Semi-interpenetrating network based on cross-linked poly(vinyl alcohol) and poly(styrene sulfonic acid-co-maleic anhydride) as proton exchange fuel cell membranes

A series of promising proton conducting membranes have been synthesized by using poly(vinyl alcohol), with sulfosuccinic acid (SSA) as a cross-linking agent and poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA) as proton source, which form a semi-interpenetrating network (semi-IPN) PVA/SSA/PSSA-MA membrane. A bridge of SSA between PVA molecules not only reinforces the network but also provides extra proton conducting paths. PSSA-MA chains trapped in the network were the major sources of protons in the membrane. FT-IR spectra confirmed the success of the cross-linking reaction and molecular interactions between PVA and PSSA-MA. Associated characteristics of a proton conducting membrane including ion-exchange capacity (IEC), proton conductivity and water uptake were investigated. The measured IECs of the membranes increased with increase of PSSA-MA content varying from 20 to 80% and correlated well with the measured uptake water and proton conductivity. The semi-IPN membranes with PSSA-MA over 60% exhibited a higher proton conductivity than Nafion-115 and also a reasonable level of water uptake. Fuel cell performance of membrane electrode assemblies (MEA) was evaluated at various temperatures with H₂/air as well as H₂/O₂ gases under ambient pressure. A power density of 0.7 W cm⁻² was obtained for the MEA using PVA/SSA20/PSSA-MA80 membrane using H₂/O₂ at 50 °C.     

Enhanced H2 production by using La5.5WO11.25-δ-La0.8Sr0.2FeO3-δ mixed oxygen ion-proton-electron triple-conducting membrane

Although lanthanum tungstates (Ln_nWO_12-δ) show superior CO₂-tolerance compared to the traditional perovskite-type oxides, their hydrogen permeation fluxes are not competitive. Herein, a mixed oxygen ion-proton-electron triple-conducting membrane with a nominal composition of La_5.5WO_11.25-δ-La_0.8Sr_0.2FeO_3-δ (LWO-LSF) was developed for H₂ production. The triple-conducting membrane is composed of a LWO phase with proton conductivity and a LSF phase with mixed oxygen ion-electron conductivities. In the LWO-LSF membrane, proton (H⁺) permeation and oxygen ion (O²⁻) counter-permeation property was simultaneously displayed. The improved H₂ production can be ascribed to (1) hydrogen permeated as H⁺ through LWO phase, and (2) hydrogen produced from water splitting that is enhanced by O²⁻ counter-permeation through LSF phase. A higher H₂ flux of 0.15 mL min⁻¹ cm⁻² was achieved at 900 °C using LWO-LSF triple-conducting membrane, compared with the conventional proton-electron conducting membranes LWO or La_5.5WO_11.25-δ-La_0.8Sr_0.2CrO_3-δ (LWO-LSC). Furthermore, the constant H₂ fluxes in various atmospheres indicated the good stability of LWO-LSF membrane in simulated raw hydrogen.     

Chemical modification of Nafion membrane with 3,4-ethylenedioxythiophene for direct methanol fuel cell application

Nafion 117 membranes were modified by in situ chemical polymerization of 3,4-ethylenedioxythiophene using H₂O₂ as oxidant for direct methanol fuel cell application. Methanol permeability and proton conductivity of the poly(3,4-ethylenedioxythiophene)-modified Nafion membranes as a function of temperature were investigated. An Arrhenius-type dependency of methanol permeability and proton conductivity on temperature exists for all the modified membranes. Compared with Nafion 117 membrane at 60 °C, the methanol permeability of these modified membranes is reduced from 30% to 72%, while the proton conductivity is decreased from 4% to 58%, respectively. Because of low methanol permeability and adequate proton conductivity, the DMFC performances of these modified membranes were better than that of Nafion 117 membrane. A maximum power density of 48.4 mW cm⁻² was obtained for the modified membrane, while under same condition Nafion 117 membrane got 37 mW cm⁻².     

