Chemical modification of polysulfone: Composite anionic exchange membrane with TiO2 nano-particles

Synthesis of quaternary polysulfone/Titanium dioxide (QPSf/TiO₂) nanocomposite membranes by the recasting procedure as suitable electrolyte in alkaline fuel cells is described. The composite membranes were characterized by ionic conductivity measurements, TGA, SEM, XRD, and AFM. Thermal analysis results showed that the composite membranes have good thermal properties. The introduction of the inorganic filler supplies the composite membrane with a good thermal resistance. The physico-chemical properties studied by means of SEM and XRD techniques suggested the uniform and homogeneous distribution of TiO₂ at 2.5 wt.% loading, and negligible agglomeration at 10 wt.% loading, also indicated enhancement of crystalline character of these membranes. The energy dispersive X-ray spectra (EDS) analysis gave proportional percentages that the distribution of Titania element on the surface of the composite membrane was uniform. Observations from the results suggest that QPSf/TiO₂ nanocomposite membranes have good prospects for possible use in AFC.     

Thermally crosslinked and quaternized polybenzimidazole ionomer binders for solid alkaline fuel cells

A novel anion-conducting ionomer binder, quaternized polybenzimidazoles (QPBIs) with 4-methyl-4-glycidylmorpholin-4-ium chloride (MGMC) in the main-chain and/or in the side group were synthesized for solid alkaline fuel cells (SAFCs). Crosslinking of the polybenzimidazole derivatives using a crosslinker containing epoxy groups formed ionomer binder in electrodes, and the crosslinked QPBIs showed better mechanical stability than non-crosslinked QPBIs. During the electrode drying process, on-site crosslinking was introduced to form thermally crosslinked ionomer binder in catalyst layers. A bench-scale SAFC with the crosslinked QPBI (CQPBI) containing 35 wt% of ionomer binder showed higher peak power density (35.3 mW cm⁻²) than the SAFC with 2,2′(m-phenylene)-5,5′bibenzimidazole (m-PBI) with 35 wt% of ionomer binder (20.9 mW cm⁻²). The membrane-electrode assembly (MEA) with CQPBI (35 wt% binder) showed two times higher chemical stability than that with m-PBI (35 wt% of ionomer binder) in load cell tests.     

A novel organic/inorganic polymer membrane based on poly(vinyl alcohol)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid/3-glycidyloxypropyl trimethoxysilane polymer electrolyte membrane for direct methanol fuel cells

Poly(vinyl alcohol)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS)/3-glycidyloxypropyl)trimethoxysilane (PVA/PAMPS/GPTMS) organic/inorganic proton-conducting polymer membranes are prepared by a solution casting method. PAMPS is a polymeric acid commonly used as a primary proton donor, while 3-(glycidyloxypropyl)trimethoxysilane (GPTMS) is an inorganic precursor forming a semi-interpenetrating network (SIPN). Varying amounts of sulfosuccinic acid (SSA) are used as the cross-linker and secondary proton source. The characteristic properties of PVA/PAMPS/GPTMS composite membranes are investigated by thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), micro-Raman spectroscopy and the AC impedance method. Direct methanol fuel cells (DMFCs) made of PVA/PAMPS/GPTMS composite membranes are assembled and examined. Experimental results indicate that DMFCs employing an inexpensive, non-perfluorinated, organic/inorganic SIPN membrane achieve good electrochemical performance. The highest peak power density of a DMFC using PVA/PAMPS/GPTMS composite membrane with 2 M CH₃OH solution fuel at ambient temperature is 23.63 mW cm⁻². The proposed organic/inorganic proton-conducting membrane based on PVA/PAMPS/GPTMS appears to be a viable candidate for future DMFC applications.     

