Durability study of KOH doped polybenzimidazole membrane for air-breathing alkaline direct ethanol fuel cell

Recently, KOH doped polybenzimidazole (PBI/KOH) membrane has been reported as polymer electrolyte membrane for alkaline direct alcohol fuel cell (ADAFC), but little is known about its durability for ADAFC application. In this paper, the durability of PBI/KOH membrane for air-breathing alkaline direct ethanol fuel cell (ADEFC) is evaluated by means of ex situ and in situ tests. In the case of ex situ durability test, the ionic conductivity of PBI/KOH degrades from initial 0.023 S cm⁻¹ to 0.01 S cm⁻¹ after 100 h, and the degrading rate was 1.3 × 10⁻⁴ S cm⁻¹ h⁻¹. As for in situ test, Pt-free air-breathing ADEFC with PBI/KOH membrane can output a peak power density of 16 mW cm⁻² at 60 °C. Moreover, it can stably operate for 336 h above 0.3 V. In addition, the interaction between KOH and PBI matrix is also explored by density functional theory study.     

Novel sulfonated poly(oxybenzimidazole) membranes bearing sulfo-napthalimide pendant groups with improved proton conductivity and fuel cell performance

The goal of the present work is to introduce a new aromatic bulky six-membered sulfo-napthalimide pendant groups, specifically 2-(2,5-dicarb-oxyphenyl-1,3-dioxo- 2,3-didihydro-1Hbenzo[de]isoquinoline-6-sulfonate (PDDDBIS), into the poly(oxybenzimidazole) (POBI) main chain. As no sulfo-napthalimide-bearing POBI has been reported yet, this could be a potential strategy to improve the solubility, processability, and proton conductivity of sulfonated POBIs in addition to boosting fuel cell performance. Out of six membranes synthesized, one sulfonated POBI membrane with pendant PDDDBIS groups (SPOBI-100) exhibited a fairly high proton conductivity of 0.172 S/cm, which is higher than Nafion-117 (0.161 S/cm) at 90 °C. Notably, an H₂/O₂ PEM fuel cell fabricated with the SPOBI-100 membrane displayed good performance with the maximum peak power density of 547 mW/cm² and output current density of 1259 mA/cm² in 0.99 V at 90 °C with100% RH, which is higher than the Nafion 117 power density (519 mW/cm²) and current density (1215 mA/cm²) under the same testing conditions.     

Electrooxidation study of pure ethanol/methanol and their mixture for the application in direct alcohol alkaline fuel cells (DAAFCs)

Aliphatic alcohol mainly, ethanol, methanol and their mixture were subjected to electrooxidation study using cyclic voltammetry (CV) technique in a three electrodes half cell assembly (PGSTAT204, Autolab Netherlands). A single cell set up of direct alcohol alkaline fuel cell (DAAFC) was fabricated using laboratory synthesized alkaline membrane to validate the CV results. The DAAFC conditions were kept similar as that of CV experiments. The anode and cathode electrocatalysts were Pt-Ru (30%:15% by wt.)/Carbon black (C) (Alfa Aesar, USA) and Pt (40% by wt.)/High Surface Area Carbon (C_HSA) (Alfa Aesar, USA) respectively. The CV and single cell experiments were performed at a temperature of 30 °C. The anode electrocatalyst was in the range of 0.5 mg/cm² to 1.5 mg/cm² for half cell CV analysis. The cell voltage and current density data were recorded for different concentrations of fuel (ethanol or methanol) and their mixture mixed with different concentration of KOH as electrolyte. The optimum electrocatalyst loading in half cell study was found to be 1 mg/cm² of Pt-Ru/C irrespective of fuel used. The single cell was tested using optimum anode loading of 1 mg/cm² of Pt-Ru/C which was found in CV experiment. Cathode loading was kept similar, in the order of 1 mg/cm² Pt/C_HSA. In single cell experiment, the maximum open circuit voltage (OCV) of 0.75 V and power density of 3.57 mW/cm² at a current density of 17.76 mA/cm² were obtained for the fuel of 2 M ethanol mixed with 1 M KOH. Whereas, maximum OCV of 0.62 V and power density of 7.10 mW/cm² at a current density of 23.53 mA/cm² were obtained for the fuel of 3 M methanol mixed with 6 M KOH. The mixture of methanol and ethanol (1:3) mixed with 0.5 M KOH produced the maximum OCV of 0.66 V and power density of 1.98 mW/cm² at a current density of 11.54 mA/cm².     

