Low Temperature Fuel Cell Applications Research Articles

Convenient graphene based materials as potential candidates for low cost fuel cell catalysts

A new and simple synthesis method of Pt nanoparticles supported on graphene materials, as potential candidates for low temperature fuel cell application, has been developed and discussed in detail. Graphene and Pt supported on graphene nano-sheets have been chemically prepared using a soft reduction method via a sequence of preparation steps based on chemical oxidation of graphite and graphene oxide exfoliation. In order to avoid the tendency of formation of irreversible agglomerates and even to restack in graphite form during the conventional drying process, a new effective drying method was proposed. By optimizing the drying process, this barrier was passed and an exceptional surface area for graphite oxide (206 m2/g) was obtained, which could provide new directions into the fabrication of graphene materials. Using several characterization methods (FTIR, BET, TGA, RAMAN, XRD and SEM) it was highlighted that the manufactured nano-structured graphene have adequate properties to become potential candidate for PEMFC electrodes.

Platinum nanocatalysts on metal oxide based supports for low temperature fuel cell applications

In this manuscript a survey of the contemporary research related to platinum nanocatalysts on metal oxide based supports for low temperature fuel cell applications is presented.

A Simple Synthesis of an Excellent Oxygen Reduction Catalyst: Nitrogen-Doped, Sharply-Mesoporous Carbon from Magnesium Salts

Any new oxygen reduction catalysts for practical low-temperature fuel cell applications must compete with the commercial platinum catalysts on efficiency and cost. Mesoporous nitrogen-doped carbon (N:C) has emerged as a leading alternative, mostly due to its high surface area, and the promise for low-cost production. While the best mesoporous N:C catalysts in the literature can operate on par with commercial platinum/carbon composites,1 their synthesis is complex and difficult – increasing their cost and rendering them impractical. We present a particularly simple synthesis of N-doped carbon, starting from magnesium salts of nitrogen-containing ligands. Pyrolysis of the salts proceeds by the little-researched mechanism of self-templating – formation of similarly sized MgO nanoparticle cores, which are then washed out with dilute acid, leaving behind a narrow pore size distribution. These carbons have high surface areas (>1400 m2/gr), nitrogen doping levels topping what is required for catalysis (>4%), and most interestingly, a very narrow pore size distribution (ranging from 10 to 20 nm for different carbons). Tested in alkaline ORR catalysis, these carbons compete successfully with commercial platinum-based electrodes, so they are efficient, cheap, and simple to prepare. (1) W. Wei, H. Liang, K. Parvez, X. Zhuang, X. Feng, K. Müllen, Angew. Chem. 2014, 126, 1596.

Fe–N supported on graphitic carbon nano-networks grown from cobalt as oxygen reduction catalysts for low-temperature fuel cells

Three iron–nitrogen-containing non-noble metal electrocatalysts supported on networked graphitic structures, carbon nano-networks (CNNs), were synthesized using a wet-impregnation method. The CNN supports were produced in-house by chemical vapor deposition of ethene over cobalt nanoparticles that were previously synthesized in bicontinuous microemulsions. The three CNN supports differed in cobalt content, ranging from 0.1 to 1.7% in weight. These CNN supports were used to prepare Fe–N/CNN electrocatalysts. The oxygen reduction reaction (ORR) activity was evaluated by rotating disk electrode measurements. Interestingly, the highest ORR activity belonged to the catalyst with the highest iron and cobalt content. The most promising catalyst was investigated as the cathode material in a polymer electrolyte membrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC). The maximum recorded power densities were 121mWcm−2 for PEMFC and 15mWcm−2 for DMFC, respectively. These values are superior or comparable to the best state of the art for similar materials. The durability to potential cycling was tested in half-cell studies and an activity loss around 10% was found after 1000 cycles, which is not significantly different from what is reported in the literature. The relatively simple synthesis approach and the cheap precursor materials make this electrocatalyst promising for low-temperature fuel cell applications.

