Yoon-Cheol Ha

Optically transparent hydrogen evolution catalysts made from networks of copper–platinum core–shell nanowires

This article reports the fabrication of copper–platinum core–shell nanowires by electroplating platinum onto copper nanowires, and the first demonstration of their use as a transparent, conducting electrocatalyst for the hydrogen evolution reaction (HER). Cu–Pt core–shell nanowire networks exhibit mass activities up to 8 times higher than carbon-supported Pt nanoparticles for the HER. Electroplating minimizes galvanic replacement, allowing the copper nanowires to retain their conductivity, and eliminating the need for a conductive substrate or overcoat. Cu–Pt core–shell nanowire networks can thus replace more expensive transparent electrodes made from indium tin oxide (ITO) in photoelectrolysis cells and dye sensitized solar cells. Unlike ITO, Cu–Pt core–shell nanowire films retain their conductivity after bending, retain their transmittance during electrochemical reduction, and have consistently high transmittance (>80%) across a wide optical window (300–1800 nm).

The Role of Cuprous Oxide Seeds in the One-Pot and Seeded Syntheses of Copper Nanowires

This paper demonstrates that Cu2O nanoparticles form in the early stages of a solution-phase synthesis of copper nanowires, and aggregate to form the seeds from which copper nanowires grow. Removal of ethylenediamine from the synthesis leads to the rapid formation of Cu2O octahedra. These octahedra are introduced as seeds in the same copper nanowire synthesis to improve the yield of copper nanowires from 12% to >55%, and to enable independent control over the length of the nanowires. Transparent conducting films are made from nanowires with different lengths to examine the effect of nanowire aspect ratio on the film performance.

Real-Time Visualization of Diffusion-Controlled Nanowire Growth in Solution

This Letter shows that copper nanowires grow through the diffusion-controlled reduction of dihydroxycopper(I), Cu(OH)2(-). A combination of potentiostatic coulometry, UV-visible spectroscopy, and thermodynamic calculations was used to determine the species adding to growing Cu nanowires is Cu(OH)2(-). Cyclic voltammetry was then used to measure the diffusion coefficient of Cu(OH)2(-) in the reaction solution. Given the diameter of a Cu nanowire and the diffusion coefficient of Cu(OH)2(-), we calculated the dependence of the diffusion-limited growth rate on the concentration of copper ions to be 26 nm s(-1) mM(-1). Independent measurements of the nanowire growth rate with dark-field optical microscopy yielded 24 nm s(-1) mM(-1) for the growth rate dependence on the concentration of copper. Dependence of the nanowire growth rate on temperature yielded a low activation energy of 11.5 kJ mol(-1), consistent with diffusion-limited growth.

Extended self-ordering regime in hard anodization and its application to make asymmetric AAO membranes for large pitch-distance nanostructures

We report here a fast and reliable hard anodization process to make asymmetric anodic aluminum oxide (AAO) membranes which can serve as a template for large pitch-distance nanostructures. In order to make larger pitch distances possible, the common burning failure associated with the high current density during the conventional constant voltage hard anodization, especially at a voltage higher than a known limit, i.e., 155 V for oxalic acid, was effectively suppressed by using a burning-protective agent. A new self-ordering regime beyond the voltage limit was observed with a different voltage-interpore distance relationship of 2.2 nm V(-1) compared to the reported 2.0 nm V(-1) for hard anodization. Combining a sulfuric acid mild anodization with this new regime of hard anodization, we further demonstrate a scalable process to make an asymmetric membrane with size up to ~47 mm in diameter and ~60 μm in thickness. This free-standing membrane can be used as a template for novel nanopatterned structures such as arrays of quantum dots, nanowires or nanotubes with diameters of a few tens of nanometers and pitch distance of over 400 nm.

Production of Oxidation-Resistant Cu-Based Nanoparticles by Wire Explosion.

The low performance or high cost of commercially available conductive inks limits the advancement of printed electronics. This article studies the explosion of metal wires in aqueous solutions as a simple, low-cost, and environmentally friendly method to prepare metallic nanoparticles consisting of Cu and Cu alloys for use in affordable, highly conductive inks. Addition of 0.2 M ascorbic acid to an aqueous explosion medium prevented the formation of Cu2O shells around Cu nanoparticles, and allowed for the printing of conductive lines directly from these nanoparticles with no post-treatment. Cu alloy nanoparticles were generated from metal wires that were alloyed as purchased, or from two wires of different metals that were twisted together. Cu nanoparticles alloyed with 1% Sn, 5% Ag, 5% Ni and 30% Ni had electrical conductivities similar to Cu but unlike Cu, remained conductive after 24 hrs at 85 °C and 85% RH.