Enhanced hydrogen permeability and reverse water–gas shift reaction activity via magneli Ti4O7 doping into SrCe0.9Y0.1O3−δ hollow fiber membrane

Hydrogen proton conducting perovskite-based hollow fiber membrane is an attractive hydrogen separation technology that shows higher stability relative to Pd-based membranes above 800 °C. One of the challenges towards high hydrogen (H₂) permeability on such proton conducting membrane is enabling simultaneously high proton and electronic conductivities to be achieved in single phase membrane. This has been addressed by developing dual-phase membrane. Here, we showed another promising approach, i.e., exploitation of beneficial phase reactions to create new conductive phases along the grain boundaries. By doping up to 8 wt. % magneli Ti₄O₇ into SrCe_0.9Y_0.1O_3?δ (SCY), Ce-doped SrTiO₃ and Y-doped CeO₂ were created in-between SCY grains. Electrical conductivity tests confirmed higher conductivities for 5 and 8 wt. % Ti₄O₇-doped SCY relative to SCY between 750 and 950 °C. These higher conductivities manifested into higher H₂ permeation fluxes for the doped SCY membranes. The highest flux of 0.17 mL min^?1 cm^?2 was observed for 5 wt. % Ti₄O₇-doped SCY at 900 °C when 50 vol. % H₂/He and 100 vol. % N₂ were used in the feed side and the permeate side, respectively. This is much higher than the flux of 0.05 mL min^?1 cm^?2 obtained from SrCe_0.9Y_0.1O₃ membrane at identical condition. More essential is the fact that the doped SCY membranes displayed catalytic activity for the reverse water-gas shift (RWGS) reaction which consumed H₂ in the permeate side; increasing the H₂ flux up to 0.57 mL min^?1 cm^?2 at 900 °C. The 5 wt. % Ti₄O₇-doped SCY furthermore showed stable flux for more than 140 h at 850 °C despite the formation of minor amount of SrCO₃ in H₂-CO₂-containing atmosphere; highlighting its potential application as membrane reactor for RWGS or dehydrogenation reaction.     

Reasonable construction of proton conducting channel via biomimetic caterpillar-like alumina fiber to improve the properties of its composite proton exchange membrane

In this paper, we prepare a novel biomimetic caterpillar-like alumina fiber with the characteristic of continuous alumina backbone and fine needle whiskers spine. Then the high-performance caterpillar-like alumina fiber composite proton exchange membrane (CAPEM) is obtained by introducing the amino modified biomimetic caterpillar-like alumina fiber into sulfonated polysulfone (SPSF) matrix, which successfully reasonable construction of the proton conducting channels in both vertical and horizontal orientation. The properties of CAPEM, including proton conductivity, methanol permeability, etc. Are systematically studied. The results show that the proton conductivity of CAPEM increases with rising the temperature, which reaches the maximum of 0.263 S/cm at 80 °C and 100% RH, respectively. The excellent proton conductivity of CAPEM is attributed to the long-range continuous proton conducting channel formed by the horizontal continuous alumina skeleton in the in-plane direction and the vertical overlapped fine needle whiskers spine in the through-plane direction. In addition, the interfacial compatibility between amino modified caterpillar-like alumina fiber and SPSF matrix is enhanced through the reasonable construction of proton conducting channels, which effectively inhibits the methanol permeation of the composite membrane with 4.18 × 10^?7 cm² s^?1 and improves the comprehensive performance of the CAPEM.     

Combined methane reforming by carbon dioxide and steam in proton conducting solid oxide fuel cells for syngas/power co-generation

Methane and carbon dioxide mixture can be used as the fuel in a proton conducting solid oxide fuel cell (SOFC) for power/syngas co-generation and greenhouse gas reduction. However, carbon deposition and low conversion ratio are potential problems for this technology. Apart from using functional catalytic layer in the SOFC to enhance CH₄ dry reforming, adding H₂O into the fuel stream could facilitate the CH₄ conversion and enhance the co-generation performance of the SOFC. In this work, the effects of adding H₂O to the CO₂CH₄ fuel on the performance of a tubular proton conducting SOFC are studied numerically. Results show that the CH₄ conversion is improved from 0.830 to 0.898 after adding 20% H₂O to the anode. Meanwhile, the current density is increased from 2832 A m⁻² to 3064 A m⁻² at 0.7 V. Sensitivity studies indicate that the H₂:CO ratio can be effectively controlled by the amount of H₂O addition and the H₂ starvation can be alleviated, especially at high current density conditions.     

