Proton Conductivity Stability Research Articles

High-performance proton exchange membrane employing water-insoluble hybrid formed by chemically bonding phosphotungstic acid with polydopamine

Heteropolyacids can retain water in a proton exchange membrane to increase proton conductivity at high temperatures and low humidity; however, their high solubility in water leads to leaching, which limits their further application. Herein, we used phosphotungstic acid (HPW) and polydopamine (PDA) particles to prepare a water-insoluble PDA/HPW hybrid (PDW) via hydrothermal reaction. The amino groups of PDA in PDW chemically bonded to HPW and acted as an anchor for HPW. The proton conductivity of the sulfonated poly(ether ether ketone) (SPEEK) composite membrane containing 15wt% PDW (SPEEK/PDW-15) in liquid water was 0.052 S⸱cm–1 at 25 ℃, which was 63% higher than that of the SPEEK control membrane (0.032 S⸱cm–1). The SPEEK/PDW-15 composite membrane also showed stable proton conductivity during 80 days of testing while immersed in water.

Double cross-linked 3D layered PBI proton exchange membranes for stable fuel cell performance above 200 °C

Phosphoric acid doped proton exchange membranes often experience performance degradation above 200 °C due to membrane creeping and phosphoric acid evaporation, migration, dehydration, and condensation. To address these issues, here we present gel-state polybenzimidazole membranes with double cross-linked three-dimensional layered structures via a polyphosphoric acid sol-gel process, enabling stable operation above 200 °C. These membranes, featuring proton-conducting cross-linking phosphate bridges and branched polybenzimidazole networks, effectively anchor and retain phosphoric acid molecules, prevent 96% of its dehydration and condensation, improve creep resistance, and maintain excellent proton conductivity stability. The resulting membrane, with superior through-plane proton conductivity of 0.348 S cm−1, delivers outstanding peak power densities ranging from 1.20–1.48 W cm−2 in fuel cells operated at 200-240 °C and a low voltage decay rate of only 0.27 mV h−1 over a 250-hour period at 220 °C, opening up possibilities for their direct integration with methanol steam reforming systems.

Constructing sandwich-like microstructure based on multi-nanofibers to accelerate proton conduction at subzero temperature

The well-ordered microstructure has been demonstrated to accelerate the proton conduction process through reducing proton conduction resistance. In this research, the proton exchange membranes (PEMs) with sandwich-like microstructure have been constructed based on Kevlar nanofibers and bifunctional nanofibers of chitosan (CS) with polyvinyl alcohol (PVA). The CS/PVA bifunctional nanofibers (CPNF) layer has been prepared with electrospinning process, which is stably adhered to the Kevlar nanofibers layer owing to compatible interfacial property. The fine structure stability without layer separation is achieved even with phosphoric acid (PA) molecules doping in the prepared PA doped composite membranes. The fibrous microstructure accelerats proton conduction through regulating proton conduction pathways. The objective of accelerating proton conduction at subzero temperature has been realized, reflecting in high and stable proton conductivities. For instance, the (Kevlar/CPNF/Kevlar)/PA membrane exhibits proton conductivities of 9.75 × 10−3 S/cm at −30 °C and 8.22 × 10−2 S/cm at 30 °C. Most importantly, the fine proton conductivity stability is identified by the results of the cycle test and long-term test. Specifically, the proton conductivities are respectively 8.62 × 10−3 S/cm at −30 °C and 8.07 × 10−2 S/cm at 30 °C after a five heating/cooling cycle process. The proton conductivities remain 2.97 × 10−2 S/cm at −25 °C and 7.19 × 10−2 S/cm at 30 °C after a 1032 h non-stop test. Additionally, the single proton exchange membrane fuel cell with the (Kevlar/CPNF/Kevlar)/PA membrane exhibits the peak power densities of 279.5 mW/cm2 at 100 °C and 352.7 mW/cm2 at 130 °C.

Imparting Stable and Ultrahigh Proton Conductivity to a Layered Rare Earth Hydroxide via Ion Exchange.

