Sulphonated Poly Ether Ether Ketone Research Articles

Sulphonated graphene oxide as functionalized filler for polymer electrolyte membrane with enhanced anti-biofouling in microbial fuel cells

This research focuses on the development of a polymer electrolyte membrane (PEM) which is intended to increase power generation while addressing the persistent issue of biofouling in microbial fuel cells (MFC). The central hypothesis of this research work is that a novel PEM made from sulphonated polyether ether ketone (SPEEK) grafted with styrene sulphonic acid (SSA) integrated with sulphonated graphene oxide (SGO) will improve the membrane properties as well as enhance the anti-biofouling effect. The optimal percentage of SSA grafting has been determined based on physicochemical properties of the membrane. Various weight percentages of SGO (2.5, 5, 7.5, & 10 wt%) were introduced to the SPEEK/SSA base polymer to augment the physicochemical properties and also to defend against biofouling. Among the tested membranes, the SPEEK/SSA+5 % SGO composite membrane demonstrates the highest water uptake (106.2±1.9 %) and ion exchange capacity (1.55±0.2 meq g−1). Due to these superior properties, it achieves the maximum power density of 203 mW m−2 and an open circuit voltage (OCV) surpassing 700 mV. The crystal violet assay performed post-MFC operation affirms that the nanocomposite membrane effectively inhibits bacterial fouling. This study positions itself as a solution for long-term, high-performance MFC operations, all while significantly increasing power output and reducing biofouling concerns.

Camellia sinensis leaf-derived magnetite nanoparticles as anti-biofouling nano-fillers in polymer electrolyte membrane for microbial fuel cell application

Membrane biofouling prevents one of the most promising bio-electrochemical systems known as microbial fuel cell (MFC) from operating at its fullest potential. Green tea leaf-mediated biosynthesized and sulphonated iron (II, III) oxide nanoparticles aim to serve as a nanofiller for polymer electrolyte membrane (PEM) to enhance the membrane physicochemical parameters and to improve the membrane anti-biofouling in MFC. Sulphonated polyether ether ketone (SPEEK) grafted styrene sulphonic acid (SSA) incorporated with biosynthesized-sulphonated Fe3O4 (BS-Fe3O4) nanoparticles is used as nanocomposite membranes in the MFC. The results show that 7.5 % BS-Fe3O4 integrated SPEEK/SSA membranes possessed high proton conductivity (8.4x10-2 S cm−1), water uptake (78.2 %), and ion exchange capacity (1.84 meq g−1) than plain SPEEK and commercially available Nafion-117 membrane. The results also reveal that SPEEK/SSA + 7.5 % BS-Fe3O4 membrane showed the highest maximum power density of 210.3 mW m−2 at 190 mA m−2 current density after 4 weeks of MFC operation. The heightened performance of the mentioned nanocomposite membranes is due to their exceptional anti-biofouling property as observed through zone of inhibition (10.25 mm) and biofilm inhibition tests (74.1 %). The prepared membranes also exhibited good mechanical and oxidative stability required for long-term operation. Finally, the phylogenetic analysis discloses the maximum presence of the Pseudomonas (∼54.75 %), Acidovax (∼9.5 %), Janthinobacteriu (∼4.84 %), Flavoacterium (∼2.77 %), and Thermomonas (∼2.66 %). This study provides avenues for interdisciplinary research in green synthesis, functionalization of nanomaterials, polymer synthesis, and MFCs to address current research gaps.

Modified polymer electrolyte membrane for microbial fuel cell: Performance analysis, investigation on anti-biofouling effect, and microbial community analysis on biofouled membrane

Sulphonation is limited in Sulphonated Polyether Ether Ketone (SPEEK) due to its solubility in water beyond an extent. However, to enhance performance of polymer electrolyte membrane (PEM) in microbial fuel cell (MFC), more functional groups are required. To facilitate effective proton transfer, styrene sulphonic acid (SSA) is grafted onto SPEEK, resulting in SPEEK/SSA, to increase the number of functional groups. Based on membrane properties, 5 wt% SSA is found to be the optimum grafting for further filler addition. Copper oxide doped reduced graphene oxide (CuO@rGO) is used as membrane filler at various concentrations to enhance anti-biofouling effect. Swelling is excessive in SPEEK/SSA (30.2%), whereas it is only 17.3% in SPEEK/SSA+1.5 wt%CuO@rGO. As evidenced by the zone of inhibition assay, biofilm inhibition test, and Bradford protein assay, the membrane's anti-biofouling impact is improved by the inherent hydrophilicity of SPEEK/SSA and antibacterial activity of CuO@rGO. The MFC with 1.5 wt% CuO@rGO membrane shows highest maximum power density of 186 ± 5 mW m−2 and Chemical Oxygen Demand removal of 81.23%. Phylogenetic analysis on biofouled membrane shows the predominance of Pseudomonas, Acidovorax and Flavobacterium. The research demonstrates that despite biofouling, the synthesized grafted PEM exhibits high resistance to it and hence performs better.