Water/Methanol Transport in Polyethylene Based Block Copolymers as Anion Conductors for Applications in Fuel Cells

Anion exchange membranes have been a central point of focus for the low temperature fuel cell application. The primary goal of AEMs in fuel cells is to transport hydroxide (OH-) ions from cathode to anode and to act as a separator between the electrodes. In this work we have studied a block copolymer of polyethylene and polyvinyl benzyl trimethyl ammonium bromide (PE-b-PVBTMA[Br], Fig. 1) for various transport properties. By using the dynamic vapor sorption apparatus we were able to study water and methanol uptake dynamics for this AEM. Fickian diffusion coefficients for both water and methanol were calculated during this study giving idea about the solvent uptake kinetics.We also measured the conductivity of the AEM under 95% relative humidity (Figure 2). It was found that the AEM followed VFT theory behavior for transporting ions through it as opposed to the classical Arrhenius behavior. VFT behavior suggests that ion transport in the membrane is facilitated by the polymer chain motion as opposed to ion transport in water which is governed mainly by the Arrhenius type of behavior.We also report methanol/water ion transport using the pulse gradient stimulated spin echo (PGSTE) NMR technique to determine the tortuosity of the membrane along with self diffusion of each species. Acknowledgements: We would like to thank the Army Research Office for funding this Multidisciplinary University Research Initiative under contract #W911NF-10-1-0520 and the Colorado School of Mines NMR facility, funded by National Science Foundation under the grant CHE-0923537. We would like to thank Yifan Li, D M Knauss for providing with the polymer for this study.

Facile synthesis of boron and nitrogen-doped graphene as efficient electrocatalyst for the oxygen reduction reaction in alkaline media

Boron-doped graphene and nitrogen-doped graphene have been respectively synthesized by a facile thermal solid-state reaction of graphene oxide with boric acid and urea. The morphology and structure of the doped graphene have been characterized by the scanning electron microscopy, infrared spectroscopy, ultraviolet visible spectroscopy and X-ray photoelectron spectroscopy, while the electrocatalytic activity toward oxygen reduction reaction has been evaluated by the cyclic voltammetry. It has been shown that the morphology, structure, doping level and fashions of graphene could be finely tuned by the thermal treatment conditions, and which have substantial effects on the activity of oxygen reduction reaction. The boron-doped graphene and nitrogen-doped graphene calcined at 700 °C demonstrate excellent electrocatalytic oxygen reduction activities as the appropriate introduction of boron and nitrogen functional groups in graphene, which might be promising for low temperature fuel cell applications.

A highly active PtCu3 intermetallic core-shell, multilayered Pt-skin, carbon embedded electrocatalyst produced by a scale-up sol-gel synthesis.

We present a novel, scaled-up sol-gel synthesis which enables one to produce 20 g batches of highly active and stable carbon supported PtCu3 nanoparticles as cathode materials for low temperature fuel cell application. We confirm the presence of an ordered intermetallic phase underneath a multilayered Pt-skin together with firm embedment of nanoparticles in the carbon matrix.

Tin oxide - mesoporous carbon composites as platinum catalyst supports for ethanol oxidation and oxygen reduction

Unique tin oxide-mesoporous carbon (SnO2-CMK-3) composites have been synthesized as platinum nanoparticle electrocatalyst supports for low temperature fuel cell applications. In comparison with state-of-the-art commercial carbon-supported platinum (Pt/C) and pure CMK-3-supported platinum (Pt/CMK-3), Pt/SnO2-CMK3 demonstrated improved Pt-mass and surface area based ethanol oxidation reaction (EOR) activity through half-cell electrochemical investigations, providing a 64.7 and 97.6mV reduction in overpotential at 100mAmg−1Pt upon comparison to Pt/CMK-3 and commercial Pt/C. Furthermore, improvements to the oxygen reduction reaction (ORR) kinetics were observed, with Pt/SnO2-CMK3 providing a kinetic current density of 3.40mAcm−2 at an electrode potential of 0.9V vs RHE. The improved performance of Pt/SnO2-CMK-3 for EOR and ORR was attributed to the beneficial impact of the support properties, along with potential interactions occurring between the support and catalyst particles. Complemented by extensive physicochemical characterization, these unique materials show high promise for application in low temperature fuel cells.

