Enhancing Physicochemical Properties and Single Cell Performance of Sulfonated Poly(arylene ether) (SPAE) Membrane by Incorporation of Phosphotungstic Acid and Graphene Oxide: A Potential Electrolyte for Proton Exchange Membrane Fuel Cells.

The development of potential and novel proton exchange membranes (PEMs) is imperative for the further commercialization of PEM fuel cells (PEMFCs). In this work, phosphotungstic acid (PWA) and graphene oxide (GO) were integrated into sulfonated poly(arylene ether) (SPAE) through a solution casting approach to create a potential composite membrane for PEMFC applications. Thermal stability of membranes was observed using thermogravimetric analysis (TGA), and the SPAE/GO/PWA membranes exhibited high thermal stability compared to pristine SPAE membranes, owing to the interaction between SPAEK, GO, and PWA. By using a scanning electron microscope (SEM) and atomic force microscope (AFM), we observed that GO and PWA were evenly distributed throughout the SPAE matrix. The SPAE/GO/PWA composite membrane comprising 0.7 wt% GO and 36 wt% PWA exhibited a maximum proton conductivity of 186.3 mS cm-1 at 90 °C under 100% relative humidity (RH). As a result, SPAE/GO/PWA composite membrane exhibited 193.3 mW cm-2 of the maximum power density at 70 °C under 100% RH in PEMFCs.

Potential carbon nanomaterials as additives for state-of-the-art Nafion electrolyte in proton-exchange membrane fuel cells: a concise review.

Proton-exchange membrane fuel cells (PEMFCs) have received great attention as a potential alternative energy device for internal combustion engines due to their high conversion efficiency compared to other fuel cells. The main hindrance for the wide commercial adoption of PEMFCs is the high cost, low proton conductivity, and high fuel permeability of the state-of-the-art Nafion membrane. Typically, to improve the Nafion membrane, a wide range of strategies have been developed, in which efforts on the incorporation of carbon nanomaterial (CN)-based fillers are highly imperative. Even though many research endeavors have been achieved in relation to CN-based fillers applicable for Nafion, still their collective summary has rarely been reported. This review aims to outline the mechanisms involved in proton conduction in proton-exchange membranes (PEMs) and the significant requirements of PEMs for PEMFCs. This review also emphasizes the improvements achieved in the proton conductivity, fuel barrier properties, and PEMFC performance of Nafion membranes by incorporating carbon nanotubes, graphene oxide, and fullerene as additives.

Ameliorated Performance of Sulfonated Poly(Arylene Ether Sulfone) Block Copolymers with Increased Hydrophilic Oligomer Ratio in Proton-Exchange Membrane Fuel Cells Operating at 80% Relative Humidity.

We designed and synthesized a series of sulfonated poly(arylene ether sulfone) (SPES) with different hydrophilic or hydrophobic oligomer ratios using poly-condensation strategy. Afterward, we fabricated the corresponding membranes via a solution-casting approach. We verified the SPES membrane chemical structure using nuclear magnetic resonance (1H NMR) and confirmed the resulting oligomer ratio. Field-emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM) results revealed that we effectively attained phase separation of the SPES membrane along with an increased hydrophilic oligomer ratio. Thermal stability, glass transition temperature (Tg) and membrane elongation increased with the ratio of hydrophilic oligomers. SPES membranes with higher hydrophilic oligomer ratios exhibited superior water uptake, ion-exchange capacity, contact angle and water sorption, while retaining reasonable swelling degree. The proton conductivity results showed that SPES containing higher amounts of hydrophilic oligomers provided a 74.7 mS cm-1 proton conductivity at 90 °C, which is better than other SPES membranes, but slightly lower than that of Nafion-117 membrane. When integrating SPES membranes with proton-exchange membrane fuel cells (PEMFCs) at 60 °C and 80% relative humidity (RH), the PEMFC power density exhibited a similar increment-pattern like proton conductivity pattern.

