Membranes For Direct Methanol Fuel Cells Research Articles

Dimethylamine-tuned guanidinium arylphosphonate iHOFs and superprotonic conduction Nafion hybrid membranes for DMFCs

The fabrication of proton exchange membranes (PEMs) with excellent conductivity and low methanol permeability is critical but challenging for the further development of high-performance direct methanol fuel cells (DMFCs). In this work, two ionic hydrogen-bonded organic frameworks (iHOF-14 and iHOF-15) are obtained from 1,3,5-tris(4-phosphonophenyl)benzene and guanidine hydrochloride under the control of dimethylamine cations. Due to the abundant hydrogen bonding network, iHOF-14 and iHOF-15 exhibit good proton conductivity of over 10–2 S cm−1. In addition, we dope the iHOFs into Nafion matrix to get the PEMs with richer proton transport pathways and good methanol barrier properties. At 100 °C and 98 % RH, the conductivity of 9 %-iHOF-14/Nafion and 9 %-iHOF-15/Nafion reaches up to 1.53 × 10–1 and 1.78 × 10–1 S cm−1, respectively. The 72 h permeation experiment results show that the methanol permeability of the composite membranes is 73.7 % lower than that of the recast Nafion. The maximum power densities of hybrid membranes for DMFCs reach about 80 mW cm−2, which is 1.5 times higher compared to the recast Nafion. This work not only enriches the high proton conductivity of arylphosphonate iHOFs, but also expands iHOFs/Nafion PEMs materials for DMFCs.

Graphene Coating of Nafion Membranes for Enhanced Fuel Cell Performance.

Electrochemically exfoliated graphene (e-G) thin films on Nafion membranes exhibit a selective barrier effect against undesirable fuel crossover. This approach combines the high proton conductivity of state-of-the-art Nafion and the ability of e-G layers to effectively block the transport of methanol and hydrogen. Nafion membranes are coated with aqueous dispersions of e-G on the anode side, making use of a facile and scalable spray process. Scanning transmission electron microscopy and electron energy-loss spectroscopy confirm the formation of a dense percolated graphene flake network, which acts as a diffusion barrier. The maximum power density in direct methanol fuel cell (DMFC) operation with e-G-coated Nafion N115 is 3.9 times higher than that of the Nafion N115 reference (39 vs 10 mW cm-2@0.3 V) at a 5M methanol feed concentration. This suggests the application of e-G-coated Nafion membranes for portable DMFCs, where the use of highly concentrated methanol is desirable.

Silica modified sulphonated Poly(ether ether ketone) proton exchange membranes for DMFC application

Herein, we report sol-gel modified sulfonated poly(ether ether ketone) (SPEEK) organo-silane based composite proton exchange membranes for their suitability in direct methanol fuel cells (DMFCs). Different concentrations (0.2–1.5 wt%) of aminopropyl trimethoxysilane (APTES) are incorporated in SPEEK matrix by in-situ sol-gel method. Physico and electrochemical performances of composite membranes are enhanced by induced H-bonding interactions between free –NH2 and –SO3H groups. With increase in APTES concentration to 0.8 wt%, the ionic conductivity illustrates improvement by ⁓80% while IEC and Proton conductivity (Pc) enhances by ∼21% and ∼70%, respectively than SPEEK. To further explore the feasibility of the membranes in DMFC. Methanol crossover resistance is calculated to as low as 5.30 × 10−7 cm2 s−1 and offers highest selectivity of 4.43 S s cm−3 in contrast to 12.55 × 10−7 cm2 s−1 and 0.31 S s cm−3 for SPEEK, respectively. This study reveals that the Si-SPEEK membrane is a potential alternate for DMFC.

직접메탄올 연료전지를 위한 Poly(vinyl alcohol-co-styrenesulfonic acid) 기반의 양성자 교환막의 제법 및 특성 연구

Development of proton conducting membrane electrolyte is one of the most important research area within the domain of direct methanol fuel cells (DMFCs). This study reports the preparation of glutaraldehyde-crosslinked poly(vinyl alcohol-co-styrenesulfonic acid) proton exchange membrane (PEM) for DMFC. In order to understand the effect of the extent of crosslinking on the PEM properties, varying concentration of glutaraldehyde was used. Key properties of PEMs such as water uptake, swelling behavior, ion-exchange capacity, proton conductivity, and methanol permeability were thoroughly analyzed. PEM formed using 0.5 M glutaraldehyde solution resulted in a crosslinked PEM with the moderate properties, such as swelling, water uptake, proton conductivity and mechanical strength, along with the exhibition of high proton conductivity and lower methanol permeability compared to commercial Nafion-117. In addition, optimized PEM produced a peak power density of 58 W/㎡ at a current density of 300 A/㎡, when DMFC fed with 2 M methanol solution at 60 °C.

