Self-humidifying Membrane Research Articles

Self-Humidifying Membrane for High-Performance Fuel Cells Operating at Harsh Conditions: Heterojunction of Proton and Anion Exchange Membranes Composed of Acceptor-Doped SnP2O7 Composites.

Here we suggest a simple and novel method for the preparation of a high-performance self-humidifying fuel cell membrane operating at high temperature (>100 °C) and low humidity conditions (<30% RH). A self-humidifying membrane was effectively prepared by laminating together proton and anion exchange membranes composed of acceptor-doped SnP2O7 composites, Sn0.9In0.1H0.1P2O7/Sn0.92Sb0.08(OH)0.08P2O7. At the operating temperature of 100 °C, the electrochemical performances of the membrane electrode assembly (MEA) with this heterojunction membrane at 3.5% RH were better than or comparable to those of each MEA with only the proton or anion exchange membranes at 50% RH or higher.

Enhanced low-humidity performance of proton exchange membrane fuel cell by incorporating phosphoric acid-loaded covalent organic framework in anode catalyst layer

Developing self-humidifying membrane electrode assembly (MEA) is of great significance for the practical use of proton exchange membrane fuel cell (PEMFC). In this work, a phosphoric acid (PA)-loaded Schiff base networks (SNW)-type covalent organic framework (COF) is proposed as the anode catalyst layer (CL) additive to enhance the PEMFC performance under low humidity conditions. The unique polymer structure and immobilized PA endow the proposed COF network with not only excellent water retention capacity but also proton transfer ability, thus leading to the superior low humidity performance of the PEMFC. The optimization of the additive content, the effect of relative humidity (RH) and PEMFC operating temperature are investigated by means of electrochemical characterization and single cell test. At a normal operation temperature of 60 °C and 38% RH, the MEA with optimized COF content (10 wt%) showes the maximum power density of 582 mW cm−2, which is almost 7 times higher than that of the routine MEA (85 mW cm−2). Furthermore, a preliminary durability test demonstrates the potential of the proposed PEMFC for practice operation under low humidity environment.

Progress of Self-Humidifying Membrane Electrode Assembly for Low Temperature Proton Exchange Membrane Fuel Cell

Progress of Self-Humidifying Membrane Electrode Assembly for Low Temperature Proton Exchange Membrane Fuel Cell

Fabrication of highly effective self-humidifying membrane electrode assembly for proton exchange membrane fuel cells via electrostatic spray deposition

One major challenge associated with proton exchange membrane fuel cells is to preserve higher proton conductivity under low-humidity atmosphere. Elevation of water uptake in the perfluorinated polymeric membrane is crucial for the facilitated transportation of proton, which dominates the fuel cell performance. Development of an intrinsic mechanism that controls water balance through the membrane electrode assembly (MEA), eliminates the need for external water management system and thus makes the system suitable for portable applications, where size is an important criterion to be considered. Herein, we report a nano-sized dense-structure (NSDS) layer coated onto the conventional catalyst layer, forming a dual-layered electrode architecture that is favorable in promoting the self-humidification process. This self-humidifying layer is fabricated by the electrostatic spray deposition with sufficiently low deposition rate, which allows for a creation of more uniformly distributed porous structure with diameters smaller than 80 nm, enabling recirculation of the water generated for proper humidification. When experimentally investigated, the MEA employing the dual-layered electrode reveals a 3.15 times elevated current density at 0.6 V than conventional MEA under 0% relative humidity. Mechanism for the water retention in the proposed electrode is further evaluated by X-ray computed tomography, which reveals dramatically increased tortuosity of 4.43 for the NSDS layer in comparison to 1.9 for the conventional catalyst layer.

