Proton Conductivity Of Membranes Research Articles

Effect of zinc oxide on the mechanical, thermal and physiochemical properties of chitosan-based hybrid membrane for DMFC application

This work uses zinc oxide (ZnO) as a filler to prepare a chitosan-based hybrid membrane. The mechanical, thermal and physiochemical properties of the membranes were studied using different experimental techniques. The water uptake capacity and swelling degree of the composite membranes were increased whereas ion exchange capacity (IEC) decreases with the increase of ZnO content. The ZnO filler reduces the crystalline phase of the hybrid membranes. The hybrid membrane's proton conductivity was measured by EIS experiment and fitted into a comparable circuit model. The ZnO filler improves the membrane's proton conductivity, and the proton transport is controlled by the Grotthus mechanism.

A high-efficiency electrochemical proton-conducting membrane reactor for ammonia production at intermediate temperatures

•Efficient electrochemical nitrogen reduction is successfully achieved at 350°C •The NH3 production and H2 purification processes are coupled in one reactor •The in situ supplied protons greatly accelerate the NH3 production rate Ammonia is a ubiquitous chemical raw material and hydrogen carrier with a wide range of industrial applications, which is mainly derived from the energy-intensive Haber-Bosch process. Herein, a high-efficiency ammonia synthesis technology through an excellent CO2-tolerant La5.5WO11.25 − δ (LWO) membrane reactor has been developed to improve electrocatalytic nitrogen reduction reaction performance by coupling with hydrogen purification at intermediate temperatures. From molecular hydrogen, the produced protons can be supplied in situ for ammonia synthesis by nitrogen hydrogenation. As a result, the superior ammonia synthesis performance with the highest Faradaic efficiency (FE) of 43.8% and corresponding ammonia rate of 231.1 μg h−1 cm−2 is achieved at 2,500 μA cm−2 at 350°C. This promising electrochemical membrane reactor for ammonia production at intermediate temperatures provides a feasible direction to promote the development of the ammonia synthesis industry. Ammonia is a ubiquitous chemical raw material and hydrogen carrier with a wide range of industrial applications, which is mainly derived from the energy-intensive Haber-Bosch process. Herein, a high-efficiency ammonia synthesis technology through an excellent CO2-tolerant La5.5WO11.25 − δ (LWO) membrane reactor has been developed to improve electrocatalytic nitrogen reduction reaction performance by coupling with hydrogen purification at intermediate temperatures. From molecular hydrogen, the produced protons can be supplied in situ for ammonia synthesis by nitrogen hydrogenation. As a result, the superior ammonia synthesis performance with the highest Faradaic efficiency (FE) of 43.8% and corresponding ammonia rate of 231.1 μg h−1 cm−2 is achieved at 2,500 μA cm−2 at 350°C. This promising electrochemical membrane reactor for ammonia production at intermediate temperatures provides a feasible direction to promote the development of the ammonia synthesis industry.

Self-Phosphorylated Polybenzimidazole: An Environmentally Friendly and Economical Approach for Hydrogen/Air High-Temperature Polymer-Electrolyte Membrane Fuel Cells.

The development of phosphorylated polybenzimidazoles (PBI) for high-temperature polymer-electrolyte membrane (HT-PEM) fuel cells is a challenge and can lead to a significant increase in the efficiency and long-term operability of fuel cells of this type. In this work, high molecular weight film-forming pre-polymers based on N1,N5-bis(3-methoxyphenyl)-1,2,4,5-benzenetetramine and [1,1'-biphenyl]-4,4'-dicarbonyl dichloride were obtained by polyamidation at room temperature for the first time. During thermal cyclization at 330-370 °C, such polyamides form N-methoxyphenyl substituted polybenzimidazoles for use as a proton-conducting membrane after doping by phosphoric acid for H2/air HT-PEM fuel cells. During operation in a membrane electrode assembly at 160-180 °C, PBI self-phosphorylation occurs due to the substitution of methoxy-groups. As a result, proton conductivity increases sharply, reaching 100 mS/cm. At the same time, the current-voltage characteristics of the fuel cell significantly exceed the power indicators of the commercial BASF Celtec® P1000 MEA. The achieved peak power is 680 mW/cm2 at 180 °C. The developed approach to the creation of effective self-phosphorylating PBI membranes can significantly reduce their cost and ensure the environmental friendliness of their production.

