Oxygen barrier coating deposited by novel plasma‐enhanced chemical vapor deposition

We report the use of a novel plasma‐enhanced chemical vapor deposition chamber with coaxial electrode geometry for the SiO_x deposition. This novel plasma setup exploits the diffusion of electrons through the inner most electrode to the interior samples space as the major energy source. This configuration enables a gentle treatment of sensitive materials like low‐density polyethylene foils and biodegradable materials. SiO_x coatings deposited in the novel setup were compared with other state of the art plasma coatings and were found to possess equally good or better barrier properties. The barrier effect of single‐layer coatings deposited under different reaction conditions was studied. The coating thickness and the carbon content in the coatings were found to be the critical parameters for the barrier property. The novel barrier coating was applied on different polymeric materials, and it increased the barrier property of the modified low‐density polyethylene, polyethylene terephthalate, and polylactide by 96.48%, 99.69%, and 99.25%, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of oxygen gas barrier poly(ethylene terephthalate) films by deposition of silicon oxide films plasma‐polymerized from a mixture of tetramethoxysilane and oxygen

To prepare silicon oxide (SiOx)‐deposited poly(ethylene terephthalate) films with high oxygen gas barrier capability, SiOx deposition by plasma polymerization has been investigated from the viewpoint of chemical composition. Tetramethoxysilane (TMOS) is suitable as a starting material for the synthesis of the SiOx films. The SiOx deposition under self‐bias, where the etching action occurs around an electrode surface, is effective in eliminating carbonaceous compounds from the deposited SiOx films. There is no difference in the chemical composition between the SiOx films deposited under self‐bias and under no self‐bias. The SiOx films are composed of a main component of Si O Si networks and a minor component of carbonized carbons. The SiOx films deposited under no self‐bias from the TMOS/O₂ mixture show good oxygen gas barrier capability, but the SiOx films deposited under the self‐bias show poor capability. The minimum oxygen permeation rate for poly(ethylene terephthalate) films deposited SiOx film is 0.10 cm³ m⁻² day⁻¹ atm⁻¹, which corresponds to an oxygen permeability coefficient of 1.4 × 10⁻¹⁷ cm³‐cm cm⁻² s⁻¹ cm⁻¹ Hg for the SiOx film itself. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2091–2100, 1999     

Degradation of proton exchange membrane by Pt dissolved/deposited in fuel cells

An accelerated single cell test and single electrode cell test were carried out to investigate membrane degradation by Pt dissolved/deposited on the membrane. For a cell operating under accelerated conditions (OCV, 90°C, anode RH 0%, cathode O₂ supply), MEA analyses revealed that Pt particles were deposited in the membrane at the anode side, with a decrease in F, O, and C content near the anode side of the membrane. Dissolved Pt from the cathode showed that Pt existed mainly in the form of Pt²⁺ ionic species. Oxygen and hydrogen helped Pt dissolution from the cathode and Pt deposition in the membrane, respectively. Radical formation on deposited Pt in the membrane was detected by electron spin resonance (ESR). Fluoride emission rate (FER, an indicator of membrane degradation rate) increased with an increase in the amount of Pt in the membrane.     

Plasma polymer deposition from mixture of tetramethoxysilane and oxygen on PET films and their oxygen gas barrier properties

Plasma polymerization of silane compounds has been discussed for deposition of SiOx positron emission tomography (PET) films at room temperature. A mixture of tetramethoxysilane (TMOS) and oxygen containing 60 mol % O₂ is a preferable raw material for SiOx formation by plasma polymerization. The deposited plasma polymers consist mainly of Si(SINGLE BOND)O networks with small amount of Si(SINGLE BOND)OH and Si(SINGLE BOND)C groups. A part of Si(SINGLE BOND)O networks in the plasma polymers is distorted by the Si(SINGLE BOND)OH and Si(SINGLE BOND)C groups. The oxygen permeability coefficient for the plasma polymer itself is 2.1 × 10⁻¹⁵ (STP) cm³/cm/cm²/s/cm Hg, which is lower than that for hydrolyzed ethylene-vinylacetate copolymer (Eval) and poly(vinylidene chloride) (Saran). Conclusively, the plasma polymer deposited from the mixture of TMOS and oxygen containing 60 mol % O₂ is a material with good oxygen barrier properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1031–1039, 1997     

