Potential membranes derived from poly (aryl hexafluoro sulfone benzimidazole) and poly (aryl hexafluoro ethoxy benzimidazole) for high-temperature PEM fuel cells

Poly (aryl hexafluoro sulfone benzimidazole) and poly (aryl hexafluoro ethoxy benzimidazole), termed as PArF₆SO₂BI and PArF₆OBI, are synthesized and characterized systematically. PArF₆SO₂BI membranes illustrate good chemical stability in terms of oxidative weight loss due to the electron-withdrawing sulfone functional group. PArF₆OPBI membranes exhibit weak chemical stability after immersion in Fenton's solution. Many of the membranes show good conductivities. Higher conductivities of 3.26 × 10^?2 S cm^?1 at 160 °C with 286.8 wt% acid doped level for 3:1 (2.335 mmol of 4,4′-sulfonyldibenzoic acid and 7.005 mmol of 2, 2-bis(4-carboxyphenyl) hexafluoropropane) ratio of PArF₆SO₂BI and 7.31 × 10^?2 S cm^?1 with 356.9 wt% for 3:1 ratio of PArF₆OBI are observed. PArF₆SO₂BI and PArF₆OPBI membranes exhibit good conductivity, thermal and mechanical stabilities which are crucial requirements for high temperature fuel cells.     

Novel acid–base molecule-enhanced blends/copolymers for fuel cell applications

A series of acid–base molecule-enhanced composite membranes are successfully prepared. The composite membranes are composed of a sulfonated poly(aryl ether ketone) (6FSPEEK) as an acidic component, and of aminated poly(aryl ether ketone) containing a naphthyl group (AmPEEKK-NA) as a basic component. The composite membranes exhibit obviously improved thermal, oxidative and dimensional stability. Especially, these composite membranes possess excellent tensile properties both in the dry and wet state. The proton conductivities of these membranes are higher than 2.45 × 10⁻² S cm⁻¹ at room temperature and higher than 6.0 × 10⁻² S cm⁻¹ at 80 °C. The morphology of the membranes is studied in detail by SEM and AFM. All the data prove that both composite and aminated/sulfonated copolymer membranes may be potential proton exchange membrane for fuel cell applications.     

Application of graft-type poly(ether ether ketone)-based polymer electrolyte membranes to electrochemical devices – Fuel cells and electrolytic enrichment of tritium

The polymer electrolyte membrane consisting of poly(styrenesulfonic acid)-grafted poly(ether ether ketone) (PEEK-PEM) was investigated for application to two electrochemical devices; a fuel cell and electrolytic enrichment of tritium. For fuel cells, high temperature operation has been required from the viewpoints of simplification of cooling systems, heat recovery systems and so forth, and durability is one critical issue affecting practical use. We performed a long term durability test for PEEK-PEM (ion exchange capacity = 2.4 mmol/g, conductivity = 0.15 S/cm) under the condition of 110 °C and 50% relative humidity, and achieved a lifetime of 1500 h at a constant current of 0.3 A/cm². The cell voltage maintained 97% of initial voltage after 1300 h of operation. There have been only a few reports that PEMs exhibit longer lifetime than 1000 h at temperatures above 100 °C. For quantitative evaluation of tritium concentration in low-level tritiated water such as environmental water, the tritium enrichment by a solid polymer electrolysis (SPE) method is required prior to the tritium concentration measurements. The SPE device composed of PEEK-PEMs with IECs of 0.9–1.2 mmol/g showed a tritium enrichment ratio of 1.35 at 30 °C, which is 20% higher than that of Nafion. Higher tritium enrichment ratios in PEEK-PEM are explained by the smaller amount of transported water. The water transport coefficient in PEEK-PEM is ～1, which is a half value of Nafion. In addition, the water transport coefficient of PEEK-PEM shows less temperature dependence, at least, up to 60 °C. These features have advantages in electrolytic enrichment of tritium for practical use.     