A State-of-Art on the Development of Nafion-Based Membrane for Performance Improvement in Direct Methanol Fuel Cells.

Nafion, a perfluorosulfonic acid proton exchange membrane (PEM), has been widely used in direct methanol fuel cells (DMFCs) to serve as a proton carrier, methanol barrier, and separator for the anode and cathode. A significant drawback of Nafion in DMFC applications is the high anode-to-cathode methanol fuel permeability that results in over 40% fuel waste. Therefore, the development of a new membrane with lower permeability while retaining the high proton conductivity and other inherent properties of Nafion is greatly desired. In light of these considerations, this paper discusses the research findings on developing Nafion-based membranes for DMFC. Several aspects of the DMFC membrane are also presented, including functional requirements, transport mechanisms, and preparation strategies. More importantly, the effect of the various modification approaches on the performance of the Nafion membrane is highlighted. These include the incorporation of inorganic fillers, carbon nanomaterials, ionic liquids, polymers, or other techniques. The feasibility of these membranes for DMFC applications is discussed critically in terms of transport phenomena-related characteristics such as proton conductivity and methanol permeability. Moreover, the current challenges and future prospects of Nafion-based membranes for DMFC are presented. This paper will serve as a resource for the DMFC research community, with the goal of improving the cost-effectiveness and performance of DMFC membranes.

Completely eliminating the metal barrier cracks on Nafion for suppressing methanol crossover with anodic aluminum oxide substrates

Methanol crossover is one of the main challenges for direct methanol fuel cells (DMFCs). Depositing a metal barrier on Nafion can reduce the crossover but usually faces the metal cracking issues. This study presents a new composite membrane in which an anodic aluminum oxide (AAO) substrate is impregnated with a Nafion solution and then coated with a layer of Au. The AAO/Nafion/Au composite membrane shows an ideal metal crack-free surface. Higher and more stable voltage has been achieved for the cell with the membrane, indicating an effectively suppressed methanol-crossover. Results reveal that there is a tradeoff between suppressing the methanol crossover and increasing the ion transmission. By optimizing the membrane, it can not only suppress the methanol crossover but also enhance the output performance of DMFCs. The current density and power density of the cells can be enhanced by 59% and 52.85%, respectively, compared to the cell with a commercial Nafion 117. Overall, this work provides a new approach to designing crack-free membranes for DMFCs.

Elucidating the Water and Methanol Dynamics in Sulfonated Polyether Ether Ketone Nanocomposite Membranes Bearing Layered Double Hydroxides.

Conventional Nafion membranes demonstrate a strong affinity for methanol, resulting in a high fuel crossover, poor mechanical stability, and thus poor performance in direct methanol fuel cells (DMFCs). This study involves the synthesis and physiochemical characterization of an alternative polymer electrolyte membrane for DMFCs based on sulfonated poly(ether ether ketone) and a layered double hydroxide (LDH) material. Nanocomposite membranes (sPL), with filler loading ranging between 1 wt% and 5 wt%, were prepared by simple solution intercalation and characterized by XRD, DMA, swelling tests, and EIS. For the first time, water and methanol mobility inside the hydrophilic channels of sPEEK-LDH membranes were characterized by NMR techniques. The introduction of LDH nanoplatelets improved the dimensional stability while having a detrimental effect on methanol mobility, with its self-diffusion coefficient almost two orders of magnitude lower than that of water. It is worth noting that anionic lamellae are directly involved in the proton transport mechanism, thus enabling the formation of highly interconnected paths for proton conduction. In this regard, sPL3 yielded a proton conductivity of 110 mS cm−1 at 120 °C and 90% RH, almost attaining the performance of the Nafion benchmark. The nanocomposite membrane also showed an excellent oxidative stability (over more than 24 h) during Fenton’s test at 80 °C. These preliminary results demonstrate that an sPL3 nanocomposite can be potentially and successfully applied in DMFCs.

