Ravi P. Pandey

Sulfonated polyimide/acid-functionalized graphene oxide composite polymer electrolyte membranes with improved proton conductivity and water-retention properties.

Sulfonated polyimide (SPI)/sulfonated propylsilane graphene oxide (SPSGO) was assessed to be a promising candidate for polymer electrolyte membranes (PEMs). Incorporation of multifunctionalized (-SO3H and -COOH) SPSGO in SPI matrix improved proton conductivity and thermal, mechanical, and chemical stabilities along with bound water content responsible for slow dehydration of the membrane matrix. The reported SPSGO/SPI composite PEM was designed to promote internal self-humidification, responsible for water-retention properties, and to promote proton conduction, due to the presence of different acidic functional groups. Strong hydrogen bonding between multifunctional groups thus led to the presence of interconnected hydrophobic graphene sheets and organic polymer chains, which provides hydrophobic-hydrophilic phase separation and suitable architecture of proton-conducting channels. In single-cell direct methanol fuel cell tests, SPI/SPSGO-8 exhibited 75.06 mW·cm(-2) maximum power density (in comparison with commercial Nafion 117 membrane, 62.40 mW·cm(-2)) under 2 M methanol fuel at 70 °C.

A N-o-sulphonic acid benzyl chitosan (NSBC) and N,N-dimethylene phosphonic acid propylsilane graphene oxide (NMPSGO) based multi-functional polymer electrolyte membrane with enhanced water retention and conductivity

To achieve good proton conductivity even under dehydrated conditions, water retention is a pervasive issue for polymer electrolyte membranes (PEMs). Herein, we report a green and easy preparation procedure for multifunctional PEM grafted with –PO3H2 and –SO3H groups based on a functionalized biopolymer (N-o-sulphonic acid benzyl chitosan (NSBC)) and N,N-dimethylene phosphonic acid propylsilane graphene oxide (NMPSGO). Loading of NMPSGO in the NSBC matrix enhanced water retention, proton conductivity, stability and other desired properties of PEM relevant for DMFC applications. The reported NSBC/NMPSGO composite PEM was designed to promote internal self-humidification responsible for water retention properties, to promote proton conduction due to the presence of different acidic functional groups. It was hypothesized that strong hydrogen bonding between multi-functional groups due to the presence of inter-connected hydrophobic graphene sheets and organic polymer chains provides a hydrophobic–hydrophilic phase separation and suitable architecture for proton conducting channels. The most suitable PEM (NSBC/NMPSGO-8) exhibited 4.42% bound water content; 8.87 × 10−2 S cm−1 proton conductivity; 2.09 mequiv. per g ion-exchange capacity; and 16.93 × 10−7 cm2 s−1 methanol permeability. The proposed route offers a facile and generic strategy to design a variety of composite functional materials, in which both organic (NSBC) and inorganic (NMPSGO) were functionalized, with superior functional group molality, proton conductivity, water retention properties and stability.

Aliphatic-aromatic sulphonated polyimide and acid functionalized polysilsesquioxane composite membranes for fuel cell applications

For the design of highly stable and proton conductive polymer electrolyte membranes (PEM), we synthesized nucleophillic attack resistant sulphonated polyimide (SPI), in which electron-withdrawing sulphonic acid groups were not directly attached through amino-phenyl rings, using diamines with high basicity and dianhydride with low electron affinity. SPI- sulphonated silica precursor (SSP) composite PEM was assessed for its high water activity (water retention capacity) and direct methanol fuel cell (DMFC) applications. SPI/SSP-40 (composite membrane with 40 wt% SSP content) showed 10.25 × 10−8 cm2 s−1 water diffusion coefficient; 1.86 mequiv. per g ion-exchange capacity (IEC); and 6.34 × 10−2 S cm−1 proton conductivity. The prepared PEM was classified as water enriched because of the presence of a high percentage of bound water content. A relatively high proton mobility (5.52 × 10−4 cm2 s−1 V−1) across the PEM was attributed to a percolated network of ionic clusters (ions and water). Frictional data confirmed the reduction in frictional coefficient between the proton and membrane matrix at a high SSP content. The reported PEM, especially SPI/SSP-40, were assessed for their suitability for DMFC applications.

Fluorenyl phenolphthalein groups containing a multi-block copolymer membrane for alkaline fuel cells

An anion-conducting aromatic multi-block copolymer (PEs-AxBy) was synthesized by a block co-polycondensation reaction between fluorene and phenolphthalein containing oligomers. The quaternized multi-block copolymers (QPEs) resulted in ductile transparent membranes with well-ordered multi-block structures. In chloroform, a thin polymer film (PE-A22B24) with hexagonal well-ordered geometry was obtained. Meanwhile, in NMP/DMAc a dense thin film for QPE-A22B24 was obtained. As an additional attractive feature, the pore structure and pore-geometry of the membrane thin film may be controlled by the membrane casting medium and conditions. The presence of hydrophilic (biphenyl fluorene)–hydrophobic (connector)–hydrophilic (phenolphthalein) groups was responsible for phase separation, and interconnected ion conducting pathways. Among many synthesized anion exchange membranes (AEMs), QPE-A22B24 exhibited excellent stabilities, 0.95–2.24 meq g−1 ion exchange capacity and 95 mS cm−1 conductivity, at 80 °C. The reported AEM retained the conductivity after 1000 h of boiling treatment. QPE-A22B24 membranes were assessed as suitable candidates for alkaline fuel cell applications.

2-Acrylamido-2-methyl-1-propanesulfonic Acid Grafted Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Acid-/Oxidative-Resistant Cation Exchange for Membrane Electrolysis

For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure.

Self-assembled silica nanocrystal-based anti-biofouling nanofilter membranes

Herein, we report synthesis of organosiloxane 3-(2-((3-aminopropyl)diethoxysilyl)ethylthio)-5-(4-((3-aminopropyl)diethoxy silyl)phenyl)-4H-1,2,4-triazol-4-amine (TS) by Barbiar–Grignard reaction. Hybrid nanofiltration (NF) membranes were prepared from TS and poly(vinyl alcohol) (PVA) via sol–gel process followed by cross-linking and grafting of phosphonic acid groups. Physicochemical properties of these membranes revealed their stable (thermal, mechanical, and chemical) and chlorine tolerant nature. HRTEM analysis reveals homogenous silica distribution in the membrane matrix. The cross-link density of the membrane and the preparation conditions were studied in terms of NF performance. An Escherichia coli bacterium was used to study antibacterial activity and anti-biofouling properties of the hybrid membrane. The short-term bacterial stability test showed that membrane TS-60a has good anti-fouling properties. Moreover TS-60a membrane showed excellent stability and anti-biofouling capability in long-time operation.