Macromolecule sulfonated Poly(ether ether ketone) crosslinked poly(4,4′-diphenylether-5,5′-bibenzimidazole) proton exchange membranes: Broaden the temperature application range and enhanced mechanical properties

Proton exchange membranes with a wide application temperature range were fabricated to start high-temperature fuel cells under room temperature. The volume swelling stability, oxidative stability as well as mechanical properties of crosslinked membranes have been improved for covalently crosslinking poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) with fluorine-terminated sulfonated poly(ether ether ketone) (F-SPEEK) via N-substitution reactions. High proton conductivity was simultaneously realized at both high (80–160 °C) and low (40–80 °C) temperatures by crosslinking and jointly constructing hydrophilic-hydrophobic channels. The crosslinked membranes exhibited the highest proton conductivity of 191 mS cm⁻¹ at 80 °C under 98% relative humidity (RH) and 38 mS cm⁻¹ at 160 °C under anhydrous, respectively. Compared with OPBI membrane, the fuel cell performance of the crosslinked membranes showed higher peak power density at full temperature range (40–160 °C).     

Nafion/Pd–SiO2 nanofiber composite membranes for direct methanol fuel cell applications

One of the major challenges for direct methanol fuel cells is the problem of methanol crossover. With the aim of solving this problem without adverse effects on the membrane conductivity, Nafion/Palladium–silica nanofiber (N/Pd–SiO₂) composite membranes with various fiber loadings were prepared by a solution casting method. The silica-supported palladium nanofibers had diameters ranging from 100 nm to 200 nm and were synthesized by a facile electro-spinning method. The thermal properties, ionic exchange capacities, water uptake, proton conductivities, methanol permeabilities, chemical structures, and micro-structural morphologies were determined for the prepared membranes. It was found that the transport properties of the membranes were affected by the fiber loading. All of the composite membranes showed higher water uptake and ion exchange capacities compared to commercial Nafion 117 and proved to be thermally stable for use as proton exchange membranes. The composite membranes with optimum fiber content (3 wt%) showed an improved proton conductivity of 0.1292 S cm⁻¹ and a reduced methanol permeability of 8.36 × 10⁻⁷ cm² s⁻¹. In single cell tests, it was observed that, the maximum power density measured with composite membrane is higher than those of commercial Nafion 117.     

Effects and properties of various molecular weights of poly(propylene oxide) oligomers/Nafion acid–base blend membranes for direct methanol fuel cells

Various molecular weights of poly(propylene oxide) diamines oligomers/Nafion^® acid–base blend membranes were prepared to improve the performance of Nafion^® membranes in direct methanol fuel cells (DMFCs). The acid–base interactions were studied by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The performance of the blend membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The proton conductivity was slightly reduced by acid–base interaction. The methanol permeability of the blend D2000/Nafion^® was 8.61 × 10⁻⁷ cm² S⁻¹, which was reduced 60% compared to that of pristine Nafion^®. The cell performance of D2000/Nafion^® blend membranes was enhanced significantly compared to pristine Nafion^®. The current densities that were measured with Nafion^® and 3.5 wt% D2000/Nafion^® blend membranes were 62.5 and 103.5 mA cm⁻², respectively, at a potential of 0.2 V. Consequently, the blend poly(propylene oxide) diamines oligomers/Nafion^® membranes critically improved the single-cell performance of DMFC.     

High-performance metal (Au,Cu)–polypyrrole nanocomposites for electrochemical borohydride oxidation in fuel cell applications

Gold polypyrrole (AuPPy) and copper polypyrrole (CuPPy) nanocomposites were prepared by a simple one-step in situ oxidative polymerization of pyrrole monomer by Au³⁺ and Cu²⁺ ions. Owing to their characteristic physicochemical properties confirmed by optical and structural characterization methods, the behavior of these materials as electrocatalysts for borohydride oxidation reaction (BOR) was considered. BOR apparent activation energy was found to be 16 and 22 kJ mol^?1 for AuPPy and CuPPy electrocatalyst, respectively. The stability of the two electrocatalysts was assessed by chronoamperometry. Moreover, fuel cell tests were carried out with AuPPy and CuPPy as anode electrocatalyst of a direct borohydride-peroxide fuel cell (DBPFC). Open circuit voltage (OCV) of 1.30 V was obtained with both AuPPy and CuPPy, with the OCV increasing to 1.45 V upon adding a small amount of carbon (AuPPy-C). The peak power density of a DBPFC with BOR at AuPPy-C anode and hydrogen peroxide reduction reaction at Pt cathode was found to be ca. 162 mW cm^?2 at 65 °C.     