Polyvinyl Alcohol Incorporated with Mesoporous Phosphotungstic Acid for Direct Methanol Fuel Cell Application

The development of potential and novel proton exchange membrane (PEMs) is imperative for further commercialization of Direct Methanol Fuel Cell (DMFC). In this study, flat sheet hybrid membrane as an alternative PEM made up of polyvinyl alcohol (PVA) and mesoporous phosphotungstic acid-Silica (mPTA-Si) at various loadings of 0.5, 1.0, 1.5 and 2.0 wt% was prepared to examine the desirable properties for DMFC application. The characteristic test such as water uptake and proton conductivity were conducted. As the mPTA-Si loading increases, the proton conductivity of PVA/mPTA-Si membrane increased up to 1.81 x 10-3 Scm-1 with 68% of water uptakes. The obtained results could reflect the enhance performance of mPTA-Si membrane and high potential alternative membrane for DMFC. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) results proved a good dispersion and the existence of Keggin anion from mPTA-Si particles formed a strong interfacial bonding between fillers and PVA matrix. Owing to these superior characteristics of the mPTA-Si, PVA/ mPTA-Si membrane is considerably promising materials as PEM for DMFC application.

Modifications on Promoting the Proton Conductivity of Polybenzimidazole-Based Polymer Electrolyte Membranes in Fuel Cells.

Hydrogen-air proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are excellent fuel cells with high limits of energy density. However, the low carbon monoxide (CO) tolerance of the Pt electrode catalyst in hydrogen-air PEMFCs and methanol permanent in DMFCs greatly hindered their extensive use. Applying polybenzimidazole (PBI) membranes can avoid these problems. The high thermal stability allows PBI membranes to work at elevated temperatures when the CO tolerance can be significantly improved; the excellent methanol resistance also makes it suitable for DMFCs. However, the poor proton conductivity of pristine PBI makes it hard to be directly applied in fuel cells. In the past decades, researchers have made great efforts to promote the proton conductivity of PBI membranes, and various effective modification methods have been proposed. To provide engineers and researchers with a basis to further promote the properties of fuel cells with PBI membranes, this paper reviews critical researches on the modification of PBI membranes in both hydrogen-air PEMFCs and DMFCs aiming at promoting the proton conductivity. The modification methods have been classified and the obtained properties have been included. A guide for designing modifications on PBI membranes for high-performance fuel cells is provided.

Synthesis and characterization of a novel poly (vinyl alcohol)-based zinc oxide (PVA-ZnO) composite proton exchange membrane for DMFC

Electrolyte polymeric membranes were synthesized by impregnating zinc oxide (ZnO) nanoparticles (NPs) in a cross-linked PVA matrix for Direct Methanol Fuel Cell (DMFC) applications. The novel membranes consist of PVA as the support while zinc oxide nanoparticles serve as inorganic ion exchangers. The fabricated composite proton exchange membranes exhibit a wide variety of advantages which include good thermal and chemical stability. The synthesized membranes demonstrate a high percentage of water uptake (85%–105%) and a low percentage of methanol uptake (17%–21%). Other important properties such as transport number (0.88) and ion exchange capacity (0.78 meq.g−1) were also determined, and they were found comparable to Nafion®117. Ionic conductivity (3.9 mS/cm) of the composite membranes was determined and found comparable to other PVA based composite membranes reported in literature. Characterization of the membranes was carried out using Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray Spectroscopy (EDX) and Thermogravimetric analysis (TGA). These characterizations revealed the structural interaction between the support and the ion exchanger, crystalline nature, surface morphology, elemental analysis and the thermal stability (upto 280 °C) of the membranes, respectively. The mechanical characterization of the membranes was also carried out on a Universal Testing Machine (UTM), revealing satisfactory mechanical stability. The results demonstrate the possibility of synthesis of a low-cost proton exchange membrane for DMFC applications.

A review of quaternized polyvinyl alcohol as an alternative polymeric membrane in DMFCs and DEFCs

Direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) have emerged as alternative power generators for portable devices and household appliances because of their easy and fast production of electricity, as well as high energy conversion to provide high-power density. However, several critical factors limit the commercialization of DMFCs and DEFCs, particularly issues related to polymer electrolyte membranes, including the high-cost production of Nafion membranes and cell degradation caused by high fuel crossover and dehydration. This review paper provides an overview of the current status and challenges in quaternized polyvinyl alcohol (QPVA)-based membranes as an alternative polymer electrolyte membrane for DMFCs and DEFCs. The main advantages of using QPVA-based membranes in fuel cells are reduced cost production of membrane, fuel-crossover minimization, and competitive conductivity with Nafion membrane. The effects of modifying the QPVA-based membrane, especially on conductivity properties, fuel crossover, uptake condition, mechanical, thermal, and chemical properties, and single-cell performance are comprehensively discussed. The best performances of DMFCs and DEFCs with utilizing QPVA-based membrane are reported as 272 and 144 mW cm−2, respectively. This paper is the first to highlight the current status and challenges of QPVA-based membranes for DMFCs and DEFCs applications.

