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The comprehensive investigation of ternary PtIrCo-alloy nanoparticles supported on 3D carbon aerogel matrix toward Methanol Oxidation Reaction (MOR) and Oxygen Reduction Reaction (ORR) is focused on CO tolerance in MOR, methanol vs. oxygen selectivity in ORR, and the structural changes within the metal alloy nanoparticles caused by the heat treatment and the electrochemical conditioning. Amorphous tri-metallic Pt 59 Ir 34 Co 7 -nanoparticles with mean size of 1.47 ± 0.21 nm were formed within 3D CA matrix in supercritical CO 2 (scCO 2 ) from the Pt, Ir, and Co organometallic precursors. Depending on the heat-treatment temperature (600 °C or 900 °C), the amorphous organometallic phase of Pt, Ir and Co was transformed into a single-phase fcc PtIrCo-alloy nanoparticles with a mean particle size of 1.68 ± 0.33 nm and 2.68 ± 0.61 nm, respectively. The fcc lattice parameters of the PtIrCo-alloy (0.389 nm at 600 °C and 0.386 nm at 900 °C) were smaller than that of the Pt fcc lattice (0.392 nm) and the lattice parameters reduced proportionally to the heat-treatment temperatures. After 50 electrochemical cycles, PtIrCo/CA catalysts display improved MOR specific activity (∼2.5 X Pt/C), mass activity (∼3 X Pt/C) at 0.7 V vs. SHE, higher CO-tolerance, and better electrochemical stability than Pt/C, but less CO-tolerance and stability than PtRu/C. Regarding ORR, the PtIrCo/CA catalysts demonstrate enhanced ORR specific activity (∼5.5 X Pt/C) and mass activity (∼6.3 X Pt/C) at 0.7 V vs. SHE along with superior methanol-tolerance in comparison to Pt/C. The structural changes associated with PtIrCo/CA fcc -lattice parameter with respect to Pt-lattice have contributed to better MOR and ORR activities. Faster surface diffusion associated with weak adsorption of hydroxide species and higher selective adsorption of oxygen in comparison to methanol onto PtIrCo-alloy surface could have contributed to their better CO-tolerant MOR and methanol-resistant ORR activity compared to Pt-catalyst. [ABSTRACT FROM AUTHOR]

Hybrid catalysts comprising of ceramic, metal, and carbon phase were synthesized by incorporating titanium and cerium oxides into PtRu/C commercial catalyst using an in-situ combustion followed by heat treatment at 600 °C. The structure dependent electrochemical behavior of as-synthesized and heat-treated materials towards methanol oxidation, carbon dioxide (CO) tolerance and chemical stability was studied by XRD, HRTEM, BET, EDS, cyclic voltammetry, chronoamperometry, and CO-stripping method. As a result of heat treatment, amorphous phase of metal oxides was transformed into a crystalline phase with particle size of about 3–7 nm. Improved methanol oxidation activity of the hybrid catalysts was compared to PtRu/C catalyst as a baseline and explained by the changes in Pt electronic behavior and excess adsorption of OH-ions. When heat-treated at 600 °C, CeO2-PtRu/C demonstrated the highest mass activity of 580 mA/mg (∼3× that of PtRu/C) compared to TiO2-PtRu/C (394 mA/mg). Heat-treated hybrid catalysts exhibited higher methanol oxidation activity at higher peak potentials than the corresponding as-synthesized materials. However, as-synthesized hybrid catalysts display higher CO-tolerance, lower CO-oxidation onset potentials, and better chemical stability in comparison to corresponding heat-treated catalysts. To explain the difference, a mechanism for ceramic oxide structure dependent electrochemical behavior of the hybrid catalysts is proposed and discussed. [ABSTRACT FROM AUTHOR]

The present study is focused on enhancing the rheological properties of the electrolyte and eliminating sedimentation of microorganisms/flocs without affecting the electron transfer kinetics for improved bioelectricity generation. Agar derived from polysaccharide agarose (0.05–0.2%, w/v) was chosen as a rheology modifying agent. Electroanalytical investigations showed that electrolytes modified with 0.15% agar display a nine-fold increase in current density (1.2 mA/cm 2 ) by a thermophilic strain ( Geobacillus sp. 44C, 60 °C) when compared with the control. Sodium phosphate buffer (0.1 M, pH 7) electrolyte with riboflavin (0.1 mM) was used as the control. Electrolytes modified with 0.15% agar significantly improved chemical oxygen demand removal rates. This developed electrolyte will aid in improving bioelectricity generation in Bioelectrochemical Systems (BES). The developed strategy avoids the use of peristaltic pumps and magnetic stirrers, thereby improving the energy efficiency of the process. [ABSTRACT FROM AUTHOR]