Reduction of hexavalent chromium using sulphonated polyether ether ketone as proton exchange membrane in microbial fuel cells

AbstractHexavalent chromium (Cr(VI)) is a major source of environmental pollutants from tannery effluents. Reduction of hexavalent chromium was performed in a 500 mL working volume dual chamber microbial fuel cell (MFC). Synthetic wastewater containing Cr(VI) was used as anolyte and substrate for mixed microbial consortia to release electrons. The ions produced were transferred to cathodic chamber via a Proton Exchange Membrane (PEM). In this study, sulphonated polyether ether ketone (SPEEK) was used as PEM and compared with Nafion 117 for Cr(VI) reduction. The microbial consortia that aided the treatment were isolated and identified to belong to Enterobacter, Acinetobacter, Stenotrophomonas and Pseudomonas species. The Cr(VI) reduction observed were 14.4% and 51% for MFCs with Nafion 117 and SPEEK as PEM, respectively. The wastewater analysis also showed improved percentage removal for SPEEK than for Nafion 117. The cost analysis shows that Nafion was 2 times higher than SPEEK to be used as PEM. This study highlights that SPEEK as PEM in MFC will be an efficient method for reduction of Cr(VI) from tannery effluents.

Effect of silver incorporated sulphonated poly ether ether ketone membranes on microbial fuel cell performance and microbial community analysis

The present study introduces silver (2.5, 5, 7.5 and 10 wt%) as an effective additive in Sulphonated Poly Ether Ether Ketone (SPEEK) membrane to reduce membrane biofouling in Microbial Fuel Cell (MFC) functioning when operated for three months. The incorporation of the inorganic filler into the polymer backbone is investigated by Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (SEM-EDAX), Fourier Transform Infra-Red (FTIR) spectroscopy, X-Ray Diffraction (XRD) and Thermo Gravimetric Analysis (TGA) studies. The suitability of the prepared composites is evaluated through several membrane studies in comparison with widely investigated Nafion 117. MFC performance studies showed the highest maximum power density of 156 ± 0.5 mW m−2 by making use of SPEEK + 7.5 wt% Ag membrane upon three months of tubular Microbial Fuel Cell (MFC) operation. The antibacterial activity of silver ions reduces biofilm formation. Microbial community analysis of the formed biofilm performed through 16S rRNA sequencing identified 33 types of phyla which contributed to the electron transfer. The present research not only provides an alternate composite membrane with reduced biofouling but also identifies the microbes that contributed effectively in bioelectrogenesis thereby providing insights for future studies on prolonged MFC operation.

Sulphonated polyhedral oligomeric silsesquioxane/sulphonated poly ether ether ketone nanocomposite membranes for microbial fuel cell: Insights to the miniatures involved

In this study we demonstrate Sulphonated Polyhedral oligomeric silsesquioxane (S-POSS) incorporated Sulphonated Poly Ether Ether Ketone (SPEEK) as an effective cation exchange membrane (CEM) for improving performance and sustainability in a fabricated tubular Microbial Fuel Cell (MFC). The organic-inorganic caged frame of S-POSS enables several ion conducting channels thereby resulting in better proton conductivity and water uptake in addition to hydroxide ions native in POSS. Among the membranes, SPEEK+ 5 wt% S-POSS exhibits a highest maximum performance of 162 ± 1.4 mW m−2 with the highest IEC of 1.8 ± 0.05 meq g−1. Microbial community analysis reveals the predominance of several bacterial strains contributing to wide range of mechanisms. Three phyla including Betaproteobacteria, Gammaproteobacteria and Firmicutes showed maximum predominance. In addition to a novel nanocomposite membrane, the present research introduces perceptions of two metabolic mechanisms of the microbial community available which opens pathway for future insights on how other miniatures involve in electron transfer mechanisms.

