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A method of ranking the rate of corrosion of metals in molten fluoride or chloride salts is proposed based on a zero-resistance ammeter (ZRA). The metal of interest for the corrosion study is shorted to a relatively noble metal counter electrode. Stainless steel 316 was tested in FLiNaK (LiF-NaF-KF). Haynes 230, stainless steel 316L, and Hastelloy C-22 were tested in MgCl2-NaCl-KCl. The ZRA oxidation current from SS-316L was reduced by 89% in FLiNaK after the addition of Li metal, which is known to reduce the redox potential. Post-test examination of metal surfaces and salt samples were also consistent with the relative ZRA current response in fluoride salt. Consistency was also observed between the relative ZRA response for the different metal alloys in the chloride salt and post-test analysis of metal and salt samples.

Co-electrodeposition of uranium and molybdenum from a LiCl-KCl melt was investigated using cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The electrochemical study showed that the electrodeposition of Mo occurred from a molten LiCl-KCl eutectic at potentials more negative than −0.3 V vs. Ag|Ag+. Electrodeposition at a low overpotential range (between −0.3 V and −0.35 V) resulted in flat, thin Mo films, whereas greater overpotentials led to the growth of 3D films. Conditions for simultaneous electrodeposition of U and Mo were then optimized by varying the concentrations of UCl3 and MoCl3 and the electrodeposition method applied. At a constant potential of −1.58 V, a melt containing 1.3 wt% UCl3 and 1.5 wt% MoCl3 resulted in the co-electrodeposition of dendrites due to the high overpotential for Mo electrodeposition. However, diffusion-controlled electrodeposition using the same potential and concentration resulted in a uniform and flat U-Mo film. This co-electrodeposition of U-Mo films could be applied to the preparation of low-cost U-Mo nuclear fuel.

With applications that include thermal energy storage in Gen3 concentrated solar power (CSP), molten salt batteries in grid scale energy storage, fuel and coolant in molten salt reactors (MSR), and oxide reduction/electrorefining of spent nuclear fuel; molten salts are potentially the most important all around medium for advanced energy systems. In particular, molten halide salts are known to be extremely hygroscopic, typically resisting complete thermal dehydration. Incomplete removal of water leads to hydrolysis; promoting formation of volatile HCl and insoluble oxide/hydroxide impurities in the molten salt. Depending on the application, this can accelerate corrosion, lower product yield through formation of insoluble oxides and oxychlorides, and/or reduce cell efficiency in electrolytic processes. Consequently, the generation, speciation, and electrochemical response of oxide and hydroxide impurities in various molten chloride salts have been widely studied. In this presentation, previously published work with LiCl-Li2O, MgCl2-KCl-NaCl, CaCl2, and CaCl2-CaO-CeCl3 molten chloride salts will be reviewed and discussed to reveal underlying commonality and lessons learned. In LiCl-Li2O and MgCl2-KCl-NaCl, LiOH and NaOH, respectively, were found in the salt after melting water-contaminated starting material. Electrode response signals were ascribed to both LiOH and NaOH contamination, and a nondestructive, in-situ method for determining their concentrations using cyclic voltammetry (CV) was developed. In CaCl2, Ca(OH)2 was found to be unstable, reverting to CaO at operating temperatures. Electrode signals were ascribed to the CaO, and an in situ measurement technique using CV to measure the CaO concentration was developed. The effect of CaO contamination on an electrorefining process was further studied in CaCl2-CaO-CeCl3, where CaO presence was shown to promote the formation of both insoluble Ce2O3 and CeClO. Electrochemical methods in all cases were further substantiated through support analyses including titration, thermogravimetric analysis, quadrupole mass spectrometry, and inductively coupled plasma mass spectrometry. These quantitative electroanalytical methods are shown to be both effective and versatile, showing promise as the development of real-time, in-line sensors for many molten salt processes continues to be of great consequence. Moreover, their versatility in different molten chloride salt systems is encouraging, as they can become an integral step in the evaluation of new use-cases for other molten halide salts and/or their suitability for new applications.