Anion Exchange Membranes Obtained from Poly(arylene ether sulfone) Block Copolymers Comprising Hydrophilic and Hydrophobic Segments.

The anion exchange membrane may have different physical and chemical properties, electrochemical performance and mechanical stability depending upon the monomer structure, hydrophilicity and hydrophobic repeating unit, surface form and degree of substitution of functional groups. In current work, poly(arylene ether sulfone) (PAES) block copolymer was created and used as the main chain. After controlling the amount of NBS, the degree of bromination (DB) was changed in Br-PAES. Following that, quaternized PAES (Q-PAES) was synthesized through quaternization. Q-PAES showed a tendency of enhancing water content, expansion rate, ion exchange capacity (IEC) as the degree of substitution of functional groups increased. However, it was confirmed that tensile strength and dimensional properties of membrane reduced while swelling degree was increased. In addition, phase separation of membrane was identified by atomic force microscope (AFM) image, while ionic conductivity is greatly affected by phase separation. The Q-PAES membrane demonstrated a reasonable power output of around 64 mW/cm2 while employed as electrolyte in fuel cell operation.

Ceria Stabilized by Titanium Carbide as a Sustainable Filler in the Nafion Matrix Improves the Mechanical Integrity, Electrochemical Durability, and Hydrogen Impermeability of Proton-Exchange Membrane Fuel Cells: Effects of the Filler Content.

Cerium oxide-anchored titanium carbide (CeO2-TiC) is realized as a potential inorganic filler when modifying the Nafion matrix of a proton-exchange membrane fuel cell (PEMFC). A hydrothermal strategy was employed to synthesize CeO2-TiC of high crystallinity as a filler to mitigate the problematic properties of a proton-exchange membrane (PEM). CeO2-TiC with a weight ratio of 0.5, 1, 1.5, or 2% was incorporated into a Nafion matrix to form a hybrid by adopting a solution-casting procedure. Reinforcement owing to the presence of TiC provides increased tensile strength to PEM, and the addition of CeO2 improves the durability of PEM by scavenging free radicals. The microstructural, thermomechanical, physiochemical, and electrochemical properties of PEM, including contact angle, water sorption, water uptake, and proton conductivity, were extensively studied. Random dispersion of CeO2-TiC in the Nafion matrix improves the thermal stability, tensile strength, and water uptake while retaining proton conductivity, as compared with those of pristine Nafion. As a result, optimized Nafion/CeO2-TiC (1 wt %) achieved undiminished PEMFC performance compared to that of pristine Nafion while operating the device at 60 °C and 100% relative humidity. In addition, Nafion/CeO2-TiC (1 wt %) experienced the degradation of merely 0.6 mV h-1 during 200 h operation under identical conditions. Compared to that of Nafion/CeO2-TiC (1 wt %), pristine Nafion and Nafion-212 displayed accelerated and comparable degradation (for pristine Nafion, 1.3 mV h-1; for Nafion-212, 0.4 mV h-1). PEMFC power output, hydrogen permeability, and morphology of samples were examined after the durability test; the results indicate that Nafion/CeO2-TiC (1 wt %) is extremely stable. Since various Nafion hybrids have been reported as highly durable PEMs, this study is expected to open up new perspectives to expanding their applications, especially in sustainable PEMFC technology.

Ultrafine Pt Nanoparticles Stabilized by MoS2/N-Doped Reduced Graphene Oxide as a Durable Electrocatalyst for Alcohol Oxidation and Oxygen Reduction Reactions.

