Bifunctional Stabilizer Research Articles

3D conifer-like WO3 branched nanowire arrays electrode for boosting electrochromic-supercapacitor performance

Electrochromic-supercapacitors (ESCs) have shown great perspective in multifunctional smart devices due to their special function of monitoring the energy storage level by the visible color changes. However, the poor areal capacitance at high optical modulation(ΔT) and the inferior bifunctional lifespan hinder the practical application of ESCs. It is thus important to develop feasible ways to boost the optical-electrochemical properties and comprehend the corresponding inner mechanism. Inspired by nature’s conifer structure, herein, 3D hexagonal WO3 branched nanowire arrays/F-doped SnO2 (h-WO3 BNW/FTO) electrode have been successfully constructed via a single-step hydrothermal reaction followed by annealing process. Such biomimetic conifer-like structure is shaped by the separating crystal growth effect coupled with the specific topological structure of h-WO3. Benefiting from bionic structure, h-WO3 BNW/FTO electrode delivers a high areal specific capacity (0.0223 mAh cm−2) and large corresponding ΔT respond (80% ΔT at 650 nm) at 5 mV s−1, as well as outstanding optical-electrochemical cycle stability. Moreover, the aluminum storage mechanism during the optical-electrochemical process is affirmed using cyclic voltammetry and in-situ X-ray method. For practical application, the assembled ESC device based on the h-WO3 BNW/FTO electrode delivers a high 22.75 mF cm−2 areal specific capacitance, corresponding 45.81% ΔT (at 650 nm) and long-term bifunctional stability (over 90% bifunctional retention after 5000 cycles). Meanwhile, the visually monitoring capacity of the device is realized through the color changes. This study provides some insights into the biomimetic design for advanced bifunctional electrodes and the underlying mechanism affecting the electrochromic-charge storage performance.

Highly efficient and stable bifunctional electrocatalysts with decoupled active sites for hydrogen evolution and oxygen reduction reactions

Alkaline electrolysis is one of the most powerful technologies to produce hydrogen energy, where the electrocatalysts play an important role. The cathode electrocatalysts often suffer from undesirable oxidation due to the oxygen gas crossover through the porous separator during electrolysis. This leads to oxygen reduction reaction (ORR) on the cathode electrocatalysts, resulting in the loss of activity for hydrogen evolution reaction (HER). Here, we report a highly efficient and durable HER and ORR bifunctional electrocatalyst derived from Ni metal-organic frameworks to address the above problem. Decoupled active sites for ORR and HER are induced in a hybrid material, NiFeP@Ni_NC, where an ORR catalytic N-doped nanocarbon layer can protect a HER catalytic Niδ+ from the undesired ORR. Therefore, excellent bifunctional stability is secured for NiFeP@Ni_NC. The strategy to enhance HER stability presented herein can be widely extended to design bifunctional electrocatalysts with improved stability in alkaline electrolysis.

Cover Feature: Polypyrrole‐Assisted Co3O4 Anchored Carbon Fiber as a Binder‐Free Electrode for Seawater Batteries (ChemElectroChem 1/2019)

The Cover Feature illustrates the morphology of the binder-free electrode (bf-PPy+Co3O4@CF) and its reactions in seawater. The binder-free (bf) air electrode is structured with Co oxide (Co3O4) anchored on carbon fiber (CF) tissues with the assistance of polypyrrole-doped carbon (PPy/C) by using a simple infiltration technique. The bf-PPy+Co3O4@CF electrode exhibits excellent bifunctional stability for seawater batteries, presenting a comparable performance to the binder-included Pt/C+IrO2 electrode. More information can be found in the Article by G. Kim and co-workers on page 136 in Issue 1, 2019 (DOI: 10.1002/celc.201801219).

Polypyrrole‐Assisted Co3O4 Anchored Carbon Fiber as a Binder‐Free Electrode for Seawater Batteries

AbstractAn efficient, durable and cost‐effective air electrode is essential to achieve a practicable metal‐air battery. The conventional preparation of electrode uses polymer binders to ensure good physical contacts between catalysts and the electrode scaffold. However, the use of polymer binders introduces inevitable loss of the electrochemically active surface area and restricts access of the reactants, owing to the electrically insulating properties and hydrophobic properties of polymer binders. In this work, a binder‐free air electrode is structured by using Co oxide anchored on carbon fiber tissues with the assistance of polypyrrole‐doped carbon (PPy/C) through a simple infiltration technique. The fabricated binder‐free electrode exhibits excellent bifunctional stability for seawater batteries, presenting a comparable performance to the binder‐included Pt/C+IrO2 electrode.