Electrodeposition of manganese dioxide in three-dimensional poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid)–polyaniline for supercapacitor

The preparation of composites of precise metal oxides/conducting polymers is important in studies of supercapacitors. In this work, a three-dimensional matrix of poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid)–polyaniline (PEDOT–PSS–PANI) was prepared by interfacial polymerization of ANI into PEDOT–PSS. Conductivity was enhanced by incorporating of PANI into PEDOT–PSS because of the decrease in the distance for electron shuttling along the conjugated polymeric chain. Composite electrodes were prepared by the electrodeposition of manganese dioxide (MnO₂) in a PEDOT–PSS–PANI three-dimensional matrix. The electrodes were characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry techniques. The results show a significant improvement in the specific capacitance of the composite electrode. For PEDOT–PSS the specific capacitance was of 0.23 F g⁻¹, while PEDOT–PSS–PANI and PEDOT–PSS–PANI–MnO₂ displayed values of 6.7 and 61.5 F g⁻¹, respectively. When only considering the MnO₂ mass, the composite had the specific capacitance of 372 F g⁻¹. The composite also had an excellent cyclic performance.     

N-Methyl-(n-butyl)pyrrolidinium bis(trifluoromethanesulfonyl)imide-LiTFSI–poly(ethylene glycol) dimethyl ether mixture as a Li/S cell electrolyte

We have characterized a ternary mixture of N-methyl-(n-butyl)pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) + 0.5 M LiTFSI + y poly(ethylene glycol) dimethyl ether (PEGDME) (y = kg PEGDME/kg PYR₁₄TFSI) as an electrolyte in Li metal/S cells. The presence of PYR₁₄TFSI in the mixture resulted in a significant improvement of the thermal stability and the ionic conductivity (σ) of the mixture with increasing PEGDME contents (for example, σ = 4.2 × 10⁻³ S cm⁻¹ at 29 °C for y = 2.0). These improvements are most significant at low temperatures, which is probably due to a lowering of the viscosity of the mixture with higher amounts of PEGDME. It is found that the mixture has good compatibility with respect to Li metal as demonstrated by time-dependent interfacial impedance and galvanostatic Li stripping/deposition measurements. We found that a Li/S cell with PYR₁₄TFSI + 0.5 M LiTFSI + y PEGDME (y = 2.0) can deliver about 1300 mAh g⁻¹-sulfur at 0.054 mA cm⁻² at ambient temperature at the first cycle. A better charge/discharge cyclability of the Li/S cell in PYR₁₄TFSI + 0.5 M LiTFSI + y PEGDME was found at higher PEGDME contents, and a Li/S cell with the mixture having y = 2.0 exhibited a capacity fading rate of 0.42% per cycle over 100 cycles at 0.054 mA cm⁻² at 40 °C. Consequently the PYR₁₄TFSI + LiTFSI + PEGDME mixture is a promising electrolyte for Li/S cells.     

Proton conductivity and fuel cell performance of organic–inorganic hybrid membrane based on poly(methyl methacrylate)/silica

Organic–inorganic hybrid membranes based on poly(methyl methacrylate) (PMMA)/silica have been synthesized using a sol-gel technique for use in polymer electrolyte fuel cells (PEFCs). The properties of these membranes were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The results indicate that these membranes are formed through hydrogen bonds between the carbonyl group of PMMA and the uncondensed alcohol functional groups of the inorganic clusters. The proton conductivity of these membranes is on the order of 10⁻¹ S cm⁻¹, and the 60PMMA–30SiO₂–10P₂O₅ membrane displays the highest proton conductivity of 3.85 × 10⁻¹ S cm⁻¹ at 90 °C and 50% RH. The performance of a fuel cell using these membranes was tested. A maximum power density of 370 mW cm⁻² is obtained at 80 °C, and the current density at 0.4 V remains almost unchanged during the 100-h test time under the test conditions. This class of hybrid membranes is an extremely promising material for use in PEFCs.     

