Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.seppur.2023.123883

Other Link： https://www.sciencedirect.com/science/article/pii/S1383586623007918

Language：English   Publishing type：Research paper (scientific journal)  

Nanocellulose is a sustainable material which holds promise for many energy-related applications. Here, nanocrystalline cellulose is used to prepare proton exchange membranes (PEMs). Normally, this nanomaterial is highly dispersible in water, preventing its use as an ionomer in many electrochemical applications. To solve this, we utilized a sulfonic acid crosslinker to simultaneously improve the mechanical robustness, water-stability, and proton conductivity (by introducing -SO3−H+ functional groups). The optimization of the proportion of crosslinker used and the crosslinking reaction time resulted in enhanced proton conductivity up to 15 mS/cm (in the fully hydrated state, at 120 °C). Considering the many advantages, we believe that nanocellulose can act as a sustainable and low-cost alternative to conventional, ecologically problematic, perfluorosulfonic acid ionomers for applications in, e. fuel cells and electrolyzers.

DOI： 10.3390/membranes12070658

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1557/s43577-022-00313-6

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/bcsj.20210323

Other Link： https://www.journal.csj.jp/doi/full/10.1246/bcsj.20210323

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Natural gas, having a significantly lower CO₂ emission factor than oil and coal when combusted, is accepted as an important transition fuel towards carbon net-zero society. To meet the calorific value requirements (≥34.0 MJ m⁻³) and reduce possible corrosion of transportation pipelines, acid gases such as CO₂ and H₂S must be removed from raw natural gas. Membrane separation is a promising alternative approach to removing acid gases from natural gas. This paper aims to review the development of various polymer-based membranes and membrane processes for H₂S separation from natural gas. Progress in glassy polymer membranes, rubbery polymer membranes, hybrid membranes, and membrane contactors for H₂S removal from natural gas are summarized and analyzed. The H₂S separation performance of various membranes are plotted in one diagram and a new H₂S/CH₄ upper bound is proposed. Challenges of membranes for H₂S separation and prospects of future development are thoroughly discussed.

DOI： 10.1039/d1ta04693d

Other Link： https://pubs.rsc.org/en/content/articlehtml/2021/ta/d1ta04693d

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: A polymer of intrinsic microporosity (PIM) consisting of Tröger's base (TB) undergoes ring-opening of the bicyclic amine upon N-methylation followed by alkaline hydrolysis, resulting in a hybrid ladder polymer that contains diazacyclooctane (DACO) units with tert- and sec-amino groups. The hybrid ladder polymers with various TB/DACO ratios can be prepared depending on the reaction conditions. Here we report a systematic study on the effect of DACO content on the thermal and gas adsorption properties of the hybrid ladder polymer. Using a PIM derived from 2,5-diamino-p-xylene, we prepared hybrid ladder polymers with a DACO content ranging from 19% to 55% while having a similar molecular weight. The thermal stability of the hybrid ladder polymers, evaluated by thermogravimetric analysis, is decreased with the increase in DACO content. Based on gas adsorption measurements, the increase in DACO content results in the decrease in the BET surface area but improves the gas adsorption selectivity for CO₂ against N₂, likely due to the high basicity of the sec-amino group of DACO unit. This result demonstrates that the partial TB-to-DACO conversion of the TB-based PIM may provide a simple but useful strategy to design polymer materials that enable selective CO₂ capture and/or separation.