Hybrid multilayer thin-film fabrication by atmospheric deposition process for enhancing the barrier performance

In this paper, a multilayer barrier thin film, based on polyvinylidene difluoride (PVDF)–silicon dioxide (SiO₂), has been fabricated on a PET substrate through a novel method of joint fabrication techniques. The inorganic SiO₂ thin film was deposited using a roll-to-roll atmospheric atomic layer deposition system (R2R-AALD), while the organic PVDF layer was deposited on the surface of SiO₂ through the electrohydrodynamic atomization (EHDA) technique. The multilayer barrier thin films exhibited very good surface morphology, chemical composition, and optical properties. The obtained values for arithmetic surface roughness and water contact angle of the as-developed multilayer barrier thin film were 3.88 nm and 125°, respectively. The total thickness of the multilayer barrier thin film was 520 nm with a high optical transmittance value (85–90%). The water vapor transmission rate (WVTR) of the barrier thin film was ~?0.9?×?10^?2 g m^?2 day^?1. This combination of dual fabrication techniques (R2R-AALD and EHDA) for the development of multilayer barrier thin films is promising for gas barrier applications.     

Preparation of oxygen gas barrier polypropylene films by deposition of SiOx films plasma‐polymerized from mixture of tetramethoxysilane and oxygen

Silicon oxide (SiOx) film deposition on the surface of oriented poly(propylene) (OPP) films was done to form a new oxygen gas barrier material using plasma polymerization of the tetramethoxysilane (TMOS)/O₂ mixture. The SiOx film deposition on OPP films never improved oxygen gas barrier properties. The inefficacy of the SiOx deposition was due to poor adhesion at the interface between the deposited SiOx and OPP films and also to the formation of cracks in the deposited SiOx film. If prior to the SiOx film deposition surface modification of OPP films was done by a combination of the argon plasma treatment and TMOS coupling treatment, this contributed effectively to strong adhesion leading to success in the SiOx deposition on the OPP film surface, and then the oxygen gas barrier ability was improved. The oxygen permeation rate through the SiOx‐deposited OPP film was decreased from 2230 to 37–52 cm³/m²/day/atm, which was comparable to that of poly(vinylidene chloride), 55 cm³/m²/day/atm at a film thickness of 11 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2389–2397, 2000     

Comparative studies on the physical properties of TEOS,TMOS and Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> based silica aerogels by ambient pressure drying method

In order to compare the various precursors of silica aerogels, three different precursors namely TMOS, TEOS and Na₂SiO₃ were studied in this paper. The property differences of the aerogels caused by the three precursors were discussed in terms of reaction process, gelation time, pore size distributions, thermal conductivity, SEM, hydrophobicity and thermal stability. It has been found that the gelation time of the silica gel is strongly dependent on the type of precursor used. During the surface modification process, organic groups were attached to the wet gel skeletons transforming the hydrophilic to the hydrophobic which were characterized by Fourier Transform Infrared spectroscopy (FTIR). It has been found that the contact angle of the Na₂SiO₃ and TMOS precursor based aerogels with water have the higher contact angle of 149° and whereas Na₂SiO₃ precursor based aerogel has the lower contact angle of 130°. The thermal conductivities of the Na₂SiO₃ and TMOS based aerogels have been found to be lower (0.025 and 0.030 W m^?1 K^?1, respectively) compared to the TEOS based (0.050 W m^?1 K^?1) aerogels. The pore sizes obtained from the N₂ adsorption measurements varied from 40 to 180, 70 to 190, and 90 to 200 nm for the TEOS, TMOS and Na₂SiO₃ precursor based aerogels, respectively. The scanning electron microscopy studies of the aerogels indicated that the Na₂SiO₃ and TMOS based aerogels show narrow and uniform pores while the particles of SiO₂ network are very small. On the other hand, TEOS aerogel show non-uniform pores such that the numbers of smaller size pores are less compared to the pores of larger size while the SiO₂ particles of the network are larger as compared to both Na₂SiO₃ and TMOS aerogels. Hence, the surface are of the aerogels prepared using TEOS precursor has been found to be the lowest (~620 m² g^?1) compared to the Na₂SiO₃ (~868 m² g^?1) and TMOS (~764 m² g^?1) aerogels.     

