Intermediate Temperature Proton Exchange Membrane Research Articles

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.

Nafion/IL Intermediate Temperature Proton Exchange Membranes Improved by Mesoporous Hollow Silica Spheres

AbstractA novel polyelectrolyte composite membrane was designed and prepared for intermediate temperature proton exchange membrane fuel cells (PEMFCs). It was composed of perfluorosulfonic acid resin (Nafion®), protic ionic liquid (IL, [dema][TfO]) and mesoporous hollow silica spheres (MHSi). The morphologies of MHSi and Nafion‐based composite membranes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of MHSi on proton conductivity of the composite membranes versus relative humidity (RH) and temperature (100–140 °C) were investigated. The results indicated, that the Nafion/IL/MHSi composite membranes exhibited excellent proton conductivity even under 30% RH or high temperature (above 100 °C). A high proton conductivity (5.41 mS cm−1) of the composite membrane at 30 °C and 30% RH can be observed from the test result, which was five times higher than that of the pristine Nafion. The N‐IL‐12S composite membrane showed an outstanding proton conductivity, as far as 14.7 mS cm−1 under 140 °C and low RH, which was almost two orders higher than that of the pristine Nafion membrane. Moreover, the unique hollow and mesoporous structure of MHSi improved IL retention rate of the membrane evidently. Together with high thermal stability of the composite membrane confirmed by thermogravimetric analysis (TGA), the Nafion/IL composite membrane improved by MHSi is a potential candidate in intermediate temperature PEMFC.

Unique Proton Transportation Pathway in a Robust Inorganic Coordination Polymer Leading to Intrinsically High and Sustainable Anhydrous Proton Conductivity.

Although comprehensive progress has been made in the area of coordination polymer (CP)/metal-organic framework (MOF)-based proton-conducting materials over the past decade, searching for a CP/MOF with stable, intrinsic, high anhydrous proton conductivity that can be directly used as a practical electrolyte in an intermediate-temperature proton-exchange membrane fuel cell assembly for durable power generation remains a substantial challenge. Here, we introduce a new proton-conducting CP, (NH4)3[Zr(H2/3PO4)3] (ZrP), which consists of one-dimensional zirconium phosphate anionic chains and fully ordered charge-balancing NH4+ cations. X-ray crystallography, neutron powder diffraction, and variable-temperature solid-state NMR spectroscopy suggest that protons are disordered within an inherent hydrogen-bonded infinite chain of acid-base pairs (N-H···O-P), leading to a stable anhydrous proton conductivity of 1.45 × 10-3 S·cm-1 at 180 °C, one of the highest values among reported intermediate-temperature proton-conducting materials. First-principles and quantum molecular dynamics simulations were used to directly visualize the unique proton transport pathway involving very efficient proton exchange between NH4+ and phosphate pairs, which is distinct from the common guest encapsulation/dehydration/superprotonic transition mechanisms. ZrP as the electrolyte was further assembled into a H2/O2 fuel cell, which showed a record-high electrical power density of 12 mW·cm-2 at 180 °C among reported cells assembled from crystalline solid electrolytes, as well as a direct methanol fuel cell for the first time to demonstrate real applications. These cells were tested for over 15 h without notable power loss.

Erratum: Substrate Grain-Dependent Chemistry of Carburized Planar Anodic TiO2 on Polycrystalline Ti.

[This corrects the article DOI: 10.1021/acsomega.6b00472.].

Substrate Grain-Dependent Chemistry of Carburized Planar Anodic TiO2 on Polycrystalline Ti.

Mixtures or composites of titania and carbon have gained considerable research interest as innovative catalyst supports for low- and intermediate-temperature proton-exchange membrane fuel cells. For applications in electrocatalysis, variations in the local physicochemical properties of the employed materials can have significant effects on their behavior as catalyst supports. To assess microscopic heterogeneities in composition, structure, and morphology, a microscopic multitechnique approach is required. In this work, compact anodic TiO2 films on planar polycrystalline Ti substrates are converted into carbon/titania composites or multiphase titanium oxycarbides through carbothermal treatment in an acetylene/argon atmosphere in a flow reactor. The local chemical composition, structure, and morphology of the converted films are studied with scanning photoelectron microscopy, micro-Raman spectroscopy, and scanning electron microscopy and are related with the crystallographic orientations of the Ti substrate grains by means of electron backscatter diffraction. Different annealing temperatures, ranging from 550 to 850 °C, are found to yield different substrate grain-dependent chemical compositions, structures, and morphologies. The present study reveals individual time scales for the carbothermal conversion and subsequent surface re-oxidation on substrate grains of a given orientation. Furthermore, it demonstrates the power of a microscopic multitechnique approach for studying polycrystalline heterogeneous materials for electrocatalytic applications.

