Pristine SPEEK Membrane Research Articles

Nucleobase-mediated hydrogen bonding crosslinked highly sulfonated poly(ether ether ketone) electrodialysis membranes for efficient waste acid recovery

Electrodialysis is a promising technology for waste acid recovery with the advantages of low energy consumption and high efficiency. In this work, two nucleobase-modified highly sulfonated poly(ether ether ketone) with adenine (SPEEK-50A) and thymine (SPEEK-50T) were successfully synthesized. Then, a series of blending SPEEK-50Ax/50Ty membranes with varying molar ratios of these two functionalized SPEEKs were fabricated by solution casting. The hydrogen bonding crosslinked structure of ‘A-T base pairs’, as well as the acid-base interactions between the incorporated nucleobases and SO3H groups of the polymer backbone, not only enhanced the mechanical properties and thermal stability of the blending membranes, but more importantly, it successfully addressed the over-swelling issue of highly sulfonated SPEEK membrane. The SPEEK-50Ax/50Ty membranes exhibited tensile strengths between 59.3 and 72.3 MPa, which is 2.2–2.6 times that of the pristine SPEEK membrane. And the water uptake of the blending membranes reduced from 116 % to 14.6–19.2 %, while the swelling ratio decreased from 27.1 % to 5.86–6.60 %. The proton affinity of the multiple basic N atoms in nucleobases, as well as the ‘A-T base pairs’ hydrogen bonding network and acid-base interactions between nucleobases and SO3H groups, all can serve as effective proton transport channels. Additionally, the charge repulsion effect of protonated nucleobases and the crosslinking structure is beneficial to the permselectivity. Therefore, the fabricated blending SPEEK-50Ax/50Ty membranes exhibited superior H+ flux (1.66–1.73 mmol m−2 s−1) and enhanced H+/Fe2+ permselectivity (40.3–43.2). The SPEEK-50A0.5/50T0.5 membrane demonstrated a H+ flux of 1.70 mmol m−2 s−1 and a H+/Fe2+ permselectivity of 43.2, which is 2.8 times that of the pristine SPEEK membrane, surpassing both commercially available and recently reported membranes. Therefore, the nucleobase-modified blending SPEEK-50Ax/50Ty membranes might be potential candidates for the efficient recovery of acid from pickling wastewater.

Tungsten oxide embedded graphene oxide doped with SPEEK composite membrane for zinc–bromine redox flow batteries

Zinc-bromine redox flow batteries (Zn/Br2 RFBs) are fingerprint candidates for large-scale energy storage applications owing to their low cost, flexibility, high energy density, and astonishing round-trip efficiency. However, during the charging and discharging process, the diffusion of bromine through the porous membrane creates significant capacity decay and reduces the membrane efficiency of Zn/Br2 RFBs. In this respect, we developed various amounts of tungsten trioxide (WO3) nanoparticle-decorated graphene oxide (WO3@GO)-loaded sulfonated poly (ether ether ketone) (SPEEK) membranes and investigated their Zn/Br2 redox flow battery performance. The optimum amount of WO3@GO-loaded WO3@GO/SPEEK-3 membrane exhibits higher mechanical stability and ionic conductivity, significantly restricting the bromine crossover through the membrane. Due to their higher hydrophilic ability and uniform dispersion, WO3-loaded GO nanosheets provide strong interaction between the sulfonic acid group of the SPEEK membrane, which acts as an effective barrier for bromine crossover and significantly alters the Zn/Br2 battery performance. As a result, at a current density of 40 mA cm−2, the Zn/Br2 single cell of the WO3@GO/SPEEK-3 demonstrated higher coulombic efficiency (96.6 %), voltage efficiency (89.6 %), and energy efficiency (86.6 %), better than the WO3@GO/SPEEK-5 and pristine SPEEK membranes. These performances indicate that the proposed low-cost WO3@GO/SPEEK membrane can be highly applicable to other energy-related fields, including fuel cells and water treatment.