Copolymer of VDF/TFE as a Promising Polymer Additive for CsH2PO4-Based Composite Electrolytes.

The composite polymer electrolytes (1-x)CsH2PO4-xF-2M (x = 0-0.3) have been first synthesized and their electrotransport, structural, and mechanical properties were investigated in detail by impedance, FTIR spectroscopy, electron microscopy, and X-ray diffraction methods. The structure of CsH2PO4 (P21/m) with salt dispersion is retained in the polymer electrolytes. The FTIR and PXRD data are consistent, showing no chemical interaction between the components in the polymer systems, but the salt dispersion is due to a weak interface interaction. The close to uniform distribution of the particles and their agglomerates is observed. The obtained polymer composites are suitable for making thin highly conductive films (60-100 μm) with high mechanical strength. The proton conductivity of the polymer membranes up to x = 0.05-0.1 is close to the pure salt. The further polymers addition up to x = 0.25 results in a significant decrease in the superproton conductivity due to the percolation effect. Despite a decrease, the conductivity values at 180-250 °C remain high enough to enable the use of (1-x)CsH2PO4-xF-2M as a proton membrane in the intermediate temperature range.

Hydrocarbon-Based Composite Membrane Using LCP-Nonwoven Fabrics for Durable Proton Exchange Membrane Water Electrolysis.

A new hydrocarbon-based (HC) composite membrane was developed using liquid crystal polymer (LCP)-nonwoven fabrics for application in proton exchange membrane water electrolysis (PEMWE). A copolymer of sulfonated poly(arylene ether sulfone) with a sulfonation degree of 50 mol% (SPAES50) was utilized as an ionomer for the HC membranes and impregnated into the LCP-nonwoven fabrics without any surface treatment of the LCP. The physical interlocking structure between the SPAES50 and LCP-nonwoven fabrics was investigated, validating the outstanding mechanical properties and dimensional stability of the composite membrane in comparison to the pristine membrane. In addition, the through-plane proton conductivity of the composite membrane at 80 °C was only 15% lower than that of the pristine membrane because of the defect-free impregnation state, minimizing the decrease in the proton conductivity caused by the non-proton conductive LCP. During the electrochemical evaluation, the superior cell performance of the composite membrane was evident, with a current density of 5.41 A/cm2 at 1.9 V, compared to 4.65 A/cm2 for the pristine membrane, which can be attributed to the smaller membrane resistance of the composite membrane. From the results of the degradation rates, the prepared composite membrane also showed enhanced cell efficiency and durability during the PEMWE operations.

Role of Side-Chain Lengths on Hydronium Mobility in Sulfonated Poly(ether sulfone) Proton-Conducting Model Membranes

Role of Side-Chain Lengths on Hydronium Mobility in Sulfonated Poly(ether sulfone) Proton-Conducting Model Membranes

Crosslinked poly (isatin biphenyl spirofluorene) membranes for proton conduction over a wide temperature range from −40 to 160 °C

It is desired to develop proton exchange membranes (PEMs) working in a wide temperature range considering the practical working condition of devices using the PEMs as the electrolyte. Herein, a novel polymer of poly (isatin biphenyl spirofluorene) (PIBS) is first synthesized and it is afterwards crosslinked by 1,3-bis(4-piperidyl) propane (P) to fabricate membranes. The membranes can work in a temperature range of −40 to 160 °C after doping with phosphoric acid (PA). The proton conductivity of the PA doped membrane reaches 4.4 × 10−3 S cm−1 at −40 °C under 80% relative humidity (RH) and 0.16 S cm−1 at 160 °C without humidifying. We demonstrate the uses of the prepared PA doped PIBS-P membranes as membrane electrolytes in single fuel cells within 100–160 °C under anhydrous condition, and in water electrolytic cells within −20 to 60 °C, respectively.

