Dissolved Metal Salts Research Articles

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]+ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

Direct Vat‐Photopolymerization 3D Printing of Hierarchically Porous SiC Loaded with Co/Ni Based Catalysts by Using Pickering Emulsions

AbstractHierarchically porous silicon carbide (SiC) is an important catalyst support widely used in various gas and liquid catalytic processes. Conventional approaches to fabricate such SiC have limited design flexibility and separated catalyst‐loading step is necessitated. Herein, a one‐step, direct vat‐photopolymerization 3D printing of hierarchically porous SiC loaded with Co/Ni based catalyst is demonstrated with Pickering emulsion as feedstock for the first time. Compared with normal ceramic slurries, Pickering emulsion dramatically increases the cure depth (by 50%) and emulsion stability, which allow continuous printing of complex SiC structures with uniform pore morphology. The resultant hierarchical porous SiC offered ≈40% better mechanical strength as compared with non‐hierarchical counterpart. By dissolving metal salts into aqueous phase in Pickering emulsions, complex architected structures with Co or Ni/Co in situ loaded in SiC matrix are printed. The metal salts are then thermally converted into oxides or silicates as catalysts anchored on SiC, exhibiting excellent catalytic activity and reusability. The emulsion templating strategy holds great facility to load various highly attractive materials such as high entropy oxides or functional fillers whilst reaping the benefits of vat photopolymerization for a myriad of applications in catalysis, batteries, and structural supports.

(Invited) Solvation Control in Deep Eutectic Solvent Electrolytes for Stable Plating/Stripping of Zn in Battery Applications

Within the field of battery applications, deep eutectic solvents (DESs) have emerged as innovative electrolytes for rechargeable Zinc-ion batteries (ZIBs) . ZIBs traditionally employ neutral or weakly acidic aqueous electrolytes, which are susceptible to the standard anode drawback such as dendrite formation and passivation. DES-based electrolytes can facilitate the reversible plating and stripping of Zn, mitigating also dendrite growth . One notable benefit of DES solvents over their aqueous counterparts is that the concentration of electroactive species controls the shape evolution of electrodes during electroplating. For this reason, the coordination chemistry and metal complex formed between the Lewis acid of the metal and the Lewis base of the DES play a central role. Moreover, water can be added to the eutectic mixtures to increase the diffusion coefficient of the electroactive species and lower the electrolyte viscosity without destroying the eutectic nature if the concentration is kept under 40%.Regarding metal plating/stripping processes, DESs offer a notable advantage due to their high capacity to dissolve metal salts, oxides, and hydroxides, inhibiting the formation of insoluble oxides and hydroxides . Moreover, the unique coordination properties of Zn2+ in DESs lead to an atypical voltammetric behavior, characterized by a cathodic peak in the cathodic branch of the anodic-going scan. The mechanistic studies of Zn electrodeposition onto glassy carbon (GC) from DESs have concluded that the metal is formed by the reduction of an intermediate Zn-containing species. Finally, the reactivity of choline chloride and ethylene glycol can impact coordination in that these species can be dehydrogenated at negative potential forming RO¯, which can replace one or more chloride ligands in [ZnCl4]2− . The correlation between the chemistry of Zn2+ solutions and DESs is elucidated, and the peculiarities of Zn electrochemistry can be rationalized in terms of the DES–electrode interface structure. Although few studies on hydrated DESs have been conducted, the literature remains scant.Shi et al. conducted a study on DES composed of ZnCl2 and acetamide with different concentration of water. The authors employed various spectroscopic techniques, including FT-IR, Raman, and 17O NMR, to investigate the effect of water on the coordination geometry of Zn2+ and its consequent impact on Zn plating. Interestingly, the authors observed that the addition of small amounts of water, below the threshold for direct water-water interaction, resulted in significant alterations of the Zn2+ coordination geometry. In fact, based on the accepted view that Zn electrodeposition is a process that involves desolvation and charge-transfer steps, [ZnCl(acetamide)2(H2O)]+ was shown to undergo successive deamidation and dehydration, yielding [ZnCl(acetamide)]+ from which the metal center is finally reduced. Although [ZnCl(acetamide)3]+ is the most stable species, the energy barrier for dehydration is significantly lower than that for deamidation. Therefore, [ZnCl(acetamide)2(H2O)]+ with lower dissociation energy is the actual electroactive species . The solvation of Zn also affects the nucleation overpotential, as Zn2+ in hydrated DES exhibits faster desolvation kinetics, resulting in a lower nucleation overpotential. In addition, Zhao et al. investigated the properties of a “water-in-DES” electrolyte (~30 mol.% H2O) based on the urea/LiTFSI/Zn(TFSI)2 mixture and discovered that the preferential interaction between water and metal cations promotes interfacial charge transfer. Notwithstanding the important contribution of these papers, the mechanism of Zn electrodeposition in DES has not been conclusively assessed. To address this knowledge gap, our research aims to investigate Zn electrodeposition from two distinct, hydrated DESs: ChU and ChEG with approximately 30% H2O content. To gain control of the impact of the cathode material, we carried out our electrochemical tests by employing GC, Zn, Pt and Au electrodes. Furthermore, to evaluate the performance of these electrolytes under realistic device conditions, electrochemical cycling tests were conducted on symmetric CR2023 coin cells.In this study, we have demonstrated the beneficial effect of water addition on reducing the electrolyte viscosity, which consequently resulted in lower anodic and cathodic overpotentials and improved charge/discharge cyclability. Specifically, the electrolytes ChEG and ChU failed due to passivation and short circuits, respectively. The ChU electrolyte showed regular chronopotentiometric transients until cell failure, and this was supported by multiple cyclic voltammetry (CV) measurements, which showed reversible Zn plating/stripping in this system. Notably, our cell cycling tests were performed at higher current densities and exhibited longer lifetimes compared to previous literature reports. The unusual CV patterns observed with gold and glassy carbon (GC) electrodes, featuring cathodic peaks on both forward and backward scans, were elucidated using complementary electrochemical and in situ Raman spectroscopy measurements. Figure 1