Chlorine-contaminated anode and cathode PEMFC-recovery perspective

Progressive thinking about future generation proton exchange membrane fuel cells (PEMFCs) leads us to cost-effective compact fuel cells operating with dry reactants using self-humidifying membranes. Presently, however, PEMFCs are limited by number of factors. One such factor is the reactant impurities present in the feed streams. Chlorine is one such impurity affecting both anode and cathode PEMFC adversely. Several studies have reported adverse impact of anionic chloride in PEMFCs but scarce or no literature is available on the effect of chlorine gas as such on PEMFCs. In the present work, we report for the first time to the best of our knowledge the adverse effects of chlorine when introduced on anode and cathode independently using a single-cell PEMFC. About 94% (anode) and 82% (cathode) loss in performance is observed at an operating voltage of 0.6 V after contamination with 100 ppm chlorine at the anode and cathode respectively. It is found that operating at higher current density plays a significant role in the PEMFC recovery process. The duration of recovery changes for anode-contaminated cell and cathode-contaminated cell, which is 2 and 4 h respectively. The protons on the anode side and the hydroxyl ion at the cathode side help in replacing the chloride species adsorbed on the platinum surface. The electrochemical impedance studies show an increase in the charge transfer resistance after cathode contamination, whereas in the case of anode contamination, the cell resistance increases while maintaining the same charge transfer resistance.

(Invited) Self-Humidifying Membrane Electrode Assembly Prepared by Adding Moisture Preserve Materials in Anode Catalyst Layer

By adding moisture preserve materials in the anode catalyst layer, we prepared a series of low humidity membrane electrode assembly (MEAs), and all the MEAs exhibited excellent performances at low humidity for both anode fuel and cathode air. The effects of the structure, used amount of the materials on the low humidity performances of the MEAs were investigated, and we also explored the mechanism for the excellent low-humidity performances of the MEAs with moisture preserve material added at anode catalyst layer.

(Invited) Self-Humidifying Membrane Electrode Assembly Prepared by Adding Moisture Preserve Materials in Anode Catalyst Layer

By adding moisture preserve materials in the anode catalyst layer, we prepared a series of low humidity membrane electrode assembly (MEAs), and all the MEAs exhibited excellent performances at low humidity for both anode fuel and cathode air. The types of the materials on the low humidity performances of the MEAs were investigated, and we also explored the mechanism for the excellent low-humidity performances of the MEAs with moisture preserve material added at anode catalyst layer.

Three-dimensional reconstruction of coarse-dense dual catalyst layer for proton exchange membrane fuel cells

ABSTRACT An exploration on self-humidifying membrane electrode assembly in proton exchange membrane fuel cells (PEMFCs) has attracted great attention for their potential use in the practical system. Recently, several researchers succeeded in improving the self-humidifying performance with multiple-layered electrodes, by retaining the liquid water, despite the fact that mechanistic details in such electrode structures are yet in vague. In this work, we report a three-dimensional reconstruction of the dual-layered electrode for PEMFCs. The PEMFC catalyst layer fabricated by a serial decal-transfer method is characterized by the focused ion beam-scanning electron microscope; the segmented images on the electrode structures are integrated by the tomography analysis. This approach allows a complete consideration of the electrode morphology, providing several key pore-structural information, e.g., porosity, diffusivity and tortuosity. As compared with the inner catalyst layer, the outer catalyst layer may significantly reduce the diffusion rate and thus promote the structural-driven retention of liquid water during the PEMFC operation.

Nanocrack-regulated self-humidifying membranes.

The regulation of water content in polymeric membranes is important in a number of applications, such as reverse electrodialysis and proton-exchange fuel-cell membranes. External thermal and water management systems add both mass and size to systems, and so intrinsic mechanisms of retaining water and maintaining ionic transport in such membranes are particularly important for applications where small system size is important. For example, in proton-exchange membrane fuel cells, where water retention in the membrane is crucial for efficient transport of hydrated ions, by operating the cells at higher temperatures without external humidification, the membrane is self-humidified with water generated by electrochemical reactions. Here we report an alternative solution that does not rely on external regulation of water supply or high temperatures. Water content in hydrocarbon polymer membranes is regulated through nanometre-scale cracks ('nanocracks') in a hydrophobic surface coating. These cracks work as nanoscale valves to retard water desorption and to maintain ion conductivity in the membrane on dehumidification. Hydrocarbon fuel-cell membranes with surface nanocrack coatings operated at intermediate temperatures show improved electrochemical performance, and coated reverse-electrodialysis membranes show enhanced ionic selectivity with low bulk resistance.