Analysis of voltages induced by distribution lines on gas pipelines

Because of the continuous growth of energy consumption and the tendency to site power lines and pipelines along the same route, the close proximity of power lines and buried metallic pipelines has become more and more frequent. Therefore, there has been and still is a growing concern about possible hazards resulting from the influence of power lines on metallic pipelines. Underground pipelines that run parallel to or in close proximity to power lines are subjected to induced voltages caused by the time-varying magnetic fields produced by the power line currents. The induced electro-motive force causes currents circulation in the pipeline and voltages between the pipeline and surrounding earth. This paper analyses the induced voltage on the gas pipelines buried in parallel with overhead power distribution lines.

Data logger apparatus for stray current measurement of subway and power line

In present, most of metallic structures (gas pipeline, oil pipeline, water pipeline, etc) are running parallel with subway and power line in Korea. Moreover subway system and power line make a stray current due to electrical corrosion on metallic structures. The owner of metallic structures has a burden of responsibility for the protection of corrosion and the prevention against big accident such as gas explosion or soil pollution and so on. So, they have to measure and analyze the data about P/S(Pipe to Soil) potential, amplitude of stray current, point of source of stray current and so. In this paper, results of development about data logger apparatus for measurement stray current of subway and power line are presented.

Electrochemical and Optical Characterization of the Corrosion Resistivity of Explosively Bonded Al-Cu Bimetal

With the usage of Al-Cu bimetals to connect aluminum and copper in power distribution systems growing persistently, efforts to mitigate the mechanical, electrical and electrochemical degradation are widely made. The explosive bonding technology has been considered as a countermeasure for the degradation. In this paper, electrochemical analysis and optical microscopic observation are carried out in order to compare the corrosion resistivity of the explosion type bimetal to the commonly used compression type bimetal. In particular, the effect of anions in the interfacial electrolyte on corrosion susceptibility was also investigated. The results show that the explosive bonding technology can prevent the interfacial corrosion caused by the formation of crevices and pits as well as by galvanic potential difference between aluminum and copper.

LiI-Doped Sulfide Solid Electrolyte: Enabling a High-Capacity Slurry-Cast Electrode by Low-Temperature Post-Sintering for Practical All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) based on sulfide solid electrolytes (SEs) have received great attention because of the high ionic conductivity of the SEs, intrinsic thermal safety, and higher energy density achievable with a Li metal anode. However, studies on practical slurry-cast composite electrodes show an extremely limited battery performance than the binder-free pelletized electrodes because of the poor interfacial robustness between the active materials and SEs by the presence of a polymeric binder. Here, we employ a low-temperature post-sintering process for the slurry-cast composite electrodes in order to overcome the binder-induced detrimental effects on the electrochemical performance. The LiI-doped Li3PS4 SEs are chosen because the addition of iodine not only improves the Li-ion conductivity and Li metal compatibility but also lowers the glass-transition and crystallization temperatures. Low-temperature post-sintering of composite cathodes consisting of a LiNi0.6Co0.2Mn0.2O2-active material, LiI-doped Li3PS4 SE, polymeric binder, and conducting agent shows a significantly improved electrochemical performance as compared to a conventional slurry-cast electrode containing pre-annealed SEs. Detailed analyses by electrochemical impedance spectroscopy and galvanostatic intermittent titration technique confirm that post-sintering effectively reduces the interfacial resistance and enhances the chemomechanical robustness at solid-solid interfaces, which enables the development of practical slurry-cast ASSLBs with sulfide SEs.

Rapid potential-controlled rectifier for securing the underground pipeline under electrolytic interference

In electrolytic interference circumstances such as underground pipelines in the vicinity of DC rail transportation power systems, either drainage methods or ICCP method has been widely used in order to secure the integrity of the pipelines. The drainage method is applied either by forced drainage system in which the driving voltage for draining the stray current from the pipelines is controlled by thyristors or by polarized drainage system which connects the pipeline with the railroads by diodes. In ICCP method, the phase-controlled rectifier with thyristors is in common use. Both methods, however, cannot respond to the dynamic fluctuation of the stray current. As a result, the pipe-to-soil potentials of the pipelines near railroads vary rapidly and therefore a new counter measure with dynamic response is necessary. In this paper, we introduce a new rapid potential-controlled rectifier consisting of full bridge circuits for bidirectional power output and IGBT switching device. Field test comparison with the existing forced drainage method showed the effectiveness of the developed rectifier for securing the pipelines under electrolytic interference.