Disordered Brownmillerite Ba2InCeO5+δ with Enhanced Oxygen Reduction Activity

A disordered brownmillerite, Ba2InCeO5+δ, with slight tetragonal distortion from ideal cubic perovskite is synthesized and its oxygen reduction reactivity tested. The material displayed oxygen reduction behavior in alkaline solution comparable to that of standard 40 wt % Pt/C catalyst and attractive activity characteristics which renders it a potential system for low temperature fuel cell applications.

γ-Fe 2O 3-supported Pt-Cu nanoparticles synthesized by radiolytic process for catalytic CO preferential oxidation

Pt-Cu bimetallic nanoparticles immobilized on γ-Fe 2O 3 support were synthesized by a unique radiolytic process and their physical properties and catalytic activity for CO preferential oxidation were investigated for various Pt/Cu atomic ratios. The chemical composition of the catalysts measured by inductively coupled plasma revealed most of the platinum and copper aqueous precursors were deposited on to the γ-Fe 2O 3 support after irradiation with electron beam. Crystallographic analysis of the catalysts by X-ray diffraction showed Pt-Cu alloy is formed for wide range of Pt/Cu ratio. From the lattice parameter of this Pt-Cu alloy, it was found that Cu can be incorporated into Pt lattice up to 30 at% with the present irradiation condition. The rest of Cu for high-Cu (low-Pt) samples was identified as divalent oxide with poor crystallinity by XANES spectrum. Detailed STEM-EDX analyses further confirmed that Pt-Cu alloy exists as nanoparticles with a few nanometers in diameter and CuO with low crystallinity distributes on entire surface of the γ-Fe 2O 3 support. The PROX activity showed different trends between high-Pt and high-Cu samples. The CO conversion decreased as the Pt loading was decreased to 50 at%, and it monotonically decreased with increasing temperature. However, as the Pt loading was further decreased, the activity increased with temperature by contraries, and reached the maximum conversion at 100 °C. Regardless of the low Pt loading, the sample with 10 at% Pt and 90 at% Cu exhibited the highest activity at 100 °C, which is preferable for low temperature fuel cell applications. This enhanced activity was attributed to oxygen supply via the copper of low crystallinity from the O 2-poor atmosphere to Pt-Cu alloy particles that chemisorbs CO molecules.

Role of metal components in Pd–Cu bimetallic catalysts supported on CeO2 for the oxygen-enhanced water gas shift

Catalytic hydrogen production and CO removal in a post-reforming process are critical for low-temperature fuel cell applications. The present study aims at clarifying the role of metal components in bimetallic catalysts for oxygen-enhanced water gas shift (OWGS), wherein a small amount of O2 is added to H2-rich reformate gas to enhance CO shift. Among CeO2-supported bimetallic catalysts, Pd–Cu and Pt–Cu combinations were found to show strong synergetic promoting effect in OWGS, which leads to much higher CO conversion and higher H2 yield than WGS at low temperature around 250°C. Temperature programmed reduction (TPR) showed strong interaction between Pd and Cu in Pd–Cu/CeO2 by a single reduction peak in contrast to multiple peaks on monometallic Cu/CeO2. Extended X-ray absorption fine structure (EXAFS) analysis revealed that such bimetallic Pd–Cu and Pt–Cu form alloy nanoparticles, where noble metal is mainly surrounded by Cu atoms. Oxygen storage capacity (OSC) measurements point to higher resistance of Pd–Cu to oxidation indicating that Pd keeps Cu in reduced state in air pulse condition. From kinetic study, Pd in Pd–Cu was found to promote CO shift, rather than CO oxidation by increasing the number of active sites and by suppressing H2 activation (that is inherent to monometallic Pd), which minimizes both the inhibition effect of H2 and the loss of H2 by oxidation in OWGS. Transient response technique revealed that Cu in Pd–Cu enhances desorption of strongly chemisorbed CO2 on catalyst surface in contrast to very slow CO2 desorption from surface of monometallic Pd. Thus, the excellent OWGS activity of Pd–Cu catalyst has been attributed to the complementary roles of the two metals for enhancing CO shift, which is realized by its alloy structure and the accompanying strong interaction between metal components.