Multilayer Si@SiOx@void@C anode materials synthesized via simultaneously carbonization and redox for Li-ion batteries

In the development of high-performance lithium-ion batteries (LIBs), the composition and structure of electrode materials are of critical importance. Silicon has a theoretical specific capacity 10 times that of graphite, nonetheless, its application as an anode material confronts challenge as it undergoes huge volume change and pulverization amidst the alloying and dealloying processes. Herein, a novel method to prepare a multilayer Si-based anode was proposed. Three layers, SiO₂, nickel and triethylene glycol (TEG), were coated successively on Si nanoparticles, which served respectively as the sources of SiO_x, sacrificial templates and carbon. Nickel can not only serve as a hollow template, but also play a catalytic role, which makes carbonization and redox reactions occur synchronously under a mild condition. Amid the carbonization process of TEG at 450 °C, several-nm-thick SiO₂ layer can react with the as-derived carbon to form a silicon suboxides (SiO_x (0 < x < 2)) intermedium layer. After removing the nickel template, a micro-nano scaled Si@SiO_x@void@C with conformal multilayer-structure can be obtained. The BET specific surface area and pore volume of powders were increased dramatically because of the derivation of abundant voids, which can not only buffer the swelling effect of silicon, but also provide richer ionic conductivity. The as-assembled half-cell with Si@SiOx@void@C as the anode material possesses high capacity (～1000 mAh g^?1 at 3 A g^?1), long cycle life (300 cycles with 77% capacity retention) and good rate performance (558 mAh g^?1 at 5 A g^?1).     

Suppression of radiation‐induced oxidation of polymers by sputtered silicon oxide coating

Oxygen barrier coating on polymers was attempted to obtain polymeric composite materials with improved radiation resistance. Silicon oxide (SiO_1.6) films ranging from 120 to 240 nm thick were formed on polypropylene (PP) and polyethylene (PE) by radio frequency (RF) magnetron sputtering. Oxygen permeability after SiO_1.6 deposition was reduced significantly in all samples studied, indicating that silicon oxide is a useful gas barrier. The oxygen permeability coefficient of deposited films for PP was 1.7–2.2 × 10^?14 cm³‐cm/cm²/s/cmHg and that for PE was 2.8–4.8 × 10^?13 cm³‐cm/cm²/s/cmHg. We studied the effect of such films on the radiation resistance of polymers in the presence of oxygen by microscopic infrared (IR) absorption spectroscopy. Silicon oxide films 180 nm thick were deposited on the surfaces of PP and PE, and the formation of carbonyl groups after irradiation in air was measured as a function of depth from the surface. Results compared with those for uncoated PE and PP showed that the radiation‐induced polymer oxidation is dramatically suppressed by silicon oxide coating. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 186–190, 2002     

Simultaneous nitrification and denitrification with electricity generation in dual‐cathode microbial fuel cells

BACKGROUND: Nitrogen removal using microbial fuel cells (MFCs) is of great interest owing to the potential benefits of bioenergy production. In this study, simultaneous nitrification and denitrification in dual‐cathode MFCs was investigated. RESULTS: The dual‐cathode MFCs investigated were capable of generating electricity and removing nitrogen, influenced by operating methods, nitrogen loading rates and external resistance. Depending on the ammonium concentration in the anode chamber, 84–97% of the ammonium nitrogen was removed via nitrification in the aerobic cathode. The removals of nitrate and total nitrogen were relatively low (～50%) at the influent ammonium concentration of 80 mg NH₄⁺‐N L^?1, but were significantly improved to more than 90% at a lower ammonium input (40 and 20 mg NH₄⁺‐N L^?1). When the electrode couples were electrically connected for different purposes, with high power output from the anode/aerobic cathode and high current generation from the anode/anoxic cathode, nitrogen removal was also improved. An investigation of aeration suggested that factors other than carbon supply, possibly inefficient reactor configuration, also limited the performance of the developed MFC. CONCLUSION: The experimental results demonstrated that the proposed pathway was feasible with effective nitrogen and organic removal. This study provided valuable information for the further development of a continuously operated dual‐cathode MFC system. Copyright © 2011 Society of Chemical Industry     