Performance of PVDF supported silica immobilized phosphotungstic acid membrane (Si-PWA/PVDF) in direct methanol fuel cell

PVDF supported silica-immobilized phosphotungstic acid membrane (Si-PWA/PVDF) was synthesized by impregnation of silica immobilized phosphotungstic acid particles in porous PVDF film. Pore size distribution as well as stability of membrane in oxidative environment was determined using Fenton's reagent test. Stability of membrane against leaching of PWA which provides ion exchanging capacity was also determined and found to be adequate. Properties which affect performance of membrane in DMFC like water uptake, methanol cross-over and proton conductivity were measured. Water uptake of the membrane increased from 30.3% to 37.9% as the temperature was increased from 25 °C to 80 °C. The proton conductivity of the membrane increased from 4.3 mS cm⁻¹ to 20 mS cm⁻¹ with increase in the temperature from 25 °C to 80 °C. Methanol uptake of the Si-PWA/PVDF membrane was low compared to Nafion membrane and changed by very small amount with increase in temperature. Effect of operating parameters on performance of direct methanol fuel cell (DMFC) with the synthesized Si-PWA/PVDF was determined. DMFC performance improved on increasing temperature. As the temperature was increased from 25 °C to 60 °C, open circuit voltage (OCV) increased from 0.685 V at 0.815 V and the peak power density increased from 21.4 mW cm⁻² to 44.0 mW cm⁻². Maximum peak power density was obtained with 1 M methanol concentration and 60% relative humidity. Peak power density decreased with further increase in both methanol concentration and relative humidity.     

Alkyl chain modified sulfonated poly(ether sulfone) for fuel cell applications

A new alkyl chain modified sulfonated poly(ether sulfone) (mPES) was synthesized and formed into membranes. The MEAs were tested in the PEMFC and evaluated systematically in the DMFC by varying the methanol concentration from 0.5 to 5.0 M at 60 °C and 70 °C. The synthesized mPES copolymer has been characterized by nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The proton conductivity of the resulting membrane is higher than the threshold value of 10⁻² S cm⁻¹ at room temperature for practical PEM fuel cells. The membrane is insoluble in boiling water, thermally stable until 250 °C and shows low methanol permeability. In the H₂/air PEMFC at 70 °C, a current density of 600 mA cm⁻² leads to a potential of 637 mV and 658 mV for 50 μm thick mPES 60 and Nafion NRE 212, respectively. In the DMFC, mPES 60's methanol crossover current density is 4 times lower than that for Nafion NRE 212, leading to higher OCV values and peak power densities. Among all investigated conditions and materials, the highest peak power density of 120 mW cm⁻² was obtained with an mPES 60 based MEA at 70 °C and a methanol feed of 2 M.     

Inorganic-organic composite membranes containing amino-functionalized mesoporous silica loaded phosphotungstic acid with enhanced fuel cell performance and stability

