DMFCs Applications Research Articles

The Tunable and Efficient Nanoporous CuAg Alloy Catalysts Toward Methanol Oxidation Reaction Synthesized by Electrochemical Dealloying of Metallic Glassy Precursors.

Three-dimensional (3D) nanoporous CuAg (NPCuAg) alloy catalysts with various Cu/Ag ratios are prepared by electrochemical dealloying of metallic glassy (MG) precursors. All dealloyed samples exhibit homogenous nanoporous structure and element composition distribution. After systematically evaluating their electrocatalytic performance toward MOR, it was found that the catalytic activity of the NPCuAg catalysts is enhanced along with the increase of Cu/Ag ratio, which may be attributed to the more exposed active reaction sites derived from high surface area of nanoporous structure and the optimal synergistic effect. Thus, the NPCu1.75 Ag alloy catalyst presents the best methanol electro-oxidation properties, including a high current density of 397.2 mA cm-2 and good operation stability that retaining 84.5 % catalytic activity even after 7200 s. These results outperform most reported copper-based MOR catalysts in alkaline methanol solution. Considering these advantages, the designed electrodes are expected to be promising catalysts for alkaline DMFCs applications.

PtPd NPs supported on nitrogen and sulfur containing polymers/special structured carbon spheres composite for methanol oxidation electrocatalysis

The support material should have strong adhesion to metal nanoparticles to provide a strong metal-support interaction and improve the performance of catalyst. Herein, we prepared the EDOT-pyridazine-EDOT decorated Double-layered Hollow Carbon Spheres (Poly(EPE)/DLHCs) to use as a new type catalyst support of PtPd alloy nanoparticles which with in different molar ratio. Finally, the Poly(EPE)/DLHCs/PtPd is calcined at high temperature in order to avoid the corrosion of polymer by alkaline solution, and further promote the modification of electronic properties on the surface of metal catalyst by adjacent carbon atoms. The morphological structure of hybrid catalysts are studied by XRD、SEM and TEM analyses, the results indicated that the uniform distribution of PtPd nanoparticles on the Poly(EPE)/DLHCs composite support with the average size of 2.63 and 2.7 nm, respectively. The obtained Poly(EPE)/DLHCs/Pt2Pd1 catalyst exhibits remarkable mass activity (1771.63 mA mg−1) and long term stability which were much higher than Poly(EPE)/DLHCs/Pt1Pd2. The favorable electrocatalytic properties of prepared catalysts can be ascribed to the interaction between Poly(EPE) and carbon spheres, which enables the hybrid catalyst own an excellent microenvironment for electron transfer reactions with the electrolyte solution, and provide more anchoring sites for PtPd alloys by increase the conjugation degree of polymer, indicating the Poly(EPE)/DLHCs can be a promising anode catalyst carrier for DMFCs applications.

Retraction Note to: Synthesis and characterization of a novel sulfonated poly (aryl ether ketone sulfone) containing rigid fluorene group for DMFCs applications

Retraction Note to: Synthesis and characterization of a novel sulfonated poly (aryl ether ketone sulfone) containing rigid fluorene group for DMFCs applications

Retraction Note to: Synthesis and characterization of a novel locally high dense sulfonated poly (aryl ether ketone sulfone) for DMFCs applications

The authors have retracted this article [1] because Scheme 1, Scheme 2, Figs. 2, 3, 4, and 8, as well as significant parts of the text were duplicated from a previously published article by Yuan and Wang [2]. Both authors agree with this retraction.

RETRACTED ARTICLE: Synthesis and characterization of a novel sulfonated poly (aryl ether ketone sulfone) containing rigid fluorene group for DMFCs applications

A new sulfonated poly (aryl ether ketone sulfone) consisting of rigid fluorene groups (SPAEKS) is synthesized from 3, 3′-disulfonate-4, 4′-dichlorodiphenylsulfone, and 9, 9-bis (4-hydroxyphenyl) fluorene by a typical condensation polymerization. The chemical structure of SPAEKS is characterized by 1H-NMR and FTIR spectra. SPAEKS-x membranes have moderate water absorption, swelling rate, good oxidative stability, and excellent thermal stability. The proton conductivity of SPAEKS-x membranes is in the range of 38.5–66.5 mS/cm. In particular, the proton conductivity of SPAEKS-50 membrane is 66.5 mS/cm, which is slightly higher than Nafion117 membrane (63.5 mS/cm) measured under the same conditions. All membranes show much lower methanol permeability and much higher proton selectivity than Nafion 117 membrane. Especially, proton selectivity of SPAEKS-40 membrane (13.8 × 104 S s cm−3) is about 4 times higher than that of Nafion 117 membrane (3.6 × 104 S s cm−3).

