Current Scenario of Poly (2,5-Benzimidazole) (ABPBI) as Prospective PEM for Application in HT-PEMFC

Abstract

In last two decades, acid doped polybenzimidazole as polymer electrolyte membrane (PEM) has been widely recognized and envisioned as “ideal” proton conducting materials for application in high temperature PEM fuel cell (HT-PEMFC). The majority of research and developmental work is mainly focused on poly (2,2´-m-phenylene-5,5´-bibenzimidazole), However, it is neither easy-processed nor inexpensive component of the respective family. On the other hand, among the various members belonging to benzimidazole family, poly (2,5-benzimidazole) is unique because it possesses a cost-attractive, single-step synthesis process, high extent of doping as well as good chemical and thermal stability. In the recent years this material has proved its potency in the earlier research. Thus this review puts special emphasis on poly (2,5-benzimidazole) and epitomizes the on-going breath-taking progress and achievements on the fabrication of poly (2,5-benzimidazole) based membranes. The write-up describes the effect of blending, cross-linking, ionic liquids and incorporation organic/inorganic nano-fillers. In addition, incorporating other protonic dopants such as heteropoly acids into the chain of poly (2,5-benzimidazole) molecular skeleton is also overviewed. Moreover, the critical interpretation of different causes responsible for earlier degradation and their effect towards the fabrication of high temperature membrane electrode assembly are visualized herein.

• Highlights

• Current developments and existing challenges of ABPBI in PEMFC have been reviewed.

• PEM Modification and addition of protonic dopants has been discussed.

• Proton migration, permeability, stability and reliability are thoroughly illustrated.

• Different ABPBI-based membranes and their performance are comparatively analyzed.

     

The reaction of IO with CH3SCH3: products and temperature dependent rate coefficients by laser induced fluorescence

The technique of pulsed laser photolysis was coupled to laser induced fluorescence detection of iodine oxide (IO) to measure rate coefficients, k(1)(T), for the title reaction IO + CH3SCH3 --> products (R1). A value of k1(298 K) = (1.44 +/- 0.15) x 10(-14) cm3 molecule(-1) s(-1) was obtained, independent of bath gas pressure (50 < P((N2 or air))/Torr < 300). The expression k1(T) = (3.2 +/- 1.4)x 10(-13)exp[(-925 +/- 136)/T)] adequately described the data over the range of temperatures (256 < T/K < 341) covered. Uncertainties (2sigma) in the 298 K rate coefficient and the pre-exponential factor include an estimate of systematic error. The conventional Arrhenius behaviour of k1(T) and the lack of pressure dependence are suggestive of an abstraction mechanism, characterised by an energy barrier of E approximately 8 kJ mol(-1). The product yield for production of I-atoms was determined indirectly to be close to unity, indicating that the reaction proceeds via transfer of the O-atom from IO to CH3SCH3 to form CH3S(O)CH3. In general, the values of k1(T) measured in this work indicate that has little impact on the chemistry of the atmosphere.     

Reaction of HO with glycolaldehyde, HOCH2CHO: rate coefficients (240-362 K) and mechanism

Absolute rate coefficients for the title reaction, HO+HOCH2CHO-->products (R1), were measured over the temperature range 240-362 K using the technique of pulsed laser photolytic generation of the HO radical coupled to detection by pulsed laser induced fluorescence. Within experimental error, the rate coefficient, k1, is independent of temperature over the range covered and is given by k1(240-362 K)=(8.0+/-0.8)x10(-12) cm3 molecule-1 s-1. The effects of the hydroxy substituent and hydrogen bonding on the rate coefficient are discussed based on theoretical calculations. The present results, which extend the database on the title reaction to a range of temperatures, indicate that R1 is the dominant loss process for HOCH2CHO throughout the troposphere. As part of this work, the absorption cross-section of HOCH2CHO at 184.9 nm was determined to be (3.85+/-0.2)x10(-18) cm2 molecule-1, and the quantum yield of HO formation from the photolysis of HOCH2CHO at 248 nm was found to be (7.0+/-1.5)x10(-2).     