Experimental and Theoretical Investigation of Alkene Transformations in Oceanic Hydrothermal Fluids: A Mechanistic Study of Styrene

AbstractNatural organic matter plays an important role in oceanic hydrothermal systems through a combination of geological and chemical processes. However, identifying the hydrothermal pathways of organic compounds is still quite limited, preventing us from understanding how organic matter is transformed in hydrothermal systems. In this study, we focus on the reaction pathways of alkenes, which represent a key functional group intermediate linking the most abundant hydrocarbons in seafloor hydrothermal environments. Three major pathways are observed for alkenes under mild hydrothermal conditions, including hydration, oxidation, and dimerization. The pathway distributions of alkenes can be affected by the presence of dissolved metal salts; hydration of alkenes is driven by metal ions via the change of solution pH, while alkene dimerization is controlled by pH and the type of metal cations and complexes. Overall, this study identifies alkene hydrothermal pathways and highlights the important roles of metal salts in controlling hydrothermal transformations.

Vapor-Phase Processing of Metal-Organic Frameworks.

ConspectusPorous metal-organic frameworks (MOFs), formed from organic linkers and metal nodes, have attracted intense research attention. Because of their high specific surface areas, uniform and adjustable pore sizes, and versatile physicochemical properties, MOFs have shown disruptive potential in adsorption, catalysis, separation, etc. For many of these applications, MOFs are synthesized solvothermally as bulk powders and subsequently shaped as pellets or extrudates. Other applications, such as membrane separations and (opto)electronics, require the implementation of MOFs as (patterned) thin films. Most thin-film formation methods are adapted from liquid-phase synthesis protocols. Precursor transport and nucleation are difficult to control in these cases, often leading to particle formation in solution. Moreover, the use of solvents gives rise to environmental and safety challenges, incompatibility issues with some substrates, and corrosion issues in the case of dissolved metal salts. In contrast, vapor-phase processing methods have the merits of environmental friendliness, control over thickness and conformality, scalability in production, and high compatibility with other workflows.In this Account, we outline some of our efforts and related studies in the development and application of vapor-phase processing of crystalline MOF materials (MOF-VPP). We first highlight the advances and mechanisms in the vapor-phase deposition of MOFs (MOF-VPD), mainly focusing on the reactions between a linker vapor and a metal-containing precursor layer. The characteristics of the obtained MOFs (thickness, porosity, crystallographic phase, orientation, etc.) and the correlation of these properties with the deposition parameters (precursors, temperatures, humidity, post-treatments, etc.) are discussed. Some in situ characterization methods that contributed to a fundamental understanding of the involved mechanisms are included in the discussion. Second, four vapor-phase postsynthetic functionalization (PSF) methods are summarized: linker exchange, guest loading, linker grafting, and metalation. These approaches eliminate potential solubility issues and enable fast diffusion of reactants and guests as well as a high loading or degree of exchange. Vapor-phase PSF provides a platform to modify the MOF porosity or even introduce new functionalities (e.g., luminescence photoswitching and catalytic activity). Third, since vapor-phase processing methods enable the integration of MOF film deposition into a (micro)fabrication workflow, they facilitate a range of applications with improved performance (low-k dielectrics, sensors, membrane separations, etc.). Finally, we provide a discussion on the limitations, challenges, and further opportunities for MOF-VPP. Through the discussion and analysis of the vapor-phase processing strategies as well as the underlying mechanisms in this Account, we hope to contribute to the development of the controllable synthesis, functionalization, and application of MOFs and related materials.