In this work, phosphotungstic acid (HPW) modified amino-functionalized mesoporous silica (AMS) as an inorganic filler (AMS@HPW) is incorporated into sulfonated poly (aryl ether sulfone) (SPAES) to prepare inorganic-organic composite membrane. The fabricated silica possesses a mesoporous structure with a surface area of 488.74 m²/g. The amino modification of silica acting as a “bridge” loads more HPW and promotes the compatibility between inorganic fillers and SPAES. The obtained SPAES/AMS@HPW composite membranes effectively inhibit HPW leakage and display better stability and fuel cell property due to the acid-base interaction and hydrogen-bond networks. Especially, the SPAES/AMS@HPW-1.0 membrane displays 18.4% higher proton conductivity (175.5 mS/cm) at 90 °C and 22.3–28.5% higher power density (470.4–678.4 mW/cm²) at 60%–100% RH than the original membrane. In addition, the SPAES/AMS@HPW-1.0 membrane still maintains stable voltage output and shows lower voltage decay (0.331 mV/h) and hydrogen permeation current density (8.28 mA/cm²) than Nafion 112 after the durability test.     

Improvement of PEMFC performance with Nafion/inorganic nanocomposite membrane electrode assembly prepared by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium silicon dioxide (TiSiO₄) composite membranes were manufactured with a novel ultrasonic-spray technique and tested in proton exchange membrane fuel cell (PEMFC). Nafion/TiO₂ and Nafion/SiO₂ nanocomposite membranes were also fabricated by the same technique and their characteristics and performances in PEMFC were compared with Nafion/TiSiO₄ mixed oxide membrane. The composite membranes have been characterized by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, water uptake, and proton conductivity. The composite membranes gained good thermal resistance with insertion of inorganic oxides. Uniform and homogeneous distribution of inorganic oxides enhanced crystalline character of these membranes. Gas diffusion electrodes (GDE) were fabricated by Ultrasonic Coating Technique. Catalyst loading was 0.4 mg Pt/cm² for both anode and cathode sides. Fuel cell performances of Nafion/TiSiO₄ composite membrane were better than that of other membranes. The power density obtained at 0.5 V at 75 °C was 0.456 W cm⁻², 0.547 W cm⁻², 0.477 W cm⁻² and 0.803 W cm⁻² for Nafion, Nafion/TiO₂, Nafion/SiO₂, and Nafion/TiSiO₄ composite membranes, respectively.     

Performance of an anion exchange membrane in association with cathodic parameters in a dual chamber microbial fuel cell

Performance of two-chambered microbial fuel cells (MFCs) using anion exchange membrane (AEM) was evaluated under batch mode with Shewanella putrefaciens in Luria broth. Maximum voltage and power density using Nafion and Ralex AEM were 0.676 V and 0.729 V and 39.2 ± 7.39 mW/m² and 57.8 ± 5.509 mW/m² respectively. Cathodic half cell potential was monitored along with cathodic pH and the results revealed that low power density was achieved in case of Nafion as compared to Ralex AEM mainly due to pH imbalance associated voltage losses using small external resistance of the same. Metabolite loss in AEM was found at higher current density which limits the Coulombic efficiency and power generation. A three parameters optimization showed that surface area of cathode had significant effect on the power generation. Effect of anode surface area, dissolve oxygen (DO) in catholyte and electrode spacing on power production were evaluated using AEM membrane.     

Preparation and characterization of quaternary ammonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) as anion exchange membrane for alkaline polymer electrolyte fuel cells

Anion exchange membrane from poly(phenylene oxide) containing pendant quaternary ammonium groups is fabricated for application in alkaline polymer electrolyte fuel cells (APEFCs). Chloromethylation of poly(phenylene oxide) (PPO) was performed by aryl substitution and then homogeneously quaternized to form an anion exchange membrane (AEM). The influence of various parameters on the chloromethylation reaction was investigated and optimized. The successful introduction of the above groups in the polymer backbone was confirmed by ¹H NMR and FT-IR spectroscopy. Membrane intrinsic properties such as ion exchange capacity, water uptake and ionic conductivity were evaluated. The membrane electrolyte exhibited an enhanced performance in comparison with the state-of-the-art commercial AHA membrane in APEFCs. A peak power density of 111 mW/cm² at a load current density of 250 mA/cm² was obtained for PPO based membrane in APEFCs at 30 °C.     

