Hydrogen-fed Proton Exchange Membrane Research Articles

Electrospun Composite Proton-Exchange and Anion-Exchange Membranes for Fuel Cells

A fuel cell is an electrochemical device that converts the chemical energy of a fuel and oxidant into electricity. Cation-exchange and anion-exchange membranes play an important role in hydrogen fed proton-exchange membrane (PEM) and anion-exchange membrane (AEM) fuel cells, respectively. Over the past 10 years, there has been growing interest in using nanofiber electrospinning to fabricate fuel cell PEMs and AEMs with improved properties, e.g., a high ion conductivity with low in-plane water swelling and good mechanical strength under wet and dry conditions. Electrospinning is used to create either reinforcing scaffolds that can be pore-filled with an ionomer or precursor mats of interwoven ionomer and reinforcing polymers, which after suitable processing (densification) form a functional membrane. In this review paper, methods of nanofiber composite PEMs and AEMs fabrication are reviewed and the properties of these membranes are discussed and contrasted with the properties of fuel cell membranes prepared using conventional methods. The information and discussions contained herein are intended to provide inspiration for the design of high-performance next-generation fuel cell ion-exchange membranes.

Carbon Monoxide Tolerant Pt-Based Electrocatalysts for H2-PEMFC Applications: Current Progress and Challenges

The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H2-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H2 fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been made, the development of a practical anode electrocatalyst with both high CO tolerance and stability has still not occurred. Currently, efforts are being devoted to Pt-based electrocatalysts, including (i) alloys developed via novel synthesis methods, (ii) Pt combinations with metal oxides, (iii) core–shell structures, and (iv) surface-modified Pt/C catalysts. Additionally, the prospect of substituting the conventional carbon black support with advanced carbonaceous materials or metal oxides and carbides has been widely explored. In the present review, we provide a brief introduction to the fundamental aspects of CO tolerance, followed by a comprehensive presentation and thorough discussion of the recent strategies applied to enhance the CO tolerance and stability of anode electrocatalysts. The aim is to determine the progress made so far, highlight the most promising state-of-the-art CO-tolerant electrocatalysts, and identify the contributions of the novel strategies and the future challenges.

CO tolerance and durability study of PtMe(Me = Ir or Pd) electrocatalysts for H2-PEMFC application

In the present work, carbon supported PtMe (Me = Ir or Pd) electrocatalysts, with different atomic ratios (Pt/Me (20 wt%) = 3:1, 1:1, 1:3), are thoroughly investigated towards CO tolerance and durability, as anode and cathode for H2-PEMFCs (hydrogen fed proton exchange membrane fuel cells) application. The electrocatalysts are prepared via a pulse-microwave assisted polyol synthesis method and their durability and electrocatalytic activity in presence and absence of CO are evaluated using the techniques of electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and rotating disk electrode (RDE). For the investigation of CO tolerance a protocol is set that could be used by other research groups, since various procedures are reported in literature. It is found that Pd/C shows higher CO tolerance than Pt/C, while the PtPd3/C exhibits the highest CO tolerance ability, even after being exposed for 9 h at 400 ppm CO. Despite the fact that Pt3Ir/C shows higher CO tolerance ability than Pt/C, it cannot resist at such high CO concentrations for more than 6 h. Finally, it is found that PtIr/C and PtPd/C exhibit very good durability even after 5000 accelerated durability test (ADT) cycles, while Pt3Pd/C and PtPd/C present the highest mass activities (339.4 and 410 mA/mgPt respectively at 0.9 V), which are 4 and 5 times higher than the one observed over commercial Pt/C (82.75 mA/mgPt).