The present study is focused on a relatively new class of solid-state lithium halide electrolytes with antiperovskite crystal structure that are designed to alleviate safety concerns related to conventional lithium-ion batteries. The solid-state Li 3 ClO electrolyte membranes were produced by a casting/delamination method and deposited on a graphite-based working electrode. The electrolyte charge transfer resistances, electrochemical performance, and chemical stability in a half-cell configuration were evaluated over a broad temperature range from room temperature up to 100 °C. The electrochemical cells with lithium metal as a reference electrode demonstrated linear Arrhenius behavior in the temperature range of 25–100 °C confirming the absence of phase transformations. Cyclic voltammetry at 50 °C and 100 °C confirms that the electrochemical cell performance during lithiation/delithiation from 0.05 to 1.00 V is reproducible within at least 100 cycles. The solid-state electrolyte electrochemical stability in contact with lithium metal is confirmed for the first time by demonstrating the constant values of charge transfer resistances during charge/discharge operations in 575 cycles at 50 °C and 1/5 C -rate. Transport of lithium ions between the lithium metal and Li 3 ClO electrolyte in contact with a graphite working electrode provides evidence that lithium halide antiperovskites can serve as effective and electrochemically stable electrolytes for a new generation of all-solid-state lithium-ion or lithium metal batteries. Image 1031 • A solid-state electrolyte with antiperovskite structure was tested in a half-cell vs. lithium anode. • Electrolyte chemical stability in presence of Li-metal at 50 °C is confirmed by AC impedance. • Continuous cycling within 6 months at 50 and 100 °C demonstrate >80% specific capacity retention. [ABSTRACT FROM AUTHOR]

Abstract Located in the north of Tajikistan, the Koni Mansur is a rich polymetallic deposit that besides other metals has high concentration of lead-containing mineral galena. The hydro metallurgical extraction of lead from the Koni Mansur lead sulfide (galena) mineral in acidic media, its chemical composition and morphological properties in comparison to the Balya deposit in Turkey are reported for the first time. Energy dispersive X-ray fluorescence spectrometry was applied for chemical analysis of galena, while mineralogical characterization before and after lead acidic extraction was performed by XRD. The nitric acid concentration, temperature, duration of the extraction process, and the particle size distribution before and after extraction have been evaluated. The amount of lead in solution after extraction and solid-liquid phase separation was determined by the flame atomic absorption spectroscopy (FAAS). The particle size distribution before and after lead extraction revealed no significant changes. Assuming spherical shape of the particles, the Shrinking Core Model (SCM) used for kinetic study of the lead extraction allowed to define the activation energies and changes in the corresponding reaction mechanisms. Specifically, the activation energy at 293-318 K (12.4 kJ/mol) was significantly lower than at higher temperatures (318–338 K) reaching ~46.778 kJ/mol which indicates the corresponding change in the extraction mechanism. Highlights • Galena concentrate from Koni Mansur deposit studied for the first time. • Shrinking Core Model for kinetic study of lead extraction has been validated. • The study confirms mixed reaction mechanism for the extraction process. [ABSTRACT FROM AUTHOR]

In this study, nine types of polyacrylonitrile (PAN) nanofibrous membranes with varied fiber diameters and different membrane porosities are prepared by electrospinning followed by hot-pressing. Subsequently, these membranes are explored as Li-ion battery (LIB) separators. The impacts of fiber diameter and membrane porosity on electrolyte uptake, Li + ion transport through the membrane, electrochemical oxidation potential, and membrane performance as LIB separator (during charge/discharge cycling and rate capability tests of a cathodic half-cell) have been investigated. When compared to commercial Celgard PP separator, hot-pressed electrospun PAN nanofibrous membranes exhibit larger electrolyte uptake, higher thermal stability, wider electrochemical potential window, higher Li + ion permeability, and better electrochemical performance in LiMn 2 O 4 /separator/Li half-cell. The results also indicate that the PAN-based membrane/separator with small fiber diameters of 200–300 nm and hot-pressed under high pressure of 20 MPa surpasses all other membranes/separators and demonstrates the best performance, leading to the highest discharge capacity (89.5 mA h g −1 at C/2 rate) and cycle life (with capacity retention ratio being 97.7%) of the half-cell. In summary, this study has revealed that the hot-pressed electrospun PAN nanofibrous membranes (particularly those consisting of thin nanofibers) are promising as high-performance LIB separators. [ABSTRACT FROM AUTHOR]