Proton conductors are essential functional materials with a wide variety of potential applications in energy storage and conversion. In order to address the issues of low proton conductivity and poor stability in conventional proton conductors, a simple and valid ion-exchange method was proposed in this study for the introduction of stable and ultrahigh proton conductivity in layered rare earth hydroxides (LRHs). Test analyses by solid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, and powder X-ray diffraction revealed that the exchange of H2PO4- not only does not disrupt the layered structure of LRHs, but also creates more active proton sites and channels necessary for proton transport, thereby creating a high-performance proton conductor (LRH-H2PO4-). By utilizing this ion-exchange method, the proton conductivity of LRHs can be significantly enhanced from a low level to an ultrahigh level (>10-2 S·cm-1), while maintaining excellent long-term stability. Moreover, through methodically manipulating the guest ions and molecules housed within the interlayers of LRHs, a comprehensive explanation has been presented regarding the proficient mechanism of proton conduction in LRH-H2PO4-. As a result, this investigation presents a feasible and available approach for advancing proton conductor.

Dual-Proton Conductor for Fuel Cells with Flexible Operational Temperature.

The properties of proton conductors determine the operating temperature range of fuel cells. Typically, phosphoric acid (PA) proton conductors exhibit excellent proton conductivity owing to their high proton dissociation and self-diffusion abilities. However, at low temperatures or high current densities, water-induced PA loss causes rapid degradation of cell performance. Maintaining efficient and stable proton conductivity within a flexible temperature range can significantly reduce the start-up temperature of PA-doped proton exchange membrane fuel cells. In this study, a dual-proton conductor composed of an organic phosphonic acid (ethylenediamine tetramethylene phosphonic acid, EDTMPA) and an inorganic PA is developed for proton exchange membranes. The proposed dual-proton conductor can operate within a flexible temperature range of 80-160 °C, benefiting from the strong interaction between EDTMPA and PA, and the enhanced proton dissociation. Fuel cells with the EDTMPA-PA dual-proton conductor showed excellent cell stability at 80 °C. In particular, under the high current density of 1.5 A cm-2 at 160 °C, the voltage decay rate of the fuel cell with the dual-proton conductor is one-thousandth of that of the fuel cell with PA-only proton conductor, indicating excellent stability.

Core-shell tin pyrophosphate-based composite membrane for fuel cell with durability enhancement at elevated temperatures

Tin pyrophosphate has been employed as a proton conductor in polymer electrolyte membranes (PEMs) at temperatures over 200 °C. However, neither the aggregation of the SnP2O7 nanoparticles nor the proton conduction mechanism of the material has been clearly clarified in PEM. The present work reports a polybenzimidazole (PBI)/SnP2O7 composite membrane with homogeneous distribution of the inorganic phase. The membrane is successfully fabricated by in-situ transformation of SnO2 nanoparticles to core-shell SnP2O7 nanoparticles in the PBI matrix during fuel cell operation. Further in-depth analysis shows that the core-shell SnP2O7 contains a crystalline SnP2O7 core, an amorphous SnP2O7 intermediate layer and a gel-like outer layer mainly containing H4P2O7. In addition, the crystal growth of the SnP2O7 nucleus consumes ions from the amorphous SnP2O7 layer, where the reacted ions are compensated by the diffusion of Sn4+ and P2O74− ions from the gel-like outer layer. Also, the fuel cell with the composite membrane shows superior proton conductivity and durability compared to the pristine phosphoric acid-doped PBI membrane at 240 °C for over 50 h. That is due to the presence of H4P2O7 in the outer layer, which contributes to high and stable proton conductivity of the core-shell SnP2O7 at 220–260 °C.

Achieving better balance on the mechanical stability and conduction performance of sulfonated poly(ether ether ketone) proton exchange membranes through polydopamine/polyethyleneimine co-modified poly(vinylidene fluoride) nanofiber as support

In this work, the polyvinylidene fluoride (PVDF) electrospun fibers was applied as robust mechanical support and subsequently functionalized with polydopamine/polyethyleneimine (PDA/PEI) composite, then filled with sulfonated poly (ether ether ketone) (SPEEK) to obtain SPEEK-PDA/PEI@PVDF composite proton exchange membranes. The composite membranes achieved better balance on the mechanical stability and conduction performance, owing to enhanced interface interactions and compatibility between robust PVDF and conductive SPEEK. In wet conditions, the composite membrane exhibited excellent mechanically robust with tensile strength of 34 MPa and elongation at break of almost 200 %. Furthermore, the composite membranes also showed high structure and performance stability during the measurement of proton conductivity and fuel cell performances, it could hold stable proton conductivity of 48 mScm−1 (at 80 °C) and maximum power density of 58.9 mWcm−2. The durability test further confirmed the super operating stability of composite membrane, only 2.6 % reduction in open circuit voltage was observed during operated at 80 °C for 100 h.