Highly efficient electrocatalysts for oxygen reduction reaction: Nitrogen-doped PtNiMo ternary alloys

The relatively low efficiency of the reaction of oxygen reduction (ORR) remains among the main obstacles for hydrogen fed proton exchange membrane fuel cells (H-PEMFCs) commercialization.In the present work, PtNiMo ternary alloy catalysts are obtained through reducing by NaBH4 and subsequent thermal annealing in NH3 at 1.0 atm. The as prepared catalysts are physico-chemically (XRD, TEM and XPS) characterized, exhibiting alloy nanostructure.From the electrochemical tests it is found that they exhibit high ORR activity in aqueous solutions saturated with O2 and acidified with HClO4. From the as synthesized catalysts, Pt3Ni3MoN/C shows the highest mass activity (539.41 mA mg−1 Pt); 3.5 times greater than that observed over commercial Pt/C (154.46 mA mg−1 Pt). Moreover, they show very good stability, while their ORR activity is only slightly altered after 5,000 cycles.These highly performing and low cost catalysts could thus open up new possibilities for the commercialization of hydrogen fed PEMFCs.

Synthesis of Active Bimetallic Catalysts for Direct Methanol Fuel Cells

The direct methanol fuel cell (DMFC) uses methanol as fuel and has significant advantages over hydrogen-fed proton exchange membrane (PEM) fuel cells for mobile applications, particularly in terms of fuel storage and supply. Platinum (Pt) catalysts are effectively able to catalyze the oxidation of methanol to carbon dioxide in this system. However, one of the main challenges of making DMFCs commercially feasible is that the surface of Pt sites become rapidly poisoned by strongly adsorbed carbon monoxide (CO) that is produced during the oxidation process, limiting the overall rate of methanol oxidation. Studies have shown that bimetallic catalysts composed of platinum (Pt) and a second metal (i.e., Ru or Ni) are more active for the oxidation of methanol compared to catalysts composed of only Pt. Results suggest the Ru or Ni component provides sites that chemisorb H2O in the moist environment which reacts with strongly adsorbed CO on an adjacent Pt site to form easily desorbed CO2 [1]. In this study, we focus on the preparation of nanometer sized Pt-Ru and Pt-Ni particles supported on carbon by using the methods of strong electrostatic adsorption (SEA) and electroless deposition (ED). The method of SEA has been used to prepare ultra-small Pt nanoparticles with high dispersions and a narrow size distribution. Catalysts prepared by SEA were then used as seed nuclei for addition of a secondary metal (Ru or Ni) using Electroless Deposition (ED). These compositions form bimetallic surfaces where Pt and Ru (or Ni) are in intimate contact to facilitate the interaction of adsorbed CO with adsorbed H2O to form CO2 during evaluation for methanol oxidation. These bimetallic catalysts show higher activity towards methanol oxidation than the analogous, commercial catalysts. Finally, the catalysts have been characterized by XRD, STEM, and temperature programmed methods to confirm the compositions of the bimetallic particles. References Ehteshami, S.M.M. and S.H. Chan, A review of electrocatalysts with enhanced CO tolerance and stability for polymer electrolyte membarane fuel cells. Electrochimica Acta, 2013. 93: p. 334-345.

Targeting optimized and robust operating conditions in a hydrogen-fed Proton Exchange Membrane Fuel Cell

Response Surface Methodology (RSM) when combined with the Propagation of Error (PoE) approach offers an efficient robust design able to find the best operating conditions to simultaneously maximize power density and reduce normal operation variability in a hydrogen-fed Proton Exchange Membrane Fuel Cell (PEMFC). To proceed with the statistical analysis, a central composite design with 20 experimental runs (6 central points were used to assess the experimental error) was adopted to inspect which factors have significant effects and how they interact each other. This allowed generating a polynomial function to determine the maximum power density at 1415 mW/cm2. Taking advantage of the desirability concept and using the PoE measure as a response, a multiple optimization under different restrictions was carried out defining a new set of operating conditions able to target the maximum possible power density at the most robust conditions (1074 mW·cm−2 at 55 °C, 50% RHC and 25 Psi). Then, actions were carried out to narrow even more the tolerance intervals towards more ambitious standards. Reducing the standard deviation from input factors through the use of adequate controlling measures led to a decrease of almost 50% in the tolerance intervals. This is an useful methodology to help the PEMFC normal operation more repeatable and predictable under its lifetime by combing both optimization and robustness goals.

Surface composition of magnetron sputtered Pt-Co thin film catalyst for proton exchange membrane fuel cells

Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.