Lignin is considered as the most abundant renewable carbon source after cellulose and non-commercialized waste product with constantly growing annual production exceeding 50 million tons per year. This article is focused on a newly developed selective synthesis of high-value phenolic products from lignin in presence of supercritical carbon dioxide (scCO 2 ) known as sustainable, non-flammable, naturally abundant, and catalytically active solvent. Depending on the synthesis conditions, such as temperature (250, 300, and 350 °C) and water-to-scCO 2 ratio (1:5, 1:2, 1:1, and 2:1), high yield of the specific phenolic compounds such as phenol, guaiacols, and vanillin has been achieved. The GCMS analysis reveals the trend of the increased total phenolic yield with temperature and strong dependence of the selectivity on the water-to-scCO 2 ratio. The maximum selectivity toward formation of the specific phenolic products, such as guaiacol and vanillin was observed at the highest H 2 O:scCO 2 = 1:5 ratio. At 350 °C the relative yield of guaiacol was ∼39% whereas at 250 °C vanillin was a dominant phenolic monomer with a relative yield of ∼33%. Moreover, at the intermediate temperature of 300 °C both guaiacol and vanillin were produced with relative yields of ∼28% and ∼13%, respectively. The highest amounts of scCO 2 resulted in the highest total relative phenolic yields of ∼79%, ∼71%, and ∼73% at 250, 300, and 350 °C, respectively. Demonstrated for the first time, the effect of water-to-scCO 2 ratio in the process of alkali lignin liquefaction will have significant impact on selective synthesis of phenolic compounds, their use in synthesis of “green” polymers with desirable properties, and sustainable utilization of both carbon dioxide and lignin waste. [ABSTRACT FROM AUTHOR]

A novel circulation type a hydrogen generator operating on sodium borohydride – sodium borate solution has been developed. The major parameters, such as operation temperature, concentration of the sodium borohydride and metaborate, catalytic activity, start up conditions, and removal of NaBO 2 as a product of the sodium borohydride hydrolysis have been analyzed. Generation of hydrogen was evaluated for aqueous NaBH 4 solutions in the range of 15–23 wt. % NaBH 4 in presence of the alumina supported Pt, Pd, Rh and Ni catalysts. The main trends in hydrogen gas generation with respect to the solution temperature and pressure in the reactor were analyzed. The catalytic efficiency and the rate of the hydrogen gas generation (1.5 Nm 3 /h) at the average hydrogen yield of 97–98.5% is sufficient for operation of the PEMFC Nexa™ Power module from Ballard. [ABSTRACT FROM AUTHOR]

CNTs were grown on iron-modified mesoporous graphitized carbon aerogel (GCA) at 700 °C, 800 °C and 900 °C using catalytic CVD method. Resultant CNT/GCA materials composition, morphology and structure were studied to understand their electrochemical stability and performance for oxygen reduction reaction (ORR) in acidic medium. CNT growth was increased from 700 °C to 800 °C, dominated by MWCNTs formation. In the temperature range from 800 °C to 900 °C, the growth was reduced by forming nanofiber/nanoribbon structures accompanied by MWCNTs. Mesoporosity of CNT/GCA composites declined at 700 °C and 800 °C due to MWCNT formation. However, CNT/GCA growth at 900 °C improved mesoporosity with substantial increase in pore volume (∼3 times of GCA) due to formation of nanofibers and nanoribbons. The structure of CNT/GCA materials revealed nitrogen doping and dispersion of FeN x phase. A synergistic contribution of CNT/GCA material structure and morphology to ORR activity was noticed. Among CNT/GCA materials, CNT-800 °C/GCA material showed ORR activity at lowest onset potential of 0.5 V. However, CNT-900 °C/GCA exhibits the highest ORR mass activity, with a half-wave onset potential difference of 120 mV with Pt (40 wt.%)/C. Moreover, CNT-900 °C/GCA demonstrates high selectivity (>3.97) to 4 electron ORR path, excellent methanol tolerance and electrochemical durability which makes it a potential DMFC cathode candidate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electrospun carbon nanofiber mats were prepared from a natural product of lignin. [•] The freestanding mats were flexible with BET specific surface area of ∼583 m2/g. [•] The mats were surface-deposited with Ag nanoparticles via the scCO2 method. [•] Novel electrocatalytic systems of Ag/ECNFs exhibited high activities towards ORR. [ABSTRACT FROM AUTHOR]