Effect of Catalyst Layer Ionomer Content on Performance of Intermediate Temperature Proton Exchange Membrane Fuel Cells (IT-PEMFCs) under Reduced Humidity Conditions

For intermediate-temperature polymer electrolyte membrane fuel cells (IT-PEMFCs), the effects of the cathode gas flow rate and the ionomer content are experimentally examined at 120°C under conditions of low relative humidity (RH). The IT-PEMFC operation at low RH should be beneficial in developing compact systems with smaller humidifiers. First, analysis of the effect of gas flow rate at various current densities confirms that drying of the membrane electrode assembly (MEA) is an important factor in IT-PEMFC operation, whereas cathode flooding becomes significant in regions of high current density with low flow rates. Then, MEAs with various contents of Aquivion™ ionomer are fabricated, and the combined effect of drying and flooding is further investigated by IT-PEMFC tests at various RH conditions and current densities. The optimum ionomer content increases with decreasing current density at 20% RH or below, indicating that MEA drying becomes dominant over cathode flooding.

Analysis of the system efficiency of an intermediate temperature proton exchange membrane fuel cell at elevated temperature and relative humidity conditions

Humidification of the membrane is very important in a proton exchange membrane fuel cell (PEMFC), to maintain high ionic conductivity. At an elevated temperature, a large amount of thermal energy is required for humidification because of the exponentially increased saturation vapor pressure. In this study, the system efficiency of a PEMFC was evaluated by considering the heat required for preheating/humidification and compression work. Three-dimensional steady-state simulations were conducted using Fluent 14 to simulate the electrochemical reactions. The operating conditions were optimized using response surface methodology by considering both the fuel cell output and system efficiency. In addition, the effects of operating parameters such as the temperature, relative humidity, and stoichiometric ratio were investigated. The system efficiency can be improved more effectively by increasing relative humidity rather than increasing operating temperature because the ionic conductivity of the membrane was strongly influenced by the relative humidity.

Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes

Herein we present the synthesis and characterization of new phosphonate-, bisphosphonate- and hydroxybisphosphonatebenzimidazole derivatives substituted at the N-1 position and new regioisomers phosphonate-, bisphosphonate-, and hydroxybisphosphonatebenzotriazole derivatives substituted at N-1 or N-2 positions. The compounds were characterized by NMR and IR spectroscopies, and mass spectrometry (low and high resolution) allowing the assignment of their structure, including the identification of regioisomers. These new azole monomers will be precursors for a mesoporous silica host to produce novel membrane materials with high proton conductivity for intermediate temperature proton exchange membrane fuel cells.

H3PO4 incorporated microporous hydrogel frameworks for intermediate temperature proton exchange membrane fuel cells

Microporous polyacrylamide/chitosan (PAAm/CS) matrix is employed as a placeholder for proton conductor H3PO4 benefiting from the adsorption of hydrogel material to H3PO4 aqueous solution. Prior to fabrication, closed microporous structure of PAAm/CS matrix is opened by a freeze drying process, following by being immersed three-dimensional PAAm/CS in concentrated H3PO4 aqueous solutions. Anhydrous H3PO4 incorporated PAAm/CS membranes are obtained after a dehydration process, which are used as intermediate-temperature proton exchange membranes (PEMs). The microporous structure, loading of H3PO4, proton conductivity, electrochemical behaviors, and fuel cell performances are systematically evaluated. Due to high H3PO4 loading in per volume unit of PEM and rapid proton migration, an impressive proton conductivity as high as 0.173 S cm−1 at 165°C under anhydrous condition is recorded. A fuel cell using a thick PEM shows a peak power density of 615 mW cm−2 with O2 and H2 as the oxidant and fuel respectively.

A new fabrication method of an intermediate temperature proton exchange membrane by the electrospinning of CsH2PO4

A novel method for the fabrication of an intermediate temperature proton conducting composite membrane was developed. Cesium dihydrogen phosphate, CsH2PO4 (CDP), was electrospun to obtain a highly interconnected proton conducting fibre mat. CsH2PO4 was heat treated above its dehydration temperature (Tdehy ∼ 230 °C) in order to induce a partial polymerisation. The partially polymerised material produced a viscous aqueous solution which could be electrospun in the absence of a carrier polymer, thus leading to pure inorganic fibres. The electrospun fibre mats were characterised in terms of composition, structure and morphology by XRD, MAS NMR and SEM and their proton conductivity determined by electrochemical impedance spectroscopy. The electrospun fibres (CDPf) showed a maximum proton conductivity of 8 × 10−3 S cm−1 at 250 °C.

Physicochemical properties of new amide-based protic ionic liquids and their use as materials for anhydrous proton conductors

We prepared 3 protic ionic liquids based on trifluoromethanesulfonic acid and an amide, namely isobutyramide (ITSA), n-butyramide(NTSA), and benzamide(BTSA). All of the protic ionic liquids exhibit excellent thermal stability (above 200 °C). ITSA has the highest ionic conductivity, which is 32.6 mS/cm at 150 °C. ITSA was used to prepare anhydrous, conducting composite membranes based on polymers of polyvinylidene-fluoride (PVDF) to serve as intermediate temperature proton exchange membrane fuel cells. This type of composite membrane possesses good thermal stability, high ionic conductivity and good mechanical properties. Increasing the polymer content leads to the improvement of mechanical properties, but is accompanied by a reduction in ionic conductivity. We made efforts to eliminate the trade-off between strength and conductivity of the ITSA/PVDF composite membrane by adding polyamide imide, which resulted in a simultaneous increase in strength and conductivity. A conductivity of 7.5 mS/cm is achieved in a membrane containing 60 wt.% ITSA and 5 wt.% PAI in PVDF at 150 °C.