Enhanced proton conductivity of sulfonated poly(ether ether ketone) membranes by constructing cation‐π through doping ammonium ionic liquid and graphene oxide

AbstractIn this paper, sulfonic acid functionalized benzothiazole ionic liquid ([(CH2)3SO3HBth] [H2PO4]) and graphene oxide were combined together through the cation‐π. The sulfonated poly (ether ether ketone) was doped with ionic liquid‐modified GO (IL‐GO) to prepare the SPEEK/IL‐GO composite membrane through the solution casting method. The SO3H and benzothiazole rings act as both proton acceptors and proton donors during proton transport and can replace the role of water in medium‐ and high‐temperature environments, increasing the proton transport sites to a certain extent and increasing the proton conductivity of the SPEEK/IL‐GO composite membrane. The proton conductivity of the SPEEK/IL‐GO‐2 composite membrane achieved an 18.02 mS/cm at 120°C, which is 2.43 times higher than that of the pristine SPEEK membrane. This paper provided a method for increasing proton conductivity and limiting IL loss of the SPEEK membrane.Highlights [(CH2)3SO3HBth][H2PO4] and graphene oxide were combined through cation‐π. The benzothiazole ring and SO3H form acid–base pairs. The proton conductivity of SPEEK/IL‐GO‐2 membrane achieved 18.02 mS/cm.

Synthesis of potassium-zinc hexacyanoferrate and their SPEEK composite cation exchange membranes for selective recovery of cesium from aqueous system

Potassium-Zinc hexacyanoferrate adsorbent was prepared by precipitation method and further its composite membrane has been fabricated using sulphonated poly (ether ether ketone) (SPEEK) to investigate cesium (Cs+) recovery from aqueous media. The formation of desired adsorbent material was confirmed by Powder X-ray diffraction (PXRD) while chemical structure was assessed by Fourier-transform infrared spectroscopy (FT-IR). The BET surface area, pore volume and pore diameter found as 298.6 m2/g, 0.1034 cm3/g and 3.04 nm respectively calculated by Brunauer and Emmett and Teller (BET) surface area analyzer. The adsorbent synthesized was observed to work efficiently with maximum adsorption capacity of 54.64 mg Cs/g of adsorbent for Langmuir isotherm model. There was no effect of competing ion (Na+, K+, Mg2+, Ca2+) on adsorption performance during Cs+ removal. Cs+ recovery from the aqueous system in presence of 1000 ppm NaCl was performed using SPEEK composite membrane by electrodialysis. Observing the electrodialysis performance, composite membrane exhibited a high removal/recovery for Cs+ ions than Na+, K+, Mg2+ and Ca2+. The composite membrane exhibited a remarkable removal efficiency for Cs+ ion, which is 33.85 times larger than pristine SPEEK membrane. These results confirm composite membrane as promising candidate for the selective recovery/removal of cesium ions from aqueous solution in existence of intrusive ions and can effectively be applicable for industrial applications.

Magnetically aligned composite membranes based on sulfonated poly(ether ether ketone) and phosphotungstic acid-loaded magnetic nanoparticles for fuel cell

In this work, phosphotungstic acid (HPW)-loaded polydopamine-coated magnetic nanoparticles (DMNPs@HPW) were prepared and incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix with magnetic field assistance to construct aligned channels to shorten proton transport pathways. The structure of the prepared composite membranes (M-SP/DMNPs@HPW) with magnetic field-induced proton channels was confirmed by SEM. The proton conductivity of M-SP/DMNPs@HPW-2 was significantly improved, with in-plane proton conductivity (σ//) of 159.3 mS/cm and through-plane proton conductivity (σ⊥) of 129.2 mS/cm in the hydrated state at 80 °C, which were 1.31 and 1.57 times higher than the pristine SPEEK membrane, due to the strong acidity of HPW and acid-base interaction of amine and sulfonic acid groups. Meanwhile, the σ⊥ of M-SP/DMNPs@HPW-2 was 1.14 times higher than that of SP/DMNPs@HPW-2 membrane prepared without magnetic field assistance. The fuel cell power output of M-SP/DMNPs@HPW-2 was 433 mW/cm2, while SP/DMNPs@HPW-2 and pristine SPEEK membranes tested under the same conditions were 360 mW/cm2 and 277 mW/cm2, respectively. The hydrogen crossover of M-SP/DMNPs@HPW-2 was slightly increased compared to SP/DMNPs@HPW-2 due to the construction of through-plane proton transport channels in the membrane.