Direct alcohol fuel cells play a pivotal role in the synthesis of catalysts because of their low cost, high catalytic activity, and long durability in half-cell reactions, which include anode (alcohol oxidation) and cathode (oxygen reduction) reactions. However, platinum catalysts suffer from CO tolerance, which affects their stability. The present study focuses on ultrafine Pt nanoparticles stabilized by flowerlike MoS2/N-doped reduced graphene oxide (Pt@MoS2/NrGO) architecture, developed via a facile and cost-competitive approach that was performed through the hydrothermal method followed by the wet-reflux strategy. Fourier transform infrared spectra, X-ray diffraction patterns, Raman spectra, X-ray photoelectron spectra, field-emission scanning electron microscopy, and transmission electron microscopy verified the conversion to Pt@MoS2/NrGO. Pt@MoS2/NrGO was applied as a potential electrocatalyst toward the anode reaction (liquid fuel oxidation) and the cathode reaction (oxygen reduction). In the anode reaction, Pt@MoS2/NrGO showed superior activity toward electro-oxidation of methanol, ethylene glycol, and glycerol with mass activities of 448.0, 158.0, and 147.0 mA/mgPt, respectively, approximately 4.14, 2.82, and 3.34 times that of a commercial Pt-C (20%) catalyst. The durability of the Pt@MoS2/NrGO catalyst was tested via 500 potential cycles, demonstrating less than 20% of catalytic activity loss for alcohol fuels. In the cathode reaction, oxygen reduction reaction results showed excellent catalytic activity with higher half-wave potential at 0.895 V versus a reversible hydrogen electrode for Pt@MoS2/NrGO. The durability of the Pt@MoS2/NrGO catalyst was tested via 30 000 potential cycles and showed only 15 mV reduction in the half-wave potential, whereas the Pt@NrGO and Pt-C catalysts experienced a much greater shift (Pt@NrGO, ∼23 mV; Pt-C, ∼20 mV).

Nitrogen-Doped Porous Carbon Derived from Biomass Used as Trifunctional Electrocatalyst toward Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution Reactions.

Tremendous developments in energy storage and conversion technologies urges researchers to develop inexpensive, greatly efficient, durable and metal-free electrocatalysts for tri-functional electrochemical reactions, namely oxygen reduction reactions (ORRs), oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs). In these regards, this present study focuses upon the synthesis of porous carbon (PC) or N-doped porous carbon (N-PC) acquired from golden shower pods biomass (GSB) via solvent-free synthesis. Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies confirmed the doping of nitrogen in N-PC. In addition, morphological analysis via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) provide evidence of the sheet-like porous structure of N-PC. ORR results from N-PC show the four-electron pathway (average n = 3.6) for ORRs with a Tafel slope of 86 mV dec-1 and a half-wave potential of 0.76 V. For OERs and HERs, N-PC@Ni shows better overpotential values of 314 and 179 mV at 10 mA cm-2, and its corresponding Tafel slopes are 132 and 98 mV dec-1, respectively. The chronopotentiometry curve of N-PC@Ni reveals better stability toward OER and HER at 50 mA cm-2 for 8 h. These consequences provide new pathways to fabricate efficient electrocatalysts of metal-free heteroatom-doped porous carbon from bio-waste/biomass for energy application in water splitting and metal air batteries.

Highly Flexible Electrospun Hybrid (Polyurethane/Dextran/Pyocyanin) Membrane for Antibacterial Activity via Generation of Oxidative Stress.

A hybrid nanofibrous mat consisting of polyurethane, dextran, and 10 wt % of biopigment (i.e., pyocyanin) was facilely fabricated using a direct-conventional electrospinning method. The field emission scanning electron microscopy showed the bead-free fibers with a twisted morphology for the pyocyanin-loaded mat. The addition of pyocyanin enables the unprecedented approach to tailor the hydrophilicity of hybrid mat, as verified from the water contact measurement. Thermomechanical stabilities of electrospun mats were investigated in terms of thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. The bacterial inhibition test revealed that the antibacterial activity of electrospun mat containing pyocyanin was 98.54 and 90.2% toward Escherichia coli and Staphylococcus aureus, respectively. By the combined efforts of rapid release of pyocyanin and oxidative stress, the PU-dextran-pyocyanin (PUDP) electrospun mat significantly declined the viable cell number that disrupts the cell morphology. Hence, the proposed PUDP electrospun mat must meet the requirements of efficient antimicrobial material in various applications such as disinfectant wiping, food packaging, and textile industries.