High-performance membrane electrode assembly with multi-functional Pt/SnO2–SiO2/C catalyst for proton exchange membrane fuel cell operated under low-humidity conditions

A novel self-humidifying membrane electrode assembly (MEA) with homemade multi-functional Pt/SnO2–SiO2/C as the anode was developed to improve the performance of a proton exchange membrane fuel cell under low humidity. The MEAs' performance was evaluated at various temperatures and relative humidity levels. One MEA with a Pt/SnO2–SiO2/C anode catalyst achieved excellent low-humidity performance at a cell temperature of up to 60 °C: the current density reached 600 mA cm−2 at 0.7 V and 1050 mA cm−2 at 0.6 V with 10% RH; after 96 h of continuous operation under the same conditions, the current density decreased by only 16% (to ∼880 mA cm−2), whereas the current density of an MEA with JM Pt/C as the anode degraded by more than 60% within 10 h. The contact angle of the Pt/SnO2–SiO2/C anode was much lower than that of the Pt/C anode, indicating the former's excellent wettability. The high performance of the MEA with the Pt/SnO2–SiO2/C anode is attributable to the wettability of the doped binary oxide, especially of silicon oxide, and the promotion of tin oxide, which caused an interaction between the Pt and the oxide, resulting in enhanced performance under low humidification.

Self-humidifying membrane electrode assembly with dual cathode catalyst layer structure prepared by introducing polyvinyl alcohol into the inner layer

Short-term constant voltage discharge test of the self-humidifying MEAs with different cathode structure at 60 °C and 30 psi under 20% RH.

Enhanced low-humidity performance in a proton exchange membrane fuel cell by the insertion of microcrystalline cellulose between the gas diffusion layer and the anode catalyst layer

A high-performance self-humidifying membrane electrode assembly (MEA) was prepared by inserting hygroscopic microcrystalline cellulose (MCC) between the gas diffusion layer (GDL) and the catalyst layer (CL). At low humidity, the MEA exhibited good self-humidification, including high output and good stability. With our optimal MEA, in which the MCC loading was ca. 0.5 mg cm−2, the current density at 0.6 V reached 1100 mA cm−2 and the maximum power density was 751 mW cm−2, at a relative humidity (RH) of 30% for both anode and cathode gases and a cell temperature of 70 °C; the performance was comparable to that of a MEA prepared without added MCC and operated at 100% RH. Further, after 24 h of operation at low humidity and 0.6 V, the MEA's current density decreased by only 9.1%, compared with the 60% decline experienced by the MEA without MCC after 3 h under the same conditions, demonstrating the former's good self-humidification stability. When we attempted to insert the MCC layer elsewhere, including between the membrane and the anode CL, we found that inserting it between the GDL and the anode CL yielded the best performance. The high self-humidification performance of this MEA is attributable to the strong wettability and water-retention capacity of MCC. The MCC layer between the GDL and the anode CL ensured the latter would remain sufficiently wet and accelerated hydrogen activation and proton transfer, resulting in the MEA having high self-humidification under conditions of low humidity and high cell temperature.

Electrophoretic Deposited Pt/C/SiO2 Anode for Self-Humidifying and Improved Catalytic Activity in PEMFC

In this study, the electrophoresis deposition (EPD) method was employed to prepare hydrophilic Pt/C/SiO2 anode for obtaining self-humidifying membrane electrolyte assemblies (MEAs). The SiO2 nanospheres prepared by sol gel method are with 65nm diameter averagely. The self-humidifying MEAs consist of hydrophilic anodes, JM-GDE cathode, and polymer electrolyte (Nafion 212, DuPont), were prepared via hot pressing and then incorporated into single cell (9cm2) for testing. Effects of SiO2 mass fraction and humidity on Pt mass activity and long-term durability are discussed. Besides the addition of SiO2 nanospheres, Pt mass activity on anode was enhanced from 1941 to 2856mA/mgPt while operating under the operating cell voltage of 0.6V and 100% relative humidity (RH) condition. Furthermore it also enhanced from 1529 to 2709mA/mgPt under cell operation conditions of 0.6V and 30 % RH. For the long-term durability under severe condition (<30% RH), the routine single cell manifests a significant voltage decline of about 15.5%. While single cell with our proposed hydrophilic anodes shows only 4.5% of voltage declining rate for exceeding 560hours operating. Our proposed methodology in this study not only results in an outstanding Pt mass activity but also in an excellent slef-humification.