Efficient proton-selective hybrid membrane embedded with polydopamine modified MOF-808 for vanadium flow battery

Membrane possessing high ion selectivity and proton conductivity is of great importance to the proper operation of energy storage techniques. Hereon, a hybrid membrane was prepared by doping polydopamine (PDA) modified MOF-808 into the sulfonated poly (ether ether ketone) (SPEEK) matrix. MOF-808 is a type of acid stable metal organic framework with abundant proton transport channels, while PDA forms a blocking shell on MOF-808, inhibiting the penetration of vanadium ions. In addition, the amino groups of PDA are beneficial to the proton transport, and at the same time the polymeric chains can be entangled with SPEEK thus improving the adhesion force between MOF and the matrix. As a consequence, an optimized hybrid membrane exhibited remarkable performance in the vanadium flow battery (VFB) with synchronous increase in coulombic efficiency as well as voltage efficiency, hence contributing to greatly enhanced energy efficiency (83.9%) surpassing the pristine SPEEK membrane (76.0%) and commercial Nafion212 (78.2%) at 120 mA cm−2. This work demonstrates that controllable surface modification of the filler may serve as a useful approach for preparing high performance proton-selective hybrid membranes.

Effect of Covalent Organic Frameworks Containing Different Groups on Properties of Sulfonated Poly(ether ether ketone) Matrix Proton Exchange Membranes.

The rich −SO3H groups enable sulfonated poly (ether ether ketone) (SPEEK) to possess excellent proton conductivities in proton exchange membrane (PEM), but cause excessive water absorption, resulting in the decline of dimensional stability. It is a challenge to resolve the conflict between conductivity and stability. Owing to its unique structural designability, covalent organic frameworks (COFs) have been used to regulate the performances of PEMs. The authors propose the use of COFs with acidic and basic groups for meeting the requirements of proton conductivity and dimensional stability. Herein, COFs containing different groups (sulfoacid, pyridine, and both) were uniformly dispersed into the SPEEK matrix by in situ synthesis, and the effects on the properties of SPEEK matrix PEMs were revealed. The sulfoacid group significantly improves proton conductivities. At 60 °C, under 95% RH, the conductivity of the SPEEK/TpPa−SO3H-20 composite membrane was 443.6 mS·cm−1, which was 3.3 times that of the pristine SPEEK membrane. The pyridine group reduced the swelling ratio at 50 °C from 220.7% to 2.4%, indicating an enhancement in dimensional stability. Combining the benefits of sulfoacid and pyridine groups, SPEEK/TpPa−(SO3H-Py) composite membrane has a conductivity of 360.3 mS·cm−1 at 60 °C and 95% RH, which is 1.86 times that of SPEEK, and its swelling ratio is 11.8%, about 1/20 of that of SPEEK membrane. The method of in situ combination and regulation of groups open up a way for the development of SPEEK/COFs composite PEMs.

Thermally stable nanoclay and functionalized graphene oxide integrated SPEEK nanocomposite membranes for direct methanol fuel cell application

Membrane-based fuel cells, particularly methanol-based fuel cells, are thriving areas with high efficiency, less material consumption, and low emission of pollutants. But commercial membranes have less thermal withstanding ability and high cost, so alternative polymeric membranes have been developed with desired properties to overcome this issue. The SPEEK membrane was fabricated with halloysite nanoclay and functionalized graphene oxide (f-GO) nanocomposites at various concentrations via dry phase inversion. The sulfonic acid group in the SPEEK and silane functionalization of GO enhanced the Ion exchange capacity from 0.22 to 0.35 meq/g which enhances the proton conductivity. Furthermore, the thermal stability and hydrophilicity of the pristine SPEEK membrane were reformed with addition of halloysite nanoclay and f-GO in SPEEK membrane. The presence of nanocomposite on the surface of the SPEEK membranes was confirmed via scanning electron microscope (SEM) analysis. The 3 wt% halloysite nanoclay and 2 wt% of f-GO composite membrane was hold the 0.47 mS cm−1 of proton conductivity and 72.2 mW cm−2 of power density, whereas pristine SPEEK membrane was 0.31 mS cm−1 and 28 mW cm−2, respectively. The 3 wt% halloysite incorporated SPEEK membrane and 1.5 wt% f-GO incorporated SPEEK membrane was shown better proton conductivity, which act as a prominent membrane for direct methanol fuel cell (DMFC) applications.

