High Performance Membrane Electrode Research Articles

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.

Fabrication and Optimization of Membrane Electrode Assembly with Support-Less Platinum Catalysts for Space Applications

Hydrogen-oxygen fuel cell technology is a critical component for crewed space exploration mission beyond low earth orbit. While lowering platinum loading is of paramount importance for automotive fuel cells, it is not a significant constraint for MEAs used for space applications. As such, support-less platinum black catalysts is a viable choice. Historically, surfactant-stabilized polytetrafluoroethylene (PTFE) emulsion is used as the binder for platinum black electrode. High temperature treatment steps needed for the PTFE emulsion prevents the direct deposition of the electrocatalysts onto the Nafion® membrane. In this study, two alternative materials have been used to replace PTFE emulsion. These include surfactant-free PTFE fine particles and functionalized carbon nanotube with Nafion®. An ultrasonic spray deposition technique was applied to directly deposit support-less Pt black catalyst ink onto the Nafion® membrane. The fabrication process was optimized to produce high performance membrane electrode assemblies that approaching NASA performance target.

High Performance Membrane Electrode Assembly with Low Platinum Loadings Prepared by Atomic Layer Deposition for PEMFC Application

High Performance Membrane Electrode Assembly with Low Platinum Loadings Prepared by Atomic Layer Deposition for PEMFC Application

Cost-Effective Materials for Direct Borohydride Fuel Cells

A direct borohydride fuel cell (DBFC) is considered as an attractive energy conversion device. Cost and performance are two major factors affecting the commercialization of DBFCs. This research attempts to develop high-performance membrane electrolyte and electrode for DBFCs using low-cost materials. An effective anode consisting of Ni-based composite electrocatalysts loaded on Ni foam substrate was developed and employed. The use of Ni-based catalyst provides a solution for cost reduction. Chitosan, a cost-effective and eco-friendly material, was employed to prepare both electrode binder and polymer electrolyte. Chitosan membrane gave more than 50 % higher power performance than the commercial Nafion® membranes in DBFCs and costs less than 10% of the cost of Nafion®.

High Performance Membrane Electrode Assembly Fabricated by Ultrasonic Spray Technique

The core of a polymer electrolyte membrane fuel cell stacks are membrane electrode assemblies (MEAs). Manufacturing processes for MEA have significant impact on their performance and durability. The authors report an ultrasonic atomization and spraying technique to deposit catalyst layer directly onto the membrane to realize membrane electrode assemblies. Electrochemical test of as-fabricated MEAs indicated very good performance and reasonable stability. The Platinum yield of the fabrication process was found to be around 89%.

Study of catalyst sprayed membrane under irradiation method to prepare high performance membrane electrode assemblies for solid polymer electrolyte water electrolysis

In this work, a catalyst sprayed membrane under irradiation (CSMUI) method was investigated to develop high performance membrane electrode assembly (MEA) for solid polymer electrolyte (SPE) water electrolysis. The water electrolysis performance and properties of the prepared MEA were evaluated and analyzed by polarization curves, electrochemistry impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The characterizations revealed that the CSMUI method is very effective for preparing high performance MEA for SPE water electrolysis: the cell voltage can be as low as 1.564 V at 1 A cm −2 and the terminal voltage is only 1.669 V at 2 A cm −2, which are among the best results yet reported for SPE water electrolysis with IrO 2 catalyst. Also, it is found that the noble metal catalysts loadings of the MEA prepared by this method can be greatly decreased without significant performance degradation. At a current density of 1 A cm −2, the MEA showed good stability for water electrolysis operating: the cell voltage remained at 1.60 V without obvious deterioration after 105 h operation under atmosphere pressure and 80 °C.

High Performance Membrane Electrode Assembly Fabricated by Ultrasonic Spray Technique

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Development of a novel decal transfer process for fabrication of high-performance and reliable membrane electrode assemblies for PEMFCs

To improve the performance of a polymer electrolyte membrane fuel cell (PEMFC), various membrane electrode assemblies (MEAs) were fabricated by the decal process. When peeling the decal films away from a Nafion membrane, a novel liquid nitrogen (LN 2) freezing method was employed. The results of a Fourier Transform Infrared (FTIR) analysis of the Nafion membranes demonstrate that this proposed method has no impact on the molecular structure of the Nafion polymer. In addition, the method makes it possible to achieve complete decal transferring under a wide range of hot-pressing pressures and temperatures: 9.8–15.7 MPa and 100–140 °C, respectively. Another approach to optimize the decal technique is to dry catalyst layers under vacuum. Catalyst layers dried under vacuum show better cell performances than atmospherically dried ones. Vacuum drying significantly facilitates the formation of small pores within Pt/C agglomerates on catalyst layers. Third, the use of Additive-A as a commercial dispersant in the catalyst ink has been investigated. From rheological characterizations, including thixotropy and catalyst ink viscosity, it is obvious that the additive plays an important role in elevating the dispersion stability of the ink. In addition, surface images of the catalyst layers revealed that the dispersing agent reduces cracks or fractures within the layers. Although adding Additive-A did not have an effect on the single-cell performance, the MEAs with the dispersant are expected to have better results for a long-term performance test of a single cell.

High performance membrane electrode assemblies by optimization of coating process and catalyst layer structure in direct methanol fuel cells

High performance membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs) are developed by changing the coating process, optimizing the structure of the catalyst layer, adding a pore forming agent to the cathode catalyst layer, and adjusting the hot-pressing conditions, such as pressure and temperature. The effects of these MEA fabrication methods on the DMFC performance are examined using a range of physicochemical and electrochemical analysis tools, such as FE-SEM, electrochemical impedance spectroscopy (EIS), polarization curves, and differential scanning calorimetry (DSC) of the membrane. EIS and polarization curve analysis show that an increase in the thickness and porosity of the cathode catalyst layer plays a key role in improving the cell performance with reduced cathode reaction resistance, whereas the MEA preparation methods have no significant effects on the anode impedance. In addition, the addition of magnesium sulfate as a pore former reduces the cathode reaction transfer resistance by approximately 30 wt%, resulting in improved cell performance.