Enhanced performance of a direct methanol alkaline fuel cell (DMAFC) using a polyvinyl alcohol/fumed silica/KOH electrolyte

A novel polymer-inorganic composite electrolyte for direct methanol alkaline fuel cells (DMAFCs) is prepared by physically blending fumed silica (FS) with polyvinyl alcohol (PVA) to suppress the methanol permeability of the resulting nano-composites. Methanol permeability is suppressed in the PVA/FS composite when comparing with the pristine PVA membrane. The PVA membrane and the PVA/FS composite are immersed in KOH solutions to prepare the hydroxide-conducting electrolytes. The ionic conductivity, cell voltage and power density are studied as a function of temperature, FS content, KOH concentration and methanol concentration. The PVA/FS/KOH electrolyte exhibits higher ionic conductivity and higher peak power density than the PVA/KOH electrolyte. In addition, the concentration of KOH in the PVA/FS/KOH electrolytes plays a major role in achieving higher ionic conductivity and improves fuel cell performance. An open-circuit voltage of 1.0 V and a maximum power density of 39 mW cm⁻² are achieved using the PVA/(20%)FS/KOH electrolyte at 60 °C with 2 M methanol and 6 M KOH as the anode fuel feed and with humidified oxygen at the cathode. The resulting maximum power density is higher than the literature data reported for DMAFCs prepared with hydroxide-conducting electrolytes and anion-exchange membranes. The long-term cell performance is sustained during a 100-h continuous operation.     

Amelioration in physicochemical properties and single cell performance of sulfonated poly(ether ether ketone) block copolymer composite membrane using sulfonated carbon nanotubes for intermediate humidity fuel cells

A composite membrane composed of a sulfonated diblock copolymer (SDBC) based on poly(ether ether ketone) blocks copolymerized with partially fluorinated poly(arylene ether sulfone) and sulfonated carbon nanotubes (SCNTs) was fabricated by simple solution casting. Addition of the SCNT filler enhanced the water absorption and proton conductivity of membranes because of the increased per‐cluster volume of sulfonic acid groups, at the same time reinforced the membranes' thermal and mechanical properties. The SDBC/SCNT‐1.5 membrane exhibited the most improved physicochemical properties among all materials. It obtained a proton conductivity of 10.1 mS/cm at 120°C under 20% relative humidity (RH) which was 2.6 times more improved than the pristine membrane (3.9 mS/cm). Moreover, the single cell performance of the SDBC/SCNT‐1.5 membrane at 60°C and 60% RH at ambient pressure exhibited a peak power density of 171 mW/cm² at a load current density of 378 mA/cm², while the pristine membrane exhibited 119 mW/cm² at a load current density of 294 mA/cm². Overall, the composite membrane exhibited very promising characteristics to be used as polymer electrolyte membrane in fuel cells operated at intermediate RH.     

Highly charged and stable cross-linked polysulfone alkaline membrane for fuel cell applications: 4,4,-((3,3'-bis(chloromethyl)-(1,1'-biphenyl)-4,4-diyl)bis(oxy))dianiline (BCBD) a novel cross-linker