Fabrication and evaluation of electrospun biomimetic sulphonated PEEK nanofibrous scaffold for human skin cell proliferation and wound regeneration potential.

Regeneration of skin wound is a challenging process since functional and architectural restoration of the damaged skin tissue is an arduous task. The use of springing up biomaterials with nano-topographic and bio-mimicking characteristics resembling natural skin's extra cellular matrix (ECM) would be a favorable approach to regenerate such an injured skin tissue. In this study an attempt has been carried out to design and develop sulphonated polyether ether ketone (SPEEK) nanofibrous scaffold to explore its role on skin cell proliferation potential. 2h-SPEEK portrayed the highest proliferative potential for HaCaT keratinocytes and fibroblasts. It was aimed for the tailored release of bio-actives from the spatiotemporally designed Aloe vera incorporated 2h-SPEEK nanoscaffold to accelerate the skin wound regeneration. FTIR, EDX and XRD analyses revealed the effective incorporation of Aloe vera in the electrospun nanofibers. SEM analysis revealed the nano-topographical morphology with highly porous, dense and interconnected fibrous structures mimicking the skin ECM. The regulated delivery of Aloe vera demonstrated the biocompatibility of the nanofibrous scaffold in skin keratinocytes (HaCaT) and fibroblasts (3T3) cells through in vitro analysis proving its non-toxic properties. Further, the fabricated nanoscaffolds exhibited excellent anti-microbial efficacy towards the tested human skin pathogenic microbes. The results of in vivo studies in Wistar rat model exhibited scar-less wound healing with complete wound closure. Thus, this nanofiber based drug delivery system implicitly acts as a skin like ECM, bio-mimicking the topographical and chemical cues of the natural skin tissues paving way for a complete regeneration and integration of the injured area strengthening the functional restoration of insulted cells around the wound area.

Nanocomposite membrane and microbial community analysis for improved performance in microbial fuel cell

To improve the performance of a microbial fuel cell (MFC), four variations of sulphonated silicon dioxide (S-SiO2) was incorporated into sulphonated poly ether ether ketone (SPEEK) membranes. S-SiO2 was characterized by scanning electron microscopy (SEM), fourier transform infra-red spectroscopy (FTIR) and X-ray diffraction (XRD) to confirm morphological, physical and chemical characteristics. The prepared membranes were incorporated into a fabricated tubular MFC of 300 mL holding capacity. Membrane characterizations such as water uptake, ion exchange capacity (IEC) and proton conductivity were determined. The highest maximum output of 154 ± 1.5 mW m−2 is produced by SPEEK +7.5 wt% S-SiO2 with an IEC of 1.82 ± 0.08 meq g-1 and an oxygen mass transfer coefficient of 1.42 × 10−6 cm s-1. Microbial community studies show the prevalence of novel microbial strains with the predominance of 3 distinct phyla, namely Betaproteobacteria, Gammaproteobacteria and Firmicutes. The results suggest that the prepared nanocomposite membrane proves to be an efficient and sustainable alternative for improving the performance of a MFC without abating the essential membrane characteristics.

Investigation of a cation exchange membrane comprising Sulphonated Poly Ether Ether Ketone and Sulphonated Titanium Nanotubes in Microbial Fuel Cell and preliminary insights on microbial adhesion

Hydrothermally synthesized Titanium Nanotubes (TNTs) are sulphonated and characterized to confirm their morphological, physical and chemical characteristics. Different weight percentages (2.5, 5, 7.5 and 10 wt%) of Sulphonated TNTs (S-TNTs) are introduced into Sulphonated Poly Ether Ether Ketone (SPEEK) where the negative channels that form with the aid of sulphonic acid groups play an essential criterion for the improved proton conductivity and better water holding capacity. A tubular-designed Microbial Fuel Cell (MFC) of 300 mL volume is fabricated to test the potentiality of the self-assembled inorganic and functionalized Titanium nanotubes incorporated SPEEK membranes. SPEEK + 7.5% S-TNT exhibits a maximum power density of 121 mW m−2 with higher ion exchange capacity of 3.2 meq g−1 and lower internal resistance of 30 Ω. Biofouling investigation after 3 weeks of operation reveals that the optimized membrane displays better proton conductivity with an electrochemically stable biofilm without deteriorating the essential membrane characteristics. Preliminary microbial studies reveal the dominance of gram negative bacteria accelerating the rate of enriched extra-electrogen transfer (EET) to the anode enabling better MFC performance.