Preparation of new self-humidifying composite membrane by incorporating graphene and phosphotungstic acid into sulfonated poly(ether ether ketone) film

In this work, a combination of constituent materials capable of improving the moisture retention and proton conductivity (PC) was incorporated into sulfonated poly (ether ether ketone) (SPEEK) membranes in order to prepare new, self-humidifying composite membranes (SHMs) for proton exchange membrane fuel cells. The property-improving components were incorporated into the cast SPEEK film in an appropriate microstructural architecture to prepare the SHMs with increased water retention and PC. SHMs were therefore prepared with the inclusion of carboxyl-functionalized graphene (G(c)) and phosphotungstic acid (PWA) with varying proportions into the SPEEK film. The structure of the SPEEK/G(c)/PWA composite membranes was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The physicochemical properties of the composite membranes, such as ion exchange capacity, water uptake, thermal stability and PC, were investigated. This work provides confirmation that self-humidifying properties are improved at temperature above 60 °C through a combinational inclusion of G(c) and PWA within SPEEK and the new self-humidifying membranes have potential for use in medium temperature direct methanol fuel cells.

Self-humidifying membrane electrode assembly prepared by adding microcrystalline cellulose in anode catalyst layer as preserve moisture

A novel self-humidifying membrane electrode assemblies (MEAs) with the addition of microcrystalline cellulose (MCC) as a hygroscopic agent into anode catalyst layer was prepared to improve the performance of proton exchange membrane fuel cell (PEMFC) under low humidity conditions. The MEAs were characterized by SEM, contact angles and water uptake measurements. The MEAs with addition of MCC exhibit excellent self-humidifying single cell performance, the cell temperature for self-humidification running is up to 60 °C. As an optimized MEA with 4 wt.％ MCC in its anode catalyst layer, its current density at 0.6 V could be up to 760 mA cm−2 under 20% of relative humidity, and remains at 680 mA cm−2 after 22 h long time continuous testing, the attenuation of the current density is only 10%. While the current density of the blank MEA without addition of MCC degraded sharply from 300 mA cm−2 to 110 mA cm−2, the attenuation of the current density is high up to 70% within 2 h.

Effect of the hydrophilic and hydrophobic characteristics of the gas diffusion medium on polymer electrolyte fuel cell performance under non-humidification condition

Water is a significant component of polymer electrolyte fuel cells, affecting the proton conductivity in the membrane electrolyte. Therefore, polymer electrolyte fuel cells are generally operated with a humidifier to maintain a high relative humidity of the supplied gases; however, the humidifier contributes additional weight and cost. Although many studies have attempted to develop polymer electrolyte fuel cells without a humidifier, the studies have been mainly focused on the self-humidified membrane electrolyte and catalyst layer. In this paper, the author investigates the effect of polytetrafluoroethylene coated gas diffusion medium on the water content in the membrane electrolyte. The water condensation on the surfaces of the gas diffusion medium is visualised when the polymer electrolyte fuel cell is operated under non-humidification conditions. Numerical simulation suggests that the optimum water saturation is between 0.1 and 0.3 at the gas diffusion medium to hydrate the membrane electrolyte sufficiently without significantly blocking the diffused species under non-humidification conditions.