Neural network model of 100 W portable PEM fuel cell and experimental verification

The inherent properties of artificial neural networks (ANNs) such as low sensitivity to noise and incomplete information make the ANN a promising candidate to model the fuel cell system. In this paper, an ANN-based model of 100 W portable direct hydrogen fed proton exchange membrane fuel cell (PEMFC) is presented. The model is built based on experimentally collected data from a portable 100 W direct hydrogen fed PEMFC in the authors’ laboratory. A multilayer feedforward ANN with back-propagation training algorithm is used to model the portable PEMFC. The ANN consists of fully connected four layers network with two hidden layers. The PEMFC ANN model is trained using extracted data from experimentally measured and calculated parameters. To validate the model, the outputs of the PEMFC ANN are compared against experimental data and results from a dynamic model of portable direct hydrogen fed PEMFC. In addition, three statistical indices to measure variations, unbiasedness (precision), and accuracy in voltage, power, and hydrogen flow are used to evaluate the PEMFC ANN model performance. The indices indicate that the maximum variations, unbiasedness, and accuracy of the voltage, power, and hydrogen flow are 1.45%, 2.04%, and 1.90%, respectively, which shows a close agreement between the outputs of the PEMFC ANN and the experimental results.

Portable direct hydrogen fed PEM fuel cell model and experimental verification

This paper focuses on the experimental verification of an electrochemical model of 100 W portable direct hydrogen fed proton exchange membrane (PEM) fuel cell (FC). The model is built based on the relationship between the FC terminal voltage and the partial pressures of hydrogen and oxygen. The model is then used to predict the output voltage and study the transient response of a PEMFC when subjected to rapid changes in the load. To validate the model, the measurements obtained from a commercially available 100 W FC are compared against the model results. Three different scenarios are considered for testing the model and the actual FC. In the first two scenarios, a step change in the load is used. In the third scenario, the load is replaced by a laptop computer. Results show a close agreement between the voltage and the power responses of the proposed model and the actual PEM FC. Copyright © 2009 John Wiley & Sons, Ltd.

Portable PEM fuel cell-ultracapacitor system: Model and experimental verification

This paper presents a comparative study between a model of portable direct hydrogen-fed proton exchange membrane fuel cell-ultracapacitor (PEMFC-UC) power source and experimental results obtained from an actual PEMFC-UC system in the authors' laboratory. In the proposed system the UC is directly connected to the PEMFC output terminals. The UC is used to supply the power mismatch during the sudden load variations when the load is higher than the PEMFC maximum capacity. The model is then used to estimate the output voltage and study the transient response of the PEMFC-UC system when subjected to rapid changes in the load. To validate the model, laboratory experiments are carried out using a 100 W commercially available PEMFC and an UC. The model results are verified against the experimental data using three statistical indices to measure the variations, unbiasedness, and accuracy. The indices indicate a maximum difference of 1.06%, which shows a close agreement between the voltage and power responses of the proposed model and the actual PEMFC-UC system. Copyright © 2009 John Wiley & Sons, Ltd.

Sodium borohydride based hybrid power system

Sodium borohydride's properties make it a good source of hydrogen for use with a fuel cell for an on-demand system that is easily controllable and has no idle costs. Previous work, as described in the literature, indicated that ruthenium (Ru) is an efficient catalyst for generating hydrogen from sodium borohydride. Tests were conducted to evaluate catalyst loading with the results of these tests indicating that the hydrolysis rate is affected by the loading of the catalyst. It was also apparent that the substrate surface is not completely occupied by Ru at the lower loadings, and that increased loadings are needed to optimize the reaction rate. A differential rate test with a fixed bed reactor was also conducted. It was observed that temperature has a significant effect on the rate of reaction. Feed rate also affected the rate of reaction with lower feed rates (longer residence time in the reactor) having higher reaction rates. A bench-top hybrid system was also developed and tested. This test bed demonstrated how a system based on a chemically generated hydrogen-fed proton exchange membrane fuel cell could be integrated with batteries to provide a hybrid power system that can meet the demands of a highly varying electrical load up to four times the rated output of the fuel cell.

Electron drag by ultrasonic waves in conductors: Fizika Tverdogo Tela, Vol 10, No 7 (1968) pp 2088–2093

Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773 K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6 nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773 K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3 eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.