Thermal-Tolerant CdPS3-Polybenzimidazole Membranes with High Proton Conductivity

Thermal-tolerant proton-exchange membranes are highly demanded for updating hydrogen–electricity conversion technologies, since the high-temperature operation is expected to suppress the catalyst poisoning of fuel cells or to increase the efficiency of water (steam) electrolysis. But it is still challenged by both stability and conductivity. Herein, two-dimensional CdPS3 nanosheets with atomically in-plane defects were synthesized and employed for the preparation of proton-conductive and thermal-tolerant membranes with polybenzimidazole (PBI). Ultrathin and Cd vacancy-containing CdPS3 two-dimensional (2D) nanolayers were successfully obtained from bulk CdPS3 crystals by ion treatments. The resultant CdPS-PBI hybrid membranes exhibit reliable long-term conductivity stability for 170 h at 180 °C and a maximum proton conductivity of 539 mS cm–1 at 200 °C, which is 1 order of magnitude higher than PBI membranes and the reported polymeric membranes. The proton-transport performance over hybrid membranes was ascribed to abundant proton donor centers, easy proton desorption, and excellent hydration of Cd vacancies on CdPS nanolayers. Therefore, the CdPS-PBI membranes with well-proven chemical/mechanical/thermal stabilities and high proton conductivity would meet the requirements of proton-exchange membranes (PEMs) for high-temperature operations.

Metal organic framework enroutes to mechanically stable and high proton conductive polybenzimidazole membranes

Different contents of metal-organic framework (3, 5, 7, 10 and 12 wt % and MOF is HKUST-1) were incorporated into cyclohexane dicarboxylic acid based polybenzimidazole (Cy-PBI). In the composite membranes, the interaction between MOF and PBI polymer resulted in peak broadening as observed in FTIR spectra (2000–3000 cm−1). The recorded proton conductivity of CM-7 at 160 °C (224 mS/cm) was almost two fold to that of pristine PBI membrane (114 mS/cm and surprisingly high mechanical strength was displayed (Tensile modulus: 671 MPa, elongation 69% under doped condition). Minimum swelling behaviour and high doping level gives the evidence that acid molecules (proton carriers) are housed within the MOF cavities those would act as proton hopping centres. The FESEM images of the composite membrane (CM-7) displayed a uniform distribution of MOF within the matrix, complementing the enhanced properties observed. This work exemplifies the mediating role of MOF in improving the conductivity of PBI membranes.

Solid-state synthesis of intrinsically proton-conducting covalent organic framework membrane

Ionic covalent organic framework (iCOF) membranes are attractive for a myriad of applications. Here, we report a mechanochemistry-based solid-state synthesis method to fabricate iCOF membranes with simplicity, scalability and sustainability. Time-dependent experiments reveal that the iCOF membrane formation process includes the structural transformation from disorder to order and the morphology change to the dense structure formed by the restacking of nanosheet-like crystallites simultaneously. The obtained free-standing iCOF membranes demonstrate high ion exchange capacity, mechanical strength and comparable proton conductivity, benefiting from the rigid crystalline framework structure and one-dimensional channels decorated with abundant proton-conducting sites. This work paves the way for synthesis of iCOF membranes in a simple and environmentally friendly manner.

Цифровая осциллография полимерных мембран с протонной проводимостью

Polyvinyl alcohol-based cast membranes have promising application in creating commonly available fuel cells and fuel synthesizers, as well as inexpensive water sources and microelectromechanical systems. In order to control the properties of such membranes a deep understanding of the charge transfer mechanisms and their relationship with the structure formed at a certain composition and manufacturing technology is required. A method for studying the structure of the proton-conductive polymer membranes using digital oscillography of ion currents excited by the low-frequency rectangular pulses with the amplitudes below the threshold voltage of the ionic conductivity in a dehydrated membrane, and for the analysis of the resulting ion current pulses (spikes) in the frames of the model of a proton pump acting in each layer of the membrane is proposed in this paper. Fast Fourier transform of these oscillograms reveals from 2 to 4 branches or spike sequences corresponding to the phases with different ionic conductivity and makes it possible to determine the thicknesses of both high-conductivity phase layers (7–30 µm) and low-conductivity phase interlayers (1–7 µm) formed in the process of polymerization. The reason of spike merging into bursts is described in terms of successively induced increase in the excited proton density over a threshold value in highly conductive layers. The resonance observed in dry proton membranes at the frequencies of about 2.2 to 3.0 kHz is interpreted as the burst merge point with the further increase in impedance due to proton lagging and respective decrease in the effective thickness of active layers. The effective charge carrier concentrations (as small as 1012 to 1013 cm−3) and the velocity (from 5 to 18 cm/s for the highly conductive phases which turned out to be much higher than those observed in solutions) are estimated. The asymmetry of the cast membranes, which becomes apparent at low frequencies and causes the generation of a direct ion current in response to excitation by a purely alternating current, is studied. It is found that the apparent conductivity determining contribution to the total ohmic resistance is made by a thin interlayer with a very low ion velocity, presumably surface layer, rather than the main layers. The conclusion on the optimization of the production technology and the composition of the proton membranes for various applications is made.