RETRACTED ARTICLE: Synthesis and characterization of a novel locally high dense sulfonated poly (aryl ether ketone sulfone) for DMFCs applications

A new sulfonated poly (aryl ether ketone sulfone) (SPAEKS-x) with locally dense sulfonic acid groups is synthesized by post-sulfonation. The SPAEKS-x membranes have a number average molecular weight of 45,000–58,000 g/mol and exhibit excellent mechanical properties. In addition, SPAEKS-x membranes have moderate water absorption, swelling rate, excellent thermal stability and good oxidative stability. The proton conductivity of SPAEKS-x membranes ranges from 35.6 to 52.4 mS/cm. All membranes show much lower methanol permeability than Nafion 117 membrane. Therefore, all membranes show higher proton selectivity than Nafion 117 membrane. In particularly, proton selectivity of SPAEKS-40 (15.8 × 104 S s cm−3) is about 5 times higher than that of Nafion 117 membrane (3.5 × 104 S s cm−3). Overall, SPAEKS-x membranes as a proton exchange membrane have shown very great application prospects in direct methanol fuel cells.

Facile synthesis of poly (arylene ether ketone)s containing flexible sulfoalkyl groups with enhanced oxidative stability for DMFCs

After tethering sodium 2-mercaptoethanesulfonate (MTS) to the bromomethylated poly(arylene ether ketone) precursor, a novel clustered sulfonated poly(arylene ether ketone) containing flexible sulfoalkyl groups (MTSPAEK) was prepared and used as polymer electrolyte membrane for application in DMFCs. The chemical structure and the degree of grafting of MTSPAEK copolymers were identified by 1H NMR spectra. The resulted MTSPAEK copolymers exhibited excellent thermal stability (Td5% > 259 °C) and good mechanical properties (tensile strength at break > 52 MPa). Compared to conventional sulfonated aromatic hydrocarbon polymers, MTSPAEK membranes displayed enhanced oxidative stability in Fenton's reagent owing to the elimination of free radicals by the sulfide groups located on the polymer side chains. Especially, MTSPAEK-2.10 with the highest content of flexible sulfoalkyl groups exhibited a highest proton conductivity of 0.181 S cm−1 at 80 °C. It could be attributed to the obvious hydrophilic/hydrophobic phase-separated structure within the membrane, which was confirmed by AFM images. Moreover, MTSPAEK-2.10 membrane performed a peak power density of 70 mW cm−2 in DMFC when feeding with 2 M methanol at 80 °C, which was comparable to the performance of recast Nafion as reported. Therefore, the combination of good thermal stability and mechanical properties, good oxidative stability, and good methanol barrier performance of MTSPAEK membranes indicated that they have potential to be alternative materials for PEMs in DMFCs.

PEMs with high proton conductivity and excellent methanol resistance based on sulfonated poly (aryl ether ketone sulfone) containing comb-shaped structures for DMFCs applications

Sulfonated poly (aryl ether ketone sulfone) polymers (SPAEKS-PSA X) with the comb-shaped structure were prepared by grafting with 1, 3-propanesultone (PSA). The successful synthesis of SPAEKS-PSA X was confirmed by the FT-IR spectra. The morphology of the membrane was investigated by the small angle X-ray scattering and the transmission electron microscopy. The nanophase separation was brought in a comb-shaped structure between the main chains and the propyl sulfonic acid groups. The SPAEKS-PSA 15 membrane exhibited the highest conductivity of 101 mS cm−1 under 80 °C and 100% relative humidity conditions (100% RH). In addition, the methanol permeability coefficients of SPAEKS-PSA X membranes (7.56 × 10−7 to 9.44 × 10−7 cm2 s−1) were much lower compared to Nafion®117 (22.37 × 10−7 cm2 s−1). Meanwhile, the SPAEKS-PSA X membranes also displayed excellent mechanical properties (tensile modulus >30 MPa), thermal, oxidative stabilities and fuel cell performance. Considering the parameters above, especially the elevated proton conductivities as well as high methanol resistance, the comb-shaped structure is a promising design for DMFCs applications.

