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Hydrogen-bromate flow battery is a promising hybrid current source for air-deficient environment that functions by electrocatalyzed reactions of hydrogen oxidation and aqueous LiBrO3 reduction. The flow cell consists of porous carbonaceous cathode, platinum catalyzed hydrogen oxidation gas diffusion anode, and separating proton exchange membrane. Performance of the hydrogen-bromate flow battery single cell has been optimized by varying the catholyte feed rate, LiBrO3 concentration in catholyte, hydrogen pressure, membrane thickness, amount of porous carbon at cathode, and Pt loading at anode. Shape of the I-V curve is characterized by a sharp maximum of current, which indicates passivation of one of the electrodes. Combination of conventional reference electrode and home-made thin-film Luggin capillary has been used to monitor separately the polarizations of both flow cell electrodes. Poisoning of platinum hydrogen oxidation electrocatalyst by bromine species, which permeated the membrane, is shown as a major source of performance losses of hydrogen-bromate flow battery at high power density. Hypothesis supported by experiments claims that the degree of the platinum electrocatalyst poisoning is determined by the balance between the rates of the bromine species supply to anode and their removal by liquid water that permeates the membrane. Use of thinner proton exchange membrane and thinner carbonaceous cathode is a prerequisite to achieving high power density of the cell at high current efficiency of the cathode process. At 40 °C, area-specific power reaches 0.74 W cm−2 at the level of catholyte utilization equal to 0.93. [ABSTRACT FROM AUTHOR]

Here, the modification of semiconductor thin film hematite photoanode by doping with Sn ions is reported. Undoped and Sn-doped hematite films are fabricated by the electrochemical deposition of FeOOH from aqueous alkaline electrolyte, followed by calcination in air. The photoanodes were tested in photoelectrocatalytic oxidation of water, methanol, ethylene glycol, and glycerol. It is shown that modification by tin dramatically increased the activity of hematite in the photoelectrochemical oxidation of alcohols upon visible light irradiation. The photoelectrocatalytic activity of Sn-modified hematite increased in the sequence of: H2O < MeOH < C2H2(OH)2 < C3H5(OH)3. The quantum yield of photocurrent in the oxidation of alcohols reached 10%. The relatively low photocurrent yield was ascribed to the recombination of photoexcited holes within the hematite layer and on surface states located at the hematite/electrolyte interface. Intensity-modulated photocurrent spectroscopy (IMPS) was used to quantify the recombination losses of holes via surface states. The IMPS results suggested that the hole acceptor in the electrolyte (alcohol) influences photocurrent both by changing the charge transfer rate in the photoelectrooxidation process and by the efficient suppression of the surface recombination of generated holes. Thin-film Sn-modified hematite photoanodes are promising instruments for the photoelectrochemical degradation of organic pollutants. [ABSTRACT FROM AUTHOR]

Characteristics of the cathode catalyst layers (CCL) containing HiSPEC 9100 Pt/C catalyst and ionomer (I) in ionomer to carbon mass ratio (I/C) range 0–2 were studied. Pt electrochemically active surface area (ECSA) and electrode low frequency capacitance were found to be independent of I/C value. Ionic resistance of CCL was found strongly dependent of I/C value. It reaches maximum value at I/C∼0.3. Ionic resistance of CCL with I/C = 0.05 increased 7 fold with the shift of electrode potential ( E ) from 0.4 V to 1.05 vs . RHE. Ionic resistance of an imitating layer, which contained ionomer-free Ketjenblack EC-300J carbon, increased by a factor of 20 with the potential shift from 0.1 V to 1.05 V vs . RHE. Ionic conductivity in ionomer-free CCLs is ascribed to the presence of protons which originate from ionization of oxygen containing acidic surface groups of carbon support. Application to the CCL of potential positive relative to potential of zero charge of carbon support (pzc) draws protons to the counter electrode, decreasing the ionic conductivity of the CCL. Pt mass specific activity ( I m ) dependence on I/C mass ratio reaches maximum at I/C ∼ 1. [ABSTRACT FROM AUTHOR]