Preparation of High Performance Core-Shell PdRu@Pt/CNT Electrocatalyst

We prepared a low Pt loading core-shell structured catalyst PdRu@Pt/CNT (carbon nanotube) with a PdRu alloy as the core and platinum as the shell in addition to carbon nanotubes as supports in a two-stage precipitation-reduction approach. For the anodic oxidation of methanol the activity in terms of Pt loading increased by 70% compared with the lab-made Pt/CNT catalyst and the ratio of the forward current density (I(subscript f)) to the backward current density (I(subscript b)) was as high as 2, which is two times of that of Pt/CNT, indicating that the dispersion and use of platinum effectively improves by covering the surface of the PdRu cores with platinum. Excellent tolerance towards the intermediates of the anodic oxidation of methanol may result from the interaction between the Pt shell and the PdRu core. The core-shell structure of the catalysts was revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM image showed that the active components are highly dispersed on the CNT with a particle size of 4.0 nm. The high platinum utilization and high performance as well as good tolerance toward poisons make the PdRu@Pt/CNT catalyst a promising low-Pt catalyst for low temperature fuel cell applications.

Sulfonated PEEK and fluorinated polymer based blends for fuel cell applications: Investigation of the effect of type and molecular weight of the fluorinated polymers on the membrane’s properties

This work clearly demonstrates the effect of the type and molecular weight of the fluorinated polymer of SPEEK/Fluorinated polymer blends for low temperature (<80 °C) Fuel Cell Applications. Comparisons with trademarks (e.g., Nafion ®) suggests that the membranes we have prepared in this study have good compatibility in all application respects. Membranes were prepared by solution casting method from four different fluorinated polymers; poly (vinylidene fluoride) with three different molecular weights (PVDF, M w: 180.000, M w: 275.000, M w: 530.000); Poli(vinylidene fluoride-co-Hexafluoro propylen) (PVDF-HFP M n:130.000) and sulfonated poly(ether ether ketone) (SPEEK) with sulfonation degree (SD) of 70. The sulfonation degree (SD) of SPEEK was determined by FTIR, 1H NMR and ion exchange capacity (IEC) measurements. Thermo-oxidative stability and proton conductivity of the membranes were determined by using thermal gravimetric analysis (TGA) and BT-512 BekkTech membrane test systems, respectively. Chemical degradation of SPEEK membranes was investigated via Fenton test. The morphology of the membranes were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Water uptake and proton conductivity values decreased with the addition of fluorinated polymers (PVDF, PVDF-HFP) as expected, but proton conductivity values were still comparable to that of Nafion 117 ® membrane. Addition of fluorinated polymers improved chemical degradation of the blend membranes in all ratios while addition of PVDF-HFP to the SPEEK70 caused phase separations in all ratios. Methanol permeability value of SPEEK70/PVDF( M w = 275.000) blend membrane (3.13E-07 (cm 2/s)) was much lower than Nafion 117 ® (1.21E-06 (cm 2/s). PVDF addition to the SPEEK polymers caused increase in elongation of the membranes. Increase in the molecular weight of the PVDF did not show any effect on the Young modulus, but resulted in high elongation values. On the other hand, increasing PVDF content of the blend membranes caused lower elongation values at break and didn’t have any effect on the Young modulus. The gas permeability values of SPEEK70/PVDF type blend membranes were lower than that of the Nafion ®. Hydrogen and oxygen permeability values were one-tenth and one-fifth of the Nafion®, respectively.