DOI： 10.1002/cnma.202100151

Other Link： https://onlinelibrary.wiley.com/doi/full/10.1002/cnma.202100151

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Nanocellulose membranes based on tunicate-derived cellulose nanofibers, starch, and ~5% wood-derived lignin were investigated using three different types of lignin. The addition of lignin into cellulose membranes increased the specific surface area (from 5 to ~50 m²/g), however, the fine porous geometry of the nanocellulose with characteristic pores below 10 nm in diameter remained similar for all membranes. The permeation of H₂, CO₂, N₂, and O₂ through the membranes was investigated and a characteristic Knudsen diffusion through the membranes was observed at a rate proportional to the inverse of their molecular sizes. Permeability values, however, varied significantly between samples containing different lignins, ranging from several to thousands of barrers (10−10 cm³ (STP) cm cm⁻² s⁻¹ cmHg ⁻¹), and were related to the observed morphology and lignin distribution inside the membranes. Additionally, the addition of ~5% lignin resulted in a significant increase in tensile strength from 3 GPa to ~6–7 GPa, but did not change thermal properties (glass transition or thermal stability). Overall, the combination of plant-derived lignin as a filler or binder in cellulose–starch composites with a sea-animal derived nanocellulose presents an interesting new approach for the fabrication of membranes from abundant bio-derived materials. Future studies should focus on the optimization of these types of membranes for the selective and fast transport of gases needed for a variety of industrial separation processes.

DOI： 10.3390/membranes11030204

Other Link： https://www.mdpi.com/2077-0375/11/3/204

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Nanocellulose is a promising new membrane material for fuel cells, with a much lower cost and environmental impact compared with Nafion or Aquivion. It is mechanically strong, is an excellent hydrogen barrier, and has reasonable proton conductivity. Here, sulfonation of cellulose nanofibers is performed to enhance the conductivity (up to 2 × 10^− 3 S cm^− 1) without compromising the membrane integrity, and fuel cells are fabricated with 30 µm-thick “paper” membranes. The hydrogen crossover current is two orders of magnitude lower than for Nafion fuel cells with equivalent thickness, but the power density is rather low. Spray-coating is used to deposit 8 µm-thick membranes directly onto the electrocatalyst layer, in a process analogous to 3D printing or additive manufacturing. The resulting paper fuel cell has a high current density (> 0.8 A cm^− 2) and power density (156 mW cm^− 2) under standard measurement conditions (H₂/air; 80°C; 95% RH; 0.1 MPa), attributed to decreased membrane resistance. The cost of the spray-painted cellulose membranes is calculated to be ~ 50 $ m^− 2, which is much lower than that of Nafion, even without taking into consideration economies of scale. This new concept in electrochemical energy conversion paves the way for the mass production of affordable, recyclable fuel cells.

DOI： 10.1007/s10570-020-03593-w

Other Link： https://link.springer.com/article/10.1007/s10570-020-03593-w

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Cellulose is derived from biomass and is useful in a wide range of applications across society, most notably in paper and cardboard. Nanocellulose is a relatively newly discovered variant of cellulose with a much smaller fibril size, leading to unique properties such as high mechanical strength. Meanwhile, electrochemical energy conversion in fuel cells will be a key technology in the development of the hydrogen economy, but new lower-cost proton exchange membrane (PEM) materials are needed. Nanocellulose has emerged as a potential candidate for this important application. In this review, we summarize scientific developments in the area of cellulosic materials with special emphasis on the proton conductivity, which is the most important parameter for application in PEMs. We cover conventional cellulose and nanostructured cellulose materials, polymer composites or blends, and chemically modified cellulose. These developments are critically reviewed, and we identify interesting trends in the literature data. Finally, we speculate on future directions for this field.

DOI： 10.3389/fenrg.2020.596164

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Fabrication and gas permselective behavior of free-standing polydimethylsiloxane (PDMS) nanomembranes is discussed. The largest CO₂ permeance is close to 40,000 GPU (the highest one ever reported) at 34-nm membrane thickness without losing the CO₂/N₂ selectivity of 10-12, indicating the formation of pin-hole free nanomembranes.