40SiO2–40P2O5–20ZrO2 sol-gel infiltrated sSEBS membranes with improved methanol crossover and cell performance for direct methanol fuel cell applications

Membranes commonly used in direct methanol fuel cell (DMFC) are expensive and show a great permeability to methanol which reduces fuel utilization and leads to mixed potential at the cathode. In this work, sulfonated styrene-ethylene-butylene-styrene (sSEBS) modified membranes with zirconia silica phosphate sol-gel phase are developed and studied in order to evaluate their potential use in DMFC applications. The synthesized hybrid membranes and sSEBS are subjected to an exhaustive physicochemical characterization by liquid uptake, ion exchange capacity, atomic force microscopy, X-ray photoelectron spectroscopy and dynamic mechanical and thermogravimetric analyses. Likewise, the potential use of the prepared membranes in DMFC is evaluated by means of electrochemical characterizations in single cell, determining the limiting methanol crossover current densities, proton conductivities and DMFC performances. The hybrid membranes show lower water and methanol uptakes, higher stiffness, water retention capability, upper power density and lower methanol crossover than sSEBS and Nafion 112.

Alkali‐doped hyperbranched cross‐linked polybenzimidazoles containing benzyltrimethyl ammoniums with improved ionic conductivity as alkaline direct methanol fuel cell membranes

Alkali‐doped hyperbranched cross‐linked polybenzimidazoles containing benzyltrimethyl ammoniums with improved ionic conductivity as alkaline direct methanol fuel cell membranes

Fabrication of functionalized nanosilicone particles-doped biodegradable eco-friendly proton exchange membranes

The functionalized nanosilicone particles with high sulfonic and carboxyl groups were prepared and incorporated into chitosan matrix to fabricate the doped biodegradable eco-friendly electrolyte materials. The functionalized nanosilicone particles not only were as crosslinkers and proton conductors, but also could form the compact silicone network. Compared with the undoped membrane, the doped ones showed better water retention, methanol barrier, thermal and mechanical stability. In particular, lower methanol uptake and diffusion in higher methanol concentration were very advantageous for reducing fuel wastage and increasing cell efficiency. The lowest methanol diffusion coefficient obtained in 12 M methanol (5.60 × 10−8 cm2 s−1) was less than 1/56 of that of Nafion® 117. In addition, proton conductivity of the doped membranes was significantly affected by nanosilicone particles content. The highest conductivity value obtained with 30% nanosilicone particles was 0.074 S cm−1 at 80 °C, which was very close to the value of Nafion® 117 at same conditions. The decreased methanol diffusion and improved conductivity conferred the super selectivity. In our work, the maximum selectivity was 5.30 × 105 Ss cm−3 which was approximately 33.5 times of that of Nafion® 117, indicating that the doped membranes were promising candidates for proton exchange membrane applications. Furthermore, the addition of functionalized nanosilicone particles endowed the membranes with many other advantages, including cost-effectiveness and simple preparation, which also improved the application potential of natural polymer chitosan as direct methanol fuel cell membrane material.

Sulfonated PEI membrane with GPTMS-TiO2 as a filler for potential direct methanol fuel cell (DMFC) applications

This study addresses the effect of GPTMS-modified titanium dioxide (TiO2) which composited sulfonated polyetherimide (SPEI) as a proton exchanger on direct methanol fuel cell (DMFC). The membrane fabrication is chiefly based on phase-inversion method after GPTMS-TiO2 and SPEI were prepared separately. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), ion exchange capacity (IEC), proton conductivity, water uptake, methanol permeability and mechanical properties were utilized to characterize and measure their physical and thermal stability. As a result, a high water uptake and IEC performance are achieved using the fabricated membrane as well as low methanol permeability which compared to Nafion 117 membranes. The membrane performance is improved using 20 wt% SPEI and 5wt% TiO2-5 wt% GPTMS with an optimum result of 3 times lower in terms of methanol uptake and methanol permeability with proton conductivity of 21 mS.cm-1 than the remaining membranes and Nafion. Thus, the obtained results of SPEI/TiO2-GPTMS can be promoted as a novel polymeric membrane for DMFC.