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

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

Synthesis and thermal properties of poly(styrene-co-ally alcohol)-graft-stearic acid copolymers as novel solid–solid PCMs for thermal energy storage

A series of poly(styrene-co-allyalcohol)-graft-stearic acid copolymers were synthesized as novel polymeric solid–solid phase change materials (SSPCMs). The graft copolymerization reactions between poly(styrene-co-allyalcohol) and stearoyl chloride were verified by Fourier transform infrared (FT-IR) and Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy techniques. The crystal morphology of the SSPCMs was investigated using polarized optical microscopy (POM) technique. Thermal energy storage properties of the synthesized SSPCMs were measured using differential scanning calorimetry (DSC) analysis. The POM results showed that the crystalline phase of the copolymers transformed to amorphous phase above their phase transition temperatures. Thermal energy storage properties of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and found that they had typical solid–solid phase transition temperatures in the range of 27–30 °C and high latent heat enthalpy between 34 and 74 J/g. Especially, the copolymer with the mole ratio of 1/1 (poly(styrene-co-allyalcohol)/stearoyl chloride) is the most attractive one due to the highest latent heat storage capacity among them. The results of DSC and FT-IR analysis indicated that the synthesized SSPCMs had good thermal reliability and chemical stability after 5000 thermal cycles. Thermogravimetric (TG) analysis results suggested that the synthesized SSPCMs had high thermal resistance. In addition, thermal conductivity measurements signified that the synthesized PCMs had higher thermal conductivity compared to that of poly(styrene-co-allyalcohol). The synthesized copolymers as novel SSPCMs have considerable potential for thermal energy storage applications such as solar space heating and cooling in buildings and greenhouses.     

Externally reformed solid oxide fuel cell–micro-gas turbine (SOFC–MGT) hybrid systems fueled by methanol and di-methyl-ether (DME)

Solid oxide fuel cell–micro-gas turbine (SOFC–MGT) hybrid power plants integrate a solid oxide fuel cell and a micro-gas turbine and can achieve efficiencies of over 60% even for small power outputs (200–500 kW). The SOFC–MGT systems currently developed are fueled with natural gas, which is reformed inside the same stack, but the use of alternative fuels can be an interesting option. In particular, as the reforming temperature of methanol and di-methyl-ether (DME) (200–350 °C) is significantly lower than that of natural gas (700–900 °C), the reformer can be sited outside the stack. External reforming in SOFC–MGT plants fueled by methanol and DME enhances efficiency due to improved exhaust heat recovery and higher voltage produced by the greater hydrogen partial pressure at the anode inlet. The study carried out in this paper shows that the main operating parameters of the fuel reforming section (temperature and steam-to-carbon ratio (SCR)) must be carefully chosen to optimise the hybrid plant performance. For the stoichiometric SCR values, the optimum reforming temperature for the methanol fueled hybrid plant is approximately 240 °C, giving efficiencies of about 67–68% with a SOFC temperature of 900 °C (the efficiency is about 72–73% at 1000 °C). Similarly, for DME the optimum reforming temperature is approximately 280 °C with efficiencies of 65% at 900 °C (69% at 1000 °C). Higher SCRs impair stack performance. As too small SCRs can lead to carbon formation, practical SCR values are around one for methanol and 1.5–2 for DME.     

TiO2–Au plasmonic nanocomposite for enhanced dye-sensitized solar cell (DSSC) performance

Anatase TiO₂ nanoparticles dressed with gold nanoparticles were synthesized by hydrothermal process by using mixed precursor and controlled conditions. Diffused Reflectance Spectra (DRS) reveal that in addition to the expected TiO₂ interband absorption below 360 nm gold surface plasmon feature occurs near 564 nm. It is shown that the dye sensitized solar cells made using TiO₂–Au plasmonic nanocomposite yield superior performance with conversion efficiency (CE) of ～6% (no light harvesting), current density (J_SC) of ～13.2 mA/cm², open circuit voltage (V_oc) of ～0.74 V and fill factor (FF) 0.61; considerably better than that with only TiO₂ nanoparticles (CE ～ 5%, J_SC ～ 12.6 mA/cm², V_oc ～ 0.70 V, FF ～ 0.56).     