A Four-Armed Polyacrylic Acid Homopolymer Binder with Enhanced Performance for SiOx/Graphite Anode

The large-scale application of Si-based anodes is impeded by their fast capacity decay, which is mainly attributed to the huge volume expansion upon cycling. The employment of functional binders is one efficient method to mitigate this issue. In this work, a four-armed polyacrylic acid (4A-PAA) homopolymer is explored as a remarkably effective binder for Si-based anodes. The 4A-PAA binder is prepared via an atom transfer radical polymerization, followed by ester hydrolysis. Compared to the conventional linear polyacrylic acid (PAA) binder, the 4A-PAA not only shows enhanced toughness due to its decreased molecular regularity and intramolecular hydrogen bond but also exhibits increased binding strength because of its multidimensional binding structure. As a result, the SiO_x/graphite electrode using the 4A-PAA retains a capacity retention of 89.1% and a capacity of 558.1 mAh g⁻¹ after 200 cycles at 0.16 A g⁻¹, which are superior to the PAA electrode, corresponding to 80.4% and 469.3 mAh g⁻¹, respectively. The improved performance is attributed to the employment of the 4A-PAA, which mitigates the volume change of the SiO_x/graphite anode. This work not only offers a promising binder for Si-based anodes but also presents a universal solution for other anodes with high volume expansion during cycling.     

Analysis of primary and secondary current distributions in a wedge-type aluminum-air cell

The primary and secondary current distributions near the leading edges of the cathode and anode of a wedge-type aluminum-air cell design were analyzed. Numerical calculations were accomplished by using a finite difference method and introducing an overlapping two-grid system technique. The calculations indicate that the current distributions on the cathode and anode at distances from the edges greater than 2 times the cell gap are uniform. In the edge region, the wedge angle between 0 and 10° has a negligible effect on the current distribution. High current densities at the cathode edge, which are detrimental to cathode life, are reduced by kinetic effects and by oversizing the cathode itself. The latter also favors cell performance but adds to the cell costs. An effectiveness factor is introduced which demonstrates the effectiveness of cathode oversize and the sensitivity to kinetics as represented by the Wagner number. The calculations indicate that only marginal performance gains can be expected when the cathode extends beyond the anode a distance greater than that of 1.5 times the amode-cathode gap.Nomenclature A1, A2, A3 anode curves 1, 2, 3 - b slope ofi vs curve at mean value of _mean (A cm^–2V^–1) - C1, C2, C3 cathode curves 1, 2, 3 - D distance between electrodes (cm) - i _s local current density on electrode (A cm^–2) - I ^* dimensionless local current value defined by Equation 9 - N dimensionless effectiveness factor defined by Equation 10 - V _met constant potential of electrode (V) - W dimensionless Wagner number defined by Equation 7 - X dimensionless cathode oversize defined asx/D - x position parallel to anode with origin at the anode apex (cm) - y position perpendicular to electrode surface (cm) - K conductivity of electrolyte (ohm cm^–1) - surface overpotential (V) - potential in solution phase (V) - ₀ potential in solution adjacent to electrode surface (V)     

Membrane electrode assembly with Pt/SiO2/C anode catalyst for proton exchange membrane fuel cell operation under low humidity conditions