New Anhydrous Proton Exchange Membrane for Intermediate Temperature Proton Exchange Membrane Fuel Cells

Herein, we study the preparation and characterization of a new kind of proton exchange membrane. In the proton-conducting membrane of poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO)/dodecyl benzenesulfonic acid (DBS-H), we use PEO as "proton solvent" due to its flexible molecular chain. Moreover, the electronegativity of the O atom on PEO may be used to attract protons under anhydrous conditions. The membranes are thermally stable up to 200 °C with less than 3 % mass loss. At 150 °C, without extra humidification, the proton conductivity of 60 % PVDF/22 % PEO/18 % DBS-H membrane is approximately 10 (-3) S cm(-1).

A cell voltage equation for an intermediate temperature proton exchange membrane fuel cell

A zero dimensional isothermal model equation for a single Intermediate Temperature Fuel Cell is developed and expressed as a semi-empirical relationship for cell potential as a function of current density. The model is applicable to fuel cells in which reactants and water product are in the gaseous or vapour phase. The model considers the influence of electrode kinetics using the Butler Volmer equation, over the complete voltage range, Ohmic potential losses and the effect of mass transport through electrolyte films covering catalyst layers on kinetics and thermodynamics. The model is used to simulate the variation in polarisation behaviour of a hydrogen fuel cell using a phosphoric acid doped PBI membrane. Performance predictions using published parameters for electrode kinetics, thermodynamics, conductivity and mass transport are compared with data from a laboratory fuel cell. Agreement between the model predictions and experimental data are good and indicate the relatively simple cell voltage model equation is suitable for estimating fuel cell voltage and power performance.

Preparation and proton conductivity of composite membranes based on sulfonated poly(phenylene oxide) and benzimidazole

The Brønsted acid–base composite membrane was prepared by entrapping benzimidazole in sulfonated poly(phenylene oxide) by tuning the doping ratios. Their thermal stability, dynamic mechanical properties and proton conductivity were investigated under the conditions for intermediate temperature proton exchange membrane (PEM) fuel cell operation. In addition, investigation of activation energies of the SPPO– xBnIm at different relative humidity was also performed. TG–DTA curves reveal these SPPO– xBnIm composite materials had the high thermal stability. The proton conductivity of SPPO– xBnIm composite material increased with the temperature, and the highest proton conductivity of SPPO– xBnIm composite materials was found to be 8.93 × 10 −4 S/cm at 200 °C under 35% relative humidity (RH) with a “doping rate” where x = 2. The SPPO–2BnIm composite membrane show higher storage moduli and loss moduli than SPPO. Tests in a hydrogen–air laboratory cell demonstrate the applicability of SPPO–2BnIm in PEMFCs at intermediate temperature under non-humidified conditions.

A High-Performance Mo2C-ZrO2 Anode Catalyst for Intermediate-Temperature Fuel Cells

Anode performance of non-Pt catalysts for hydrogen oxidation was investigated in intermediate-temperature proton exchange membrane fuel cells. Molybdenum carbide showed the highest catalytic activity among the transition metal carbides tested. Furthermore, the catalytic activity of was significantly improved by the addition of to the anode. Transmission electron microscopy and X-ray diffraction measurements revealed that was more highly dispersed in the than in the , suggesting that the particle growth of was suppressed by the addition of . We also tested the performance of a fuel cell using and as the anode and electrolyte materials, respectively, between 150 and . At or higher, the anode showed a cell performance comparable to that of the anode. However, cell performance was strongly dependent on the operating temperature, reflecting that the catalytic activity of was greatly lowered by the decrease in operating temperature. Thus it was concluded that the catalyst is a promising alternative anode material to Pt, especially at intermediate temperatures.

Analytical correlations for intermediate temperature PEM fuel cells

This paper presents analytical correlations, which predict the polarization performance and thermal effects in an intermediate temperature proton exchange membrane fuel cell (PEMFC). Such correlations are useful for engineers and designers of fuel cells to expedite calculations without depending on complex computational models. Analytical results compare well with published experimental polarization data. They also indicate the temperature variations and dominant modes of heat transfer in a unit cell.

Parametric model of an intermediate temperature PEMFC

Proton exchange membrane fuel cells operating with Nafion ® membranes have encountered numerous problems associated with water management and CO poisoning because of their low temperature of operation. Higher temperature membranes have been investigated, one such membrane being polybenzimidazole (PBI). This paper presents a parametric model, which predicts the polarization performance of an intermediate temperature proton exchange membrane fuel cell (PEMFC). It also investigates the effects of porous media characteristics on fuel cell performance. Results show that for intermediate temperature fuel cells, mass limitation effects are absent as long as the catalyst regions are sufficiently permeable. It is predicted that the greatest scope for improving PBI PEMFC performance is increasing the membrane conductivity and improving the catalyst performance, as it interfaces with the PBI membrane.