The speciation of polysulfides in aqueous solutions was investigated by electrospray – ion trap and electrospray – time of flight mass spectrometry. The pH dependence of the observed total dissolved polysulfides’ concentration followed the trend calculated based on reported thermodynamic constants. However, the observed species’ distributions were substantially different from those calculated based on thermodynamic coefficients derived by UV spectroscopy. Notably, large abundances of heptasulfide, octasulfide and nonasulfide species were observed throughout the pH range 6 to 11. The large molecular weight anions had not been reported before in aqueous solutions although indirect evidence had suggested their existence. [ABSTRACT FROM AUTHOR]

The mechanism of electrochemical oxidation of N,N-dimethyl-p-phenylenediamine (DPD) in aqueous electrolyte solutions in the pH range 1.4–9.7 was studied using on-line electrochemical–mass spectrometry. A radial flow electrochemical cell was used to generate the product stream which was analyzed by a mass spectrometer equipped with an electrospray interface (ESI-MS). It was shown that DPD oxidation in the pH 1.4–9.7 range brings about formation of the Wurster red cation radical, quinonediimine, quinonemonoimine and dimer and trimer products of coupling reactions of DPD with quinonediimine and quinonemonoimine. Coupling reactions were found to be strongly pH dependent. The kinetics of the coupling reaction between DPD and quinonemonoimine were studied at pH 3.6. [Copyright &y& Elsevier]

Presents technique for microscopic imaging of electrochemically active surfaces. Theoretical spatial resolutions of the scanning capillary microscopy/mass spectrometry; Electrochemistry of dimethyl-p-phenylenediamine (DPD); Flow characteristics in the flow cell scanner; Mass spectrometric monitoring of DPD and its oxidation products during potential scan.

High-temperature polymer-electrolyte membrane fuel cells (HT-PEMFCs) are a very important type of fuel cells since they operate at 150–200 °C, making it possible to use hydrogen contaminated with CO. However, the need to improve the stability and other properties of gas-diffusion electrodes still impedes their distribution. Self-supporting anodes based on carbon nanofibers (CNF) are prepared using the electrospinning method from a polyacrylonitrile solution containing zirconium salt, followed by pyrolysis. After the deposition of Pt nanoparticles on the CNF surface, the composite anodes are obtained. A new self-phosphorylating polybenzimidazole of the 6F family is applied to the Pt/CNF surface to improve the triple-phase boundary, gas transport, and proton conductivity of the anode. This polymer coating ensures a continuous interface between the anode and proton-conducting membrane. The polymer is investigated using CO2 adsorption, TGA, DTA, FTIR, GPC, and gas permeability measurements. The anodes are studied using SEM, HAADF STEM, and CV. The operation of the membrane–electrode assembly in the H2/air HT-PEMFC shows that the application of the new PBI of the 6F family with good gas permeability as a coating for the CNF anodes results in an enhancement of HT-PEMFC performance, reaching 500 mW/cm2 at 1.3 A/cm2 (at 180 °C), compared with the previously studied PBI-O-PhT-P polymer. [ABSTRACT FROM AUTHOR]

Nanosized bimetallic PtMo, PtFe and trimetallic PtMoSn catalysts deposited on highly dispersed carbon black Vulcan XC-72 were synthesized from the cluster complex compounds PtCl(P(C6H5)3)(C3H2N2(CH3)2)Mo(C5H4CH3)(CO)3, Pt(P(C6H5)3)(C3N2H2(CH3)2)Fe(CO)3(COC6H5C2C6H5), and PtCl(P(C6H5)3)(C3N2H2(CH3)2)C5H4CH3Mo(CO)3SnCl2, respectively. Structural characteristics of these catalysts were studied using X-ray diffraction (XRD), microprobe energy dispersive spectroscopy (EDX), and transmission electron microscopy (TEM). The synthesized catalysts were tested in aqueous 0.5 M H2SO4 in a three-electrode electrochemical cells and in single fuel cells. Electrocatalytic activity of PtMo/C and PtFe/C in the oxygen reduction reaction (ORR) and the activity of PtMoSn/C in electrochemical oxidation of ethanol were evaluated. It was shown that specific characteristics of the synthesized catalysts are 1.5–2 times higher than those of a commercial Pt(20%)/C catalyst. The results of experiments indicate that PtFe/C, PtMo/C, and PtMoSn/C catalysts prepared from the corresponding complex precursors can be regarded as promising candidates for application in fuel cells due to their high specific activity. [ABSTRACT FROM AUTHOR]