Microwave sintering coupled with sintering aids for proton-conducting oxide membranes

The BaCe0·4Zr0·4Y0·2O3 (BCZY) was modified with the NiO sintering aid and prepared by a microwave sintering (MVS) method as the electrolyte for proton-conducting solid oxide fuel cells (H–SOFCs). The incorporation of NiO into the BCZY lattice improves the sinterability of the material, leading to the increase of the shrinkage from 3% to 26% after the high-temperature sintering. The dense BaCe0·4Zr0·4Y0·15Ni0·05O3 (BCZYN) pellet can be obtained after sintering at 1500 °C, whereas the Ni-free BCZY is porous after sintering at the same condition. By further using the MVS method, the BCZYN can be densified at 1300 °C, which is 200 °C lower than conventional sintering. Furthermore, the microwave-sintered BCZYN has a higher conductivity than the conventionally sintered one due to the larger grain size. Using the MVS method in the H–SOFCs fabrication, the high porosity of the anode substrate can be retained. In contrast, the cell prepared by the conventional sintering (CS) method has a relatively dense anode, which is detrimental to gas fuel transportation. As a result, the microwave sintered cell exhibits an output of 1010 mW cm−2 at 700 °C, which is significantly larger than that for the conventionally sintered cell, being 535 mW cm−2 at the same testing condition, suggesting the advantage of using the MVS method for the fuel cell fabrication.

In-situ growth of PPy/MnOx radical quenching layer for durability enhancement of proton exchange membrane in PEMFCs

Proton exchange membrane fuel cells (PEMFCs), which exhibit low environmental impact and high power density, have attracted considerable interest as clean and efficient energy conversion technology. However, the oxidative degradation of the proton exchange membrane (PEM) by in-situ generated peroxide and hydroxyl free radicals commonly leads to performance losses in PEMFC. To alleviate the chemical attack on PEM, we report an antioxidant approach to growing a polypyrrole/manganese dioxide (PPy/MnOx) radical quenching layer on a highly proton conductive membrane surface. The resulting PEM displays improved durability in PEMFC compared with the pristine membrane, as evidenced by at least 150 h stable discharging performance in an H2/O2 PEMFC at a current density of 200 mA cm−2 at 80 °C and a much slower open circuit voltage (OCV) decay. Moreover, the ex-situ conductivity and in-situ fuel cell test indicate that the porous radical quenching layer has a tiny impact on the fuel cell performance. The resultant H2/O2 PEMFC single cell containing the chemically stable PEM exhibits a promisingly high power density of over 900 mW cm−2 at 80 °C with 100% RH.

A Study on the Synthesis and Proton Transport Behavior of Multilayered ZSM-5 Zeolite Nanosheet Membranes Laminated on Polymer Substrates