Enhanced properties of SPEEK with incorporating of PFSA and barium strontium titanate nanoparticles for application in DMFCs

Novel blend nanocomposite proton-exchange membranes were prepared using sulfonated poly (ether ether ketone) (SPEEK), perfluorosulfonic acid (PFSA), and Ba0.9Sr0.1TiO3 (BST) doped-perovskite nanoparticles. The membranes were evaluated by attenuated total reflection, X-ray diffraction spectroscopy, water uptake, proton conductivity, methanol permeability, and direct methanol fuel cell test. The effect of two additives, PFSA and BST, were investigated. Results indicated that both proton conductivity and methanol barrier of the blend nanocomposite membranes improved compared with pristine SPEEK and the as-prepared blend membranes. The methanol permeability and the proton conductivity of the blend membrane containing 6 wt% BST obtained 3.56 × 10−7 cm2 s−1 (at 25 °C) and 0.110 S cm−1 (at 80 °C), respectively. The power density value for the optimum blend nanocomposite membrane (15 wt% PFSA and 6 wt% BST) (54.89 mW cm-2) was higher than that of pristine SPEEK (31.34 mW cm-2) and SPF15 blend membrane (36.12 mW cm-2).

Novel pore-filling membrane based on block sulfonated poly (ether sulphone) with enhanced proton conductivity and methanol resistance for direct methanol fuel cells

The problem remains unsolved in DMFCs applications that the increase in proton conductivity is usually caused the permeation of methanol. Herein, a novel kind of pore-filling membrane is investigated to meet this challenge. The porous substrate is fabricated from block poly (ether sulphone) with low degree of sulfonation, which form well-developed conductive channels owing to an aggregation of sulfonic acid groups, ensuring low methonal crossover and swelling ratio. The pore structures are achieved by a solution casting method which introduces alpha-cyclodextrin as the porogen. The resulting porous substrate possesses homogeneous opening pore structures. Then, the filling electrolyte, an organic-soluble tetrabutylammonium 4-vinylbenzene sulfonate, is used to fill the substrate and form a crosslinked network inside the pores to ensure high proton conductivity. The pore-filling membrane with block polymers shows higher proton conductivity (0.083 S cm−1 at 80 °C) than that prepared by random polymers (0.072 S cm−1 at 80 °C). Compared with Nafion 117, the composite membrane exhibits higher dimensional stability (6.6%) and methanol resistance (4.0 × 10−7 cm2 s−1). Furthermore, the pore-filling membrane outperforms Nafion 117 with an open circuit voltage of 0.61 V as well as a maximum power density of 46.8 mW/cm2 under 10 M methanol condition.

Effect of Filler Content on Transport Properties of Sulfonated Polyether Ether Ketone (SPEEK) Composite Proton Exchange Membranes

Proton exchange membrane for direct methanol fuel cell was developed by the incorporation of silicotungstic acid supported on silica (SiO2-SiWA) into SPEEK polymer. The properties of composite membranes with various silica/SiWA ratios were investigated and compared in this study. It was found that high silica to SiWA weight ratio (2:1) resulted in porous membrane with high proton conductivity and moderate methanol permeability. Reduction in the aforementioned ratio to 1:1 resulted in a more compact structure with better thermal stability, however, leaching of SiWA from the membrane occurred due to insufficient support. SPEEK membrane incorporated with 10 wt% SiO2 and 5 wt% SiWA showed the highest selectivity of 6.44 × 104 S.s/cm3 and performed better than that of the pure SPEEK membrane. These results suggested that these membranes have potential to be considered for DMFCs applications.