Characterization of Pd–Cu membranes fabricated by surfactant induced electroless plating (SIEP) for hydrogen separation

Pd–Cu composite membranes on microporous stainless steel (MPSS) substrate were fabricated using surfactant induced electroless plating (SIEP). In the SIEP method, dodecyl trimethyl ammonium bromide (DTAB), a cationic surfactant, was used in Pd- and Cu-baths for the sequential deposition of metals on MPSS substrates. The SIEP Pd–Cu membrane performance was compared with membranes fabricated by conventional electroless plating (CEP). The pre- and post-annealing characterizations of these membranes were carried out by SEM, XRD, EDX and AFM studies. The SEM images showed a significant improvement of the membrane surface morphology, in terms of metal grain structures and grain agglomeration compared to the CEP membranes. The SEM images and helium gas-tightness studies indicated that dense and thinner films of Pd–Cu can be produced with shorter deposition time using SIEP method. From XRD, cross-sectional SEM and EDS studies, alloying of Pd–Cu was confirmed at an annealing temperature of 773 K under hydrogen environment. These membranes were also studied for H₂ perm-selectivity as a function of temperature and feed pressure. SIEP membranes had significantly higher H₂ perm-selectivity compared to CEP membranes. Under thermal cycling (573 K – 873 K – 573 K), the SIEP Pd–Cu membrane was stable and retained hydrogen permeation characteristics for over three months of operation.     

CuxCo3-xO4-δ (0≤x≤1) coatings for solid oxide fuel cell interconnect applications

In order to obtain the solid oxide fuel cell (SOFC) interconnect coatings with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion, a series of Cu_xCo_3-xO_4-δ (x = 0, 0.5, 0.8, and 1.0) coatings are prepared by supersonic spraying via subsequent sintering. The chemical composition, lattice and morphological structures, electrical properties, and thermal expansion are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), area-specific resistance (ASR), and coefficient of thermal expansion (CTE) measurements. The experimental results show that the formation of CuCo₂O₄ is a reversible and incomplete reaction at the elevated temperature, and the coexistence of CuO, Co₃O₄, and CuCo₂O₄ is inevitable in the coatings. The concentration of the chemicals mentioned above is highly related to the coatings’ Cu:Co molar ratio. The correlation between the chemical composition and the properties is comprehensively studied in this research. The Cu_xCo_3-xO_4-δ coatings exhibit good electrical conductivity when 0 ≤ x ≤ 0.8, satisfactory protectiveness when 0.5 ≤ x ≤ 1.0, and fitting CTE with remarkable robustness through the quick heating-cooling cycles when 0.8 ≤ x ≤ 1.0. In general, Cu_0.8Co_2.2O_4-δ can be an appropriate candidate to meet the advancing interconnect coating demands with high electrical conductivity, satisfactory protectiveness, and well-fitting thermal expansion properties.     

South Korea's national pursuit for fuel cell electric vehicle development: The role of government R&D programs over 30 years (1989–2021)

This paper explains the role of the Korean government's National R&D Program over three decades for fuel cell electric vehicle (FCEV) development. The R&D programs had started far before FCEV was considered feasible. We call this as a national pursuit, since the R&D programs has been participated by not only car manufacturers but also various research institutions, including universities, in Korea's national innovation system. The Korean government has implemented a series of National R&D Programs throughout many stages, from selection of technology, building infrastructure and legislations, demonstration, and subsidizing mass-produced FCEVs. The authors analyzed all the government R&D programs from 1989 to 2021 to show the evolutionary changes in contexts and contents of the programs that have reflected varying expectations, government's industrial strategy, and the maturity of technologies through periods. This paper claims that Korea's FCEV development has been regarded as a long-run national industrial strategy, and the development has been persistently pursued in a national innovation systemic manner, such as combining public R&D sector with industries and strong institutional and organizational supports by government.