DOI： 10.1246/cl.190558

Other Link： https://doi.org/10.1246/cl.190558

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Multilayers of polyethyleneimine and graphene oxide, (PEI/GO)₁₅, were coated onto steel substrates via electrostatic layer-by-layer (LbL) deposition, and their tribological properties were investigated as solid lubricants. The coefficient of friction (COF) and specific wear rate (SWR) were measured against a poly(methyl methacrylate) (PMMA) counterface ball, in various gas environments with different oxygen concentrations. The COF and SWR both significantly decreased with decreasing oxygen content. Detailed surface characterization of the contact area of the counterface ball revealed that continuous transfer films were formed in oxygen-free environments, but not in oxygen-rich environments. This is attributed to an increased proportion of sp³ bonding in the wear debris in the presence of oxygen (as confirmed by Raman spectroscopy), as well as possible suppression of wear debris adhesion on the counterface ball due to oxygen adsorption on the surface.

DOI： 10.1016/j.wear.2019.05.035

Other Link： https://doi.org/10.1016/j.wear.2019.05.035

Language：English   Publishing type：Research paper (scientific journal)  

ABSTRACT: Inorganic–organic nanocomposite hybrids containing zirconium dioxide (ZrO₂) as inorganic cross-linker/filler and polydimethylsiloxane (PDMS) as a polymeric matrix have been synthesized using the in situ sol-gel reaction between silanol-terminated PDMS and zirconium normal butoxide (Zr(OC₄H₉)₄). Hybrid materials were used to fabricate gas separation membranes which were characterized by scanning electron microscopy, dynamic scanning calorimetry, nanoindentation, ATR-FTIR, and XPS spectroscopies. The amorphous structure of incorporated ZrO₂ fillers was verified by X-ray diffraction. Small gases (He, H₂, O₂, N₂, and CO₂) permeability experiments were carried out to study the effect of the inorganic component amount on the properties of the ZrO₂@PDMS hybrids. The permeability of the developed hybrids considerably exceeded the permeability of conventional PDMS which is known as “gold standard” highly gas-permeable rubbery polymer. Depending on the ZrO2 content, fabricated hybrids demonstrated increased permeability for all gases with improvement inversely proportional to the kinetic diameter of gas molecules, that is, the highest permeability increase (relatively to PDMS) was observed for H₂ and lowest for N₂. Such behavior suggests the formation of the size-sieving amorphous zirconia domains within PDMS which do not impede gas transport due to the nanosize of the fillers. As a result, gas separation membranes prepared using the developed materials demonstrated better separation performance for CO₂/N₂, H₂/N₂, and O₂/N₂ pairs compared to the conventional PDMS.

DOI： 10.1021/acsapm.9b00178

Other Link： https://pubs.acs.org/doi/10.1021/acsapm.9b00178

Language：English   Publishing type：Research paper (scientific journal)  

The transport of small gases (H₂, CO₂, N₂, O₂) through a series of novel membranes based on necklace-shaped inorganic polymers (DMS@POSS), in which a polyhedral oligomeric silsesquioxane (POSS) cage unit and soft chains of oligo-dimethyl siloxane (DMS) were alternately connected, was investigated. The influence of the DMS chain length and crosslinking density of the DMS@POSS on membrane properties were studied. The membranes revealed characteristic structure-property relation towards both glass transition and gases transport. Specifically, a clear dependence of properties from the length of DMS units (or overall siloxane content) was revealed. Gas transport properties, when compared to state-of-art polydimethylsiloxane and commercial silicone rubber, demonstrated significantly higher selectivity of DMS@POSS for carbon dioxide (in CO₂/N₂), hydrogen (in H₂/N₂) and oxygen (in O₂/N₂) but lowered permeability, proportional to the amount of POSS in the material. With precise control over mechanical and thermal properties compared to conventional silicone rubbers, described materials could be considered as materials of choice in niche gas separation or other applications.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/membranes8040121

Other Link： https://www.mdpi.com/2077-0375/8/4/121

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.triboint.2018.06.003

Other Link： https://www.sciencedirect.com/science/article/pii/S0301679X18302895

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.optlastec.2017.10.027

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.memsci.2017.11.025

Other Link： https://www.sciencedirect.com/science/article/pii/S0376738817325140

Language：English   Publishing type：Research paper (scientific journal)  