Molten fluoride salts have attracted interest as fuel and/or coolant for several different molten salt reactor (MSR) designs. Fluoride salts have many advantageous properties for these applications, such as high ionic conductivity, good heat transfer capacity, and high solubility for actinides. However, the impurities of the fluoride salt corrode the metals of MSR such as H2O, HF, and metal impurities. Therefore, it is important to monitor the oxides in molten fluoride salt. In this study, LiF-NaF-KF (FLiNaK) salt was used as a less toxic surrogate for FLiBe because of the toxicity of beryllium. In this work, we focused on measuring the concentration of oxide by adding Li2O in the FLiNaK salt using two electrochemical methods: cyclic voltammetry (CV) and square waver voltammetry (SWV). Moreover, after the electrochemical tests, the salts were analyzed for concentration of oxygen by LECO in order to compare with electrochemical results. We observed an oxidation peak corresponding to oxide using CV with a tungsten working electrode. Then SWV was used to measure the oxidation peak for oxide at various concentrations (0.1 to 2.0 wt.% of Li2O). SWV can measure the low concentration, because SWV is more sensitive to the oxidation current than CV through eliminating the non-faradaic current.

에 해당하는 백금 나노구조에서 가장 우수한 촉매 활성이 관찰되었다. 전하량에 따른 표면적의 변화보다 형성된 구조적 특이성과 결정면이 촉매 활성에 많은 영향을 미쳤다. 세밀한 백금 나노구조의 변화에 따른 전기화학적 촉매 활성 변화에 관한 본 연구결과는 보다 우수한 촉매 시스템을 고안하는 연구에 도움이될 것이다.Abstract : We report on the electrocatalytic activities at Pt nanostructure surfaces electrode-posited with different deposition charges on indium tin oxide electrodes for oxygen reductionand methanol oxidation reactions. The surface properties of Pt nanostructures depending ondeposition charges were characterized by scanning electron microscopy, electrochemical sur-face area measurement, X-ray diffraction, and CO stripping analysis, which were correlatedto the electrocatalytic activities. Pt nanostructures with deposition charge of 0.03 C exhibitedthe highest electrocatalytic activity for oxygen reduction and methanol oxidation. The sharpsites of Pt nanostructure and the presence of highly active facet play a key role, whereasthe electrochemical surface area does not significantly affect the electrocatalytic activity. Theresults obtained in this work with regard to the dependence of electrocatalytic activity onthe variation of the Pt nanostructures will give insights into the development of advancedelectrocatalytic systems.Keywords : Electrodeposition, Dendritic Pt, Oxygen reduction, Methanol oxidation

Molten chloride salts have recently gained attention for application to heat transfer and thermal energy storage in concentrating solar power (CSP) plants. In this study, we studied the electrochemical effect of addition of hydroxide ions and/or dissolved metals added to MgCl2–KCl–NaCl salt mixture. Open circuit potentiometry indicated that the salt's redox potential increased with addition of hydroxide ions and decreased with the addition of soluble magnesium metal. Cyclic voltammetry indicated that a reduction peak associated with hydroxides vanished with addition of Mg0. Hydrogen gas was evolved when a mixture of Mg metal and MgCl2–KCl–NaCl containing NaOH was heated to 650 °C. These results demonstrate the benefit and mechanism for redox potential control in this salt using dissolved Mg metal.

전기화학적 석출에 의해 Ag-Au 합금층을 전극표면에 형성한 후 진한 질산으로 Ag만을 녹여내는 기법으로 나노다공성 금 (nanoporous gold, NPG) 구조를 만들어 전기화학적 산소환원에 대한 촉매현상을 관찰하였다. 석출과정의 전구체의 농도비를 달리하였을 때 나타나는 NPG 표면구조의 변화를 주사전자현미경으로 관찰하고 전기화학적 표면적을 측정하였다. 전기화학적 산소환원 촉매 효율은 NPG 표면의 구조에 따라 달라졌는데, Ag/Au 비율이 2.0에 해당하는 NPG 구조에서 가장 우수한 촉매 현상이 관찰 되었다. 표면구조의 변화에 따른 촉매 활성 변화에서 다공성 구조의 역할이 매우 큰 기여를 하는 반면 표면적의 변화는 큰 영향을 미치지 않았다. 최적 조건의 NPG 구조상의 전기화학적 산소환원 과정의 메커니즘을 회전원판전극 실험을 통해 관찰하였는데, 산성 조건에서 NPG 전극에서 전기화학적 산소환원은 과산화수소를 거쳐 물이 생성되는 2-단계 4-전자 환원 메커니즘으로 진행되었고 염기성 조건에서는 산소가 4개의 전자 전달을 통해 물로 직접적으로 환원 되었다. Abstract : We investigate the electrocatalytic activities for oxygen reduction at nanoporousgold (NPG) surfaces fabricated by selective dissolution of Ag from electrodeposited Ag-Au lay-ers on electrode surfaces. The structure of NPG was controlled by changing the concentrationratios of precursor metal complexes during the electrodeposition of Ag-Au layers and the cor-responding surface morphology and surface area was examined. NPG structures with Ag/Auratio of 2.0 exhibited the highest electrocatalytic activity for oxygen reduction, where the nan-oporous structure plays a key role, but the surface area does not affect on the electrocatalyticactivity. The mechanism of electroreduction of oxygen was investigated by rotating disk elec-trode techniques. In acidic media, oxygen was first reduced to hydrogen peroxide followed byfurther reduction to water through 2-step 4-electron mechanism, whereas the oxygen wasreduced directly to water by 4-electron mechanism in basic media.Keywords : Nanoporous gold, Electrocatalysis, Oxygen reduction, Rotating disk electrode