Highly Stable Mn-Based Nanocarbon Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions in Reversible Fuel Cells

Carbon has many advantages over transitional metal oxide for being an oxygen reduction reaction (ORR) electrocatalyst due to high activity, low cost, excellent electrical conductivity, and high surface area. Nevertheless, its intrinsic instability in oxygen evolution reaction (OER) potential regime (>1.23 V vs. RHE) has largely inhibited the potential for bifunctional ORR and OER applications in reversible electrochemical energy devices. Here, we reported a new class of highly stable carbon nanocomposite bifunctional catalysts consisting of substantial carbon tubes growing from a very thick and dense graphitic substrate, which is derived from an inexpensive dicyandiamide as carbon/nitrogen precursor simultaneously catalyzed by Fe, Co, Ni, and Mn during carbonization. The dense substrate leverages the characteristics of high degree of graphitization carbon derived from Mn; active nitrogen-doped carbon tubes are stemmed from FeCoNi during carbonization process. The bifunctional stability and activity of the carbon nanocomposite catalysts were found greatly dependent on content of Mn. The existences of various metal/metal oxides and effective nitrogen doping was responsible for its high bifunctional activities for the ORR and the OER. The unprecedented stability of the bifunctional catalyst was verified by using various accelerated stress tests up to 60,000 potential cycles (0-1.9 V vs. RHE) at 25oC and 100-hour life test at constant current density of 10 mA cm-2 at 60oC. Instead of degradation, ORR and OER activity was considerably increased during the long-term potential cycling tests, indicating more active sites gradually exposed. The OER current was verified to be a sole outcome of oxygen evolution, rather than carbon or metal oxidations. The remarkable electrochemical stability of this catalyst was primarily attributed to its unique hybrid carbon structures featured with a very high graphitization degree, thick graphitic layers, and abundances of carbon tubes grown from a dense substrate. More importantly, the irreversible formation of β-MnO2 phase and FeCoNi based metals oxides provide crucial protection roles in enhancing carbon corrosion resistance.

Electron microscopy reveals a soluble hybrid network of individual nanocrystals self-anchored by bifunctional thiol fluorescent bridges.

Today, nanochemistry research of hybrid materials growth in liquid media represents a new challenge for tailoring specific nano-sized materials directly related to the hybrid electron-optical properties. Distinctive assumptions about the origin, the growth, and the functionalization of hybrid nanoparticles have recently been proposed by scientific research to attend the different aspects of observable behaviors. Therefore, appropriate morpho-structural observation of the hybrid nanoparticles is the most important factor for controlling the chemical and physical properties. Here, we report how the gold nanocrystals (Au-NCs) structurally covered by an outer layer material of 9,9-didodecyl-2,7-bisthiofluorene (FL) bifunctional stabilizer evolve into a self-organized 2D-network as a function of different nano-structural features. Detailed morpho-structural investigation of this hybrid material through electron microscopy techniques has been performed from the atomic-scale to hundreds of nanometers. The experimental information gathered allowed us to figure out the evolution growth of the gold-FL nanoparticles (AuFL-NPs) from the early stage of the gold-organic nucleation to the final assembled bi-dimensional network. The reported results represent a valuable background toward the full comprehension of growth mechanisms of organic-inorganic materials responsible for the final chemical and physical properties.

Photooxidation of poly[methyl(phenyl)silylene] and effect of photostabilizers

Poly[methyl(phenyl)silylene] (PMPSi) samples were irradiated in air atmosphere using either a weatherometer ATLAS Ci 3000+ or a mercury discharge lamp HBO 200. The kinetics of photodegradation was determined by FTIR and UV spectroscopies. The absorption changes in the siloxane, carbonyl and hydroxyl regions were monitored and analyzed. It is assumed that photodegradation of neat PMPSi in air atmosphere is an irreversible dual photoprocess consisting of primary photolysis followed by the photooxidation to oxygenated products such as siloxanes and species containing hydroxyl and carbonyl groups. Degradative changes can be retarded by the addition of photostabilizers. Triazine-based phenolic UV absorber protecting the polymer by the excited-state intramolecular proton transfer mechanism, bifunctional stabilizer (consisting of UV absorber and HAS functions) and the combination of triazine-based phenolic UV absorber with HAS was rather effective in retardation of photodegradation of PMPSi.

