Effect of composition on the properties of PEM based on polybenzimidazole and poly(vinylidene fluoride) blends

Inadequate performance, short term durability and high cost of polymer electrolyte membrane (PEM) are the major roadblocks that need to be resolved for successful commercialization of high temperature PEM fuel cell. In this report, we investigated the viability of previously developed miscible blend membranes of polybenzimidazole and poly (vinylidene fluoride) (PBI/PVDF), as potential PEMs. In addition, we have carried out several advanced analytical techniques such as dynamic mechanical analysis (DMA), ¹³C CP-MAS solid state NMR (SS-NMR) and wide-angle X-Ray diffraction (WAXD) to prove the miscible behavior of the polymer pair. Sub-ambient temperature DMA studies confirmed the miscible behavior of PBI/PVDF blends at different compositions based on single T_g criterion. SS-NMR and WAXD showed the presence of interactions between the functional groups of the polymers and their dependence on blend composition. Thermogravimetric analysis of phosphoric acid (PA) doped and undoped blend membranes confirmed the improved thermal stability of the membranes compared to neat PBI. The membranes exhibited excellent oxidative stability than pristine PBI membrane. The swelling ratio and volume after dipping in PA was found to be significantly low in the blend membranes owing to the hydrophobic nature of PVDF. Among the blends prepared, 90/10 and 75/25 membranes showed higher proton conductivity than PBI, attributed in part, to electronegativity of fluorine and crystallinity of PBI in PA that activate proton transport. The results demonstrated the potential usefulness of the blend membranes as PEM in fuel cell.     

Functionalization of terminal carbon atoms of hydroxyl terminated polybutadiene by polyazido nitrogen rich molecules

We report a novel synthetic approach for the attachment of the polyazido nitrogen rich molecule on to the hydroxyl terminated polybutadiene (HTPB) backbone. The terminal carbon atoms of the HTPB are functionalized by attaching cyanuric chloride (CYC) covalently on the HTPB backbone. Further reaction of this modified HTPB with sodium azide yields polyazido nitrogen rich HTPB. The unique physico-chemical properties and the microstructure of the HTPB do not get affected upon modification. IR, gel permeable chromatography (GPC) and absorption spectroscopy studies prove that the polyazido nitrogen rich molecules are covalently attached at the terminal carbon atoms of the HTPB. The π electron delocalization owing to long butadiene chain, strong electron withdrawing effect of the triazine molecules are the major driving forces for the covalent attachment of the triazine at the terminal carbon atoms of the HTPB. The disruption of the intermolecular hydrogen bonding between the terminal hydroxyl groups of the HTPB chains and the presence of hydrogen bonding between the N atoms of the triazine ring with OH group of the HTPB are observed. Theoretical study also reveals the existence of the hydrogen bonding between the OH and N. Theoretical calculation shows that the detonation performance of the polyazido nitrogen rich HTPB are very promising.     

Crystalline ZnO and ZnO/TiO2 nanoparticles derived from tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) chelate: Electrocatalytic studies for H2 generation in alkaline electrolytes

A newly synthesized zinc(II) complex, namely tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) complex [Zn(Boc-S)₂] (Boc = tert-butyl N-[2-mercaptoethyl]carbamate), has been used as an organozinc precursor for the production of crystalline ZnO and ZnO/TiO₂ nanoparticles. The synthesized complex and the obtained nanomaterials were fully characterized using various spectroscopic and surface analysis techniques. Their surface morphology, chemical purity and stoichiometry have been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) as well as X-ray fluorescence. The synthesized Zn(II) molecular complex, ZnO and ZnO/TiO₂ nanomaterials have been tested in alkaline aqueous solution (1.0 MNaOH) for the hydrogen evolution reaction (HER) using various electrochemical techniques. The results revealed high HER catalytic performance of ZnO and ZnO/TiO₂ cathode materials, with the latter exhibiting higher catalytic activity recording an exchange current density (j_o) of 0.3 mA cm⁻². This current value, which approaches that of Pt wire (0.5 mA cm⁻²), cross-sectional area ~0.008 cm², is about 11 and 100 times greater than those measured for ZnO alone (0.028 mA cm⁻²) and TiO₂ alone (0.0032 mA cm⁻²), respectively. Moderate catalytic activity was recorded for the complex catalyst, namely GC-Zn(Boc-S)₂ with j_o value of (0.01 mA cm⁻²). Tafel slope values of 130 and 122 mV dec⁻¹ were calculated for ZnO and ZnO/TiO₂, respectively. Such Tafel slope values, which are close to that of the Pt wire (120 mV dec⁻¹), referred to a Volmer-controlled HER kinetics. Other important electrochemical parameters describing the kinetics of the HER, such as roughness factor (R_f) and turnover frequency (TOF) were also estimated and discussed. The high numerical values of the various HER kinetic parameters recorded for the ZnO/TiO₂ catalyst, in addition to its high stability and durability (stable for up to 10 000 continuous cathodic polarization cycles), besides maintaining its morphology and chemical composition after stability test (confirmed from SEM/EDX and XRD examinations), located it in a privileged position among the most efficient HER electrocatalysts reported in the literature.     

Large-Area Si Solar Cells Based on Molybdenum Oxide Hole Selective Contacts

Silicon - Carrier selective contacts based heterojunction Si solar cells are an emerging photovoltaic technology. This paper reports the fabrication of large area Si solar cells based on molybdenum...     

Enabling computer-aided food process engineering: Property estimation equations for transport phenomena-based models

During processing of a food, its temperature, moisture and other compositions, structure, etc., can change, continuously changing its physical properties. Realistic simulation of food processes require dynamic estimation of the food physical properties as they continue to change during the process. Having a few data points for a few states of the material, as is true for the majority of food properties data, is not sufficient for realistic process simulations. The goal of this article is a practical one: it is to develop a concise resource for the equations that can estimate food properties as they change during processing. Such a resource should make computer-aided food product, process and equipment design one step closer to reality by making the necessary input parameters available in one location and in a format that can be readily used in a simulation software. Several equilibrium, transport and electrical properties are included. The estimation equations for any property are chosen from among the most successful and accurate, staying away from property estimators that have theoretical basis but have not been as successful for food materials. For each property, implementation of its prediction equations in a computer model has also been discussed. Accuracy of each property estimation process have been included from the literature, showing most properties can be estimated to within 10% accuracy, sufficient for modeling purposes. Having such reasonable prediction models has the important implication that unavailability of sufficient data, that is expected to be always true due to the variety and complexity of food materials and processes, is not a bottleneck for computer-aided food process engineering.     

Pathways to improve nephrologist comfort in managing patients on in-center or home self-care dialysis

In end-stage kidney disease (ESKD), patient engagement and empowerment are associated with improved survival and complications. However, patients lack education and confidence to participate in self-care. The development of in center self-care hemodialysis can enable motivated patients to allocate autonomy, increase satisfaction and engagement, reduce human resource intensiveness, and cultivate a curiosity about home dialysis. In this review, we emphasize the role of education to overcome barriers to home dialysis, strategies of improving home dialysis utilization in the COVID 19 era, the significance of in-center self-care dialysis (e.g., cost containment and empowering patients), and implementation of an in-center self-care dialysis as a bridge to home hemodialysis (HHD).