Preliminary Study of ABS/Chitosan Blend Polymer for DMFC Membranes

The low cost of ABS polymer and natural polymer chitosan offer attractive chemical and physical properties for direct methanol fuel cells (DMFC). In this contribution, investigation of blend membrane made of ABS and chitosan, and their characterization for water uptake, swelling degree and ion exchange capacity (IEC) and methanol crossover are reported. This membrane was also assessed for its intermolecular interactions and thermal stability using FTIR and TGA compared to the pristine membrane. The water absorption and IEC values were affected by membrane network structure. The polymer blend had better thermal stability and a reduction of methanol permeability, this indicated the viability of utilization these materials as polymer electrolyte membrane in DMFC

Chitosan/sulfonated graphene oxide/silica nanocomposite membranes for direct methanol fuel cells

Silica nanoparticles on sulfonated graphene oxide (sGO/SiO2) are incorporated with chitosan (CS) in tunable compositions and their performances as ion conductors in direct methanol fuel cells (DMFC) are evaluated. The morphological observations reveal that sGO/SiO2 nanocomposite is homogeneously distributed throughout the CS matrix. The anisotropic and strong bonds created among the carbon atoms of functionalized GO nanosheets and the ceramic characteristic of SiO2 nanofillers promote the thermal stability of CS/sGO/SiO2 composite membrane than that of bare CS membrane. The hydrophilic sites provided via the sulfonated moieties of GO and hygroscopic characteristics of SiO2 nanoparticles improve the water adsorption channels. The hydrogen bonding and acid-base pair interaction exerted between the CS and sGO/SiO2 facilitate the continuous and rapid ion conduction via grotthuss mechanism. The high aspect ratio of sGO and the effectively piled SiO2 nanoparticles generate tortuous channels for methanol diffusion. Thus the selective passage of ions and fuel in CS/sGO/SiO2 composite membrane provides the maximum DMFC power density of 87.18 mW cm−2 with considerable duration, which confers the prosperous light on the utility of environmentally benign and bio-degradable CS membrane in DMFCs.

Multidimensional nanostructured membrane electrode assemblies for proton exchange membrane fuel cell applications

This review highlights the recent progress in multidimensional nanostructured membrane electrode assemblies for PEMFCs and DMFCs.

Preparation and properties of direct methanol fuel cell membranes by embedding sulfunic titania into sulfonated poly(arylene ether nitrile)s

In order to improve the performance of DMFCs, sulfunic Titania have been synthesized and incorporated sulfonated poly (arylene ether nitrile) s to fabricate hybrid membranes with enhanced proton conductivity and methanol resistance. The introduction of particle content caused significant improvement in thermal property, methanol permeability, proton conductivity and dimensional stability. For instance, SPEN-5 wt% showed the highest selectivity of 5.05×105 S s cm-3, which was more than 10 times higher than that of Nafion 117. All the results make the hybrid membranes as potential candidate for applications in fuel cells.

Tailored SPVdF-co-HFP/SGO nanocomposite proton exchange membranes for direct methanol fuel cells

Sulfonated poly (vinylidenefluoride-co-hexafluoropropylene) (SPVdF-co-HFP) based polymer nanocomposite proton exchange membranes (PEMs) were successfully fabricated in the presence of sulfonated graphene oxide (SGO) as nano-filler for direct methanol fuel cell (DMFC) applications. Sulfonation of GO was carried out using sulfanilic acid and the incorporation of -SO3H groups were confirmed by FTIR, HR-TEM and Raman spectroscopy. The physicochemical properties of the fabricated membranes such as ion exchange capacity (IEC), water uptake (WU), swelling ratio (SR), oxidative, thermal and mechanical stability, proton conductivity, methanol permeability and membrane selectivity were determined. Among the various nanocomposite PEMs were prepared, SPVdF-co-HFP/SGO-7 exhibited good tensile strength (29.7 MPa), improved Young's modulus (432.5 MPa), high proton conductivity (5.52 × 10−3 S/cm, at 30 °C), superior selectivity (2.99 × 104 Scm−3s) and reduced methanol cross-over (1.846 × 10−7cm2s−1) and this nanocomposite membrane can possibly be a superior and alternate candidate to Nafion membrane in DMFCs.