Non-invasive macroscopic and molecular quantification of water in Nafion® and SPEEK Proton Exchange Membranes using terahertz spectroscopy

Hydration of Proton Exchange Membranes (PEM) is vital in PEM fuel cells as it is critical in determining the overall proton conductivity. Traditional gravimetric analysis to quantify PEM's hydration is cumbersome, demands contact and importantly cannot differentiate the nature of water - bulk, bound or free water. As terahertz spectroscopy probes bulk and free water relaxations' contributions, it is an attractive non-invasive technique for studying membrane hydration dynamics - water uptake and retention. Here, THz spectroscopy measurements for hydrated Nafion® and sulphonated Polyether Ether Ketone (sPEEK) membranes in ambient atmosphere have been carried out for 100 minutes. Variation in THz absorption by the hydrated membranes with time is used for non-invasive estimation of percentage water content demonstrating good agreement with gravimetric measurements. In addition, proportion of bulk, bound and free water with time has been estimated by fitting the complex permittivity using double Debye model. Results show that % water content in hydrated sPEEK at 0th minute is 2.36 times than hydrated Nafion due to its higher porosity. Further, sPEEK has better water retention capability, especially higher bound water proportion at longer time intervals (85% more at 100th minute) than Nafion due to the presence of widely distributed small pores and comparatively stronger hydrogen bonding between the sulphonic acid and water. Thus, THz spectroscopy can be employed as an effective non-invasive tool for macroscopic and molecular quantification of water in hydrated PEMs.

Synthesis characterization and performance evaluation of tungstic acid functionalized SBA-15/SPEEK composite membrane for proton exchange membrane fuel cell

Mesoporous Santa Barbara Amorphous (SBA-15) was synthesized and covalently bonded with tungstic acid group using a simple two-step process involving chloromethylation, followed by reaction with disodium tungstate. The tungstic acid functionalized SBA-15 (W-SBA-15) was characterized using FTIR, solid-state 13C CP/MAS NMR, low-angle XRD, SEM, TEM and BET analyses. Sulphonated poly ether ether ketone (SPEEK) was chosen as a base membrane for fabricating the composite membranes. Composite W-SBA-15/SPEEK membranes were prepared with different filler concentrations (2, 4, 6 and 8%) of W-SBA-15. Various studies such as water uptake, ion exchange capacity and proton conductivity of the composite membranes were carried out with respect to fuel cell applications. From the studies, it was found that the W-SBA-15/SPEEK membrane with wt. 6% of filler exhibited superior electrochemical properties. Finally, membrane electrode assembly (MEA) fabricated using 6% W-SBA-15/SPEEK composite membrane, Pt anode and Pt cathode was tested in an in-house built fuel cell setup of area 25 cm2. A maximum power density of 405 mW/cm2 and open circuit voltage of 0.95 V were achieved at 80 °C.

Preliminary Study of the Use of Sulphonated Polyether Ether Ketone (SPEEK) as Proton Exchange Membrane for Microbial Fuel Cell (MFC)

Sulfonated polyether ether ketone (SPEEK) was utilized as a proton exchange membrane (PEM) in Microbial Fuel Cell (MFC). The SPEEK performance in producing electricity had been observed in MFC using wastewater and glucose as substrates. The MFC with catering and tofu wastewater produced maximum power density about 0.31 mW/m2 and 0.03 mW/m2, respectively, lower that of MFC with tapioca average power density of 39.4 W/m2 over 48 h. The power density boosted because of the presence of Saccharomyces cerevisiae as inoculum. The study using of S. cerevisiae and Acetobacter acetii, separately, were also conducted in with glucose as substrate. The MFC produced an average power densities were 7.3 and 6.4 mW/m2 for S. cerevisiae and A. acetii, respectively. The results of this study indicated that SPEEK membrane has the potential usage in MFCs and can substitute the commercial membrane, Nafion.Article History: Received: Juni 14th 2017; Received: Sept 25th 2017; Accepted: December 16th 2017; Available onlineHow to Cite This Article: Putra, H.E., Permana, D and Djaenudin, D. (2018) Preliminary Study of the Use of Sulfonated Polyether Ether Ketone (SPEEK) as Proton Exchange Membrane for Microbial Fuel Cell (MFC). International Journal of Renewable Energy Development, 7(1), 7-12.https://doi.org/10.14710/ijred.7.1.7-12