Alkaline membrane (AM) shows fast transport of OH⁻ towards the anode, separates both electrodes, and prevents fuel cross-over. To achieve good membrane conductivity and performance, high concentration of positively charged groups (quaternary ammonium) is an essential requirement, which also leads excessive swelling and mechanical instability of the AMs. Further, directly grafted quaternary ammonium (QA) with main polymer chain substitution and/or elimination reactions under strong alkaline environment. To avoid above-mentioned problems, we report preparation of cross-linked chloromethylated polysulfone based AM using (4,4^,-((3,3′-bis(chloromethyl)-[1.1′-biphenyl]-4,4-diyl)bis(oxy))dianiline) (BCBD), a multi-functional novel cross-linking agent. Reported strategy compensates 2 mol of chloromethyl groups consumed during cross-linking, but additional functional groups (4 mol) with cross-linking agent. These AMs are designed to avoid the nucleophilic substitution (S_N²) (grafting quaternary ammonium (QA) groups at benzylic position), and Hofmann elimination (E²) reactions (unavailability of β-H), under strong alkaline environment. Effective cross-linking has been confirmed by spectral analysis, and improves membrane stabilities and fuel cell performance. Single-cell alkaline membrane fuel cell (AEMFC) performance of most suitable (CR-QPS-03) membrane, showed comparatively high performance (open circuit voltage (OCV): 0.813 V, maximum power density: 103.6 mW/cm² at 260.0 mA/cm²) in compare with Nafion 117 membrane (OCV: 0.682 V, maximum power density: 63.36 mW/cm² at 220.0 mA/cm²) under similar experimental conditions.     

Assimilation of highly porous sulfonated carbon nanospheres into Nafion matrix as proton and water reservoirs

A unique form of carbon nanospheres possessing an immense number of micropores and pendant surface sulfonic acid groups was synthesized and used as an effective filler to enhance proton transfer in Nafion^® membrane at elevated temperatures. The synthesis of the filler involved the formation of polypyrrole nanoparticles and pyrolysis of them to generate carbon nanospheres (CN). Alkaline etching was then carried out to create the porous structure, and the resulting porous carbon nanospheres were then sulfonated to attain the sulfonated porous carbon nanospheres (sPCN, 1300 m²/g, 6.9 mmol-SO₃H/g). Dispersion of a substantially small amount of sPCN in a Nafion matrix brought about a cross-adsorption between the hydrophilic side-chain of Nafion molecules and sPCN. This causes the formation of a cross-linking network with sPCN junctions. The scope of this network, however, decreased with the increase in the sPCN loading from 1 to 2 wt% due to a reduction in extent of the cross-adsorption. The sPCN loading of 1 wt% reached the highest crosslinking degree that displayed the maximum enhancement on proton transport. It can be attributed to the role of the sPCN crosslinking junctions in keeping moisture and supplying protons. The characterizations of glass transition behaviour, hydrophilic microenvironments, and proton conductivity under low humidity levels reflected the impact of crosslinking extent. In the single H₂-PEMFC test at 70 °C using dry H₂/O₂, 1 wt%-sPCN Nafion composite membrane manifested a power density of 571 mW/cm² as compared to the pristine Nafion membrane that showed uppermost value of 388 mW/cm².     

An electro-kinetic study of oxygen reduction in polymer electrolyte fuel cells at intermediate temperatures

The oxygen reduction process in polymer electrolyte fuel cells (PEMFCs) was in-situ investigated at intermediate temperatures (80°–130 °C) by using a carbon supported PtCo catalyst and Nafion membrane as electrolyte. To overcome the Nafion dehydration above 100 °C, the experiments were carried out under pressurized conditions. Electro-kinetic parameters such as reaction order and activation energy were determined from the steady-state galvanostatic polarization curves obtained for the PEM single cell. Negative activation energies of 40 kJ mol⁻¹ and 18 kJ mol⁻¹ were observed at 0.9 V and 0.65 V, respectively, in the temperature range 100°–130 °C. This was a consequence of ionomer and membrane dry-out. The ionomer dry-out effect appears to depress reaction kinetics as the temperature increases above 100 °C since the availability of protons at the catalyst–electrolyte interface is linked to the presence of proper water contents. An oxygen reduction reaction of the first order with respect to the oxygen partial pressure was determined at low current densities. Maximum power densities of 990 mW cm⁻² and 780 mW cm⁻² at 100 °C and 110 °C (H₂–O₂) with 100% R.H., were achieved at 3 bars abs.     