Photolysis of CH3C(O)CH3 (248 nm, 266 nm), CH3C(O)C2H5 (248 nm) and CH3C(O)Br (248 nm): pressure dependent quantum yields of CH3 formation

The formation of CH(3) in the 248 or 266 nm photolysis of acetone (CH(3)C(O)CH(3)), 2-butanone (methylethylketone, MEK, CH(3)C(O)C(2)H(5)) and acetyl bromide (CH(3)C(O)Br) was examined using the pulsed photolytic generation of the radical and its detection by transient absorption spectroscopy at 216.4 nm. Experiments were carried out at room temperature (298 +/- 3 K) and at pressures between approximately 5 and 1500 Torr N(2). Quantum yields for CH(3) formation were derived relative to CH(3)I photolysis at the same wavelength in back-to-back experiments. For acetone at 248 nm, the yield of CH(3) was greater than unity at low pressures (1.42 +/- 0.15 extrapolated to zero pressure) confirming that a substantial fraction of the CH(3)CO co-product can dissociate to CH(3) + CO under these conditions. At pressures close to atmospheric the quantum yield approached unity, indicative of almost complete collisional relaxation of the CH(3)CO radical. Measurements of increasing CH(3)CO yield with pressure confirmed this. Contrasting results were obtained at 266 nm, where the yields of CH(3) (and CH(3)CO) were close to unity (0.93 +/- 0.1) and independent of pressure, strongly suggesting that nascent CH(3)CO is insufficiently activated to decompose on the time scales of these experiments at 298 K. In the 248 nm photolysis of CH(3)C(O)Br, CH(3) was observed with a pressure independent quantum yield of 0.92 +/- 0.1 and CH(3)CO remained below the detection limit, suggesting that CH(3)CO generated from CH(3)COBr photolysis at 248 nm is too highly activated to be quenched by collision. Similar to CH(3)C(O)CH(3), the photolysis of CH(3)C(O)C(2)H(5) at 248 nm revealed pressure dependent yields of CH(3), decreasing from 0.45 at zero pressure to 0.19 at pressures greater than 1000 Torr with a concomitant increase in the CH(3)CO yield. As part of this study, the absorption cross section of CH(3) at 216.4 nm (instrumental resolution of 0.5 nm) was measured to be (4.27 +/- 0.2) x 10(-17) cm(2) molecule(-1) and that of C(2)H(5) at 222 nm was (2.5 +/- 0.6) x 10(-18) cm(2) molecule(-1). An absorption spectrum of gas-phase CH(3)C(O)Br (210-305 nm) is also reported for the first time.     

Determination of metal content in superoxide dismutase enzymes by capillary electrophoresis†

Superoxide dismutases are antioxidant scavenger enzymes that contain a metal cofactor (copper, zinc, iron, and manganese) in their active site. Metal content measurement is one of the essential steps to characterize enzyme biological activity. We have developed a capillary electrophoretic protocol for the determination of the metal content in superoxide dismutase enzymes. The background electrolyte containing 10 mM pyridine‐2,6‐dicarboxylic acid and 1 mM 1‐methyl‐3‐tetradecylimidazolium chloride at pH 3.8 was optimized for on‐column complexation of the above‐mentioned metals. The minimum detectable levels of metals ranged from 0.3 to 1.2 μg/mL. The reliability of the method was checked by parallel quantitative determination of the metal content in superoxide dismutase enzymes by graphite furnace or flame atomic absorption spectrophotometry methods.     

Wetting Properties of Barium Sodium Niobate Filled Polystyrene Nanocomposite

Nano crystalline powders of Barium Sodium Niobate (BNN) with the composition (Ba₃ Na₄Nb₁₀ O₃₀) have been prepared by conventional ceramic technique. XRD and SEM studies revealed that its particle size is in the nanometer range. Composites were prepared by mixing powders of BNN with polystyrene at different volume fractions of the material. Melt mixing technique was carried out in brabender plasticoder at a rotor speed of 60 rpm for composite preparation. Surface energy characteristics of the composites are measured using contact angle measurements of the composites with water and methlene iodide. The solid surface free energy is calculated from harmonic mean equations. The results are quantitatively analyzed with Girifalco-Good empirical model and provide unique insight into its properties. Various wettability parameters such as total solid surface free energy, work of adhesion, interfacial free energy and spreading coefficient are analyzed. The different parameters are calculated from the harmonic mean equation. The work of adhesion and interfacial free energy, spreading coefficient, and Girifalco-Good's interaction parameter had changed with composition. The surface properties can be controlled for a given polymer-surface pair by controlling the chemical structure, composition etc.