Different Approaches for the Preparation of Composite Ionic Liquid-Based Membranes for Proton Exchange Membrane Fuel Cell Applications—Recent Advancements

The use of ionic liquid-based membranes as polymer electrolyte membranes for fuel cell applications increases significantly due to the major features of ionic liquids (i.e., high thermal stability and ion conductivity, non-volatility, and non-flammability). In general, there are three major methods to introduce ionic liquids into the polymer membrane, such as incorporating ionic liquid into a polymer solution, impregnating the polymer with ionic liquid, and cross-linking. The incorporation of ionic liquids into a polymer solution is the most common method, owing to easy operation of process and quick membrane formation. However, the prepared composite membranes suffer from a reduction in mechanical stability and ionic liquid leakage. While mechanical stability may be enhanced by the membrane’s impregnation with ionic liquid, ionic liquid leaching is still the main drawback of this method. The presence of covalent bonds between ionic liquids and polymer chains during the cross-linking reaction can decrease the ionic liquid release. Cross-linked membranes reveal more stable proton conductivity, although a decrease in ionic mobility can be noticed. In the present work, the main approaches for ionic liquid introduction into the polymer film are presented in detail, and the recently obtained results (2019–2023) are discussed in correlation with the composite membrane structure. In addition, some promising new methods (i.e., layer-by-layer self-assembly, vacuum-assisted flocculation, spin coating, and freeze drying) are described.

Thermally stable proton conductivity from nanodiamond oxide.

Herein, we report nanodiamond oxide (NDOx), obtained from modified Hummers' oxidation of nanodiamond (ND), showing excellent proton conductivity and thermal stability. NDOx possesses hydrophilicity resulting in higher water adsorption and the retention of functional groups at elevated temperatures can be attributed to the high proton conductivity and thermal stability, respectively.

Researching proton conduction behavior at subzero temperature of lamellar anhydrous proton exchange membranes

For proton exchange membranes (PEMs), many studies have been going into the anhydrous PEMs with the working temperature exceeding 110 °C and the humidified PEMs below 80 °C. However, the PEMs fracture can cause cold start failure while the fuel cell vehicles are exposed to a colder climate for a long-time parking. In this study, low temperature PEMs (LTPEMs) with the lamellar structure was constructed through the well-ordered dispersion of Kevlar nanofibers, thioglycollic acid capping cadmium telluride (CdTe) nanocrystals and polyurethane (PU) polymer, expecting to enhance the mechanical property and improve the proton conductivity at subzero temperature. The successful preparation of the LTPEMs with spin coating technique and layer by layer self-assembly technique was determined by the structure analysis and the property measurement. The compact microstructure was constructed owing to electrostatic attraction and intermolecular hydrogen bonding. In the prepared (Kevlar/CdTe)25/(PU/CdTe)100 membrane, Kevlar nanofibers provided the support and PU molecular chains guaranteed enough flexibility. Furthermore, a massive amount of CdTe nanocrystals could tolerate low temperature condition, which was derived from the high proton conductivity at subzero temperature. Specifically, the (Kevlar/CdTe)25/(PU/CdTe)100/PA membrane exhibited the proton conductivity values of (2.23 ± 0.39) × 10−2 S/cm at −30 °C, (6.59 ± 0.15) × 10−2 S/cm at 0 °C and (1.73 ± 0.04) × 10−1 S/cm at 30 °C. Most importantly, the fine proton conductivity stability was revealed from the proton conductivity values of 3.72 × 10−2 S/cm at −30 °C after a thirty-cycle heating/cooling process and 3.53 × 10−2 S/cm at −30 °C after a 1020 h non-stop test. Furthermore, there was a slight decrease on the tensile stress with PA molecules doping owing to the compact microstructure.

Keeping Superprotonic Conductivity over a Wide Temperature Region via Sulfate Hopping Sites-Decorated Zirconium-Oxo Clusters.

Metal-oxo clusters have emerged as advanced proton conductors with well-defined and tunable structures. Nevertheless, the exploitation of metal-oxo clusters with high and stable proton conductivity over a relatively wide temperature range still remains a great challenge. Herein, three sulfate groups decorated zirconium-oxo clusters (Zr6 , Zr18 , and Zr70 ) as proton conductors are reported, which exhibit ultrahigh bulk proton conductivities of 1.71×10-1 , 2.01×10-2 , and 3.73×10-2 Scm-1 under 70°C and 98% relative humidity (RH), respectively. Remarkably, Zr6 and Zr70 with multiple sulfate groups as proton hopping sites show ultralow activation energies of 0.22 and 0.18eV, respectively, and stable bulk conductivities of >10-2 Scm-1 between 30 and 70°C at 98% RH. Moreover, a time-dependent proton conductivity test reveals that the best performing Zr6 can maintain high proton conductivity up to 15h with negligible loss at 70°C and 98% RH, representing one of the best crystalline cluster-based proton conducting materials.