Optimization of process parameters using response surface methodology (RSM) for power generation via electrooxidation of glycerol in T-Shaped air breathing microfluidic fuel cell (MFC)

The present work focuses on the optimization of operating parameters using Box Behnken design (BBD) in RSM to obtain maximum power density from a glycerol based air-breathing T-shaped MFC. The major parameters influencing the experiment for enhancing the cell performance in MFC are glycerol/fuel concentration, anode electrolyte/KOH concentration, anode electrocatalyst loading and cathode electrolyte/KOH concentration. The ambient oxygen is used as the oxidant. The acetylene black carbon (C_AB) supported laboratory synthesized electrocatalyst Pd–Pt (16:4)/C_AB is used as anode electrocatalyst and commercial Pt (40 wt%)/C_HSA as the cathode electrocatalyst. The quadratic model predicts the appropriate operating conditions to achieve highest power density from the laboratory designed T-shaped MFC. The p-value of less than 0.0001 and F-value of greater than 1 i.e., 26.32 indicate that the model is significant. The optimum conditions predicted by the RSM model were glycerol concentration of 1.07 M, anode electrolyte concentration of 1.62 M anode electrocatalyst loading of 1.12 mg/cm² and cathode electrolyte concentration of 0.69 M. The negligible deviation of only 1.07% between actual/experimental power density (2.76 mW/cm²) and predicted power density (2.79 mW/cm²) was recorded. This model reasonably predicts the optimum conditions using Pd–Pt (16:4)/C_AB electrocatalyst to obtain maximum power density from glycerol based MFC.     

Control of self-organization of drop-casted Nafion film for improving proton conduction in a polymer-electrolyte-membrane fuel cell to raise its output power density

A simple drop-cast method to directly deposit Nafion polymer electrolyte membrane (PEM) on nanostructured thin-film catalyst layer composed of stacked Pt nanoparticles prepared by pulsed laser deposition (PLD) was demonstrated. Through optimization of solvent composition and drying temperature of Nafion solution to control self-organization of Nafion, a uniform PEM with better bulk and interface microstructures could be produced, leading to a significant improvement in the output current density of a PEM fuel cell over that using reference commercial PEMs. The formation of facile proton conduction pathways in the bulk Nafion membrane resulted in a 35% reduction in ohmic resistance compared to that with the commercial membrane. Moreover, the infiltration of Nafion in the catalyst layer formed suitable proton transport network to render more catalyst nanoparticles effective and thus lower charge-transfer resistance. With the optimized PLD, drop-cast, and hot-pressing conditions, the current density of PEMFCs using drop-casted PEM reached 1902 mA cm⁻² at 0.6 V at 2 atm H₂ and O₂ pressures with a cathode Pt loading of 100 μg cm⁻², corresponding to a power density of 1.14 W cm⁻² and a cathode mass-specific power density of 11.4 kW g⁻¹.     

Alkali doped polybenzimidazole membrane for alkaline direct methanol fuel cell

An anion exchange membrane for alkaline direct methanol fuel cell (ADMFC) was prepared by doping polybenzimidazole(PBI) membrane with KOH. The obtained membrane was characterized by means of XRD, TGA–DTA, AC and so on. The results suggested that it possessed satisfying thermal stability and comparable mechanical strength with acid doped PBI. At room temperature, methanol permeability through this membrane was one order of magnitude lower than that of Nafion^® membrane, while its ionic conductivity was comparable with that of other anion exchange membranes in literatures. For ADMFC at 90 °C based on this PBI/KOH membrane electrolyte, the peak power density was about 31 mW/cm², which was significantly improved mainly due to this membrane's high thermal stability, fast kinetics of electrochemical reactions and lower methanol permeability.     