Novel preparation method of composite catalyst composed of Pt wires and particles for low-temperature fuel cell applications

Abstract A novel composite type catalyst of Pt particles and Pt wires was prepared for low-temperature fuel cell applications. For this preparation, a specialized multi-wall carbon nanotube with an amorphous carbon structure on the outside wall was used, and a sub-substrate method using silica as the sub-substrate material was performed. According to HR-TEM analysis, about 30–40% Pt wire-type catalyst was observed with respect to the total Pt catalysts. This new type of catalyst showed about twice the oxygen reduction activity of normal particle type catalysts. The enhanced activity results from the active planes, which were especially exposed on the surface of the Pt wire-type catalyst. From the cyclic voltammogram, an increased peak area of the Pt(1 0 0) plane was confirmed. This paper suggests a novel method that is able to prepare the composite type catalyst of Pt wires and particles without any sort of template.

Facet-Selective Platinum Electrodeposition at Free-standing Polycrystalline Boron-Doped Diamond Films

In the present investigation, electrochemical deposition of platinum particles was carried out on boron doped diamond (BDD) films by using cyclic voltammetry at different potential sweep rates while maintaining the Pt concentration and number of potential cycles during the deposition as constant for all samples. The BDD film surfaces were studied using Raman spectroscopy, X-ray diffraction, and scanning electrochemical microscopy. The deposited particles were characterized by scanning electron microscopy/X-ray energy dispersive analysis, X-ray photoelectron spectroscopy, and cyclic voltammetry before and after methanol oxidation. The platinum nanoparticles are found to be selectively electrodeposited on the (111) facets of the BDD. In addition, the location of the Pt particles on the diamond facets was affected by the potential sweep rate. For higher sweep rates, the particle size was dependent on the facet on which the particles are electrodeposited with smooth (110) facets exhibiting a smaller number of particles but with a larger particle diameter. After methanol oxidation studies using cyclic voltammetry and controlled potential electrolysis for several hours, the platinum particles remained attached to the (111) facets of the BDD, while the particles on the (110) facets of the BDD became agglomerated along grain boundaries. Functional groups present on the (111) facet of the diamond surface play an important role on the stability of the particles attached to the diamond surface. After methanol oxidation, the particles deposited on other facets appeared to lose their adhesion leading to agglomeration on the grain boundaries. BDD appears to be a promising electrocatalyst support material that can help to resist platinum nanoparticle agglomeration in direct methanol and other low temperature fuel cell applications.

Membranes produced by plasma enhanced chemical vapor deposition technique for low temperature fuel cell applications

A plasma polymerization process using a continuous glow discharge has been implemented for preparing proton conducting membranes from trifluoromethane sulfonic acid and styrene. The chemical and physical structure of plasma membranes has been investigated using FTIR and SEM. The films are homogeneous with a good adhesion on commercial gas diffusion layer (E-Tek ®). Their deposition rate can be increased with increasing flow rate and input power. The thermogravimetric analysis under air of plasma polymers has showed a thermal stability up to 140 °C. Compared to the pulsed glow discharge studied in a previous paper, the continuous glow discharge has enabled to enhance the proton conductivity of membranes by a factor 3 (up to 1.7 mS cm −1). Moreover, the low methanol permeability (methanol diffusion coefficient down to 5 × 10 −13 m 2 s −1) of membranes has been confirmed by this study. In an industrial context, a reactor prototype has been developed to manufacture by plasma processes all active layers of fuel cell cores to be integrated in original compact PEMFC or DMFC.