Preparation and performance of sulfonated poly(ether ether ketone) membranes enhanced with ammonium ionic liquid and graphene oxide

The exploration of proton exchange membranes with excellent performance has always been under focus for improving the performance of proton exchange membrane fuel cells. In this study, novel ternary composite proton exchange membranes based on sulfonated poly(ether ether ketone) (SPEEK), triethylamine phosphate (TEAP) as the ammonium ionic liquid (AIL), and graphene oxide (GO) were prepared. The prepared membranes were characterized for their physical, physico-chemical, structural, morphological, thermal, mechanical, and electrical characteristics. The thermal stability of the SPEEK membrane was improved by the addition of GO and TEAP. GO was inserted into the composite membrane to form proton transfer channels. The amine ions in AIL formed acid–base pairs with the sulfonic acid group, whereas the oxygen-containing group on GO formed hydrogen bonds with the phosphate group. These groups interacted with each other to form a honeycomb-like structure, which anchored the AIL in the membrane and reduced its loss, providing additional sites for proton transport at higher temperatures. The proton conductivity of the SPEEK/AIL/GO-2 membrane reached 17.345 mS/cm at 120°C, which was 2.09 times higher than that of the pristine SPEEK membrane. This study provides the possibility for better preparation of proton exchange membranes used for high-temperature proton exchange membrane fuel cells.

MXene-copper oxide/sulfonated polyether ether ketone as a hybrid composite proton exchange membrane in electrochemical water electrolysis

Water electrolysis through a proton exchange membrane is one approach for hydrogen energy production via a simple redox reaction. This work focused on the development of a hybrid composite proton exchange membrane (PEM), MXene-Cu2O/SPEEK, which was used for proton transfer in a water electrolysis process. The sample of the 4%MXene-Cu2O/SPEEK membrane demonstrated the highest proton conductivity of 0.0105 Scm−1 at 30 °C. Further, the oxygen transmission rate of the 4%MXene-Cu2O/SPEEK was 33.67 cc m−2 day−1, whereas that of the commercially available Nafion 212 was 28.53 cc m−2 day−1. The flow rate of H2 gas evolution was 3.68 mL min−1 when using the 4%MXene-Cu2O/SPEEK composite PEM as the H+ ion exchange separator in the water electrolysis system; this flow rate is faster than that of a pristine SPEEK membrane. Interestingly, the addition of the MXene-Cu2O composite into the SPEEK polymer matrix promoted the oxidative stability of the composite PEM, which is vital for the long-term operation of the PEM water electrolysis. The 4%MXene-Cu2O/SPEEK composite membrane produced 0.083 μmol of H2 gas in 1 h, and it slightly reduced to 0.074 μmol after 8 h, which shows a stable H2 production and good efficiency of the membrane.

Oxidized black phosphorus nanosheets/sulfonated poly (ether ether ketone) composite membrane for vanadium redox flow battery

A novel oxidized black phosphorus nanosheet (O-bPn) is proposed to improve ion selectivity of sulfonated poly (ether ether ketone) (SPEEK) membrane for vanadium redox flow battery (VRFB). O-bPn possesses a unique two-dimensional (2D) puckered lattice structure, which could function as an effective blocker for vanadium ion permeability. Moreover, diverse oxygen-containing groups on O-bPn surface introduce additional acidic proton carriers and also form hydrogen bonds with –SO3H in polymer matrix, promoting proton transport. The incorporation of O-bPn into the SPEEK matrix increases proton conductivity, and markedly reduces vanadium crossover, achieving a nearly 1.8-fold increase of ion selectivity than the pristine SPEEK membrane. With an optimal O-bPn content of 1.5 wt%, the composite membrane (S/O-bPn-1.5%) exhibits a 7% higher coulombic efficiency (CE, 98.3% vs. 92.1%) and 10% higher energy efficiency (EE, 86.6% vs. 78.9%) at 100 mA/cm2, and retains a higher capacity (30.1% vs. 7.8%) after 100 cycles as compared with Nafion212 membrane. The EE value of the S/O-bPn-1.5% is also at the top level of the previously reported SPEEK-based composite membranes. These superior performances of the S/O-bPn membrane demonstrate that O-bPn is a promising 2D nanofiller for highly ion-selective composite membrane for VRFB.

