Impact of Surface Hydrophilicity on Electrochemical Water Splitting.

The activity of electrocatalysts can be improved by modifying their electronic structures and surface morphologies. In electrochemical reactions with gas evolution, the performance of an electrocatalyst is also affected by how easily gas bubbles depart from an electrocatalyst surface. However, it is difficult to quantitatively estimate the improvement in the performance that can be achieved by promoting the departure of gas bubbles from the electrocatalyst surface. This study investigated the effect of surface hydrophilicity on the hydrogen evolution reaction (HER). The water contact angles of the nickel phosphorous (NiP) films were controlled from 40.3 to 77.2° with imperceptible differences in their intrinsic electronic structures and surface areas. Electrochemical analyses and in situ visualization of the gas evolution on the NiP films indicated that an increase in the hydrophilicity of the electrocatalysts reduced the size of gas bubbles formed on the NiP films and shortened the duration of the bubbles' stay on the NiP surface. A faster gas departure enabled continuous participation of the electrocatalyst surface in hydrogen evolution, leading to a stable electrochemical behavior of the electrocatalyst and a decrease in the overpotential at a given current density. A full-cell test revealed that the enhancement of hydrogen bubble departure on a hydrophilic NiP surface with a contact angle of 40.3° reduced the overpotential by 134 mV at a current density of 100 mA/cm2 compared to a more hydrophobic film with a contact angle of 77.2°.

Gravimetric analysis of the autocatalytic growth of copper microparticles in aqueous solution.

The growth kinetics of copper microparticles was analysed by using the gravimetric method. The copper microparticles were synthesized in aqueous solution containing cupric ion and HCHO under various conditions (temperature, additive) and the total mass was monitored during the synthesis. The relation between the total mass and time was formularized using heterogeneous and pseudo-first order reaction kinetics of the autocatalytic surface growth of copper with a modification of the Finke-Watzky kinetic model. Fitting of theoretical curves to the experimental results with various temperatures provided the rate constants of the surface growth, and the reaction activation energy was found from the Arrhenius plot to be 105.4 kJ mol-1. The obtained value was validated by comparing it with one from copper film growth. Its change was observed with the addition of 2,2'-dipyridyl during synthesis.

Fabrication of Uniform Wrinkled Silica Nanoparticles and Their Application to Abrasives in Chemical Mechanical Planarization.

A simple one-pot method is reported for the fabrication of uniform wrinkled silica nanoparticles (WSNs). Rapid cooling of reactants at the appropriate moment during synthesis allowed the separation of nucleation and growth stages, resulting in uniform particles. The factors affecting particle size and interwrinkle distance were also investigated. WSNs with particle sizes of 65-400 nm, interwrinkle distances of 10-33 nm, and surface areas up to 617 m2 g-1 were fabricated. Furthermore, our results demonstrate the advantages of WSNs over comparable nonporous silica nanospheres and fumed silica-based products as an abrasive material in chemical mechanical planarization processes.

Ethylenediamine Promotes Cu Nanowire Growth by Inhibiting Oxidation of Cu(111).

The synthesis of metal nanostructures usually requires a capping agent that is generally thought to cause anisotropic growth by blocking the addition of atoms to specific crystal facets. This work uses a series of electrochemical measurements with a quartz crystal microbalance and single-crystal electrodes to elucidate the facet-selective chemistry occurring in the synthesis of Cu nanowires. Contrary to prevailing hypotheses, ethylenediamine, a so-called capping agent in the synthesis of Cu nanowires, causes anisotropic growth by increasing the rate of atomic addition to (111) facets at the end of a growing nanowire relative to (100) facets on the sides of a nanowire. Ethylenediamine increases the reduction rate of Cu(OH)2- on a Cu(111) surface relative to Cu(100) by selectively inhibiting the formation of Cu oxide on Cu(111). This work demonstrates how studying facet-selective electrochemistry can improve the understanding of the processes by which atoms assemble to form anisotropic metal nanostructures.