The effect of temperature on the permeation properties of Sulphonated Poly (Ether Ether) Ketone in wet flue gas streams

Membrane technology can be used to recover high purity water from power station flue gas streams. In this work, the effect of temperature on water vapour and CO2 permeation properties of Sulphonated Poly (Ether Ether) Ketone (SPEEK) with two different ion exchange capacities were investigated (IEC 1.6meq/g and 1.9meq/g). It was found that both permeabilities increased with increasing water activity due to increased water solubility as water concentration increased. SPEEK with IEC 1.9meq/g exhibited higher water permeability and selectivity than IEC 1.6meq/g. At humidities greater than 50%, both water vapour and CO2 permeabilities also increased as temperature increased up to 50°C due to the increase in diffusion of the penetrating molecules. However as temperature increased further, a significant drop in the permeability of both water and carbon dioxide occurred. This decrease was attributed to the formation of water clusters that filled the free volume in the polymer and hindered the diffusion of isolated molecules. This decrease in diffusion coupled with a reduction in solubility with increasing temperature resulted in the performance decline.

Sulfonated poly ether ether ketone with different degree of sulphonation in microbial fuel cell: Application study and economical analysis

A microbial fuel cell (MFC) is a device for the simultaneous treatment of wastewater and the generation of electricity with the aid of microorganisms as a biocatalyst. Membranes play an important role in the power generation of microbial fuel cells. Nafion 117, the most common proton exchange membrane (PEM), is expensive and this is the main obstacle for commercialization of MFC. In this study, four kinds of sulphonated poly ether ether ketone (SPEEK) with different degrees of sulphonation (DS) referred to hereafter as SPEEK 1 (DS = 20.8%), SPEEK 2 (DS = 41%), SPEEK 3 (DS = 63.6%), and SPEEK 4 (DS = 76%), were fabricated, characterized and applied in an MFC. The membranes were characterized by thermogravimetric analysis TGA) and differential scanning calorimetry (DSC) and their morphologies were observed by scanning electron microscopy (SEM). The degree of sulphonation was determined by nuclear magnetic resonance (NMR). Then the membranes were applied to the MFC system. The results indicated that the power produced by MFC with SPEEK 3 (68.64 mW/m2) was higher than with the other SPEEK membranes while it was lower than with Nafion 117 (74.8 mW/m2). SPEEK3 also had the highest chemical oxygen demand removal (91%) and coulombic efficiency (26%) compared to other SPEEK membranes. The cost evaluation suggests that application of SPEEK 3 is more cost effective than applications of the other types of SPEEK and Nafion 117, due to its high power density generation per cost.

Enhancement of current density using effective membranes electrode assemblies for water electrolyser system

The goal of this study was to develop and design a composite proton exchange membrane (PEM) and membrane electrode assembly (MEA) that are suitable for the PEM based water electrolysis system. In particular, it focuses on the development of sulphonated polyether ether ketone (SPEEK) based membranes and caesium salt of silico-tungstic acid (CsSiWA) matrix compared with one of the transition metal oxides such as titanium dioxide (TiO2), silicon dioxide (SiO2) and zirconium dioxide (ZrO2). The resultant membranes have been characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, ion exchange capacity (IEC), water uptake and atomic force microscopy. Comparative studies on the performance of MEAs were also conducted utilizing impregnation-reduction and conventional brush coating methods. The PEM electrolysis performance of SPEEK-CsSiWA-ZrO2 composite membrane was more superior than that of other membranes involved in this study. Electrochemical characterization shows that a maximum current density of 1.4 A/cm2 was achieved at 60 °C, explained by an increased concentration of protonic sites available at the interface.

Mechanical Properties of Composite SPEEK Polymer Membranes Modified with Ionic Liquids

In this work, the mechanical properties of sulphonated polyetheretherketone (SPEEK) membranes impregnated with 3 different ionic liquids (1-butyl-2,3-dimethyl- imidazolium dimethylphosphate ([BMMIM][Me2PO4])), 1,2,3-trimethylimidazolium dimethylphosphate ([MMMIM][Me2PO4])), 1,3-dimethylimidazolium dimethylphosphate ([MMIM][Me2PO4])) have been investigated.Prepared SPEEK/ionic liquid composite membranes are characterized by mechanical testing both in room and elevated temperatures. It was found that the stiffness and tensile strength of composites decreased by increasing the content of ionic liquid and the length of alkyl radical in ionic liquid as well as by increasing the temperature.