Direct methane cracking using a mixed conducting ceramic membrane for production of hydrogen and carbon

The direct cracking of methane can be used to produce CO_x and NO_x-free hydrogen for proton exchange membrane fuel cells. Recent studies have been focused on enhancing the hydrogen production using the direct thermocatalytic decomposition of methane as an attractive alternative to the conventional steam reforming process. We present the results of a systematic study of methane direct decomposition using a mixed conducting oxide, Y-doped BaCeO₃, membrane. A dense disk-shaped BaCe_0.85Y_0.15O₃ membrane was successfully prepared and covered with Pd film, as the catalyst for the methane decomposition. For the methane thermocatalytic decomposition, the methane gas was employed as reactant on the membrane side with a pressure of 10² kPa and rate of 70 ml/min at the reaction temperatures of 600, 700, and 800 °C. The hydrogen was selectively transported through the mixed conducting oxide membrane to the outer side. In addition, the carbon, which is a by-product after methane decomposition, showed the morphologies of sphere-shaped nanoparticles and the transparent sheets.     

Process simulation and integration of IGCC systems with novel mixed ionic and electronic conducting membrane-based water gas shift membrane reactors for CO2 capture

A mixed ionic and electronic conducting (MIEC) membrane provides an alternative to the palladium alloy membrane for water gas shift membrane reactor. It exhibits much better sulfur resistance performance than the palladium alloy membrane. In this paper, the thermodynamic performance of the integrated gasification combined cycle (IGCC) system with MIEC membrane reactor is predicted for the first time. The effects of reactor operation parameters on system flowsheet and performance are investigated and illustrated by sensitive analysis. When the reactor operation temperature is 900 °C and the H₂O decomposition ratio is 0.5, the system net efficiency is about 38.90%, which is 2.6% points higher than that of the IGCC with Selexol. The system net efficiency increases with the decrease of operation temperature. With the net efficiency of the conventional system as the reference, the minimum H₂O decomposition ratios at different operating temperatures are provided.     

Nanostructured electrolyte membranes based on zeotypes,protic ionic liquids and porous PBI membranes: Preparation,characterization and MEA testing

An innovative electrolyte membrane concept based on the synergic combination of randomly porous doped PBI membranes 80% in porosity containing H-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as intrinsic proton conductor and microporous ETS-10 coatings as diffusional barriers has been developed for High Temperature PEMFC applications. The preparation route, involving up to 5 different steps, has been carefully optimized based on the evaluated proton conductivity and durability properties in presence of humidity at temperatures above 150 °C. The proton/methanol transport selectivity values of the optimized nanostructured membranes at 50°, 100° and 150 °C clearly outperform dense PBI and Nafion counterparts used as references. Moreover, the H₂ permeability values for both the optimized nanostructured electrolyte membrane and dense PBI are quite similar at the examined conditions; indicating the suitability of the preparation procedure in terms of fuel cross-over. Finally, the as prepared membranes have been validated in H₂/O₂ single cell under non humidified conditions up to 180 °C as a “proof of concept” demonstration.     

Electrode performance and analysis of reversible solid oxide fuel cells with proton conducting electrolyte of BaCe0.5Zr0.3Y0.2O3−δ

Reversible solid oxide fuel cells (R-SOFCs) are regarded as a promising solution to the discontinuity in electric energy, since they can generate electric powder as solid oxide fuel cells (SOFCs) at the time of electricity shortage, and store the electrical power as solid oxide electrolysis cells (SOECs) at the time of electricity over-plus. In this work, R-SOFCs with thin proton conducting electrolyte films of BaCe_0.5Zr_0.3Y_0.2O_3−δ were fabricated and their electro-performance was characterized with various reacting atmospheres. At 700 °C, the charging current (in SOFC mode) is 251 mA cm⁻² at 0.7 V, and the electrolysis current densities (in SOEC mode) reaches −830 mA cm⁻² at 1.5 V with 50% H₂O-air and H₂ as reacting gases, respectively. Their electrode performance was investigated by impedance spectra in discharging mode (SOFC mode), electrolysis mode (SOEC mode) and open circuit mode (OCV mode). The results show that impedance spectra have different shapes in all the three modes, implying different rate-limiting steps. In SOFC mode, the high frequency resistance (R_H) is 0.07 Ωcm² and low frequency resistances (R_L) are 0.37 Ωcm². While in SOEC mode, R_H is 0.15 Ωcm², twice of that in SOFC mode, and R_L is only 0.07 Ωcm², about 19% of that in SOFC mode. Moreover, the spectra under OCV conditions seems like a combination of those in SOEC mode and SOFC mode, since that R_H in OCV mode is about 0.13 Ωcm², close to R_H in SOEC mode, while R_L in OCV mode is 0.39 Ωcm², close to R_L in SOFC mode. The elementary steps for SOEC with proton conducting electrolyte were proposed to account for this phenomenon.     