Tuning the Excited-State Dynamics of Acetophenone Using Metal Ions in Solution.

The effects of dissolved metal salts on the excited-state dynamics of acetophenone in solution have been explored by using ultrafast transient absorption spectroscopy at two UV excitation wavelengths. In the absence of metal ions, the S1(nπ*) transition of acetophenone is excited at 320 nm, with intersystem crossing (ISC) occurring with a time constant τISC = 5.95 ± 0.47 ps in acetonitrile solution. Excitation at 280 nm accesses the S2(ππ*) state, which internally converts (<0.2 ps) to S1 before undergoing ISC with τISC = 4.36 ± 0.14 ps. Coordination to Mg2+ ions makes the S2 state accessible to excitation at 320 nm, with the rate of S2 → S1 internal conversion reducing 3-fold but the ISC rate increasing. These changes to the excited-state energies and dynamics of this model photosensitizer indicate that dissolved metal salts could modify the photochemistry of synthetically useful homogeneous photocatalytic systems.

Low temperature CO oxidation by doped cerium oxide electrospun fibers

We investigated CO oxidation behavior of doped cerium oxide fibers. Electrospinning technique was used to fabricate the inorganic fibers after burning off polymer component at 600 °C in air. Cu, Ni, Co, Mn, Fe, and La were doped at 10 and 30 mol% by dissolving metal salts into the polymeric electrospinning solution. 10 mol% Cu-doped ceria fiber showed excellent catalytic activity for low temperature CO oxidation with 50% CO conversion at just 52 °C. This 10 mol% Cu-doped sample showed unexpected regeneration behavior under simple ambient air annealing at 400 °C. From the CO oxidation behavior of the 12 samples, we conclude that absolute oxygen vacancy concentration estimated by Raman spectroscopy is not a good indicator for low temperature CO oxidation catalysts unless extra care is taken such that the Raman signal reflects oxide surface status. The experimental trend over the six dopants showed limited agreement with theoretically calculated oxygen vacancy formation energy in the literature.

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes

AbstractThe electrodeposition of noble metals using corresponding dissolved metal salts represents an interesting process for the improvement of the electrocatalytic hydrogen evolution reaction (HER) properties of less active substrate materials. The fact that only a small fraction of the dissolved noble metals reaches the substrate represents a serious obstacle to this common procedure. We therefore chose a different path. It was found that the HER activity of Ni42 alloy drastically increased (η=140 mV at j=10 mA cm−2; pH 1) when a platinum counter electrode was used during polarization experiments in acid. This improvement was caused by a platinum transfer from the platinum anode to the steel cathode, a process which occurred simultaneously to the hydrogen evolution. The negligible accumulation of Pt (26 μg) in the electrolyte turns this straight‐forward transfer procedure into a highly cost‐effective, environmentally friendly, and waste reducing approach for the generation of cheap, stable and effective HER electrodes.

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes.

The electrodeposition of noble metals using corresponding dissolved metal salts represents an interesting process for the improvement of the electrocatalytic hydrogen evolution reaction (HER) properties of less active substrate materials. The fact that only a small fraction of the dissolved noble metals reaches the substrate represents a serious obstacle to this common procedure. We therefore chose a different path. It was found that the HER activity of Ni42 alloy drastically increased (η=140 mV at j=10 mA cm−2; pH 1) when a platinum counter electrode was used during polarization experiments in acid. This improvement was caused by a platinum transfer from the platinum anode to the steel cathode, a process which occurred simultaneously to the hydrogen evolution. The negligible accumulation of Pt (26 μg) in the electrolyte turns this straight‐forward transfer procedure into a highly cost‐effective, environmentally friendly, and waste reducing approach for the generation of cheap, stable and effective HER electrodes.