Facile synthesis of three-dimensional platinum nanoflowers decorated reduced graphene oxide: An ultra-high performance electro-catalyst for direct methanol fuel cells

In this work, we demonstrate platinum (Pt) nanoflowers-reduced graphene oxide (rGO) composite as an efficient electrocatalyst for methanol oxidation reaction (MOR) in acidic medium. rGO was prepared by low-cost, eco-friendly hydrothermal method and electro-deposition of Pt yielded three-dimensional large area Pt nanoflowers distributed over and among thin rGO nanosheets, thereby preventing restacking of rGO sheets. The composite exhibited outstanding electro-catalytic activity (15.3 mA cm−2), stability with CO tolerance ability (If/Ib = 6.99) which is, to the best of our knowledge, ∼2.2 folds greater than other previously reported carbon nanomaterials based catalysts. Values of If, Ib and If/Ib ratio of Pt-rGO based electrode were 13.2, 5.2 and 2.55 folds higher than only Pt respectively, which are ascribed to higher surface area of Pt nanoflowers that offers multidimensional pathways for easy diffusion of methanol to Pt, more catalytic active sites and excellent utilization of Pt for MOR. The composite shows huge potential to be used as binder free, cost-effective and durable electrocatalyst for electrochemical sensing and DMFCs applications.

A strategy in deep eutectic solvents for carbon nanotube-supported PtCo nanocatalysts with enhanced performance toward methanol electrooxidation

We herein report a novel strategy for multi-walled carbon nanotube (MWCNT)-supported PtCo nanocatalysts, which are synthesized in deep eutectic solvents (DESs) by a chemical reduction route. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicate that the alloyed PtCo nanoparticles of ca. 2.4 nm are deposited on the surface of MWCNTs with less aggregation in larger clusters. X-ray photoelectron spectroscopy (XPS) measurements reveal the strong charge transfer interaction between Pt and Co atoms in the PtCo/MWCNT catalyst. The electrochemical tests illustrate that the PtCo/MWCNT exhibits much higher electrocatalytic activity, stability and CO tolerance ability than the Pt/MWCNT catalyst for the methanol oxidation reaction (MOR). This study implies that the method based on DESs will be potential in design and fabrication of the highly efficient electrocatalysts for DMFCs applications.

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K2CO3 mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by 1H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01 × 10−6–0.58 × 10−6 cm2·s−1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm−1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11 × 105 S·s·cm−3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.

Platinum nanoparticles on porphyrin functionalized graphene nanosheets as a superior catalyst for methanol electrooxidation.

A novel nanostructured catalyst of platinum nanoparticles supported on 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP) functionalized graphene (TMPyP-graphene) is synthesized by the hydrothermal polyol process. The as-synthesized nanocomposites are characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis absorption spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. It has been found that Pt nanoparticles of ca. 3.4 nm are uniformly dispersed on the surface of TMPyP-graphene, and hold a high electrochemical active surface area (ECSA) of 126.2 m(2) g(-1). The results demonstrate that the Pt/TMPyP-graphene catalyst exhibits a much higher electrocatalytic activity and stability than the Pt/graphene and commercial Pt/C catalysts for methanol oxidation, which is of significant importance in improving the efficiency of Pt-based electrocatalysts for DMFCs applications.

The high performance of tungsten carbides/porous bamboo charcoals supported Pt catalysts for methanol electrooxidation

In this paper, a kind of environmental friendly and cost-effective bamboo charcoal (BC) is used as catalyst support in DMFCs instead of carbon nanotubes (CNTs), which is toxic and expensive. After special treatments, we obtain a sponge-like three-dimensional (3D) BC, which can provide high specific surface area (1264.5 m2 g−1) and porous matrices. Then, tungsten carbide (WC) and Pt are loaded on the BCs with microwave-assisted technique and 3D structural Pt/WC/BCs electro-catalyst is finally fabricated. Subsequently, the catalyst is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the further electrochemical investigation, it was found that Pt/WC/BCs catalyst has higher performance (2.76 mA cm−2) and better CO-tolerance for methanol oxidation compared with Pt/WC/CNTs and commercial Pt/C. Herein, we believe that the as-synthesized 3D Pt/WC/BCs catalyst has great promising application in DMFCs.

Copper phthalocyanine functionalization of graphene nanosheets as support for platinum nanoparticles and their enhanced performance toward methanol oxidation

We herein report a facile and effective ultrasonication method to non-covalently functionalize graphene with copper phthalocyanine-3,4′,4″,4‴-tetrasulfonic acid tetrasodium salt (TSCuPc) as a promising catalyst support for Pt nanoparticles. With the assistance of TSCuPc, Pt nanoparticles are homogeneously deposited on the surface of graphene, and their dispersivity and electrochemical active surface area (ECSA) are obviously enhanced. Studies of cyclic voltammetry and chronoamperometry demonstrate that the as-prepared Pt/TSCuPc–graphene catalyst exhibits much higher electrocatalytic activity and stability than the Pt/graphene and commercial Pt/C catalysts for methanol oxidation. It is concluded that the strategy of TSCuPc-functionalized graphene with Pt catalysts will be potential in design and synthesis of the highly efficient electrocatalysts for DMFCs applications.