The efficient use of renewable energy sources requires development of new electrocatalytic materials for electrochemical energy storage systems, particularly fuel cells. To increase durability of high temperature polymer electrolyte fuel cell (HT-PEMFC), Pt/carbon black based catalysts should be replaced by more durable ones, for example Pt/carbon nanofibers (CNF). Here, we report for the first time the quantitative ascorbic acid assisted deposition of Pt onto electrospun polyacrylonitrile-based CNF composite materials. The effect of their subsequent post-treatment at various temperatures (250 and 500 °C) and media (vacuum or argon-hydrogen mixture) on the Pt/C catalyst morphology is investigated. All obtained samples are thoroughly studied by high resolution electron microscopy, and Pt electrochemically active specific surface area was evaluated by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

New mechanisms of the anticorrosion action of superhydrophobic coatings (SHCs), additional to electrolyte repellency, namely, the suppression of adsorption of aggressive ions, the barrier effect of a modified surface layer, and the specific charging of a hydrophobic layer in electrolytes, are considered and illustrated by the electrochemical behavior of an SHC on aluminum alloy in KCl solutions. [ABSTRACT FROM AUTHOR]

The relationship between homogeneouscatalysis and electrochemistry is examined in light of two examplesbased on our work concerning (a) catalyst activation, regarding selectiveelectrochemical C–H oxidation with RuIII/RuIVmediation, and (b) catalyst suppression, regarding controllingselectivity in electrochemical aromatic chlorination. The first example(a) deals with the role of catalysis at the working electrode. Theelectrochemical (EC) oxidation of specific hydrocarbons such as tetralinand indane is performed using tris(acetonitrile)ruthenium trichloride(Ru(CH3CN)3Cl3) as a mediator. Therole of this mediator in the oxidation of tetralin has been reported.This homogeneous C–H activation by electron transfer (ET) isaccompanied by the redox transitions of the mediator in the courseof the catalytic oxidation, and these are the main points of interesthere. Additional studies with a rotating ring disk electrode (RRDE)provided a follow-up of creation and recovery of RuIII/RuIIand RuIII/RuIVspecies in the process.Using electrochemistry linked with electrospray ionization mass spectrometry(EC/ESI-MS) gave additional information on the structure of the reducedand oxidized forms of Ru(CH3CN)3Cl3and the effect of water in the solvent on their lifetimes. The secondexample (b) of electrochlorination has been reported elsewhere andis brought up as complementary remarks. Aromatic electrophilic chlorinationof 1,4-dimethoxy-2-tertbutylbenzene is autocatalyzed and unselective.The EC procedure provides a simple means to inhibit the catalyticrunaway reaction. This example shows how the counter electrode affectscatalysis and selectivity. [ABSTRACT FROM AUTHOR]

Abstract: The reinforced composite membranes based on Nafion® membranes attract a lot of attention as proton exchange membrane (PEM) for polymer electrolyte membrane fuel cells (PEMFCs). Fluorine-containing polyimide (FPI), end-capped with alkynyl, is synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)- 4,4′-diaminobiphenyl (TFMB), and 3-aminophenylacetylene (APA). The chemical structure of FPI is characterized by 1H-NMR. The reinforced composite membrane based-on semi-interpenetrating polymer network (semi-IPN) is prepared via solution casting of FPI and Nafion®212, and crosslinking thereafter. During the membrane preparation, alkynyl in FPI reacts with azide and itself via click chemistry and addition polymerization. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and oxidative stability of the composite membranes are investigated. Compared to Nafion®212, the composite membrane shows improved thermal stability, mechanical properties, and dimensional stability. The tensile strength of the composite membranes is in the range of 35.0–55.6MPa, which is much higher than that of Nafion®212 membrane. The composite membranes show considerable proton conductivity from 2.0×10−2 Scm−1 to 9.9×10−2 Scm−1 at a temperature range from 30°C to 100°C, depending on FPI content. [Copyright &y& Elsevier]