Development of MFC using sulphonated polyether ether ketone (SPEEK) membrane for electricity generation from waste water

Polyether ether ketone was sulphonated polyether ether ketone (SPEEK) and utilized as a proton exchange membrane (PEM) in a single chamber MFC (SCMFC). The SPEEK was compared with Nafion® 117 in the SCMFC using Escherichia coli. The MFC with the SPEEK membrane produced 55.2% higher power density than Nafion® 117. The oxygen mass transfer coefficient ( K O) for SPEEK and Nafion® 117 was estimated to be 2.4 × 10 −6 cm/s and 1.6 × 10 −5 cm/s, respectively resulting in reduced substrate loss and increased columbic efficiency (CE) in the case of SPEEK. When the dairy and domestic waste water was treated in SPEEK–SCMFC, fitted with a membrane electrode assembly (MEA), a higher maximum power density was obtained for dairy waste water (5.7 W/m 3). The results of this study indicate that SPEEK membrane has the potential to greatly enhance the efficiency of MFCs.

Effect of a Proton Conducting Filler on the Physico‐Chemical Properties of SPEEK‐Based Membranes

AbstractComposite membranes based on sulphonated polyetherether ketone (SPEEK) having a 60% degree of sulphonation (DS = 0.6) and containing 23 and 50 wt.‐% hydrated tin oxide (SnO2·nH2O) were prepared and characterised. The lower water uptake (WU) and the higher conductivity values recorded for the composite membranes with respect to pure SPEEK reference suggested the involvement of SnO2·nH2O in the proton conduction mechanism. Pulsed‐field‐gradient spin‐echo (PFGSE) NMR was employed to obtain a direct measurement of water self‐diffusion coefficient in the membranes. Differences were observed between the unfilled SPEEK and the composites, including departures from the normal correlation between water diffusivity and proton conductivity in the case of composites. To better understand the SnO2·nH2O effect on the proton transport properties of the SPEEK‐based membrane, we employed an analytical model that predicts the membrane conductivity as a function of its hydration level and porous structure. The comparison of the model results with the experimental proton conductivity values demonstrated that the tin oxide phase provides additional paths between the water clusters for proton transport, resulting in reduced tortuosity and enhanced proton conductivity. Moreover, the composite showed reduced methanol crossover with respect to the unfilled membrane.

SULPHONATED POLY ETHER ETHER KETONE/POLYVINYL ALCOHOL/PHOSPHOTUNGSTIC ACID COMPOSITE MEMBRANES FOR PEM FUEL CELLS

Composite membranes with polyvinyl alcohol (PVA), sulphonated poly ether ether ketone (SPEEK) and phosphotungstic acid (PWA) were prepared using solvent casting method. The proton conductivities of such membranes were found to be in the order of 10–3S/cm in the fully hydrated condition at room temperature as measured by impedance spectroscopy. The crystalline properties were studied by X-ray diffraction analysis. The thermal properties were determined by TGA and DSC techniques. The tensile strength and percentage elongation were obtained from UTM studies. Water and methanol uptake of these membranes were studied.

Role of membrane surface in concentration polarization at cation exchange membranes

Cation exchange membranes made of blends of sulphonated polyetherether ketone (S-PEEK) and poly(ether sulphone) (PES) were thoroughly characterized with respect to their concentration polarization properties. Current–voltage curves and chronopotentiometry reveal some extent of membrane heterogeneity. Membranes cast on a glass plate and dried in air are characterized and the current–voltage curves are determined for each of the two membrane sides (glass side contact and air side contact). Detailed analysis of the plateau length at the limiting current density reveals differences as the orientation of the membrane towards the feed is changed. The plateau length of the air side of the membrane always shows larger values compared to the glass side. Moreover, we discovered that the plateau length of the glass side remains constant whereas the air side value increases over a period more than 500 h approaching a quasi-equilibrium value, asymptotically. These data are the first ones suggesting an influence of orientation on the concentration polarization behavior as well as relaxation phenomena occurring in cation exchange membranes. The paper discusses strategies to gain new fundamental insight in the relationship between membrane morphology and transport properties by for instance microstructuring the surface.