Piece by Piece-Electrochemical Synthesis of Individual Nanoparticles and their Performance in ORR Electrocatalysis.

The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well-defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution-phase precursor entities are then reduced electrochemically-one by one-to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl4 -filled micelles. These Au NP-decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor-filled nanocontainers are presented as a new route to nanoparticle-modified electrodes with high catalyst utilization.

Piezoelectric Effect and Electroactive Phase Nucleation in Self-Standing Films of Unpoled PVDF Nanocomposite Films

Novel polymer-based piezoelectric nanocomposites with enhanced electromechanical properties open new opportunities for the development of wearable energy harvesters and sensors. This paper investigates how the dissolution of different types of hexahydrate metal salts affects β-phase content and piezoelectric response (d33) at nano- and macroscales of polyvinylidene fluoride (PVDF) nanocomposite films. The strongest enhancement of the piezoresponse is observed in PVDF nanocomposites processed with Mg(NO3)2⋅6H2O. The increased piezoresponse is attributed to the synergistic effect of the dipole moment associated with the nucleation of the electroactive phase and with the electrostatic interaction between the CF2 group of PVDF and the dissolved salt through hydrogen bonding. The combination of nanofillers like graphene nanoplatelets or zinc oxide nanorods with the hexahydrate salt dissolution in PVDF results in a dramatic reduction of d33, because the nanofiller assumes a competitive role with respect to H-bond formation between PVDF and the dissolved metal salt. The measured peak value of d33 reaches the local value of 13.49 pm/V, with an average of 8.88 pm/V over an area of 1 cm2. The proposed selection of metal salt enables low-cost production of piezoelectric PVDF nanocomposite films, without electrical poling or mechanical stretching, offering new opportunities for the development of devices for energy harvesting and wearable sensors.

Electrochemical Removal of Copper from Regenerated Pickling Solutions of Steel Plants

The spent pickle liquor contains the dissolved metal salts of iron, chrome, copper, nickel and zinc [1]. The acid can be cleaned from its impurities, except for its copper ion, by the regeneration process. When the copper concentration of the pickling solution exceeds the level of about 100 ppm, the copper inside the solution replaces the iron in the steel and copper starts plating randomly on the metal surface in the following pickling processes. Because of the plating problem, the acid needs to be discard from the acid line. By adding fresh acid to the line the discarding can be delayed [2]. An electrochemical procedure was conducted to overcome the cementation problem experimentally in an environmental and economical way. Electrowinning of dilute copper from strong acid solution is a challenge in this case so the optimum current density, electrolysis duration and the electrode materials were determined in this study. It was found that increase in the current density and electrolysis duration increases the copper removal, but changes the morphology of deposits. A slower compact deposition procedure was selected to achieve continuous removal of copper instead of faster discontinuous powder deposition from the regenerated pickling solutions of steel plants.

Highly Uniform Resistive Switching Properties of Solution-Processed Silver-Embedded Gelatin Thin Film.

The silver-embedded gelatin (AgG) thin film produced by the solution method of metal salts dissolved in gelatin is presented. Its simple fabrication method ensures the uniform distribution of Ag dots. Memory devices based on AgG exhibit good device performance, such as the ON/OFF ratio in excess of 105 and the coefficient of variation in less of 50%. To further investigate the position of filament formation and the role of each element, current sensing atomic force microscopy (CSAFM) analysis as well as elemental line profiles across the two different conditions in the LRS and HRS are analyzed. The conductive and nonconductive regions in the current map of the CSAFM image show that the conductive filaments occur in the AgG layer around Ag dots. The migration of oxygen ions and the redox reaction of carbon are demonstrated to be the driving mechanism for the resistive switching of AgG memory devices. The results show that dissolving metal salts in gelatin is an effective way to achieve high-performance organic-electronic applications.