Constructing foldable and stretchable proton exchange membranes through spin coating technology

The convenient storage of fuel cells requires the foldable and stretchable membrane electrolytes. However, there was the risk of sacrificing the charge transport mobility and mechanical strength to achieve the foldability and stretchability. The spin coating technology provided an facile strategy to prepare the well-ordered structure of membranes. In this study, the foldable and stretchable proton exchange membranes (PEMs) based on Kevlar nanofibers and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) were constructed through spin coating technology. After the folded and stretched operations, the membranes exhibited the negligible effect on proton conductivity and mechanical strength. In our opinion, the components of SEBS supported the membranes deformation and Kevlar naonfibers supplied the proton conduction channels. As a result, the prepared (Kevlar/SEBS)5 membranes can be folded in the width direction for 3 times and be stretched up to 10 % strain parallel to the length direction for 50 times. The folded membranes and stretched membranes respectively exhibited the proton conductivities of 9.55 × 10-2 S/cm and 1.98 × 10-1 S/cm, which were comparable with 1.58 × 10-1 S/cm at 160 °C of the original membranes. The tensile stress of (Kevlar/SEBS)5-fold/PA and (Kevlar/SEBS)5–50/PA respectively reached 5.23 MPa and 6.43 MPa, even a little higher than 3.59 MPa of the (Kevlar/SEBS)5/PA membranes. Furthermore, the folded and stretched membranes showed the fine component stability and proton conductivity stability. This study provided the support to exploit foldable and stretchable PEMs with spin coating technique, facilitating the easy storage of PEMs and future portable fuel cells.

Highly Efficient Proton Conduction in the Metal-Organic Framework Material MFM-300(Cr)·SO4(H3O)2.

The development of materials showing rapid proton conduction with a low activation energy and stable performance over a wide temperature range is an important and challenging line of research. Here, we report confinement of sulfuric acid within porous MFM-300(Cr) to give MFM-300(Cr)·SO4(H3O)2, which exhibits a record-low activation energy of 0.04 eV, resulting in stable proton conductivity between 25 and 80 °C of >10–2 S cm–1. In situ synchrotron X-ray powder diffraction (SXPD), neutron powder diffraction (NPD), quasielastic neutron scattering (QENS), and molecular dynamics (MD) simulation reveal the pathways of proton transport and the molecular mechanism of proton diffusion within the pores. Confined sulfuric acid species together with adsorbed water molecules play a critical role in promoting the proton transfer through this robust network to afford a material in which proton conductivity is almost temperature-independent.

Comparative study on proton conductivity of P- and G-UC

Developing novel proton conductors is crucial to the electrochemical technology for energy conversion and storage. Metal-organic frameworks (MOFs) have been attracting wide attention in this regard. P-UC (UC = UiO-66-COOH) and G-UC were prepared with different methods. The structures of products were characterized by XRD and IR. Then, the proton conductivities of P-UC and G-UC at different temperatures were measured at 75% RH (RH ​= ​relative humidity) and 100% RH. The results show that the proton conductivity of G-UC is better than that of P-UC under the humidity conditions above. At 100% RH, the proton conductivity of G-UC reaches 8.53 ​× 10−2 ​S ​cm−1 ​at 353 ​K, which is 1.7 times that of P-UC. And at 303 ​K, the proton conductivity of G-UC is 4.55 ​× ​10−2 ​S ​cm−1, which is three times that of P-UC. The Ea values of G-UC and P-UC at 100% RH were lower than that at 75% RH. Under the two kinds of relative-humidity conditions above, relative to P-UC, G-UC is a better proton conductive material, with more stable high proton conductivity and lower activation energy.

Developing a Unique Hydrogen-Bond Network in a Uranyl Coordination Framework for Fuel Cell Applications.

Crystalline materials with persistent high anhydrous proton conductivity that can be directly used as a practical electrolyte of the intermediate-temperature proton exchange membrane fuel cells for durable power generation remain a substantial challenge. The present work proposes a unique way of the axial uranyl oxo atoms as hydrogen-bond acceptors to form a dense hydrogen-bonded network within a stable uranyl-based coordination polymer, UO2(H2PO3)2(C3N2H4)2 (HUP-3). It exhibits stable and efficient anhydrous proton conductivity over a super-wide temperature range (-40-170 °C). It was also assembled into a H2/O2 fuel cell as the electrolyte and shows a high electrical power density of 11.8 mW·cm-2 at 170 °C, which is among one of the highest values reported from crystalline solid electrolytes. The cell was tested for over 12 h without notable power loss.