Single crystalline ZSM-5 ZNs with thicknesses around 6 nm were obtained by secondary growth of silicalite nanoparticles using diquaternary bis-1,5(tripropyl ammonium) pentamethylene diiodide (dC5) as a structure-directing agent (SDA). The dC5 could be effectively removed from the ZN pores by either high-temperature calcination or UV irradiation in air at room temperature but not by the piranha solution treatment. Ultrathin ZN-laminated membranes (ZNLMs) were fabricated by sandwiching a UV-activated multilayered ZN film between two recast Nafion® layers (ZNLM-Nafion) and by filtration coating from a suspension of thermally activated ZNs on a nonionic porous PVDF (ZNLM-PVDF). The ZNLMs on both supports demonstrated the ability of highly proton-selective ion conduction with low resistances in aqueous electrolyte solutions. The ZNLM-PVDF with PVDF binder was structurally stable, and it achieved a comparably low ASR but much higher proton selectivity compared with a Nafion membrane of same overall thickness. However, detachment between the ZNLM and Nafion layers occurred when the ZNLM-Nafion operated in aqueous electrolyte solutions. Results of this study show the potential for developing ZNLMs as efficient proton-conducting membranes without using expensive ionic polymer matrices. However, the development of polymer-supported ZNLMs is hindered by the current inefficiency in preparing well-dispersed suspensions of open-pore ZNs. Future development of efficient methods for synthesizing open-pore ZNs in dispersed states is key to realizing high-performance ZNLMs on polymers.

High performance bismuth oxide embedded sulfonated poly ether sulfone composite membranes for fuel cell applications

Organic-inorganic sulfonated poly(ether sulfone) (SPES)-bismuth oxide (Bi2O3) composite membranes were prepared by the facile solution casting method. Poly(ether sulfone) (PES) polymer was sulfonated using concentrated sulfuric acid as a sulfonating agent and the degree of sulfonation was found to be 42.6%. Structural analysis of prepared samples was characterized using FT-IR, proton NMR, XRD, GPC, SEM and XPS. Physicochemical properties like water uptake, ion exchange capability, thermal properties and proton conductivity of pristine and composite membranes were analyzed. The ion-exchange capacity of the prepared electrolyte membranes was found in the range between 1.5 and 2.4 meq g−1. SPES composite membrane loaded with 6 wt.% Bi2O3 displayed the highest ionic conductivity of 0.045 S cm−1 than the pristine membrane (0.023 S cm−1). The overall results validate that the impregnation of Bi2O3 into SPES polymer exhibits good performance over the neat membrane. This research demonstrates that SPES/Bi2O3 composite membranes are viable electrolytes for fuel cell practice.

Enhanced proton conductivity and power density of HT-PEMFCs using tin pyrophosphate microparticles-dispersed polybenzimidazole composite electrolyte membranes

Proton conductivity and acid retention property of PBI-based polymer electrolyte membrane is critical factor for high-temperature PEMFCs with high performance. The present study was undertaken in order to demonstrate the effect of SnP2O7 microparticles incorporation for the PBI-based membrane to the fuel cell performance. Besides, the correlation between dispersion property of additives and fuel cell performance was investigated, by taking the larger particle sizes of Sn-originated material into account. Highly dispersed SnP2O7 microparticles derived by the wet mechanochemical treatment has resulted in the novel PBI-based composite membrane with high-proton conductivity (4.17 mS cm−1 at 160 °C, anhydrous) and superior acid retention property. Consequently, the highest peak power density of 373 mW cm−2 at 160 °C under anhydrous conditions was achieved for the composite membrane with wet-mechanical milled SnP2O7, while the membrane without mechanochemical treatment showed lowest peak power density (168 mW cm−2) even inferior to the pure PBI membrane. Investigations into the PBI-based composite electrolyte membrane incorporated with highly dispersed SnP2O7 protonic conductive microparticles have yielded a performance enhancement of high-temperature PEMFCs.

Structural Features of 4-VP-HEMA-SiO<sub>2</sub> Hybrid Membranes and Their Proton Conductivity

Hybrid organic-inorganic membranes based on tetraethoxysilane and orthophosphoric acid-doped copolymers of 4-vinylpyridine (4-VP) and 2-hydroxyethyl methacrylate (HEMA) were formed by the sol-gel synthesis method. The membranes are characterized by high values of exchange capacity and proton conductivity. An increase in the proton conductivity of hybrid organo-inorganic membranes compared to the initial copolymer can be associated with the generation of water of crystallization during the formation of a silicon dioxide fragment, which follows from quantum-chemical modeling of the local structure of the membrane, which includes an organic part from the copolymerization product of 4-VP with HEMA (44 atoms) and an inorganic part of 27 atoms, repeating the structure of the silicon dioxide block.