In this work, a novel self-humidifying membrane electrode assembly (MEA) with Pt/SiO₂/C as anode catalyst was developed to improve the performance of proton exchange membrane fuel cell (PEMFC) operating at low humidity conditions. The characteristics of the composite catalysts were investigated by XRD, TEM and water uptake measurement. The optimal performance of the MEA was obtained with the 10 wt.% of silica in the composite catalyst by single cell tests under both high and low humidity conditions. The low humidity performance of the novel self-humidifying MEA was evaluated in a H₂/air PEMFC at ambient pressure under different relative humidity (RH) and cell temperature conditions. The results show that the MEA performance was hardly changed even if the RHs of both the anode and cathode decreased from 100% to 28%. However, the low humidity performance of the MEA was quite susceptible to the cell temperature, which decreased steeply as the cell temperature increased. At a cell temperature of 50 °C, the MEA shows good stability for low humidity operating: the current density remained at 0.65 A cm⁻² at a usual work voltage of 0.6 V without any degradation after 120 h operation under 28% RH for both the anode and cathode.     

Boron doped graphene cathode for capacitor via a new one-step method

The graphene cathode was doped with boron via a new and fast method of plasma enhanced chemical vapor deposition (PECVD) at room temperature. Various plasma species of BH_x (x?=?0–3) with high reactivity reacted with graphene electrode via surface re-reactions and gas-interface intersection. The cathode made of boron doping into graphene (BG) exhibited excellent electrochemical performances in Li-ion capacitors, including a large discharge capacity of 140?mAh?g^?1 (voltage range: 1.5–4.2?V vs. Li/Li⁺, current density: 100?mA?g^?1) and the coulombic efficiency of more than 99.6% within 1000 circles. The capacity, coulombic efficiency and circle performance of the BG electrode were more superior to the undoped graphene electrode owing to the uniform doping of boron plasma species. The PECVD method has the advantages of being simple, is conducted at room-temperature, is time efficient and uniform, thus making it a fast and effective way for doping hetero-atoms into the electrode.     

Improved electrochemical activity of Bi0.5Sr0.5FeO3-δ–Ce0.9Gd0.1O1.95composite cathode electrocatalyst for solid oxide fuel cells

Developing MIEC materials with high electrocatalytic performance for the ORR and good thermal/chemical/structural stability is of paramount importance to the success of solid oxide fuel cells (SOFCs). In this work, high-activity Bi_0.5Sr_0.5FeO_3-δ-xCe_0.9Gd_0.1O_1.95 (BSFO-xGDC, x = 10, 20, 30 and 40 wt%) oxygen electrodes are synthesized, and confirmed by XRD, SEM and EIS, respectively. The crystal structure, microstructure, electrochemical property and performance stability of the promising BSFO-xGDC composite cathodes are systematically evaluated. It is found that introducing GDC nanoparticles can obviously improve the electrochemical property of the porous composite electrode. Among all these composite cathodes, BSFO-30GDC composite cathode shows the best ORR activity. The peak power density of anode supported single cells employing BSFO-30GDC composite cathode reaches 709 mW cm^?2 and the electrode polarization resistance (R_p) of the BSFO-30GDC is about 0.14 Ω cm² at 700 °C. The analysis of the oxygen reduction kinetic indicates that the major electrochemical process of the GDC-decorated composite cathode is oxygen adsorption-dissociation. These preliminary results demonstrated that BSFO-30GDC is a prospective composite cathode catalyst for SOFCs because of its outstanding ORR activity.     

Barrier and thermal properties of polyimide derived from a diamine monomer containing a rigid planar moiety

An aromatic polyimide (3,6‐CPI ) was prepared by the polymerization of pyromellitic dianhydride and diamine (3,6‐CDA ) containing a rigid planar carbazole moiety. The synthesized polyimide shows outstanding barrier properties with oxygen permeation rate and water vapor permeation rate low at 7.9 cm³ m^?2 day^?1 and 9.8 g m^?2 day^?1, respectively. Wide angle X‐ray diffraction, positron annihilation lifetime spectroscopy and molecular dynamics simulations reveal that the excellent barrier properties of 3,6‐CPI are mainly due to the crystallinity and low free volume of the polymer, which result from the rigid planar backbone structure and strong interchain hydrogen bonding. In addition, the polyimide exhibits excellent thermal stability and favorable mechanical properties with a 5 wt% weight‐loss temperature of 559 °C in nitrogen, a glass transition temperature (T _g) of 397 °C and a tensile strength of 115.4 MPa . The as‐synthesized polyimide shows potential packaging applications in the field of flexible electronics and displays, flexible and thin film photovoltaics, and light‐emitting diodes. © 2017 Society of Chemical Industry     