Fabrication and evaluation of stable micro tubular solid oxide fuel cells with BZCY-BZY bi-layer proton conducting electrolytes

Anode-supported proton conducting micro tubular solid oxide fuel cells (MT-SOFCs) with the configuration of Ni–BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY)/BZCY/BaZr_0.8Y_0.2O_3-δ (BZY)/La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)-BZY have been prepared by a combination of phase inversion method and suspension-coating technique. The obtained Ni-BZCY anode hollow fiber presents a special asymmetrical structure consisting of a sponge-like layer and a finger-like porous layer, which is propitious to anode electrochemical process. Bi-layer electrolytes consisting of 5 μm thick BZCY and 3 μm thick BZY are successfully fabricated by suspension-coating technique. BZY electrolytes are placed at the cathode side, in order to improve the chemical stability against CO₂. The considerable electrochemical performance and good stability in the presence of CO₂ indicate that the construction of BZY-BZCY bi-layer electrolytes is an effective way for the development of stable proton conducting MT-SOFCs.     

Construction of fuel reformer using proton conducting oxides electrolyte and hydrogen-permeable metal membrane cathode

We constructed a reformer of methane based on an electrochemical principle. This apparatus consists of the proton conducting ceramics electrolyte and the hydrogen-permeable metal membrane cathode. For methane reforming, a mixture of methane and oxygen gas is supplied to the porous Ag cathode. The hydrogen ions, which formed by the anode reaction: CH₄ + O₂ → CO₂ + 4H⁺ + 4e⁻, are transported through the proton conducting ceramics to the cathode. Then, the hydrogen is formed at the cathode by the reaction: 4H⁺ + 4e⁻ → 2H₂. The hydrogen, which permeates through the metal membrane cathode, is 100% purity.The hydrogen separation ability of the reformer was investigated at 400–650 °C by measuring the electric current through the proton conducting oxide electrolyte. Since the ionic transport number of the proton conducting oxide is nearly unity, the current through the electrolyte corresponds to the proton flux through the electrolyte.The current measurements showed that the extracted proton flux through the electrolyte increased with increasing the applied voltage as well as temperature as we expected. However, the current measurements under the low voltage revealed that the extracted current was lesser than the expected value from Ohm's law. The decrease of the current is possibly caused for the reduction of the effective voltage by the anode polarization. In order to separate the hydrogen with higher efficiency, the applied voltage must be as low as possible using the thinner electrolyte and the improved anode.     

The effect of Cr deposition and poisoning on BaZr0.1Ce0.7Y0.2O3−δ proton conducting electrolyte

With the development of chromium tolerant electrode materials, the evaluation of the chromium deposition and poisoning on electrolyte is critical significance for the commercial and widespread application of solid oxide fuel cell stacks (SOFCs). The Cr deposition and poisoning on BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) proton conducting electrolyte are initially studied, in order to understand and develop the compatibility for proton conducting SOFC (H-SOFCs). The XRD results imply that Cr₂O₃ is not chemically compatible with BZCY and BaCrO₄ is formed at high temperature above 600 °C. To simulate the Cr volatilization from interconnect and poisoning on BZCY surface, the BZCY bar sample is heat-treated in the presence of Cr₂O₃ at 600 °C, 700 °C, and 800 °C for 50 h. It is clear that Cr deposition occurs even at 600 °C by SEM examination. The XPS results indicate the chemical deposition of BaCrO₄ and physical deposition of Cr₂O₃ on BZCY surface at 600 °C but only chemical deposition at 700 °C and 800 °C. The content of Cr deposition increases with the increase of poisoning temperature. Moreover, the proton conductivity of BZCY after Cr deposition reduces after Cr deposition, indicating the Cr poisoning effect of the electrochemical performance of BZCY electrolyte.     