SPEEK membranes by incorporation of NaY zeolite for CO2/N2 separation

• The SPEEK/NaY mixed matrix membranes were prepared for CO 2 /N 2 separation. • The string-like nanochannels for facilitating CO 2 transport in MMMs were formed. • NaY zeolite was uniformly dispersed in SPEEK matrix due to good compatibility between two phases. • Improved CO 2 permeability and CO 2 /N 2 selectivity of MMM were simultaneously obtained due to selective surface flow effect. Mixed-matrix membranes (MMMs) have aroused great attention for CO 2 capture due to high gas separation properties and good processability. However, besides high cost, poor interfacial compatibility and inorganic particles aggregation in MMMs hinder their further development. Herein, we chose microporous sodium zeolite-Y (NaY) as a filler, which was added into sulfonated poly (ether ether ketone) (SPEEK) to engineer the MMMs for CO 2 /N 2 separation. We deeply studied the influence of NaY incorporation on microstructure and separation properties of the membrane. It is obvious that NaY particles were evenly distributed in the SPEEK matrix due to strong interfacial interaction by hydrogen bonding, which was verified by ATR-FTIR and SEM results, and the string-like nanochannels were formed from the SAXS observation. MMM incorporated with 20 wt% NaY exhibited the separation properties (CO 2 permeability of 765 Barrer; CO 2 /N 2 selectivity of 63) at 1 bar under the pure gas conditions, which were superior to the pristine SPEEK membrane as well as the MMMs incorporated with other zeolites, transcending the 2008 Robeson's upper bound. The enhancement in separation properties is due to the fact that CO 2 molecules preferentially pass through the string-like nanochannels faster than N 2 molecules under elevated relative humidity owing to selective surface flow effect. Moreover, an increase in total water of MMMs loaded with NaY also contributed to enhanced CO 2 permeability, while improved CO 2 /N 2 selectivity resulted from high bound water. More importantly, stability studies reveal that the MMM (with 20 wt% NaY loading) held outstanding CO 2 separation properties for over 360 h, demonstrating outstanding stability under a gas mixture testing condition.

Evaluation of power generation and treatment efficiency of dairy wastewater in microbial fuel cell using TiO2 - SPEEK as proton exchange membrane.

The aim of this study is to synthesise SPEEK composite proton exchange membrane with the addition of TiO2 nanofillers for microbial fuel cell application. SPEEK composite membrane with varying weight percentage of TiO2 (2.5, 5, 7.5 and 10%) was prepared to study the effect of TiO2 concentration on membrane performance. Synthesized composite membranes were subjected to various characterization studies such as FT-IR, XRD, Raman spectroscopy, TGA, UTM and SEM. Physico-chemical properties of membrane such as water uptake capacity, ion exchange capacity and thickness were also analyzed. 5% TiO2 - SPEEK composite membrane exhibited the higher water uptake capacity value and Ion exchange capacity value of 31% and 1.71 meq/g respectively. Performance of the MFC system with TiO2 - SPEEK membranes were evaluated and compared with the pristine SPEEK and Nafion membrane. 5% TiO2 - SPEEK membrane produced the higher power density (1.22 W/m2) and voltage (0.635 V) than the other membranes investigated. Efficacy of MFC in wastewater treatment was evaluated based on the chemical oxygen demand (COD), total organic carbon content and turbidity. Biofilm growth over the surface of the electrodes was also analyzed using scanning electron microscopy.

Transport and photophysical studies on porphyrin-containing sulfonated poly(etheretherketone) composite membranes

The development of efficient and reliable membranes for redox flow batteries (RFBs) with high ionic conductivity and selectivity is challenging. Aiming the development of better membranes, we have synthesized porphyrin-containing sulfonated poly(etheretherketone) (SPEEK). In particular, the effect of water soluble 5,10,15,20-tetrakis(N-methyl-4-pyridinyl)porphyrin iodide (TMePyPI4) and its Cu(II) complex, 5,10,15,20-tetrakis(N-methyl-4-pyridinyl)porphyrinate copper(II) iodide, (CuTMePyPI4), at 0.1–0.3 wt%, have been assessed. Photophysical studies have shown that porphyrins are aggregated in the J-type. The obtained composite membranes show high macroscopic homogeneity and lower ability to sorb water when compared with pristine SPEEK membranes but comparable protonic conductivity. The hydronium diffusion and permeability coefficients suggest that at low porphyrin concentrations an enhancement of proton channels occurs, whilst at high concentration that effect decreases due to the formation of porphyrin aggregates. A similar effect occurs in the permeation of vanadium ions through composite membranes with a remarkable lower permeability and diffusion coefficients when compared with those obtained for Nafion 115 membranes. This along with the improved thermal stability of porphyrin-containing SPEEK composite membranes indicate that these advanced materials can be used for improving the performance of RFBs.