A solid state lithium concentration cell with LixV2O5

A solid state lithium concentration cell Li_xV₂O₅/LISICON/Li_0.25V₂O₅ (0.25 x 0.55) was investigated. The open circuit voltage increased monotonously from about 0 mV atx=0.25 to about 270 mV atx=0.55. Cells with variousx-values in the single phase showed similar polarization curves, and their cathode polarizations were slightly larger than the anode polarizations. The cathode potential vs a platinum wire as the third electrode was nearly constant under nitrogen flow, but the anode potential decreased with increase of the lithium content of the sample. During the experiment, Lisicon was satisfactorily stable in contact with Li_xV₂O₅.     

Entropy change in lithium ion cells on charge and discharge

Open circuit voltage (OCV) was measured as a function of temperature and state of charge (SOC) for six kinds of lithium ion cells. The following cells were used: four kinds of commercial cell using a LiCoO₂ cathode and a graphite or hard carbon anode; a trial manufacture cell using a Li–Ni–Co complex oxide cathode and a graphite-coke hybrid carbon anode; and a trial manufacture cell using a LiMn₂O₄ cathode and a graphite anode. The entropy change in the cell reaction was determined by calculating the derivative of the OCV with temperature. Results were compared and discussed to determine the influence of the phase transition in the electrode materials due to cell reaction. It was clarified that the entropy change in cells using a LiCoO₂ cathode is negative except for the part of the SOC region where Li _x CoO₂ phase transition occurred. An endothermic reaction then occurs during discharge and an exothermic reaction during charge. In cells using LiCoO₂ cathodes, there was a fluctuation in the entropy change originating from the Li _x CoO₂ phase transition in the SOC range between 70% and 90%. This fluctuation was influenced by temperature and by additives or excess lithium in the cathode material. The entropy change in both cells using a Li–Ni–Co complex oxide cathode or a LiMn₂O₄ cathode was comparatively small.     

Synthesis and hydrothermal stability of U doped zirconolite–sphene composite materials

Two series of U doped zirconolite–sphene composite materials were prepared by solid state reaction method: CaZr_(1?m)U_mTi₂O₇?(1?m) Ca_(1?x)U_xAl_2xTi_(1?2x)SiO₅ (m?=?7x) and Ca_(1?n)U_6nZr_(1?5n)Al_2nTi_(2?2n)O₇?(1?5n) Ca_(1?y)U_yAl_2yTi_(1?2y)SiO₅ (n?=?5y/6). The effects of U content on the phase structure of the composite materials were mainly investigated. The results show that the optimal synthesis temperature of the composite material is ～1230°C. In comparison with the incorporation of U in the Zr site of zirconolite, U incorporation in the Ca site of zirconolite using Al as charge compensating ions was not very efficient. Hydrothermal stability of the U doped zirconolite–sphene composite material was examined by modified product consistency test method at 90°C in deionised water (pH 7). The normalised U leach rate is fairly constant in a low value below 10^?5 g m^?2 day^?1 after 28 days.     

Electrochemical investigation of the influence of thin SiOx films deposited on gold on charge transfer characteristics

The paper reports on the investigation of the electrochemical behavior of a thin gold film electrode coated with silicon dioxide (SiO_x) layers of increasing thickness. Stable thin films of amorphous silica (SiO_x) were deposited on glass slides coated with a 5 nm adhesion layer of titanium and 50 nm of gold, using plasma-enhanced chemical vapor deposition (PECVD) technique. Scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of the interfaces. In the case of SECM, the influence of the SiO_x thicknesses on the electron transfer kinetics of three redox mediators was investigated. Normalized current-distance curves (approach curves) were fitted to the theoretical model in order to find the effective heterogeneous first order rate constant (k_eff) at the sample. EIS was in addition used to confirm the diffusion barrier character of the SiO_x interlayer.