Cross-linked poly(arylene ether ketone) electrolyte membranes with enhanced proton conduction for fuel cells

A new class of covalently cross-linkable poly(arylene ether ketone)s (cPAEKs) with sulfonic acid groups on both the backbone and pedant positions were synthesized. 3-Amino-1,5-napthalene disulfonic acid salt was chosen as a strong sulfonating agent for the preparation of csPAEK membranes with high sulfonation degree (SD). The major advantage of synthesized membranes is their exceptionally high-proton conductivities but still maintaining low methanol permeability and water uptake. All csPAEK membranes exhibited higher proton conductivity than Nafion®117 over the temperature range of 40–90 °C. For example, among these membranes, csPAEK0 with the lowest SD shows a proton conductivities of 0.071 S cm−1 at 40 °C and 0.118 S cm−1 at 90 °C, which are higher than those of Nafion®117 (0.057 S cm−1 at 40 °C and 0.108 S cm−1 at 90 °C). More interestingly, csPAEK0 appears to have a low water uptake, with values of only 22% at 40 °C and 27% at 90 °C, indicating high dimensional stability in hot water. Moreover, in many cases, csPAEK membranes with 15% cross-linking degree (CD) exhibited low methanol permeability, good thermal stability, and showed very high strain at break. The superior proton conduction, methanol permeation, and water uptake properties of the prepared membranes are of significant interest for both PEMFCs and DMFCs applications.

Synthesis and Characterization of Hybrid Pt/NiO/MWCNTs Electrocatalysts

AbstractTo search for more efficient and inexpensive electrocatalysts is one of the main research directions for the electrocatalytic application of direct liquid fuel cells. Nanohybrid Pt/NiO/MWCNTs are synthesized by impregnation and polyol methods. Two different series denoted as Pt/[NiO/MWCNTs (1:4)] and NiO/[Pt/MWCNTs (1:4)] are prepared. The sizes of the nanoparticles are 3‐7 nm and 10 nm for Pt and NiO, respectively. By observing the morphology images, NiO will aggregate more on Pt modified MWCNTs than those without Pt adding. The catalytic properties of these hybrid catalysts are characterized by methanol electro‐oxidation. The addition of 20 wt% NiO, before or after Pt synthesis, can better enhance the catalysis ability of Pt and help Pt catalyst convert CO in lower temperature. This study indicates the 10 wt% Pt/[NiO/MWCNTs (1:4)] catalyst has the best performance in electrocatalytic activity for methanol. The NiO is a cheaper material than other commonly used oxides; the novel hybrid catalysts are a promised candidate for the electrocatalytic application in DMFCs.

NMR and Electrochemical Investigation of the Transport Properties of Methanol and Water in Nafion and Clay-Nanocomposites Membranes for DMFCs.

Water and methanol transport behavior, solvents adsorption and electrochemical properties of filler-free Nafion and nanocomposites based on two smectite clays, were investigated using impedance spectroscopy, DMFC tests and NMR methods, including spin-lattice relaxation and pulsed-gradient spin-echo (PGSE) diffusion under variable temperature conditions. Synthetic (Laponite) and natural (Swy-2) smectite clays, with different structural and physical parameters, were incorporated into the Nafion for the creation of exfoliated nanocomposites. Transport mechanism of water and methanol appears to be influenced from the dimensions of the dispersed platelike silicate layers as well as from their cation exchange capacity (CEC). The details of the NMR results and the effect of the methanol solution concentration are discussed. Clays particles, and in particular Swy-2, demonstrate to be a potential physical barrier for methanol cross-over, reducing the methanol diffusion with an evident blocking effect yet nevertheless ensuring a high water mobility up to 130 °C and for several hours, proving the exceptional water retention property of these materials and their possible use in the DMFCs applications. Electrochemical behavior is investigated by cell resistance and polarization measurements. From these analyses it is derived that the addition of clay materials to recast Nafion decreases the ohmic losses at high temperatures extending in this way the operating range of a direct methanol fuel cell.