Unprecedented sulphonated poly(ether ether ketone)–bismuth cobalt zinc oxide composites: physicochemical and electrochemical performance in fuel cell

Advanced polymer composite membranes were prepared from a linear sulphonated poly(ether ether ketone) (SPEEK) with bismuth cobalt zinc oxide [BCZO, (Bi2O3)0.07(CoO)0.03(ZnO)0.90] nanopowder as an inorganic additive for the application of H2–O2 fuel cell. Morphological data tend to provide evidences for the incorporation of BCZO into SPEEK polymer. Indeed, the composite membrane loaded with 7.5 wt.% of BCZO was identified to uptake maximum water, whilst the pristine SPEEK membrane occurred to retain only 24.0%. As such SPEEK matrix loaded with 7.5 wt.% of BCZO was found to exhibit the maximum proton conductivity of 0.030 S cm−1, whereas the pristine membrane was restricted to 0.021 S cm−1. Evidently, TGA profile of the composite membrane was measured to exhibit sufficient thermal stability to employ as the electrolyte in fuel cell. The membrane electrode assembly of pristine SPEEK and SP-BCZO-7.5 wt.% membranes were fabricated and studied for their electrochemical performance. Indeed, the characteristics of those newly developed composite membranes led to possess incredible feature towards the fuel cell applications.

Zr‐MOF‐Enabled Controllable Ion Sieving and Proton Conductivity in Flow Battery Membrane

AbstractMembrane with ordered channels is the key to controlling ion sieving and proton conductivity in flow batteries. However, it remains a great challenge for finely controlling the nanochannels of polymeric membranes. Herein, two types of acid‐stable Zr‐metal organic framework (MOF‐801 and MOF‐808) with variable pore structures and channel properties are introduced as fillers into a non‐fluorinated sulfonated poly (ether ether ketone) (SPEEK). The membrane incorporated with MOF‐801 of a smaller triangular window (≈3.5 Å) successfully translates the molecular sieving property into the flow battery membrane, resulting in enhanced coulombic efficiency (98.5–99.2%) at 40–120 mA cm−2 compared with the pristine SPEEK membrane (97.1–98.5%). In contrast, more protophilic internal interconnected channels of MOF‐808 yield faster proton highway, leading to a significant increase of voltage efficiency (93.7–84.1%) at 40–120 mA cm−2 compared with the pristine SPEEK membrane (91.7–78.9%). By regulating the ion sieving and proton conductivity, MOF‐801/MOF‐808 binary composite membrane exhibits synchronously improved performance in the vanadium redox flow battery system. The revealed structure–property relationship in the Zr‐MOFs‐based membranes provides a general guideline to design new proton exchange membranes with ordered channels for flow battery application.

Improved proton conduction of sulfonated poly (ether ether ketone) membrane by sulfonated covalent organic framework nanosheets

A type of sulfonated covalent organic framework nanosheets (TpPa-SO3H) was synthesized via interfacial polymerization and incorporated into sulfonated poly (ether ether ketone) (SPEEK) matrix to prepare proton exchange membranes (PEMs). The densely and orderly arranged sulfonic acid groups in the rigid skeleton of the TpPa-SO3H nanosheets, together with their high-aspect-ratio and well-defined porous structure provide proton-conducting highways in the membrane. The doping of TpPa-SO3H nanosheets led to an increased ion exchange capacity up to 2.34 mmol g−1 but a 2-folds reduced swelling ratio, remarkably mitigating the trade-off between high IEC and excessive swelling ratio. Based on the high IEC and orderly arranged proton-conducting sites, the SPEEK/TpPa–SO3H–5 membrane exhibited the maximum proton conductivity of 0.346 S cm−1 at 80 °C, 1.91-folds higher than the pristine SPEEK membrane. The mechanical strength of the composite membrane was also improved by 2.05-folds–74.5 MPa. The single H2/O2 fuel cell using the SPEEK/TpPa–SO3H–5 membrane presented favorable performance with an open voltage of 1.01 V and a power density of 86.54 mW cm−2.