Synthesis of Pt–Ru nanoparticles with a bifunctional stabilizer

A synthetic method for bimetallic Pt–Ru nanoparticles with a bifunctional stabilizer, (3-aminopropyl)trimethoxysilane (APS), is proposed. Sodium borohydride was used to induce simultaneous reduction of platinum and ruthenium ions in the presence of APS. The concentration of each metal ion was 0.06 mM, and sodium borohydride concentration was 10 times higher than the total metal ion concentration. X-ray diffraction measurement showed that the nanoparticles formed by the reduction contained alloy of Pt and Ru. Comparison of the Pt–Ru nanoparticles prepared in the presence of APS with those in the absence of APS confirmed that APS played a role of stabilizer in synthesis of the nanoparticles. The number-averaged size of Pt–Ru nanoparticles could be varied in the range of 2.1–3.7 nm at APS concentrations of 0.13–0.26 mM, and the narrowest size distribution of Pt–Ru nanoparticles appeared with the minimum average size (2.1 nm) around an APS concentration of 0.1 mM.

The effect of stabilizer concentration on the air-plasma-induced surface oxidation of crosslinked polydimethylsiloxane

The concentrations of three stabilizers—a hindered phenol (Irganox 1076), a hindered amine light stabilizer (Tinuvin 770) and a bifunctional stabilizer with chain-breaking hindered phenol and secondary amine and hydroperoxide-decomposing sulphide moieties (Irganox 565)—in crosslinked polydimethylsiloxane were varied using swelling solutions of the stabilizers at different concentrations. The concentration of the stabilizer in the rubber was assessed by UV-Vis spectroscopy of Soxhlet and microwave assisted extracts. Irganox 1076 and Tinuvin 770 were soluble in polydimethylsiloxane to at least 0.2–0.3 wt.%, whereas the solubility of Irganox 565 was considerably lower. The samples were exposed to GHz air plasma and the surface structures of the exposed samples were studied by X-ray photoelectron spectroscopy, and by optical and scanning electron microscopy after uniaxial stretching. The plasma exposure time required for the formation of an oxidised glassy layer increased in a linear fashion with increasing stabilizer concentration, suggesting that the consumption rate was constant in time during the plasma exposure. Tinuvin 770 showed the strongest overall protecting effect whereas Irganox 565 showed the strongest protecting effect per mass fraction of stabilizer. Irganox 1076 was of moderate efficiency. The results suggest that efficient protection towards air plasma is achieved with hindered amine stabilizers or with stabilizers combining chain-breaking and hydroperoxide-decomposing functions. Differential scanning calorimetry showed that Tinuvin 770 and Irganox 565 protected polydimethylsiloxane against thermal oxidation at elevated temperatures. The chemical consumption of these stabilizers followed basically the classical scheme with zero-order kinetics and a rate constant obeying the Arrhenius law.

Synthesis and performance of new bifunctional stabilizers

Six new bifunctional stabilizers have been synthesized by a two-step controlled isocyanation. In the first step a compound containing a stabilizing functional group, 2,4-dihydroxy benzophenone (DHBP) or 2,2,6,6-tetramethyl-4-piperidinol (TMP), reacts with toluene-2,4-diisocyanate (TDI) or hexamethylene diisocyanate (HMDI) at a mole ratio of 1 to 1 to form an intermediate I. In the second step I was directly added to another compound containing a different stabilizing functional group such as TMP or 2,6-di-tert-butyl-4-hydroxy methyl phenol (DBHMP) at a 1 to 1 mole ratio at a given temperature in the presence of dibutyltin dilaurate (DBTDL) catalyst. These six new stabilizers are 2-hydroxy-4-benzophenonyl, 2,2,6,6-tetramethyl-4-piperidinyl hexamethylene dicarbamate ( A, MW=540); 2-hydroxy-4-benzophenonyl, 3,5-di- tert-butyl-4-hydroxyl benzyl hexamethylene dicarbamate ( B, MW=619); 3,5-di- tert-butyl-4-hydroxyl benzyl, 2,2,6,6-tetramethyl-4-piperidinyl hexamethylene dicarbamate ( C, MW=562); 2,2,6,6-tetramethyl-4-piperidinyl, 2-hydroxy-4-benzophenonyl toluene 2,4-dicarbamate ( D, MW=546); 3,5-di- tert-butyl-4-hydroxyl benzyl, 2-hydroxy-4-benzophenonyl toluene 2,4-dicarbamate ( E, MW=625) and 3,5-di- tert-butyl-4-hydroxyl benzyl, 2,2,6,6-tetramethyl-4-piperidinyl toluene 2,4-dicarbamate ( F, MW=568). Their structures have been characterized by IR, NMR, UV and elemental analysis. The photostabilizing and thermal stabilizing effectiveness of these new stabilizers for polypropylene (PP) had been examined. Experimental results show that these new bifunctional stabilizers are effective in protecting PP against photo-oxidation and thermal-oxidation. The effectiveness in relation to the structures of these new bifunctional stabilizers is discussed.