Novel quaternized polysulfone/ZrO2 composite membranes for solid alkaline fuel cell applications

A novel composite anion exchange membrane, zirconia incorporated quaternized polysulfone (designated as QPSU/ZrO₂), is prepared by solution casting method. The characteristic properties of the QPSU/ZrO₂ composite polymer membranes are investigated by thermogravimetric analysis, X-ray diffraction and electrochemical impedance spectroscopy. The morphology of the composite membrane is observed by SEM and TEM studies. A study of an alkaline membrane fuel cell (AMFC) operating with hydroxide ion conducting membrane is reported. Evaluation of the fuel cell is performed using membrane electrode assemblies made up of carbon supported platinum (Vulcan XC-72) anode and platinum cathode catalysts and QPSU/ZrO₂ composite membrane. Experimental results indicate that the AMFC employing a cheap non-perflourinated (QPSU/ZrO₂) composite polymer membrane shows better electrochemical performance. The maximum power density observed is 250 mW/cm² for QPSU/10% ZrO₂ at 60 °C. The QPSU/ZrO₂ composite membrane constitutes a good candidate for alkaline membrane fuel cell applications.     

Electrochemical performance of an air-breathing direct methanol fuel cell using poly(vinyl alcohol)/hydroxyapatite composite polymer membrane

A novel composite polymer membrane based on poly(vinyl alcohol)/hydroxyapatite (PVA/HAP) was successfully prepared by a solution casting method. The characteristic properties of the PVA/HAP composite polymer membranes were examined by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-Raman spectroscopy and AC impedance method. An air-breathing DMFC, comprised of an air cathode electrode with MnO₂/BP2000 carbon inks on Ni-foam, an anode electrode with PtRu black on Ti-mesh, and the PVA/HAP composite polymer membrane, was assembled and studied. It was found that this alkaline DMFC showed an improved electrochemical performance at ambient temperature and pressure; the maximum peak power density of an air-breathing DMFC in 8 M KOH + 2 M CH₃OH solution is about 11.48 mW cm⁻². From the application point of view, these composite polymer membranes show a high potential for the DMFC applications.     

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

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

A direct borohydride fuel cell based on poly(vinyl alcohol)/hydroxyapatite composite polymer electrolyte membrane

A new poly(vinyl alcohol)/hydroxyapatite (PVA/HAP) composite polymer membrane was synthesized using a solution casting method. Alkaline direct borohydride fuel cells (DBFCs), consisting of an air cathode based on MnO₂/C inks on Ni-foam, anodes based on PtRu black and Au catalysts on Ni-foam, and the PVA/HAP composite polymer membrane, were assembled and investigated for the first time. It was demonstrated that the alkaline direct borohydride fuel cell comprised of this low-cost PVA/HAP composite polymer membrane showed good electrochemical performance. As a result, the maximum power density of the alkaline DBFC based on the PtRu anode (45 mW cm⁻²) proved higher than that of the DBFC based on the Au anode (33 mW cm⁻²) in a 4 M KOH + 1 M KBH₄ solution at ambient conditions. This novel PVA/HAP composite polymer electrolyte membrane with high ionic conductivity at the order of 10⁻² S cm⁻¹ has great potential for alkaline DBFC applications.     

Implantation of Nafion ionomer into polyvinyl alcohol/chitosan composites to form novel proton-conducting membranes for direct methanol fuel cells

A series of cost-effective, proton-conducting composite membranes, comprising of Nafion^® ionomer, chitosan (CS), and polyvinyl alcohol (PVA), is successfully prepared. By taking advantage of the strong electrostatic interactions between Nafion^® ionomer and CS component, Nafion ionomer is effectively implanted into the PVA/CS composite membranes, and improves proton conductivity of the PVA/CS composite membranes. Furthermore, this effect dramatically depends on the composition ratio of PVA/CS, and the optimum conductivity is obtained at the PVA/CS ratio of 1:1. The developed composite membranes exhibit much lower methanol permeability compared with the widely used Nafion^® membrane, indicating that these novel membranes have great potential for direct methanol fuel cells (DMFCs).     

Review of gas diffusion cathodes for alkaline fuel cells

This paper gives a technical background to alkaline fuel cells (AFCs), introducing the advantages and drawbacks of the technology. AFCs offer the potential for low cost, mass producible fuel cells, without the dependency on platinum based catalysts and (currently) expensive membrane electrolytes. The AFC uses relatively low cost electrolytes based on aqueous bases such as potassium hydroxide. The inherent CO₂ sensitivity of the electrolyte can be addressed by filtering out the CO₂ from the air intake using a simple scrubber and periodically replacing the liquid electrolyte.     