A New Incorporation Method of Metallic Precursors Into a Nafion Film via a Drying Process for thePreparation of Metallic Nanocatalysts/Nafion

A new simple drying process was developed in order to prepare a metallic nanocatalysts/Nafion for self-humidifying membrane in a proton-exchange membrane fuel cell (PEMFC). Metallic precursors such as platinum(ll) bis(acetylacetonate) or palladium(ll) bis(acetylacetonate) was sublimed and simultaneously penetrated into the surface of a Nafion film. And then it was reduced to Pt or Pd nanoparticles beneath the film surface without a special reducing agent in a glass reactor of N2 atmosphere at 180 degrees C for 5, 10, 30 and 60 min, respectively. The morphology and distribution of the Pt or Pd nanoparticles were observed by transmission electron microscopy (TEM) and elemental analysis was carried out by an energy dispersive spectroscopy (EDS), and we found that the penetration depth of the metallic nanoparticles and the particle sizes increased with increasing exposure time to the metallic precursors, and the particle size at the surface area was larger than that at the deeper area.

High-performance self-humidifying membrane electrode assembly prepared by simultaneously adding inorganic and organic hygroscopic materials to the anode catalyst layer

A novel self-humidifying membrane electrode assembly (MEA) has been successfully prepared by adding both a hydrophilic organic polymer (polyvinyl alcohol, PVA) and an inorganic oxide (silica) to the anode catalyst layer. This MEA shows excellent self-humidification performance under low-humidity conditions. A sample containing 3 wt.% PVA and 3 wt.% silica in the anode catalyst layer achieves a current density as high as 1100 mA cm−2 at 0.6 V, and the highest peak power density is 780 mW cm−2, operating at 60 °C and 15% relative humidity for both anode and cathode. The sample also shows excellent stability at low-humidity: after 30 h of continuous operation under the same conditions, the current density decreases just slightly, from 1100 mA cm−2 to ca. 900 mA cm−2, whereas with MEAs to which only PVA or silica alone had been added, the current densities after 30 h is just 700 mA cm−2 and 800 mA cm−2, respectively. The improved self-humidification performance can be attributed to the synergistic effect of two hygroscopic materials in the anode catalyst layer.

Self-humidifying membrane electrode assembly prepared by adding PVA as hygroscopic agent in anode catalyst layer

In this work, a novel self-humidifying membrane electrode assembly (MEA) with addition of polyvinyl alcohol (PVA) as the hygroscopic agent into anode catalyst layer was developed for proton exchange membrane fuel cell (PEMFC). The MEA shows good self humidification performance, for the sample with PVA addition of 5 wt.% (MEA PVA5), the maximum power density can reach up to 623.3 mW·cm−2, with current densities of 1000 mA·cm−2 at 0.6 V and 600 mA·cm−2 at 0.7 V respectively, at 50 °C and 34% of relative humidity (RH). It is interesting that the performance of MEA PVA5 hardly changes even if the relative humidity of both the anode and cathode decreased from 100% to 34%. The MEA PVA5 also shows good stability at low humidity operating conditions: keeping the MEA discharged at constant voltage of 0.6 V for 60 h at 34% of RH, the attenuation of the current density is less than 10%, whilst for the MEA without addition of PVA, the attenuation is high up to 80% within 5 h.

Zeolite applications in fuel cells: Water management and proton conductivity

Zeolites are increasingly used in fuel cell, from fuel conversion and conditioning to membrane additives as well as support for electrocatalysts. Zeolites’ ionic conductivity and capacity for water adsorption and retention were exploited to create zeolite and zeolite-PFSA proton conducting membranes for PEMFC. HZSM-5 micromembranes of different Si/Al ratios (from ∞ for Sil-1 to 30) were fabricated in a regular array on silicon followed by assembly and test for fuel cell performance. HZSM-5 with high aluminum content exhibits good proton conductivity and better PEMFC performance that approaches that of Nafion MEA. A rational approach in the design of structured HZSM-5-PFSA composite membrane was demonstrated. The PFSA was confined in subnanoliter volumes within zeolite sleeves to obtain self-humidifying membrane and enhanced PEMFC performance (i.e., up to nine-fold in MPD) at elevated temperatures (i.e., up to 100°C) and dry conditions. Higher water retention and improved membrane thermomechanical properties are believed to be responsible.