One-Pot Facile Synthesis of Pt Nanoparticles Using Cultural Filtrate of Microgravity Simulated Grown P. chrysogenum and Their Activity on Bacteria and Cancer Cells.

Platinum nanoparticles (Pt NPs) was synthesized via a facile and cost competitive ont-pot green mediated synthesis using cell free cultural filtrate (microgravity simulated grown Penicillium chrysogenum) as a reducing agent. The toxicity effect of synthesized Pt NPs toward myoblast C2C12 carcinoma cells was then investigated. The particle size analyzer (DLS) and transmission electron microscopy (TEM) results demonstrates that both NG-Pt NPs and MG-Pt NPS are spherical in shape with an average diameter of 15 nm and 8.5 nm, respectively. The results from UV-visible (UV-vis) spectroscopy and X-ray diffraction (XRD) analysis show a characteristic strong resonance centered at 265 nm and a single crystalline nature, respectively. The results derived from in vitro cytotoxicity showed a significant concentration-dependent decrement in cell viability when C2C12 cells were exposed to Pt NPs. Such decrement in cell viability is because of increased reactive oxygen species (ROS) generation. Cell apoptosis was proved by acridine orange-ethidium bromide (AO/EtBr) dual staining, annexin V-FITC/PI-staining and immunocytochemistry. Moreover, the protein expression of both (i) apoptosis related proteins such as cas-3 and cas-9, (ii) inflammatory response proteins such as TNF-α, TGF-ß and NF-κB were significantly upregulated in MG-Pt NPs treated cells than NG-Pt NPs treated cells. Uptake and intracellular localization of MG-Pt NPs caused by accumulation of autophagosomes in C2C12 cells and bacterial cells, indicate that synthesized MG-Pt NPs enable for the swift cell apoptosis than NG-Pt NPs. Interestingly, At the concentration of 40 and 80 µg/ml MG-Pt NPs showed more potent cytotoxicity toward cancer cells while, under identical concentration, NG-Pt NPs exhibited rather lower cytotoxicity. Overall, our results demonstrated that MG-Pt NPs could be selectively inhibit the growth of cancer cells via ROS-mediated nucleus NF-κB and caspases activation when compared to NG-Pt NPs.

Alleviating the Mechanical and Thermal Degradations of Highly Sulfonated Poly(Ether Ether Ketone) Blocks via Copolymerization with Hydrophobic Unit for Intermediate Humidity Fuel Cells.

In this contribution, sulfonated poly(ether ether ketone) (SPEEK) is inter-connected using a hydrophobic oligomer via poly-condensation reaction to produce SPEEK analogues as PEMs. Prior sulfonation is performed for SPEEK to avoid random sulfonation of multi-block copolymers that may destroy the mechanical toughness of polymer backbone. A greater local density of ionic moieties exist in SPEEK and good thermomechanical properties of hydrophobic unit offer an unique approach to promote the proton conductivity as well as thermomechanical stability of membrane, as verify from AC impedance and TGA. The morphological behavior and phase variation of membranes are explored using FE-SEM and AFM; the triblock (XYX) membranes exhibits a nano-phase separated morphology. Performance of PEFC integrated with blend and block copolymer membranes is determined at 60 °C under 60% RH. As a result, the triblock (XYX) membrane has a high power density than blend (2X1Y) membrane.

Sulfonated graphene oxide/Nafion composite membranes for high temperature and low humidity proton exchange membrane fuel cells.

Iron oxide (Fe3O4) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe3O4-SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe3O4 nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe3O4-SGO composite membranes. Nafion/Fe3O4-SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe3O4-SGO (3 wt%) composite membrane at 120 °C under 20% relative humidity (RH) was 11.62 mS cm-1, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe3O4-SGO composite membrane delivered a peak power density of 258.82 mW cm-2 at a load current density of 640.73 mA cm-2 while operating at 120 °C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm-2 was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm-2. Thus, Nafion/Fe3O4-SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.