Direct-coated copper nickel tin sulphide (Cu2NiSnS4) thin films from molecular ink

This paper describes direct-coating of earth-abundant Cu2NiSnS4 (CNTS) thin films on glass from molecular ink synthesized easily by dissolving metal salts and thiourea in methanol. Films were prepared by dip-coating and drop-casting of precursor films and subsequent annealing at 160 °C in air. X-ray Diffraction (XRD) of films confirmed cubic CNTS. Scanning Electron Microscope (SEM) revealed that dip-coated films are continuous whereas drop-casted ones are granular with voids between the grains. The band gap of CNTS is about 1.6 eV with electrical conductivity of 1.7 × 10−3 S/cm and hole mobility of 2.3 × 10−3 cm2/Vs.

Preparation of Supported Palladium Catalysts using Deep Eutectic Solvents.

Deep eutectic solvents (DESs) dissolve metal salts or oxides and are used as solvent and carbon source for the preparation of supported palladium catalysts. After dissolving of the palladium salt in the DES, the pyrolysis of the mixture under nitrogen atmosphere yields catalytically active palladium on supporting material composed of carbon, nitrogen and oxygen (CNO) by a simple single step preparation method without further activation. The catalysts were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and CHNS/O elementary analysis. The amount of functional groups on the surface of the supporting material was determined by Boehm titrations. Moreover, the activity of the prepared catalysts was evaluated in the hydrogenation of linear alkenes and compared with a commercial Pd/C catalyst.

Quantitative evaluation of inhibitory effect of various substances on anaerobic ammonia oxidation (anammox)

The inhibitory effect of 20 substances of various chemical species on the anaerobic ammonia oxidation (anammox) activity of an enrichment culture, predominated by Candidatus Brocadia, was determined systematically by using a 15N tracer technique. The initial anammox rate was determined during first 25min with a small-scale anaerobic batch incubation supplemented with possible inhibitors. Although Cu2+ and Mn2+ did not inhibit anammox, the remaining 18 substances [Ni2+, Zn2+, Co2+, [Formula: see text] , Fe2+, 4 amines, ethylenediaminetetraacetic acid (EDTA), ethylenediamine-N,N'-bis (2-hydroxyphenylacetic acid) (EDDHA), citric acid, nitrilotriacetic acid (NTA), N,N-dimethylacetamide (DMA), 1,4-dioxane, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and tetrahydrofuran (THF)] were inhibitory. Inhibitory effect of NTA, EDDHA, THF, DMF, DMA and amines on anammox was first determined in this study. Inhibitory effects of metals were re-evaluated because chelators, which may interfere inhibitory effect, have been used to dissolve metal salts into assay solution. The relative anammox activities as a function of concentration of each substance were described successfully (R2>0.91) either with a linear inhibition model or with a Michaelis-Menten-based inhibition model. IC50 values were estimated based on either model, and were compared. The IC50 values of the 4 chelators (0.06-2.7mM) and 5 metal ions (0.02-1.09mM) were significantly lower than those of the 4 amines (10.6-29.1mM) and 5 organic solvents (3.5-82mM). Although it did not show any inhibition within 25min, 0.1mM Cu2+ completely inhibited anammox activity in 240min, suggesting that the inhibitory effect caused by Cu2+ is time-dependent.

Binary Fe and Mn Oxide Nanoparticle Supported Polymeric Anion Exchanger for Arsenic Adsorption: Role of Oxides, Supported Materials, and Preparation Solvent

In this work, binary Fe/Mn oxide nanoparticles were incorporated onto the matrix of anion exchange resin, resulting in hybrid polymeric/inorganic nanoadsorbent named as A502P-Fe/Mn. During synthesis process, effects of various types of metal oxides, preparation solvent, supporting materials, and loading cycles were also investigated. To reduce the charge repulsion force between cationic Fe3+ and Mn4+ ions and fixed-positively charged quaternary amine (R4N+) functional groups of the anion exchange support, mixed solution containing DI/ethanol was introduced to dissolve metal salts during the preparation process. The data obtained by equilibrium batch test indicated that the A502P-Fe/Mn prepared from mixed 50:50 of DI and ethanol exhibited the highest As (V) sorption capacity. The synthesized material was further characterized by using scanning electron microscope (SEM) equipped with energy dispersive X ray spectroscopy (EDX) to verify the existence and distribution of elemental Fe, Mn, and As inside the polymeric beads. Equilibrium As (V) sorption isotherm, effect of solution pH, and point of zero charge of material were also evaluated. This A502P-Fe/Mn can have a promising potential for arsenic removal applications.