Enhancing proton conductivity at subzero temperature through constructing the well-ordered structure based on carbon dots

The layer-by-layer (LBL) self-assembly technique could nanoscopically construct the composite membranes with multilayered structures. It has been frequently mentioned in the field of microelectronics, biology and clean energy, etc. In this research, low temperature proton exchange membranes (LTPEMs) were fabricated through alternate deposition of polyurethane (PU) as polyanions, Nafion and carbon dots (CDs) as polycations. The successful preparation of LTPEMs with multilayered structure has been demonstrated by the structure characterization and property analysis of the (PU/Nafion/PU/CDs)200 membrane. The CDs and PU can combine phosphoric acid (PA) molecules owing to the hydrogen-bond interaction. The (PU/Nafion/PU/CDs)200/PA membrane was thus obtained with the combination of a large number of PA molecules. The target of enhancing the proton conductivity at subzero temperature was achieved since the well-ordered dispersion of components could reduce proton conduction resistance. Specifically, the (PU/Nafion/PU/CDs)200/PA membrane exhibited the proton conductivities of (3.29 ± 3.16) × 10−3 S/cm at −30 °C and (2.99 ± 0.39) × 10−2 S/cm at 30 °C. Furthermore, the membranes exhibited the fine proton conductivity stability, such as 3.69 × 10−3 S/cm at −30 °C and 3.34 × 10−2 S/cm at 30 °C even if the membrane underwent a five-cycle heating/cooling process of −30 °C–30 °C. Furthermore, the values could reach 9.34 × 10−3 S/cm at −30 °C and 1.58 × 10−2 S/cm at 0 °C after a 315 h non-stop test. The results can reveal that the LBL self-assembly technique was a prospective strategy to construct LTPEMs for the application at subzero temperature.

Constructing proton exchange membranes with high and stable proton conductivity at subzero temperature through vacuum assisted flocculation technique

The application of proton exchange membranes in low temperature proton exchange membrane fuel cells requires the quick and stable proton conduction at subzero temperature. In this research, we constructed the multilayered membranes through the alternate deposition of poly(vinyl alcohol) (PVA), Kevlar nanofibers and carbon nanotube oxides (OCNTs) through the vacuum assisted flocculation (VAF) technique. The intermolecular hydrogen bonds resulted in the preparation of (PVA/Kevlar/OCNTs)3 membranes with layered structure. Phosphoric acid (PA) molecules entered the gaps between the neighboring layers accompanying with the phase separation. The prepared membranes exhibited the high and stable proton conductivity at subzero temperature, such as 2.04 × 10-2 S/cm at −30 °C and 1.52 × 10-1 S/cm at 30 °C. The proton conductivity gradually changed to 5.52 × 10-2 S/cm and 1.84 × 10-1 S/cm even after the ten-cycles process of −30 °C–30 °C. In addition, the value can retain 1.42 × 10-2 S/cm at −30 °C in a 1900 h non-stop test. The evaporation and liquefaction of water molecules could affect proton conductivity besides PA dominating the proton conduction behavior during heating/cooling processes. Furthermore, the balance on low temperature proton conduction and mechanical strength makes the multilayered (PVA/Kevlar/OCNTs)3/PA membranes as a promising PEM candidate at subzero temperature.

Effectively facilitating the proton conduction of proton exchange membrane by polydopamine modified hollow metal−organic framework