Methacrylic maleic bifunctional stabilizer in emulsion polymerization

A new type of reactive surfactant, containing both a methacrylic and a maleic group, was prepared and engaged in batch and seeded emulsion polymerization of styrene and styrene-butyl acrylate. The stability of core-shell latexes versus electrolytes has been studied.

Methacrylic maleic bifunctional stabilizer in emulsion polymerization

Methacrylic maleic bifunctional stabilizer in emulsion polymerization

Antioxidant interaction between organic phosphites and hindered amine light stabilizers: effects during photoxidation of polypropylene—II

The behaviour of mixtures of hindered amine light stabilizers (HALS), their nitroxyl radical, and alkylamine analogues, with aromatic and aliphatic phosphites during photoxidation of polypropylene (PP) has been examined. The photostabilizing performance of the above mixtures of stabilizers was compared with that of the individual antioxidants and with the performance of a number of synthesized bifunctional stabilizers containing aromatic phosphite or phosphonite and either of the above HALS or related functions in the same molecule (referred to as ‘HALS-Phosphites’ or ‘HALS-Phosphonite’). Combinations of the hindered aryl phosphite Irgafos 168, with the hindered amine Tinuvin 770, the tertiary amine Tinuvin 292 and the bis-nitroxyl-analogue of Tinuvin 770, gave antagonistic effects at most molar ratios examined. Furthermore, in all cases, the extent of antagonism was reduced with increasing the amount of Irgafos 168 in the mixtures. Combination of the aliphatic phosphite, trilaurylphosphite, TLP, with Tinuvin 770 in PP, on the other hand, has shown synergistic effect under photoxidative conditions. The HALS-Phosphites and HALS-Phosphonite examined have shown better stabilizing efficiency than the corresponding mixtures of the individual stabilizers.

Current of status of exploitation of radical scavenging stabilizers in advanced polymer stabilization

AbstractPrincipal chemical pathways characteristic of active participation of radical scavenging polymer stabilizers (phenols, aromatic, hydroaromatic and hindered aliphatic amines) are outlined. Pathways resulting in a partial depletion or distortion of activity of stabilizers, in formation of polymer discolouring products, or in interactions in bifunctional stabilizers are involved.

Chemical and photochemical behaviour of phenolic antioxidants in polymer stabilization: A state of the art report, part II

In practical stabilization of polymers, phenols are mostly applied in combination with secondary antioxidants and light stabilizers. Mechanisms of interaction with these additives, as well as specific features of the reactivity of phenolic moieties creating a part of UV absorbers and bifunctional stabilizers, are presented together with the chemistry of the undesired reactivity of phenols with environmental pollutants and metallic impurities in polymers. The chemistry of α-tocopherol is mentioned as an example of an environmentally safe stabilizer.

Shelf Life Study of Oil/Water Emulsions using Various Commercial Hydrocolloids

ABSTRACTThis study compares and evaluates commercial hydrocolloids for shelf life stability in an oil/water emulsion system stored at 25°C. Observations of surface or interfacial changes and rheological parameters took place over 90 days. Parameters; n, pseudoplastic index; K, consistency index; and τ0, yield stress were reported. Apparent viscosities τ20 (quality control index) and τ50 (oral flow index) were monitored throughout the study and correlated well with stability changes. The study produced the following results: propylene glycol alginate promotes creaminess without significant rheological contribution (τa, τ20, τ50 and τ0). Xanthan gum contributes to body; however, oiling off was observed. Gum tragacanth and combination(xanthan, tragacanth and PGA, 1:1:1) act as bifunctional stabilizers, controlling both oiling off and body.

Reactions of stabilizer compounds. IV. ESR studies of the formation of stable nitroxyl radicals in the photooxidation of polypropylene containing hindered amine light stabilizers

AbstractESR studies of the formation of stable nitroxyl radicals in the photooxidation of polypropylene containing 2,2,6,6‐tetramethyl‐4‐hydroxypiperidine (II) and the commercial light stabilizer bis(2,2,6,6‐tetramethyl‐4‐piperidinyl)sebacate (III) are described. Spectra of the stable nitroxyl radicals in solid polymer and in solution after extraction from the polymer were obtained. The extract from photooxidized polypropylene containing the bifunctional stabilizer (III) showed only the mononitroxyl radical. The possible formation of polymer‐bonded nitroxyl radicals from (III) is discussed.