Investigation of a methanol processing system comprising of a steam reformer and two preferential oxidation reactors for fuel cells

Methanol steam reforming is able to produce hydrogen-rich syngas onsite for fuel cells and avoids the problems of hydrogen storage. Nevertheless, CO in the reformate needs to be further removed to ppm level before it can be fed into proton exchange membrane fuel cells. In this study, a methanol processing system consisting of a methanol reformer and two-stage preferential oxidation reactors is developed. The hydrogen production performance and scalability of the reformer are experimentally investigated under various operating conditions. The methanol reformer system shows stable methanol conversion rate and linearly increased H₂ flow rate as the number of repeating unit increases. Methanol conversion rate of 96.8% with CO concentration of 1.78% are achieved in the scaled-up system. CO cleanup ability of the two-stage preferential oxidation reactors is experimentally investigated based on the reformate compositions by varying the operating temperature and O₂ to CO ratios. The results demonstrate that the developed CO cleanup train can decrease the CO concentration from 1.6% to below 10 ppm, which meets the requirement of the fuel cell. Finally, stability of the integrated methanol processing system is tested for 180 h operation.     

Performance analysis of a novel heat recovery system with hydrogen production designed for the improvement of boiler effectiveness

In this study, a multi-generation system is designed for the waste recovery of a 150 MW coal-fired power plant. The waste heat from the boiler system of the power plant is recycled in the power block with supercritical organic Rankine Cycle to obtain the required energy for the proton exchange membrane electrolyzer block. Then, two different cases are handled to utilize the products of the proton exchange membrane electrolyzer block. In the first case, H₂ is stored as an energy carrier to be used for external operations where O₂ was used for the enrichment of the combustion air. In the second case, H₂ is used for the enrichment of the fuel where O₂ is used for the enrichment of the combustion air as in the first case. It is determined that it is available to produce H₂ in an amount of 0.0417–0.0433 kmol/s. The energy efficiency of the overall system is determined as 25.37% and 24.05% where the exergy efficiency of the overall system is determined as 31.56% and 29.80% for the first and second cases, respectively.     

Atomistic insight into the hydration and proton conducting mechanisms of the cobalt doped Ruddlesden-Popper structure Sr3Fe2O7-δ

Sr₃Fe₂O_7-δ (SFO) with two-layer Ruddlesden-Popper (R–P) structure has recently been proved to be a promising material for the single phase cathode in proton conducting solid oxide fuel cells (P–SOFCs). To investigate the hydration reactions and proton conducting mechanisms of SFO and cobalt doped SFO (SFCO), both bulk and surface properties were calculated. We conclude that R–P structures have advantages in P–SOFCs. The unique Sr–O–M layer can facilitate the hydration process. Although in Sr–O–F and Sr–O–N layers, it is difficult for the formation and migration of oxygen vacancies, protons are most stable. Furthermore, cobalt doping can not only improve the electronic conductivity but also enhance surface properties of SFCO. The easily exposed Co–Fe–O surface can also facilitate the hydration reactions on the surface. Our work could give an informative insight into the relationships among the doped elements, the R–P structures, the hydration process and the proton conducting properties.     

Nano-sized Fe2O3–SO4 solid superacid composite Nafion membranes for direct methanol fuel cells

In this paper, Fe₂O₃–SO₄²⁻/Nafion^® composite membranes were prepared by a solution casting method. The physico-chemical properties of composite membranes were characterized by X-ray diffraction (XRD), SEM–EDX and thermogravimetric analysis (TGA). The water uptake ability, proton conductivity, and methanol permeability of the composite membranes were evaluated and compared with the recast Nafion^® membrane. The results showed that the proton conductivity and the water uptake of the composite membranes were slightly higher than that of the recast Nafion^® membrane. The composite membrane containing 5 wt.% Fe₂O₃–SO₄^2- showed superior ability to suppress methanol crossover, and it further improved the direct methanol fuel cell (DMFC) performances with both 1 M and 5 M methanol feeding, compared with the recast Nafion^® membrane. The preliminary 30 h lifetime test of the DMFC with the composite membrane with 5% Fe₂O₃–SO₄²⁻ indicated that the composite membrane is stable working at the real DMFC operating conditions at least during the test. These results suggest the applicability of the composite membranes in DMFCs.     