An effective proton conduction accelerator, polydopamine (PDA) modified hollow metal−organic framework (DHZIF-8), was designed and constructed. Composite proton exchange membrane (PEM) with excellent proton conductivities was obtained by incorporation of DHZIF-8 into Nafion matrix. The hydrophilic groups on surface and hollow structure of DHZIF-8 endowed the composite PEM with higher water retention capacity, which was especially conducive to fast transportation of protons. Moreover, the proton conducting hindrance throughout DHZIF-8 was sufficiently alleviated by the hollow structure. Besides, the constituted acid−base pairs between –SO 3 H of Nafion and –NH 2 /–NH– of DHZIF-8 could work as effective proton transfer pathways. These greatly facilitated the proton conduction of the composite PEM. Its proton conductivities boosted up to 0.255 S/cm under 80 °C, 95% RH, and 3.66 mS/cm under 120 °C, anhydrous condition, which were approximately 1.5 and 2.2 times greater than those of Nafion control-membrane (0.104 S/cm and 1.14 mS/cm), respectively. Additionally, the maximum power density of the composite PEM reached up to 270.8 mW/cm 2 , which was about 58% higher than that of Nafion control-membrane (171.5 mW/cm 2 ). This study provides a referable strategy for designing and constructing functionalized MOFs with specific structures to effectively facilitate the proton conduction of PEMs. An effective proton conduction accelerator, polydopamine (PDA) modified hollow metal−organic framework (DHZIF-8), was incorporated into Nafion matrix to construct composite proton exchange membrane (PEM) with excellent proton conductivities. The proton conduction of composite PEM was greatly facilitated mainly by higher water retention capacity and formed acid-base pairs. • Polydopamine modified hollow MOF (DHZIF-8) was constructed as excellent proton conduction accelerator. • Proton conduction of PEM was effectively facilitated by DHZIF-8. • PEM displayed satisfactory proton conductivity stability. • Maximum power density and current density of PEM were obviously promoted.

Sandwich-structure PI/SPEEK/PI proton exchange membrane developed for achieving the high durability on excellent proton conductivity and stability

The proton exchange membrane (PEM) is the core unit in fuel cells, in which the balance among proton conductivity, dimensional stability and durability is a long-term pursuit. Nanofiber composite membrane as the most facile and practical strategy, however, commonly suffers from the obviously reduced proton conductivity although the dimensional stability and durability can be improved distinctly. Herein this work, we proposed a sandwich-structure nanofiber composite PEM, in which the inexpensive proton-transport matrix of sulfonated poly (ether ether ketone) (SPEEK) is sandwiched between polyimide (PI) nanofibers mats via simple steps. Thanks to the support for the matrix and resistance to the tough working condition provided by the PI nanofiber mats, significantly improved stability and durability in contrast to the referenced PEM of SPEEK. More importantly, with respect to the proton conductivity, a numerically equivalent initial proton conductivity and significantly improved proton conductivity stability, in comparing to the SPEEK membrane, has been achieved; where the conductivity only decreased by 21% in our sandwich-structure PEM after 6 weeks, much less than that of commercial Nafion 117 of 30% and pure SPEEK of 55%. Such results can be attributed to the hydrogen bond interaction between PI nanofibers and SPEEK matrix and thus the formation of the sulfonic acid-rich layer in our developed PI/SPEEK/PI membrane, confirmed by in situ Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). This combination of high proton conductivity, long-term stability, low cost, simple preparation suggests the sandwich-like PEM will provide a promising commercial application for future PEMs. • The sandwich structure PI/SPEEK/PI nanofiber composite membrane was proposed. • The proton conductivity of PI/SPEEK/PI membrane with high durability was achieved. • The interaction between PI nanofiber and SPEEK matrix was confirmed by in-suit FTIR, XPS and TEM.

A facile strategy to construct layered membranes with high and stable proton conductivity based on sulfonated graphene oxide

Spin coating as an easy-operation strategy to construct layered membranes has been widely mentioned in the fields of microelectronics, energy storage, and conversion, etc. In this research, the successful construction of proton exchange membranes (PEMs) bearing layered structure consisting of sulfonated graphene oxide (SGO) nanosheets and polyvinyl chloride (PVC) with the spin coating method has been demonstrated by the identification of the multilayered dispersion of components and compact structure. The hydrophilic SGO nanosheets could increase the hydrophilicity of composite membranes since they bore a large number of polar oxygen functional groups. Phosphoric acid (PA) can be combined through the formed intermolecular hydrogen bonds between PA molecules and SGO nanosheets. The content of PA in PEMs can be adjusted by controlling the concentration of PA solutions, immersion temperature, and duration time. A comparative study with the membrane from the solution casting method has been performed, expecting to understand the influence of layered structure on membrane performance. It was found that the well-ordered distribution of SGO nanosheets facilitated proton conduction, demonstrating from the proton conductivity of 3.63 × 10−2 S/cm at 150°C. The fine proton conductivity stability, for instance, the result of 2.71 × 10−2 S/cm at 140°C lasting 1000-hour supported the component stability and mechanical strength. The research revealed that the spin coating technique could provide a facile and effective strategy to construct well-ordered membrane electrolytes for the application of high- temperature proton exchange membrane fuel cells.