In this work, fabrication of free-standing nanomembranes of metal oxide (MO_x) and polymers by the simple spin-coating method is discussed. First, double-layer nanomembranes containing MO_x and epoxy resin of polyethyleneimine and poly[(o-cresyl glycidyl ether)-co-formaldehyde] were prepared. Free-standing nanomembranes were successfully prepared, but defects formed in the metal oxide nanolayer during sharp bending of the nanomembrane. To overcome the fragility of MO_x nanolayer, poly(vinyl alcohol) nanolayers were introduced between MOx nanolayers by layer-by-layer (LbL) assembly process. The LbL nanomembrane was also free-standing and was highly flexible during macroscopic membrane manipulations. Even after the transfer of the LbL nanomembrane onto a porous support, it did not have apparent cracks, confirmed by scanning electron microscopy (SEM). The LbL nanomembrane sustained low gas permeance, confirming the absence of significant defects, although it shows excellent flexibility. We believe that the presented LbL nanomembrane could be a platform useful for the design of molecular nanochannels, which is the next challenge for efficient gas separation.

Language：English   Publishing type：Research paper (scientific journal)  

The efficiency and lifetime of mechanical devices is significantly decreased by friction and wear, significantly contributing to global energy consumption. We previously showed that multilayer polyethyleneimine/graphene oxide thin films, (PEI/GO)₁₅, on steel display superlubricity against a steel counterface ball. Here, the coefficient of friction (COF) and wear of (PEI/GO)₁₅ with six different counterface polymer balls is investigated in air and in nitrogen, with particular focus on the formation of tribological transfer films. The polymers polyoxymethylene (POM), polyetheretherketone (PEEK), polyethylene (PE), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polytetrafluoroethylene (PTFE) are utilized. The COF of (PEI/GO)₁₅ vs steel is 0.35 in both air and nitrogen. In air, the COF ranges from 0.06 to 0.17 for all polymers. Significantly, in nitrogen, four polymers (POM, PEEK, PMMA and PC) display ultra-low friction (COF ∼0.02) whilst two do not (PTFE and PE). The wear tracks and transfer films are investigated using e.g. optical microscopy, electron microscopy, and Raman mapping, and the tribological behavior is correlated to the hydrophilicity and relative hardness of the polymer balls compared to GO.

DOI： 10.1016/j.carbon.2017.06.090

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/14686996.2017.1386531

Other Link： https://www.tandfonline.com/doi/full/10.1080/14686996.2017.1386531%40tsta20.2017.18.issue-NRG1?scroll=top&needAccess=true

Language：English   Publishing type：Research paper (scientific journal)  

Graphene oxide (GO) is potentially a useful electrolyte material for polymer electrolyte membrane fuel cells due to its high strength, excellent hydrogen gas barrier properties, hydrophilicity, and proton conducting acidic functional groups. Here, GO paper is prepared from aqueous dispersion by vacuum-filtration, and the hydrogen permeability (2 × 10⁻² barrer) is measured to be 3 orders of magnitude lower than Nafion (30 barrer) at 30 °C. The in-plane and through-plane conductivities are measured to be 49.9 and 0.3 mS cm⁻¹, respectively. This significant anisotropy is attributed to the lamellar structure of GO, and the physical anisotropy between the thickness and lateral size of the GO nanoplatelets. Interestingly, the in-plane conductivity of GO is comparable to the through-plane conductivity of Nafion. GO membrane fuel cells (GOMFCs) are fabricated. To compensate for the low in-plane conductivity of GO, whilst taking advantage of the excellent hydrogen gas barrier properties, extremely thin electrode-supported GOMFCs are prepared by spray painting GO directly onto the electrocatalyst layer. The effect of membrane thickness on cell performance is investigated. Decreasing membrane thickness by spray painting improves the power density from 3.7 mW cm⁻² for a 50 μm-thick membrane-supported GOMFC, to 79 mW cm⁻² for a 3 µm-thick, spray-painted membrane, electrode-supported GOMFC.