Abstract: Experimental results regarding long-term stability of the alkaline-water borohydride solutions for hydrogen generation are presented. The influence of the concentration of sodium borohydride and sodium hydroxide on the rate of borohydride hydrolysis is analyzed at various temperatures, such as 25 °C, 40 °C, and 80 °C, and various concentrations of NaOH. The rate of hydrolysis decreases with the increase of the water to sodium borohydride mole ratio. For diluted solutions at H2O/NaBH4 >30, the rate of hydrolysis and hydrogen generation at a given temperature remains constant. At room temperature in 1.0 N NaOH, the degree of hydrolysis is 0.01% NaBH4/h that meets the stability requirements for the borohydride solutions during the long-term storage. [Copyright &y& Elsevier]

Abstract: As a source of the high purity hydrogen, sodium and potassium borohydrides are investigated in terms of long-term stability in the form of the concentrated solutions, heterogeneous mixtures and in the solid state corresponding to NaBH4 or KBH4 crystal hydrates. In order to improve their stability during the long-term storage sodium and potassium hydroxides were added to the initial borohydride compositions. The effect of temperature, concentration of the borohydride and the alkaline solution, and the nature of the cation in the alkaline solution on the rate of borohydride hydrolysis was investigated. The differential technique developed for evaluation of the rate of borohydride hydrolysis was successfully applied for the determination of the long-term stability of the water-alkaline solutions containing NaBH4(KBH4)·5H2O with 1–10wt.% of NaOH or KOH at 30°C and 50°C. [Copyright &y& Elsevier]

The present study ellucidates bi-functional catalytic activity of the graphene-supported praseodymium (PrNi x Co 1-x O 3-δ) and samarium (SmNi x Co 1-x O 3-δ) perovskites towards oxygen evolution and oxygen reduction reactions in alkaline solutions. The perovskites with varied Ni and Co content (of x = 0.1, 0.5, and 0.9) were synthesized via sol-gel glycine-nitrite combustion followed by heat-treated at 700, 900 and 1200 °C. The cubic perovskite phase of PrNi x Co 1-x O 3-δ was stabilized at x = 0.1, 0.5 in the entire temperature range (of 700 °C–1200 °C), while the perovskite phase of SmNi x Co 1-x O 3-δ (x = 0.1, 0.5) was observed only at lower temperatures (of 700 and 900 °C). Consequently, changes in structural properties resulted in superior oxygen evolution reaction (OER) electrochemical activity in comparison to the state-of-the-art IrO 2. Among the Sm-based perovskites, SmNi 0.1 Co 0.9 O 3-δ (700 °C) demonstrated OER mass activity of 495 mA/mg and the highest oxygen reduction reaction (ORR) activity of 95 mA/cm2·mg. For Pr-based perovskites, the highest electrocatalytic activity toward OER and ORR was observed for PrNi 0.1 Co 0.9 O 3-δ (900 °C) resulting in 60 mA/mg for ORR and 680 mA/mg for OER which is 50% higher than the mass activity of the state-of-the-art IrO 2 catalyst. The overall performance of the composites is discussed in terms of graphene support interactions, Co and Ni redox processes, relative concentration of oxygen-vacancy sites and OER/ORR bi-functionality. Image 1 • Praseodymium and samarium-based perovskites were synthesized. • Catalytic activity towards OER and ORR is observed in alkaline media. • OER/ORR bi-functionality is described through graphene support-catalyst interaction. [ABSTRACT FROM AUTHOR]