High performance membrane electrode assembly with ultra-low platinum loading prepared by a novel multi catalyst layer technique

An ultra-low platinum loading membrane electrode assembly (MEA) with a novel double catalyst layer (DCL) structure was prepared by using two layers of platinum catalysts with different loadings. The inner layer consisted of a high loading platinum catalyst and high Nafion content for keeping good platinum utilization efficiency and the outer layer contained a low loading platinum catalyst with low Nafion content for obtaining a proper thickness thereby enhancing mass transfer in the catalyst layers. Polarization characteristics of MEAs with novel DCL, conventional DCL and single catalyst layer (SCL) were evaluated in a H 2–air single cell system. The results show that the performance of the novel DCL MEA is improved substantially, particularly at high current densities. Although the platinum loadings of the anode and cathode are as low as 0.04 and 0.12 mg cm −2 respectively, the current density of the novel DCL MEA still reached 0.73 A cm −2 at a working voltage of 0.65 V, comparable to that of the SCL MEA. In addition, the maximum power density of the novel DCL MEA reached 0.66 W cm −2 at 1.3 A cm −2 and 0.51 V, 11.9% higher than that of the SCL MEA, indicative of improved mass transfer for the novel MEA. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) tests revealed that the novel DCL MEA possesses an efficient electrochemical active layer and good platinum utilization efficiency.

Novel application of Hicon Black in PEMFC microporous sublayer: Effects of composition and subsequent membrane selection

This research was carried out to prepare high performance membrane electrode assemblies (MEAs) for a proton exchange membrane fuel cell (PEMFC). The MEAs were prepared by introducing a microporous sublayer (MPS) between the gas diffusion layer and the catalyst layer. Main parameters for MPS preparation, which are microporous carbon types and the polytetrafluoroethylene (PTFE) content in the MPS, were investigated. Three microporous carbon types, which are Hicon Black, RGN and Vulcan, were evaluated. Then, Nafion membranes with two thicknesses were employed to form an MEA. The preliminary results demonstrated that a high performance could be achieved with the presence of Hicon Black in the MPS and the performance was comparable to those with the presence of Vulcan XC-72, particularly in the high current density region. The optimum PTFE content was found to be 6 wt% and the thinner membrane provided a better cell performance. The highest current density was 858 mA cm −2 at the cell potential of 0.6 V.

Preparation of high loading Pt nanoparticles on ordered mesoporous carbon with a controlled Pt size and its effects on oxygen reduction and methanol oxidation reactions

A series of ordered mesoporous carbon (OMC) supported Pt (Pt/OMC) catalysts with a controlled Pt size from 2.7 to 6.7 nm at high Pt loading around 60 wt.% have been prepared and their electrocatalytic activities for the electrode reactions relevant to the direct methanol fuel cells have been investigated. The Pt/OMC catalysts with a high dispersion (Pt size around 3 nm) could be prepared by the use of a modified, sequential impregnation–reduction method. The Pt/OMC catalysts containing larger Pt particles were obtained by increasing reduction temperature under hydrogen flow and Pt loading, and by performing impregnation–reduction in a single cycle. The oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities of Pt/OMC catalysts as a function of Pt size were investigated at room temperature in 0.1 M HClO 4 and (0.1 M HClO 4 + 0.5 M methanol), respectively. The specific activity of Pt/OMC for ORR steeply increased up to 3.3 nm and became independent of Pt size from 3.3 to 6.7 nm, and the mass activity curve exhibited maximum activity at 3.3 nm. The MOR activity of Pt/OMC also exhibited the similar trend with the ORR activity, as the maximum of mass activity was also found at 3.3 nm. The results of the present work indicate that the Pt catalysts of ca. 3 nm is an optimum particle size for both ORR and MOR, and this information may be translated into design of high performance membrane electrode assembly.

High-Performance Nafion-based Membrane Electrode Assemblies for Hydrogen/Oxygen Fuel Cells

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Estimated Rate Constants for CO Poisoning of High-Performance Pt/Ru–C Anodes

A consistent set of rate constants describing simultaneous H 2 and CO adsorption and electro-oxidation in a proton exchange membrane fuel cell with high-performance membrane electrode assemblies is reported. The parameters were estimated from regression of a first-principles model to anode overpotential data collected at 70 and 90°C at 101 and 202 kPa. A Langmuir isotherm was found to be sufficient for the CO adsorption equilibrium for this catalyst when the Heyrowski-Volmer mechanism for H 2 oxidation on a Pt/Ru-C catalyst is used. These parameters and the ability to predict performance loss that are critical as standards for hydrogen quality are established.

High‐Performance Nanostructured Membrane Electrode Assemblies for Fuel Cells Made by Layer‐By‐Layer Assembly of Carbon Nanocolloids

Layer-by-layer (LBL) assembly is used to produce high-performance nanostructured membrane electrode assemblies for H2/O2 fuel cells (see figure) for which porosity, platinum loading, electronic conductivity, and proton conductivity can be finely tuned. Free-standing membranes are made from negatively charged Nafion-wrapped carbon fibers (CFs) and single-walled carbon nanotubes (SWNTs) with Pt nanoparticles deposited by a selective heterogeneous nucleation reaction.