A Modified Solid-State Reduction Method to Prepare Supported Platinum Nanoparticle Catalysts for Low Temperature Fuel Cell Application

A modified solid state reduction (SSR) method, by which the platinum salt is reduced into platinum nanoparticles by sodium formate in solid state and under low temperature (below 180 C) conditions, is introduced here. The high performance catalysts based on carbon nanotubes (CNTs) supported platinum and platinum promoted by Mo (VI) and Si (IV) were prepared successfully by this method. The catalysts, with small particle size and uniform distribution were active toward the electrooxidation reaction of methanol. Among a few catalysts promoted by silicon, molybdenum and tungsten elements, catalysts co-promoted by silicon and molybdenum elements shows best performance. The particle size of promoted Pt/CNTs, calculated from XRD patterns, is small as 3.0 1.5 nm, and the results of transmission electron microscopy (TEM) revealed that the distribution of particle size is uniform. In comparison with the liquid-state synthesis, the advantages of SSR method include its environmental benefits due to less water usage and significantly reduced pollutants generation, as well as its suitability for large scale preparation.

Substantial emission of NH3 during thermal decomposition of sodium amidoborane, NaNH2BH3

Sodium amidoborane (SAB, NaNH2BH3), an ammonia borane (AB, NH3BH3) derivative, was recently reported as a novel solid-state hydrogen storage material. We reinvestigate its thermal decomposition using the best grade commercially available AB (98%) and technical quality (90%) substrates. We characterize evolved gases with mass and FT-IR spectroscopy and observe emission of hydrogen contaminated with significant amounts of ammonia making it undesirable for low-temperature fuel cell applications. We propose a reaction scheme which explains the evolution of NH3 from SAB.

Polyelectrolyte functionalized carbon nanotubes as a support for noble metalelectrocatalysts and their activity for methanol oxidation

A highly effective polyelectrolyte functionalization of multi-walled carbon nanotubes(MWCNTs) by poly(diallyldimethylammonium chloride) (PDDA-MWCNTs) was employedfor low temperature fuel cell applications. PDDA-MWCNTs were employed as supportmaterials for the in situ deposition and formation of platinum nanoparticles, via theself-assembly between the negative Pt precursor and positively charged functionalgroups of PDDA-functionalized MWCNTs. The effect of the functionalization onthe deposition and distribution of Pt nanoparticles was investigated in detail.Compared with MWCNTs functionalized by conventional acid-oxidation treatment(AO-MWCNTs), the PDDA-functionalized MWCNTs cause no structural damage onMWCNTs and provide high density and homogeneous surface functional groups for theanchoring Pt nanoparticles. Pt nanoparticles with an average particle size of1.8 ± 0.4 nm and loading as high as 60 wt% were realized on PDDA-MWCNTs supports. ThePt/PDDA-MWCNTs electrocatalysts show significantly higher electrochemically activesurface area and higher electro-catalytic activity for methanol oxidation than that ofPt/AO-MWCNTs and E-TEK Pt/C electrocatalysts.

Hydrogen production by coal plasma gasification for fuel cell technology

Coal gasification in steam and air atmosphere under arc plasma conditions has been investigated with Podmoskovnyi brown coal, Kuuchekinski bituminous coal and Canadian petrocoke. It was found that for those coals the gasification degree to synthesis gas were 92.3%, 95.8 and 78.6% correspondingly. The amount of produced syngas was 30–40% higher in steam than in air gasification of the coal. The reduction of the carbon monoxide content in the hydrogen-rich reformate gas for low-temperature fuel cell applications normally involves high- and low-temperature water gas shift reactors followed by selective oxidation of residual carbon monoxide. It is shown that the carbon monoxide content can be reduced in one single reactor, which is based on an iron redox cycle. During the reduction phase of the cycle, the raw gas mixture of H 2 and CO reduces a Fe 3 O 4 – CeO 2 – ZrO 2 sample, while during the oxidation phase steam re-oxidizes the iron and simultaneously hydrogen is being produced. The integration of the redox iron process with a coal plasma gasification technology in future allows the production of CO x -free hydrogen.