Study of poly(vinyl alcohol)/titanium oxide composite polymer membranes and their application on alkaline direct alcohol fuel cell

The novel poly(vinyl alcohol)/titanium oxide (PVA/TiO₂) composite polymer membrane was prepared using a solution casting method. The characteristic properties of the PVA/TiO₂ composite polymer membrane were investigated by thermal gravimetric analysis (TGA), a scanning electron microscopy (SEM), a micro-Raman spectroscopy, a methanol permeability measurement and the AC impedance method. An alkaline direct alcohol (methanol, ethanol and isopropanol) fuel cell (DAFC), consisting of an air cathode based on MnO₂/C inks, an anode based on PtRu (1:1) black and a PVA/TiO₂ composite polymer membrane, was assembled and examined for the first time. The results indicate that the alkaline DAFC comprised of a cheap, non-perfluorinated PVA/TiO₂ composite polymer membrane shows an improved electrochemical performances. The maximum power densities of alkaline DAFCs with 4 M KOH + 2 M CH₃OH, 2 M C₂H₅OH and 2 M isopropanol (IPA) solutions at room temperature and ambient air are 9.25, 8.00, and 5.45 mW cm⁻², respectively. As a result, methanol shows the highest maximum power density among three alcohols. The PVA/TiO₂ composite polymer membrane with the permeability values in the order of 10⁻⁷ to 10⁻⁸ cm² s⁻¹ is a potential candidate for use on alkaline DAFCs.     

Fabrication and characterization of poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) proton-conducting composite membranes for direct methanol fuel cells

A high performance poly(vinyl alcohol)/montmorillonite/poly(styrene sulfonic acid) (PVA/MMT/PSSA) proton-conducting composite membrane was fabricated by a solution casting method. The characteristic properties of these blend composite membranes were investigated by using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, methanol permeability measurement, and the AC impedance method. The ionic conductivities for the composite membranes are in the order of 10⁻³ S cm⁻¹ at ambient temperature. There are two proton sources used on this novel composite membrane: the modified MMT fillers and PSSA polymer, both materials all contain the -SO₃H group. Therefore, the ionic conductivity was greatly enhanced. The methanol permeabilities of PVA/MMT/PSSA composite membranes is of the order of 10⁻⁷ cm² s⁻¹. It is due to the excellent methanol barrier properties of the PVA polymer. The peak power densities of the air-breathing direct methanol fuel cells (DMFCs) with 1M, 2M, 4M CH₃OH fuels were 14.22, 20.00, and 13.09 mW cm⁻², respectively, at ambient conditions. The direct methanol fuel cell with this composite polymer membrane exhibited good electrochemical performance. The proposed PVA/MMT/PSSA composite membrane is therefore a potential candidate for future applications in DMFC.     

Synthesis and characterization of anion exchange membranes for alkaline direct methanol fuel cells

Alkaline fuel cells suggest solution for the problems of low methanol oxidation kinetics and methanol crossover, which are limiting the development of direct methanol fuel cells. In this work, a novel anion exchange membrane, quaternized poly(aryl ether oxadiazole), was prepared through polycondensation, grafting and quaternization. The ionic conductivity of as-synthesized anion exchange membrane can reach up to 2.79 × 10⁻² S/cm at 70 °C. The physical and chemical stability of the anion exchange membranes could also meet the requirement for alkaline direct methanol fuel cells.     

ZrO2 incorporated polysulfone anion exchange membranes for fuel cell applications

Novel imidazolium functionalized polysulfone (ImPS) membranes modified with zirconia (ZrO₂) were synthesized through solution casting technique. Structural, morphological, thermal and mechanical analysis of the composite membranes confirmed adhesion and property enhancement caused by ZrO₂. Water absorption investigations revealed better water absorption of the ImPS/ZrO₂ membranes with intact morphology. Maximum ion exchange capacity and ionic conductivity for the composite membranes were obtained as 2.84 mmol/g and 80.2 mS/cm (50 ^°C) which was 21% and 47% higher as compared to pure ImPS membrane. Alkaline stability of the blend membranes was increased due to strong interaction between ZrO₂ and ImPS molecules. Fuel cell performance using Pt/C catalysts exhibited OCP and power density elevation with incremental amounts of ZrO₂ in the composite membrane composition. ImPS membrane with 10% ZrO₂ recorded a highest OCP and power density of 1.04 V and 270 mW/cm² which was 35% and 39% higher than the pure ImPS. Thus, the anion exchange membranes developed by ImPS/ZrO₂ blending could be suiting well for alkaline fuel cells applications.     