High resolution nanofabrication using self-assembly of metal salt-polymer nanocomposite film

For fabrication of nanostructures that do not need long range ordering and precise placement, such as antireflective structure for photovoltaic and display applications and super-hydrophobic surface for lab-on-chip applications, bottom-up fabrication techniques are more preferable than top-down techniques due to their low cost. Here, the authors report a simple process to obtain nanostructures using low-cost spin-coating method and pattern transfer. They first dissolved metal salt and polymer in a solvent. After spin-coating to form a thin film, the authors annealed the film to attain a phase separation. Next, the nanocomposite film was etched with oxygen plasma to remove the polymer matrix, leaving behind nanoscale metal salt islands that can be used as a hard mask for dry etching the substrate or sublayer. With optimal metal salt (nickel nitrate hexahydrate) and polymer (polymethylmethacrylate) weight ratio, the authors achieved wafer-scale high resolution (down to 20 nm) pillar structures etched in silicon with 100 nm height and ∼100 nm spacing.

Nickel Selenide As High-Efficiency Catalyst for Oxygen Evolution Reaction

Electrolytic water splitting is considered to be clean energy generation and a substitute for fossil fuels and oxygen evolution reaction (OER) is an important reaction involved in water splitting. However, OER typically being a 4 electron process requiring O – O bond formation is a kinetically slow process typically requiring catalysts.1Identifying more-efficient, stable, earth-abundant catalysts for the OER has long been researched. Recently, Ni-oxide based OER electrocatalysts were found to exhibit high efficiency, and it was stated that the catalytic performance can be further tuned by increasing covalency in the metal-oxygen bonds. The catalytic properties of the metal oxides can also be influenced through other variables of the electrodeposition reaction such as the total and relative concentration(s) and composition(s) of dissolved metal salts and extra electrolytes, the pH, and the duration of the electrodeposition current.2 Here we report, for the first time, a metal-rich form of Ni-selenide, Nickel subselenide, Ni3Se2 as a potential oxygen evolution electrocatalyst in alkaline condition. The Ni3Se2 phase has a structure similar to the sulfur mineral Heazlewoodite, which contains metal – metal bonding. The electrocatalytic activities of Ni3Se2towards OER was seen to be at par with or even superior to the transition metal oxide based electrocatalyst in terms of onset overpotential for O2 evolution as well as overpotential to reach a current density of 10 mA/cm2 (observed at 290 mV). The electrocatalytic Ni3Se2 were grown by electrodeposition on conducting substrates and the deposition parameters including pH of the electrolytic bath, deposition potential, and substrate composition were seen to have some influence on the catalytic activity. Annealing of the as-deposited electrocatalytic films in an inert atmosphere enhanced their catalytic efficiencies by decreasing the overpotential (@10 mA/cm2) as well increasing the current density. In addition to low overpotentials, these Ni3Se2 electrodeposited films were seen to be exceptionally stable under conditions of continuous O2 evolution for extended period (48 – 66 h). The structure and morphology of these films has been characterized with powder X-ray diffraction, Scanning and Transmission electron microscopy, Raman, and X-ray photoelectron spectroscopy. We will discuss in detail the electrochemical and structural characterizations of these films along with catalytic activities.

Unexpected Fluorescence of Polyols and PEGylated Nanoparticles Derived from Carbon Dot Formation

Synthesis of nanoparticles in high-boiling alcohols (so-called polyol synthesis) and surface functionalization of nanoparticles with polyethylene glycol (so-called PEGylation) in combination with certain heating are often accompanied with an intense fluorescence in the blue to green spectral range. Based on the polyol synthesis of Zn3(PO4)2 nanoparticles and a critical consideration of the relevant experimental conditions—including the presence of nanoparticles, the role of dissolved metal salts (ZnCl2, MgCl2, KCl), the type of the polyol (DEG, GLY, PEG400), the temperature and time of heating (150–230 °C, 1–6 h)—we can correlate the observed fluorescence to the formation of carbon dots (C-dots) stemming from thermal decomposition (i.e., dehydration and carbonization) of the polyol. Thus, the thermal decomposition of polyols results in C-dots with a diameter of 3–5 nm at narrow size distribution. The formation of C-dots is confirmed by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and fluorescence spectra.