DOI： 10.1016/j.memsci.2017.07.012

Language：English   Publishing type：Research paper (scientific journal)  

Friction and wear decrease the efficiency and lifetimes of mechanical devices. Solving this problem will potentially lead to a significant reduction in global energy consumption. We show that multilayer polyethylenimine/graphene oxide thin films, prepared via a highly scalable layer-by-layer (LbL) deposition technique, can be used as solid lubricants. The tribological properties are investigated in air, under vacuum, in hydrogen, and in nitrogen gas environments. In all cases the coefficient of friction (COF) significantly decreased after application of the coating, and the wear life was enhanced by increasing the film thickness. The COF was lower in dry environments than in more humid environments, in contrast to traditional graphite and diamond-like carbon films. Superlubricity (COF < 0.01) was achieved for the thickest films in dry N₂. Microstructural analysis of the wear debris revealed that carbon nanoparticles were formed exclusively in dry conditions (i.e., N₂, vacuum), and it is postulated that these act as rolling asperities, decreasing the contact area and the COF. Density functional theory (DFT) simulations were performed on graphene oxide sheets under pressure, showing that strong hydrogen bonding occurs in the presence of intercalated water molecules compared with weak repulsion in the absence of water. It is suggested that this mechanism prevents the separation graphene oxide layers and subsequent formation of nanostructures in humid conditions.

DOI： 10.1021/acsami.6b06779

Language：English   Publishing type：Research paper (scientific journal)  

Polymer electrolyte membrane fuel cells are an efficient and clean alternative power source, but high cost impedes widespread commercialization. The fuel cell membrane, e.g., Nafion, contributes significantly to this cost, and therefore, novel alternatives are required. Temperature is also an important factor; high temperature operation leads to faster reaction kinetics, lower electrocatalyst loading, and improved water management, thereby further reducing cost. However, higher temperature puts greater demands on the membrane. Conductivity is related strongly to humidification, and therefore, this generally decreases above 100 °C. Nanocellulose membranes for fuel cells in which the proton conductivity increases up to 120 °C are reported here for the first time. The hydrogen barrier properties are far superior to conventional ionomer membranes. Fuel cells with nanocellulose membranes are successfully operated at 80 °C. Additionally, these membranes are environmentally friendly and biodegradable.

DOI： 10.1021/acs.chemmater.6b01990

Language：English   Publishing type：Research paper (scientific journal)  

A novel class of alkaline anion exchange membrane (AAEM) is presented, in the form of KOH-modified multilayer graphene oxide paper (GO_KOH). Such membranes can be easily fabricated at large scale with varying thickness using conventional filtration techniques, and have high tensile strength (24.5 MPa). However, a large degree of swelling is observed. SEM investigations show that the morphology of GO changes after KOH-treatment, whilst XPS measurements and XRD analysis confirm successful chemical modification. The hydrogen gas permeability is several orders of magnitude lower than conventional polymer-based ionomer membranes. The maximum anion conductivity is 6.1 mS/cm at 70 °C, and the dominant charge carrier is confirmed to be OH^- by utilization of anion and proton-conducting blocking layers. The ion exchange capacity is 6.1 mmol/g, measured by titration. A water-mediated reverse Grotthuss-like mechanism is proposed as the main diffusion mode of OH^- ions. Finally, a prototype AAEM fuel cell is fabricated using a GO_KOH membrane, confirming the applicability to real systems.

DOI： 10.1016/j.memsci.2016.02.017

Language：English   Publishing type：Research paper (scientific journal)  

Here we report a preferential CO₂ separation membrane consisting of a nanometer-thick TiO₂ layer incorporated with phtalic acid (PA) molecules on polydimethylsiloxane (PDMS) (PA@TiO₂/PDMS). Incorporated PAs in TiO₂ act as CO₂-philic pores for preferential CO-₂ permeation over nitrogen. CO₂ binding to the PA incorporated in TiO₂ is confirmed by the density functional theory calculation (DFT). As a result, membranes with of PA@TiO₂ layer demonstrated much higher selectivity to CO₂ for mixed CO₂/N₂ gas separation compared to a conventional PDMS membrane. The exceptional selectivity of the composite layer alone (>150) was estimated by a resistance model.