The most environmentally safe method of PBI synthesis is reported and applied in the high proton conductivity membrane production for high temperature polymer electrolyte membrane fuel cell. [Display omitted] • Breakthrough PBI synthesis for HT-PEMFC proton-conducting membrane is suggested. • The environmentally safe method of PBI synthesis is developed. • The membrane was successfully tested in HT-PEM fuel cell. • Extremely low hydrogen crossover through the membrane at 180 °C was registered. The article presents a new environmentally safe synthetic approach towards durable polybenzimidazole proton-conducting membrane via polyamidation at ambient conditions and subsequent thermal heterocyclization of films cast from reaction solution followed by phosphoric acid doping. The method avoids exhausts, acid waste and inorganic salts, compared with the existing methods and technologies, allowing to minimize the negative environmental impact related to the process. The membrane possesses an excellent proton conductivity of 105 mS cm−1 and good mechanical properties and has been successfully tested in high temperature polymer electrolyte membrane fuel cells. An extremely low hydrogen crossover through the membrane of 0.040 mA cm−2 at 180 °C has been registered compared with quite high 4–5 mA cm−2 for Celazole® m -PBI. [ABSTRACT FROM AUTHOR]

The sulfonated polynaphthoyleneimide polymer (co-PNIS70/30) was prepared by copolymerization of 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODAS) and 4,4'-methylenebisanthranilic acid (MDAC) with ODAS/MDAC molar ratio 0.7/0.3. High molecular weight co-PNIS70/30 polymers were synthesized either in phenol or in DMSO by catalytic polyheterocyclization in the presence of benzoic acid and triethylamine. The titration reveals the ion-exchange capacity of the polymer equal to 2.13 meq/g. The membrane films were prepared by casting polymer solution. Conductivities of the polymer films were determined using both in- and through-plane geometries and reached ~96 and ~60 mS/cm, respectively. The anisotropy of the conductivity is ascribed to high hydration of the surface layer compared to the bulk. SFG NMR diffusometry shows that, in the temperature range from 213 to 353 K, the 1H self-diffusion coefficient of the co-PNIS70/30 membrane is about one third of the diffusion coefficient of Nafion® at the same humidity. However, temperature dependences of proton conductivities of Nafion® and of co-PNIS70/30 membranes are nearly identical. Membrane–electrode assemblies (MEAs) based on co-PNIS70/30 were fabricated by different procedures. The optimal MEAs with co-PNIS70/30 membranes are characterized by maximum output power of ~370 mW/cm2 at 80 °C. It allows considering sulfonated co-PNIS70/30 polynaphthoyleneimides membrane attractive for practical applications. [ABSTRACT FROM AUTHOR]

Electrospinning of polyacrylonitrile/DMF dopes containing salts of nickel, cobalt, zirconium, cerium, gadolinium, and samarium, makes it possible to obtain precursor nanofiber mats which can be subsequently converted into carbon nanofiber (CNF) composites by pyrolysis at 1000–1200 °C. Inorganic additives were found to be uniformly distributed in CNFs. Metal states were investigated by transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). According to XPS in CNF/Zr/Ni/Gd composites pyrolyzed at 1000 °C, nickel exists as Ni0 and as Ni2+, gadolinium as Gd3+, and zirconium as Zr4+. If CNF/Zr/Ni/Gd is pyrolyzed at 1200 °C, nickel exists only as Ni0. For CNF/Sm/Co composite, samarium is in Sm3+ form when cobalt is not found on a surface. For CNF/Zr/Ni/Ce composite, cerium exists both as Ce4+ and as Ce3+. Composite CNF mats were platinized and tested as cathodes in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). Such approach allows to introduce Pt–M and Pt–MOx into CNF, which are more durable compared to carbon black under HT-PEMFC operation. For CNF/Zr/Ni/Gd composite cathode, higher performance in the HT-PEMFC at I >1.2 A cm-2 is achieved due to elimination of mass transfer losses in gas-diffusion electrode compared to commercial Celtec®P1000. [ABSTRACT FROM AUTHOR]