Rapeseed meal-based autochthonous N and S-doped non-metallic porous carbon electrode material for oxygen reduction reaction catalysis

The heteroatom-doped porous carbon material as an alternative to commercial Pt/C catalysts in oxygen reduction reaction has attracted extensive attention. In this study, the rapeseed meal-based material (ARM-900) prepared by carbonization with high temperature and activation with ZnCl₂ had a porous structure and was doped with N and S heteroatoms. Compared to commercial Pt/C catalysts (onset potential of 0.95 V vs. RHE and limiting diffusion current of ?5.7 mA cm^?2), ARM-900 demonstrated excellent electrocatalytic performance with an onset potential of 0.98 V vs. RHE and limiting diffusion current of ?8.1 mA cm^?2 in O₂ saturated 0.1 M KOH solution. Meanwhile, ARM-900 had higher durability and more superior methanol tolerance than Pt/C catalyst. The excellent ORR performance of ARM-900 was derived from the formation of abundant pore structure and the doping of the autochthonous N and S heteroatoms. MFCs with ARM-900 as the cathode had the maximum power density of 808 mW/m², which was obviously better than Pt/C (709 mW/m²). This study provided an environment-friendly and effective strategy for the reuse of rapeseed meal and the preparation of N and S-doped non-metallic ORR catalysts.     

Investigation of the effects of SPEEK and its clay composite membranes on the performance of Direct Borohydride Fuel Cell

In this study, composite cation exchange membranes (CEM) were developed. With the experience from widely studied proton exchange membrane fuel cells (PEMFC), sulfonated polyether ether ketone (SPEEK) was prepared to be a more effective and cheaper ionomer alternative to the industry standard Nafion ®. SPEEK polymer membrane can reach sufficient ionic conductivities but have some mechanical and chemical stability problems (at a high degree of sulfonations (DS)). Therefore, in order to optimize the membrane, composite mixing with a well-known organic/inorganic clays called Cloisite® 15A, Cloisite ® 30B and MMT were used. Test cells for both single-cell and conductivity were designed and constructed. The ionic conductivity cell was different than the ones used in most studies, measuring conductivity in-plane with 4 probes using EIS. The membranes were characterized for their proton conductivity with electrochemical impedance spectroscopy (EIS), for DS with H NMR, water uptake, and fuel cell performance tests. First results showed that the acidic sulfonic groups of SPEEK interacted with organic/inorganic clays and as a result of partial barrier the ionic conductivity was decreased but power densities were increased. SPEEK-Cloisite® 30B composite membrane has given 40 mW/cm² power density value which is higher than pure SPEEK membrane (35 mW/cm²). The proton conductivities of the final composite membranes were close to bare SPEEK membranes which are 0,065 and 0,075 S/cm for SPEEK-Cloisite ® 30B and pristine SPEEK, respectively.     

Self-assembly of metal-organic framework onto nanofibrous mats to enhance proton conductivity for proton exchange membrane

Constructing consecutive proton-conducting nanochannels and optimizing nanophase-separation within proton exchange membrane (PEM) was of guiding significance for improving proton transfer. Metal organic framework (MOF), as a novel and functional material had drawn increasing attention in the research of proton PEM because of its flexible tunability and designability. Herein, a novel MOF-based nanofibrous mats (NFMs) were prepared by the self-assembly of zeolitic imidazole framework-67 (ZIF-67) onto polyacrylonitrile (PAN) NFMs. Subsequently, the ZIF-67 NFMs were incorporated into Nafion matrix to prepare ZIF-67@Nafion composite membrane which aimed at constructing consecutive proton-conducting channels. Especially, the acid–base pairs between N–H (ZIF-67 NFMs) and –SO₃H (Nafion) could promote the protonation/deprotonation and subsequent proton leaping via Grotthuss mechanisms. As expected, the ZIF-67@Nafion-5 composite membrane showed a promising proton conductivity of 288 mS/cm at 80 °C and 100% RH, low methanol permeability of 7.98 × 10⁻⁷ cm²s⁻¹, and superior power density of 298.68 mW/cm² at 80 °C and 100% RH. In addition, the resulting composite membrane exhibited considerable enhancement in thermal stability and dimensional stability. This promising strategy provided a valuable reference for designing high-performance PEMs.