has improved the ORR activity (2.7 mA mg⁻¹ vs. 2.2 mA mg⁻¹ at 0.85 V vs. RHE) as well as stability (decay 18.7 mV vs. 21.6 mV after 10 h charged) in 0.1 M H₂SO₄. This work puts forward some unique insights for improving the stability of transition metal oxygen reduction catalysts.

Synthesis and Photoelectrochemical Activity of α‐Fe2O3−CdFe2O4 Hybrid Structure for the Water Oxidation Reaction

Posted on 30 October 2020 by nMichael Volokh, nMahmud Diabn

Abstract

The electrochemical properties of spinel ferrites have been studied since the 1970s after the pioneering discovery of water electrolysis by using TiO₂ as the photoanode in a photoelectrochemical cell. Several approaches have been developed to fabricate ferrites of different sizes and shapes but most of these methods suffer from several disadvantages, such as the difficulty to produce the ferrite in a thin layer form or on top of another (pre-prepared) structure as a second layer. Moreover, the formation process requires calcination at high temperatures, and the electrode fabrication requires an additional assembly method. Herein, a CdFe₂O₄ ferrite was formed via chemical vapor deposition of a single-source precursor directly on a hematite structure followed by an annealing process. This thermal treatment simultaneously achieves both activation of the hematite and the formation of CdFe₂O₄. Three different iron oxide (rectangular, nanobelt, and mesoporous) structures were examined as photoanode electrodes. The maximum current at 1.65 V vs. RHE of the mesoporous film was more than two times higher than the rectangular and the nanobelt films. Therefore, iron oxide with mesoporous structures was used to form the hybrid structure of α-Fe₂O₃−CdFe₂O₄. The hybrid structure presents stable and high photocurrent density (about 20 % enhancement in the measured maximum current density at 1.65 V vs. RHE).