A novel electroless Pt deposition method was exploited by employing the galvanic replacement process occurring between the Mn(3)O(4) surface and PtCl(4)(2-) complexes. The newly discovered process provides a simple protocol to produce the catalytic nanocomposite, in which a high density of ultrafine Pt nanocrystals is stably immobilized in a homogeneously dispersive state on the surface of Mn(3)O(4) nanoparticles. When the eletrocatalytic activity was tested for the oxygen reduction reaction, which limits the rate of the overall process in proton-exchange membrane fuel cells, the resulting Pt/Mn(3)O(4) nanocomposite showed highly enhanced specific activity and durability, compared with those of the commercial Pt/C catalyst.

Fabrication of dendritic Au rod (DAR) structures on Au surfaces via a simple electrodeposition from sulfite-based electrolytes containing Au(I) has been demonstrated. Scanning electron microscopic images show that the DAR structures contain highly faceted star-shaped protrusions in sub-100 nm scale. Electrochemical and X-ray diffraction results reveal that the DAR structures retain high amount of (110) and (100) crystalline domains on their surfaces. The unique morphology and surface orientation of DAR provide high electrocatalytic activities for glucose oxidation and oxygen reduction and efficient surface-enhanced Raman scattering activities.

The heterogeneous electron transfer at SiMo 12 O 40 4- monolayers on GC, HOPG, and Au electrode surfaces are investigated using cyclic voltammetric and electrochemical impedance spectroscopic (EIS) methods. The electron transfer of negatively charged Fe(CN) 6 3- species is retarded at SiMo 12 O 40 4- -modified electrode surfaces, while that of positively charged Ru(NH 3 ) 6 3+ species is accelerated at the modified surfaces. This is due to the electrostatic interactions between SiMo 12 O 40 4- layers on surfaces and charged redox species. The electron transfer kinetics of a neutral redox species, 1,1'-ferrocenedimethanol (FDM), is not affected by the modification of electrode surfaces with SiMo 12 O 40 4- , indicating the SiMo 12 O 40 4- monolayers do not impart barriers to electron transfer of neutral redox species. This is different from the case of thiolate SAMs which always add barriers to electron transfer. The effect of SiMo 12 O 40 4- layers on the electron transfer of charged redox species is dependent on the kind of electrodes, where HOPG surfaces exhibit marked effects. Possible mechanisms responsible for different electron transfer behaviors at SiMo 12 O 40 4- layers are proposed.

The interactions between four Keggin-type POMs (SiW 12 O 40 4- , PW 12 O 40 3- SiMo 12 O 40 4- , and PMo 12 O 40 3- ) and glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG) surfaces are investigated in a systematic way. Electrochemical results show that molibdate series POMs adsorb relatively stronger than tungstate POMs on GC and HOPG surfaces. Adsorption of POMs on HOPG electrode surfaces is relatively stronger than on GC surfaces. SiMo 12 O 40 4- species exhibits unique adsorption behaviors on HOPG surfaces. Surface-confined SiMo 12 O 40 4- species on HOPG surfaces exhibit unique adsorption behaviors and inhibit the electron transfer from the solution phase species. The catalytic activity of the surface-confined POMs for hydrogen peroxide electroreduction is also examined, where PW 12 O 40 3- species adsorbed on GC surfaces exhibits the highest catalytic efficiency among the investigated POM modified electrode systems.