Preparation and characterization of imidazolium-based membranes for anion exchange membrane fuel cell applications

New anion exchange membranes (AEMs) with high conductivity, good dimensional and alkaline stability are currently required in order to develop alkaline fuel cells into efficient and clean energy conversion devices. In this study, a series of AEMs based on 1, 2-dimethyl-3-(4-vinylbenzyl) imidazolium chloride ([DMVIm][Cl]) are prepared and investigated. [DMVIm][Cl] is synthesized and used as ion carriers and hydrophilic phase in the membranes. The water uptake, swelling ratio, IEC and conductivity of the AEMs increase with increasing the [DMVIm][Cl]. The imidazolium-based AEMs show excellent thermal stability, sufficient mechanical strength, the membrane which containing 30% mass fraction of [DMVIm][Cl] shows conductivity up to 1.0 × 10^?2 S cm^?1 at room temperature and good long-term alkaline stability in 1 M KOH solution at 80 °C. The results of this study suggest that this type of AEMs have good perspectives for alkaline anion exchange membrane fuel cell applications.     

Development of electrocatalysts for solid alkaline fuel cell (SAFC)

It is now widely accepted that the proton exchange membrane fuel cell (PEMFC) concepts can be applied for a rather large range of power production at low temperature, including ambient conditions for some applications. For small power units, the concept of fuel cell with a solid electrolytic membrane can be extended to the alkaline medium. The main condition is to develop an anionic membrane with a sufficient stability and a good electric conductivity. The aim of this paper is to discuss on the development of electrocatalysts (both anodic and cathodic) suitable with their use in a solid alkaline fuel cell working at room temperature. The fuel cell is conceived around a new kind of anionic membrane developed by an industrial partner.The catalysts need to be adapted to this new concepts and working conditions. For oxygen reduction, catalysts containing silver have been prepared and gave encouraging results. For the anodic side, fuels such as methanol or ethylene-glycol have been considered. Platinum-based catalysts have been developed and tested in addition with platinum-free electrocatalysts. The electrocatalytic activity of Pt–Pd catalysts was first evaluated in semi-cell in order to optimize the composition of the electrodes. Then, tests in fuel cells working at room temperature were carried out, and confirm the validity of the solid alkaline fuel cell (SAFC). A power density of 18–20 mW cm⁻² was observed with methanol or ethylene-glycol at 20 °C.     

Highly stable hydroxyl anion conducting membranes poly(vinyl alcohol)/poly(acrylamide-co-diallyldimethylammonium chloride) (PVA/PAADDA) for alkaline fuel cells: Effect of cross-linking

Highly stable hydroxyl anion conducting membranes have been developed using poly(vinyl alcohol) (PVA) as matrix by incorporation of poly(acrylamide-co-diallyldimethylammonium chloride) (PAADDA) as anion charge carriers. In order to clarifying the cross-linking effect on membrane performances, two series of PVA/PAADDA membranes were prepared by direct and indirect chemical cross-linking ways, and have been characterized in detail at structural and hydroxyl ion (OH⁻) conducting property by FTIR spectroscopy, thermal gravity analysis (TG), scanning electron microscopy (SEM), water sorption, ion exchange capacity and alkaline resistance stability. The OH⁻ conductivity of the membranes increased with increasing the content of PAADDA in polymer and temperature, and reached 0.74–12 mS cm⁻¹ with direct cross-linking way and 0.66–7.1 mS cm⁻¹ with indirect cross-linking way in the temperature range 30–90 °C. The membranes are found to have the same IEC values but the membranes with direct cross-linking way showed higher water uptake than that with indirect cross-link one. Both membranes showed the thermal stability above 200 °C, and can integrity in 100 °C hot water and methanol solution, where the swelling are better suppressed as high dense chemical cross-linkages in PVA network. Very low methanol permeability (from 1.82 × 10⁻⁷ to 3.03 × 10⁻⁷ cm² s⁻¹) in 50% methanol solution was obtained at 30 °C. Besides, the chemical stability in 80 °C, 6 M hot alkali conditions and long-term stability of 350 h in 60 °C hot water revealed that the PVA/PAADDA membranes are promising for potential application in alkaline fuel cells.     