Advanced hybrid polybenzimidazole membrane enabled by a “linker” of metal-organic framework for high-performance vanadium flow battery

High current density vanadium flow batteries (VFBs) are important for the wide range of applications of renewable energy. The balance between proton conductivity and vanadium permeability of proton exchange membrane has been a huge challenge for the development of high-power density VFBs. Herein, a post-synthetic modification of Zr-MOFs (PSM) is introduced into PBI matrix to break the trade-off between vanadium permeability and ion selectivity, and remarkably improves the power density of VFBs. As a “linker” between the PBI backbone, the PSM creates more proton transport sites in the hybrid membrane, which significantly increases the proton conductivity. Meanwhile, the “acid-base” pairs are formed between PSM and PBI matrix, further promoting the proton transfer in the hybrid membrane. More importantly, the denser structure of hybrid membrane blocks the vanadium ion permeation based on the Donnan exclusion and size sieving effect, respectively. In consequence, the ion selectivity of the PBI/PSM hybrid membrane is substantially improved, almost four times that of the pure PBI membrane. Benefiting from such rational design, the VFB equipped with the PBI/PSM hybrid membrane exhibits an excellent energy efficiency of 75.4% at 500 mA cm−2, and at 300 mA cm−2, the energy efficiency can reach 81.2%, and the efficiency stability can maintain 600 cycles in charge and discharge. Consequently, the use of “linker” offers a very prospective strategy for the development of high-performance proton exchange membrane.

Incorporating functionalized graphene oxide in green material-based membrane for proton exchange membrane fuel cell application

A novel organic-inorganic nanocomposite membrane with green material based is prepared by incorporating sulfonated holey graphene oxide (SHGO) into nanocrystalline cellulose/polyvinyl alcohol (NCC/PVA) matrix as polymer electrolyte membrane (PEMs) via solution casting method. Introducing sulfonic acid group in graphene oxide (GO) yielded sulfonated graphene oxide (SGO) and the hole effect on the graphitic plane of GO for SHGO on NCC/PVA significantly improves the proton conductivity of membranes by creating more interconnected proton transfer channels and promoting proton transfer across the membrane. Highest proton conductivity values of 1.1 × 10-2 S cm-1 is obtained by NCC/PVA-SHGO-1.0 at 80o C under 100% relative humidity (RH). Additionally, mechanical and chemical stability tests indicate an enhancement in those properties. However, hydrogen permeation has slightly increase due to the hole effect. Increasing SHGO loading in NCC/PVA has improve its properties and performance. At 80o C, under 100% RH, NCC/PVA-SHGO-1.0 exhibit the highest power density and current density of 31.4 mW/cm2 and 60.2 mA/cm2, respectively which is three times higher compared to pristine NCC/PVA. This work summarise that incorporating SHGO into NCC/PVA membranes can significantly improves its properties, performance and membrane durability which entitle them as a potential candidate for PEMs.

Modeling and optimization of fuel cell systems combined with a gasifier for producing heat and electricity

In this research, a proton-conducting membrane fuel cell is used in conjunction with a gasifier for producing electricity with air considered as the gasification agent. The simultaneous electricity, heat, and hot water generation of these two when coupled with an Organic Rankine Cycle (ORC) installed within a Thermoelectric Generator (TEG) was studied. Additionally, to utilize the electricity generated from various parts of the process; i.e. the fuel cell, organic Rankine cycle turbine, and the thermoelectric generator, the reverse osmosis (OR) water desalination unit was coupled to the process. The aforementioned system was studied and analyzed based on thermodynamic and thermos-economic aspects. A parametric study was also carried out to analyze the effect of main factors on power output, energy/exergy yield, and the total cost of each system. Finally, a dual objective optimization was achieved by taking the main factors into consideration and using a genetic algorithm. Results indicated that the work generated by the system was not significant; however, the amount of hot water produced was relatively promising. Based on exergy and exergoeconomic evaluation, the After-Burner is an important non-renewable energy source while the fuel cell has a higher inefficiency cost which could be due to low work generation. Results indicate that the moisture in the biomass and the figure of merit, are important parameters that have to be kept as low as possible. The energy yield of the fuel cell was calculated to be 45.05%. Additionally, considering the optimized operating point, pure power output and system cost rate will be 1.81 KW and 5.15 $/hr respectively.