DOI： 10.1039/c6ra18419g

Language：English   Publishing type：Research paper (scientific journal)  

Quartz crystal microbalance (QCM) sensors with porous films comprising silica nanoparticles and poly(allylamine hydrochloride) (PAH) were fabricated. The films were deposited via an electrostatic self-assembly method, and they exhibited considerable sensitivity to relative humidity. The infusion of poly(acrylic acid) (PAA) into multi-layer porous films (5 or 10 cycles) enabled the construction of a highly sensitive and selective QCM sensor device for the detection of gaseous ammonia. Two types of QCM sensors, with and without PAA, were used as sensors for the simultaneous quantitative detection of humidity and ammonia. A comprehensive Fourier transform infrared (FTIR) investigation of the fabricated films was conducted to elucidate the mechanism of the chemical interaction at the sensor device interface. Preliminary tests were conducted to detect low concentrations of ammonia in human breath, which are of clinical relevance. The results of these tests showed that the sensor can detect ammonia in human breath at pathological levels (greater than 3 ppm).

DOI： 10.1016/j.snb.2015.03.103

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：United States  

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：United States  

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：United States  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：United Kingdom  

Gas separation membranes suitable for economically feasible post-combustion CO₂ capture should combine the moderate CO₂/N₂ selectivity (20-60) with a substantial values of CO₂ permeances (>1000 GPU). Most the membranes tailored to have these properties are so-called thin-film composite membranes (TFCM) containing different layers it structure, each having a specific function (porous support, gutter, selective, protective layer). Due to the highest resistance towards gas transport, selective layers in TFCM are commonly fabricated with thicknesses below 100 nm. In this work, in order to achieve high CO₂ permeances in TFCM we have fabricated ultra-thin selective layers (2-20 nm) composed of well-known hydrophilic and CO₂-selective block-copolymer (Pebax MH-1657). It was deposited on the O₂-plasma-activated surface of a much thicker (~400 nm) gutter layer composed of polydimethylsiloxane (PDMS). The structure was subsequently transferred on the polyacrylonitrile (PAN) microporous support to complete the TFCM. We have found that contrary to the theoretical predictions (resistance in the series model) for the layered membrane, highly selective CO₂/N₂ separation membrane was achieved in the TFCM with ultra-thin selective layer. The critical role to achieve this selectivity was attributed to the specific interface formed between selective and gutter layers which were controlled by the duration of oxygen plasma treatment (PDMS activation). Permeances of CO₂ in the developed TFCM were between 1000-3000 GPU and CO₂/N₂ selectivities between 30-100, providing the gas separation parameters that are within the optimal range for cost-efficient CO₂ capture in post-combustion processes. Detailed characterization of the interface revealed the chemical structure of the outermost membrane surface suggesting the blending of the ultra-thin Pebax-1657 layer with the activated surface of PDMS. This nano-thick blend layer contributed to the overall selectivity of the membrane significantly exceeding the selectivity that can be achieved by Pebax-1657 alone. The formed interface demonstrates stable gas separation with a moderate change of performance over one year.

Event date： 2020.12

Language：English  

Venue：Online   Country：United Kingdom  

Event date： 2019.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Sixth International Conference of Multifunctional, Hybrid and Nanomaterials   Country：Japan  

Other Link： https://www.elsevier.com/events/conferences/international-conference-on-multifunctional-hybrid-and-nanomaterials

Event date： 2019.3

Language：English  

Venue：Sixth International Conference of Multifunctional, Hybrid and Nanomaterials   Country：Spain  

Other Link： https://www.elsevier.com/events/conferences/international-conference-on-multifunctional-hybrid-and-nanomaterials