Synthesis of dendritic iridium nanostructures based on the oriented attachment mechanism and their enhanced CO and ammonia catalytic activities

Study on Oxygen Evolution Reaction of Ir Nanodendrites Supported on Antimony Tin Oxide

In this study, the iridium nanodendrites (Ir NDs) and antimony tin oxide (ATO)-supported Ir NDs (Ir ND/ATO) were prepared by a surfactant-mediated method to investigate the effect of ATO support and evaluate the electrocatalytic activity for the oxygen evolution reaction (OER). The nano-branched Ir ND structures were successfully prepared alone or supported on ATO. The Ir NDs exhibited major diffraction peaks of the fcc Ir metal, though the Ir NDs consisted of metallic Ir as well as Ir oxides. Among the Ir ND samples, Ir ND2 showed the highest mass-based OER catalytic activity (116 mA/mg at 1.8 V), while it suffered from high degradation in activity after a long-term test. On the other hand, Ir ND2/ATO had OER activity of 798 mA/mg, and this activity remained >99% after 100 cycles of LSV and the charge transfer resistance increased by less than 3 ohm. The enhanced durability of the OER mass activities of Ir ND2/ATO catalysts over Ir NDs and Ir black could be attributed to the small crystallite size of Ir and the increase in the ratio of Ir (III) to Ir (IV), improving the interactions between the Ir NDs and the ATO support.

Understanding the Copper-Iridium Nanocrystals as Highly Effective Bifunctional pH-universal Electrocatalysts for Water Splitting

It is pivotal to develop an economical, effective, and stable catalyst to promote the oxygen/hydrogen evolution reaction (OER/HER) throughout pH electrolytes, as the demand for hydrogen energy will increase greatly with the future development. Herein, a series of Ir-Cu nanoparticle composite carbon (Ir_xCu_y/C) catalysts are successfully synthesized using ethylene glycol reduction. In addition, the structure, morphology and composition of the electrocatalysts were systematically characterized, and the OER/HER performance of the catalysts was also tested under different pH conditions. According to experimental findings, amorphous Ir₃Cu/C has superior competent performance to catalyze oxygen (O₂) production in alkaline and acidic environments. The comparatively low overpotentials required are 222 mV and 304 mV, respectively, while generating a current density of 10 mA cm^-2. The reduced amount of precious metal and the further improvement in activity and durability make Ir₃Cu/C an excellent noble metal-based electrocatalyst. Meanwhile, IrCu/C has significant electrocatalytic performance for the HER in acidic media.

Understanding the relationship between particle size and ultrasonic treatment during the synthesis of metal nanoparticles

Ultrasonic treatment is an effective method for size refinement and dispersion of nanomaterials during their synthesis process. However, the quantitative relationship between ultrasonic conditions and particle size in the synthesis of metal nanoparticles has not been fully revealed. In this study, Cu nanoparticles were synthesized via the wet-chemical redox method under ultrasonic treatment, and statistical analysis on the evolution of particle size distribution was carried out. It was found that the particle size decreased exponentially with increasing ultrasonic power. A quantitative model was then proposed to describe the influence of ultrasonic power on the size distribution of metal nanoparticles from the perspective of the competition between the surface energy and the ultrasonic force. A relational expression of R_c∝γ⁴⁷P^-37 was revealed, and it was proved to fit well with the experimental results. Our study provides new experimental basis and theoretical method for understanding the mechanism of ultrasonic-induced size refinement of metal nanoparticles.

Ir3Pb alloy nanodendrites with high performance for ethanol electrooxidation and their enhanced durability by alloying trace Au

Porous Ir₃Pb nanodendrites exhibit excellent activity and superior CO₂ selectivity for the EOR under acidic conditions, and their durability can be enhanced dramatically by alloying trace Au.

Synthesis of branched Pd nanocrystals with tunable structures, their growth mechanism, and enhanced electrocatalytic properties

Branched Pd nanocrystals (NCs) with tunable architectures are synthesized in high yields (>95%) by simply adjusting the concentration of H2PdCl4 in the presence of fixed amounts of cetyltrimethylammonium bromide (CTAB), L-ascorbic acid (L-AA), and CuBr2(-) that is produced by reducing CuBr2 with L-AA. The as-synthesized branched Pd NCs have long, straight branches with thin diameters. At the same time, the growth process of the branched Pd NCs is monitored, which provides mechanistic insights for the branching growth of Pd NCs. It is identified that a high concentration of CTAB combined with an appropriate amount of CuBr2(-) species, acting as an in situ cooperatively organized template, is a decisive factor for the anisotropic growth of the branched Pd nanostructures during aqueous-phase reduction of the Pd precursor, using L-AA as a reducing agent. The electrocatalytic activities of the branched Pd NCs were tested. The branched Pd NCs are found to be an excellent electrocatalyst for the methanol oxidation reaction (MOR) largely due to the size and morphological effects of the branched structures.

Anisotropically branched metal nanostructures

This tutorial review provides an essential introduction to colloidally prepared branched metal nanostructures and their utility in plasmonics, catalysis and biomedicine.