Characterization of Pt supported on commercial fluorinated carbon as cathode catalysts for Polymer Electrolyte Membrane Fuel Cell

Pt nanoparticles supported on carbon monofluoride (CFx), synthesized from H₂PtCl₆ using NaHB₄ as a reducing agent has been investigated as a cathode electrocatalyst in fuel cells. Surface characterization, performed by transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD), shows a homogeneous distribution and high dispersion of metal particles. Kinetic parameters for the electrocatalyst are also obtained from the steady state measurements using a rotating disk electrode (RDE) in 0.5 M H₂SO₄ solution. Analysis by Koutecky–Levich equation indicates an overall 4 e^? oxygen reduction reaction (ORR). Evaluation of the catalyst in single cell membrane electrode assemblies (MEAs) for proton exchange membrane based Direct Methanol Fuel Cell (DMFC) and H₂ Fuel Cell at different temperatures and flows of O₂ and Air are shown and compared against commercial Pt/C as the cathode electrocatalyst. Evaluation of Pt/CFx in H₂ fed fuel cells shows a comparable performance against a commercial catalyst having a higher platinum loading. However, in direct methanol fuel cell cathodes, an improved performance is observed at low O₂ and air flows showing up to 60–70% increase in the peak power density at very low flows (60 mL min^?1).     

BaCo0·4Fe0·4Zr0·1Y0·1O3 –δ triple conductor for boosting electrode efficiency for proton conducting fuel cells

Proton conducting fuel cells (PCFCs) are considered as promising energy generation system due to their possibility for lowering the operation temperature. PCFCs operated at low temperature by conducting small and light protons, which enables stable operation without undesirable side reactions by thermal corrosion. However, kinetic energy for redox reaction at electrodes is insufficient due to the decreased operating temperature, resulting in degraded electrochemical performance. In this study, by forming BaCo_0·4Fe_0·4Zr_0·1Y_0·1O_3-δ (BCFZY), a triple conducting material which could conduct proton, oxygen ions, and electrons at the electrodes, the power generation performance of PCFCs has been improved dramatically. BCFZY nanoparticles provide a charge passage, and effectively expand the reaction site. A proton conducting fuel cells with electrodes containing BCFZY exhibit an enhanced power density of 1.06 W cm^?2 at 650 °C, which is almost 3 times higher value than the cell without formation of BCFZY on the electrodes. Our study proposes an effective strategy for enhancing the performance PCFCs by facilitating the conduction of charge carriers within the electrodes through applying BCFZY triple conductor.     

Hydrogen production in solid oxide electrolyzers coupled with nuclear reactors

In this study, two types of high temperature electrolyzers (O⁼SOE and H⁺SOE) were investigated for hydrogen generation in relation to nuclear power plant operations. The analysis encompasses the thermal integration of proton and ion conducting solid oxide electrolyzers, which are fed with steam generated in the nuclear plant. Under consideration in the study was the steam turbine cycle of an AP1000 nuclear power plant. The main parameters of electrolysis were tailored to match the typical operating temperature of the electrolyzers, and the water utilization factor was set at the same value for the two technologies under consideration. There are some advantages to applying high temperature electrolysis to the deaerator steam feed: first, there is almost no modification of the nuclear steam turbine cycle; second, flexibility of the nuclear power plant rises by 20% with almost constant thermal load of the nuclear reactor; and third, high pressure hydrogen is obtained for commercial purposes. The analysis concludes that hydrogen can be produced in electrolyzers integrated with nuclear plants at an energy cost of 38.83 and 37.55 kWh kg_H2⁻¹ for protonic and ionic solid oxide electrolyzers, respectively.