Poly (vinyl alcohol)/3-(trimethylammonium) propyl-functionalized silica hybrid membranes for alkaline direct ethanol fuel cells

A novel hybrid membrane based on poly (vinyl alcohol)/3-(trimethylammonium) propyl-functionalized silica (PVA-TMAPS) is prepared by a simple solution-casting method. The properties of the PVA-TMAPS membranes are characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and X-ray diffraction (XRD). It is found that the thermal stability of the membranes increases with the addition of TMAPS particles. Moreover, the study of the effect of different weight ratios of PVA to TMAPS on the OH⁻ conductivity shows that the membrane with a ratio of PVA:TMAPS = 90:10 exhibited the highest OH⁻ conductivity. Finally, it is shown that the application of the alkaline membrane (PVA:TMAPS = 90:10) to an direct ethanol fuel cell can yield a peak power density of about 50 mW cm⁻² at 60 °C.     

Performance of organic–inorganic hybrid anion-exchange membranes for alkaline direct methanol fuel cells

A series of organic–inorganic membranes were prepared through sol–gel reaction of quaternized poly(vinyl alcohol) (QAPVA) with different contents of tetraethoxysilanes (TEOS) for alkaline direct methanol fuel cells. These hybrid membranes are characterized by FTIR, X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDXA) and thermo gravimetric analysis (TGA). The ion exchange content (IEC), water content, methanol permeability and conductivity of the hybrid membranes were measured to evaluate their applicability in fuel cells. It was found that the addition of silica enhanced the thermal stability and reduced the methanol permeability of the hybrid membranes. The hybrid membrane M-5, for which the silica content was 5 wt%, showed the lowest methanol permeability and the highest ion conductivity among the three hybrid membranes. The ratio of conductivity to methanol permeability of the membrane M-5 indicated that it had a high potential for alkaline direct methanol fuel cell applications.     

Comparison of different types of membrane in alkaline direct ethanol fuel cells

It has been understood that the use of cation-exchange membranes (CEM) and alkali-doped polybenizimidazole membranes (APM) in alkaline direct ethanol fuel cells (DEFC) with an added base in the fuel exhibits performance similar to the use of anion-exchange membranes (AEM). The present work is to assess the suitability of the three types of membrane to alkaline DEFCs by measuring and comparing the membrane properties including the ionic conductivity, the species permeability, as well as the thermal and mechanical properties. The comparison shows that: (i) the AEM is still the most promising membrane for the alkaline DEFC, although the thermal stability needs to be further enhanced; (ii) before solving the problem of the poor thermal stability of AEMs, the CEM is another choice for the alkaline DEFC running at high temperatures (<90 °C); and (iii) the APM can also be applied to the alkaline DEFC operating at high temperatures, but its mechanical property needs to be substantially enhanced and the species permeability needs to be dramatically decreased.     

Hydroxide exchange composite membrane based on soluble quaternized polyetherimide for potential applications in fuel cells

A series of soluble quaternized polyetherimides (QAPEIs) have been successfully synthesized by homogeneous quaternization in trimethylamine aqueous solution. ¹H NMR spectra confirm the successful synthesis of QAPEI. The QAPEIs exhibit good solubility in membrane-preparation solvents, making it possible to prepare the QAPEI composite membrane. Novel composite hydroxide exchange membranes have been prepared by incorporating QAPEIs with polytetrafluoroethylene (PTFE) membranes. The SEM images, gas permeation measurements and FTIR spectra show that the QAPEI is successfully filled in PTFE membrane and the resulted composite membrane is dense and smooth. The ion exchange capacity of composite membranes ranges from 0.35 to 0.58 mmol g⁻¹. The composite membranes have appropriate water uptake (≤154%) and moderate swelling ratio (≤42%) even at 60 °C. The hydroxide conductivity of the composite membrane reaches 11.9 mS cm⁻¹ at 20 °C that increases to 35.2 mS cm⁻¹ at 60 °C. TGA curve shows that the composite membrane possesses high thermal stability (T_OD: 210 °C). All these properties indicate that the QAPEI/PTFE composite membranes are good candidates for use as HEMs in HEM fuel cells.