The effect of polyoxometalate monolayers on the electrodeposition of Au nanoparticles (AuNPs) on glassy carbon (GC) surfaces was examined by electrochemical and scanning electron microscope techniques. The presence of -layers resulted in average particle sizes of ca. 60 nm, which is larger than AuNPs deposited on bare GC surfaces. AuNPs electrodeposited on -modified GC surfaces for 20 s exhibited the best electrocatalytic activity for oxygen reduction. This system exhibited similar or slightly better efficiency for oxygen reduction than a bare Au electrode. Rotating disk electrode experiments were also performed and revealed that the catalytic reduction of oxygen on AuNPs deposited on -modified GC electrodes is a two-electron process.

Platinum and its alloys play important roles in many industrial applications, such as CO/NOx oxidation in catalytic converters, synthesis of nitric acid, oil cracking, and fuel cells. In particular, platinum has been the most effective catalyst in proton-exchange membrane fuel cells (PEMFCs) owing to its outstanding electrocatalytic characteristics, which facilitate both hydrogen oxidation and oxygen reduction. Although carbon-supported platinum nanoparticles are currently used as cathode catalysts in fuel-cell technology, the commercialization of this technology for automotive applications still requires more economical and effective catalytic materials that can operate with a much smaller amount of expensive platinum. Over the last decade, pioneering researchers reported that the electrocatalytic performance of platinumbased materials can be improved by controlling the morphology of platinum nanocrystals or alloying platinum with other transition metals. In particular, the recently developed platinum nanocrystals with dendritic structures displaying a large number of edges and corner atoms exhibit dramatically enhanced catalytic activity in the oxygen reduction reaction (ORR), the slow kinetics of which is a major problem limiting the efficiency of PEMFCs. Although there has been considerable progress in the preparation of platinum nanodendrites through metal seed or block copolymer mediated processes, the lack of a facile synthetic route has limited the practical applications of nanodendrites. In particular, there is strong demand for a new synthetic method for the mass production of nanodendrites. In this context, the study described herein examines the possibility of large-scale synthesis of platinum nanodendrites in a controllable manner using the recently developed hollow nanoreactor, consisting of a porous silica nanoshell and an entrapped Au nanocrystal, which can confine the growth of metal species inside the silica cavity. The hollow silica nanoreactors provide a consistent and well-isolated environment for the growth of nanocrystals, which enables the morphologycontrolled synthesis of Pt nanodendrites even from a highly concentrated reaction suspension. Moreover, the porous silica shell can be removed readily under basic conditions, leaving a Pt nanodendrite in a surfactant-free form. The surfactant-free Pt dendrites were ready for catalytic applications without additional surfactant-removing processes under harsh conditions, which frequently cause the deformation of the nanocrystals and the decline of catalytic activities. In addition, the surfactant-free nature of the nanocrystals could make it possible to lend the surface various properties and functions through simply coordination of functional ligand molecules. Herein we report the novel synthesis of Pt nanodendrites by Au-seed-mediated growth inside hollow silica nanospheres. The proposed synthetic protocol based on isolated nanoreactors is quite remarkable in terms of the product yield per unit reaction volume compared to traditional cappingagent-based synthesis, which produces only a few milligrams of Pt nanodendrites per milliliter of reaction suspension. The nanoreactor-based synthetic route enabled the synthesis of as much as 1.5 g of uniform Pt nanodendrites from a single reaction in 40 mL aqueous suspension. The prepared ligandfree Pt nanodendrites exhibited greater ORR activity than commercial Pt black catalysts. We also report the extendable utility of the current method to prepare Pt nanodendrite colloid with tunable dispersity and hybrid nanocrystals of various metals. Scheme 1 summarizes the general synthetic routes for various Pt-based nanoparticles based on seed-mediated growth inside porous hollow silica nanospheres. The hollow nanoreactor (Au@h-SiO2), which consists of a porous silica nanoshell with inner and outer diameters of (14 2) and (28 2) nm, respectively, and a (4.0 0.6) nm Au nanocrystal captured inside the cavity, was prepared by selective etching of Fe3O4 from a silica nanosphere encapsulating a Fe3O4/Au hybrid nanocrystal. When an aliquot of Na2PtCl4 was added to an aqueous suspension containing Au@h-SiO2 nanospheres