Novel amphoteric ion exchange membranes by blending sulfonated poly(ether ether ketone) with ammonium polyphosphate for vanadium redox flow battery applications

AbstractA novel amphoteric ion exchange membrane for vanadium redox flow battery (VRFB) was explored by blending sulfonated poly(ether ether ketone) (SPEEK) and ammonium polyphosphate (APP). The high‐stability flame retardant of cross‐linked APP with a large number of NH4+ groups was first introduced into SPEEK membrane. It was observed that the addition of APP with special structure could achieve a good balance between proton conductivity and vanadium ions permeability. The abundant NH4+ in APP could block the penetration of vanadium ions by Donnan/Manning exclusion effect and ionic crossing networks due to the ionic bonds between cation and anion groups, and specially a small amount of APP within 5% could remarkably improve the proton conductivity of pristine SPEEK membrane might be ascribed to the unique fast proton transport channels formed by hydrogen bond networks and particular micro‐phase separation as a result of interaction between SPEEK and APP. When 5% APP was blended, the SPEEK/APP‐5% (S/APP‐5%) amphoteric membrane showed a higher selectivity of 20.87 × 104 S min/cm3 (with a good proton conductivity of 0.075 S/cm and a lower VO2+ permeability of 3.45 × 10−7 cm2/ min) and presented better thermal and chemical stability compared to Nafion115 and SPEEK membranes. The VRFB single cell assembled with S/APP‐5% amphoteric membrane exhibited more excellent performance than that of Nafion115 and pristine SPEEK membranes, which revealed a higher coulombic efficiency of 96.3%–98.3%, comparable voltage efficiency of 88.4%–78.7% and higher energy efficiency of 85.1%–77.4% from 40 to 80 mA/cm2, respectively, and showed relatively good stability of the efficiency up to 50 cycles at 60 mA/cm2. The results demonstrated that the designed S/APP amphiprotic membrane of outstanding selectivity, high battery efficiency, and good durability is a prospected VRFB separator.

Porous PTFE reinforced SPEEK proton exchange membranes for enhanced mechanical, dimensional, and electrochemical stability

The pores of polytetrafluoroethylene (PTFE) film were filled with the sulfonated poly (ether ketone) (SPEEK) electrolyte molecules to prepare the proton exchange membrane with the enhanced mechanical, dimensional and electrochemical stability for fuel cell application. Catechol/polyethyleneimine was co-deposited on the PTFE pore surface as an adhesive mediator for the feasible impregnation of SPEEK. The chemical composition, morphology, and wettability of the porous PTFE film were investigated by electron spectroscopy for chemical analysis, scanning electron microscope, mercury porosimetry, and water contact angle measurements. After pore filling with SPEEK electrolytes, several essential properties of membranes (e.g. water uptake, proton conductivity, mechanical property) and wet/dry cyclic cell performance were examined. The prepared pore-filled electrolyte membranes showed the superior mechanical and dimensional stability at the reduced water uptake to the pristine SPEEK membrane. Those excellent properties of the electrolyte membranes are reflected in the stable electrochemical cell performance over the repeated wet/dry cycles with suppression of crack/void formation and edge breakdown.

Incorporating of layered double hydroxide/sepiolite to improve the performance of sulfonated poly(ether ether ketone) composite membranes for proton exchange membrane fuel cells

AbstractSulfonated poly(ether ether ketone) (SPEEK) with a low sulfonation degree was blended using nanofiller layered double hydroxide (LDH, Mg2AlCl)/sepiolite nanostructured material as additive to use as an electrolyte membrane for fuel cell application. Characterization assessments, that is, mechanical stability, thermal gravimetric analysis, ion exchange capability, swelling properties, water uptake capacities, electrochemical impedance spectroscopy analysis, and Fourier transform infrared spectroscopy of the composite membranes were conducted. The presence of LDH/sepiolite nanoarchitectured material within SPEEK was found to have the highest water retention and proton conductivity value at high temperature rather than LDH/SPEEK and pristine SPEEK membranes.