Search

Microbial fuel cells (MFCs) represent a promising approach for remediation of toxic vanadium (V) contaminated environment. Herein, enhanced V(V) reduction and bioelectricity generation are realized in MFCs with biocathode. Synergistically electrochemical and microbial reductions result in the nearly complete removals of V(V) within 7 d operation with initial concentration of 200 mg L −1 . Maximum power density of 529 ± 12 mW m −2 is obtained. Electrochemical tests reveal that biocathode promotes electron transfers and reduces charge transfer resistance. XPS analysis confirms that V(IV) is the main reduction product, which precipitates naturally under neutral conditions. High-throughput 16S rRNA gene sequencing analysis indicates that the newly appeared Dysgonomonas is responsible for V(V) reduction and Klebsiella contributes mainly to bioelectricity generation in MFCs with biocathode. This study further improves the performance of remediating V(V) contaminated environment based on MFC technology. [ABSTRACT FROM AUTHOR]

Direct borohydride fuel cells (DBFCs) exhibit the potential for a wide range of applications due to their high energy and power density; however, the hydrolysis of BH 4 − significantly limits the use of DBFCs. In this paper, PdNi x -B/carbon nanotubes (PdNi x -B/CNTs) (x = 0, 0.3, 0.6, 0.9) composites have been prepared by a chemical reduction method in which PdNi x -B nanoparticles of approximately 3.5 nm are grown on the surface of carbon nanotubes. A cell was assembled with PdNi x -B/CNTs as the anode catalyst, a polymer fibre membrane (PFM) as a substitute for the Nafion membrane and LaNiO 3 as the cathode catalyst. The results show that the Ni element displays an ability to balance the competition between the hydrolysis and oxidation of BH 4 − . A peak power density of 105 mW cm −2 (x = 0.9) was achieved at 25 °C. However, the highest fuel efficiency of 69% was achieved at x = 0.3, and the corresponding power density was 87 mW cm −2 , which represents the best comprehensive performance of these DBFCs. [ABSTRACT FROM AUTHOR]

A 2D Ti 3 C 2 MXene is introduced into NaAlH 4 to improve its hydrogen storage properties for the first time. In the presence of Ti 3 C 2 , the operating temperatures for hydrogen storage in NaAlH 4 are remarkably reduced, and the hydrogenation/dehydrogenation kinetics are significantly enhanced. The onset dehydrogenation temperature of the 7 wt% Ti 3 C 2 -containing NaAlH 4 sample is reduced to 100 °C, and hydrogen recharging starts at 50 °C. Approximately 4.7 wt% hydrogen is released from the NaAlH 4 -7 wt% Ti 3 C 2 sample within 100 min at 140 °C, and the dehydrogenated sample absorbs 4.6 wt% hydrogen within 60 min at 120 °C. However, pristine NaAlH 4 only absorbs 0.4 wt% hydrogen under identical conditions. Further cycling measurements show significantly improved cycling stability for the Ti 3 C 2 -containing NaAlH 4 ; the hydrogenation/dehydrogenation behaviour remains nearly constant after 10 cycles. XRD and XPS analyses reveal that the Ti 3 C 2 reacts with NaAlH 4 and is reduced to metallic Ti and Ti 3+ species, which are responsible for the lowered operating temperatures and improved dehydrogenation/hydrogenation kinetics. [ABSTRACT FROM AUTHOR]

Vertically oriented graphene-based nanocatalysts represent an emerging class of electrocatalysts due to their large surface area and excellent electrical transport ability. Herein, we report a vertically oriented reduced graphene oxide supported dealloyed palladium–copper nanoparticle catalyst (PdCu/VrGO) synthesized by a facile cyclic voltammetric electrodeposition of graphene oxide in the presence of Na 2 PdCl 4 and copper ethylenediamine tetraacetate. The structure and composition are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Meanwhile, the electrochemical properties are measured by cyclic voltammetry and chronoamperometry. The PdCu/VrGO catalyst exhibits excellent electrocatalytic activity towards methanol oxidation, with the mass activity of 762.8 A g −1 , which is 7.1 times that of a commercial Pd/C catalyst. In addition, PdCu/VrGO shows good chemical stability and superior tolerance to CO poisoning. These results demonstrate that vertical reduced graphene oxide provides a promising platform for the development of electrochemical nanocatalysts. [ABSTRACT FROM AUTHOR]

A novel bimetallic Pt–Fe electrode supported on carbon fibers (CFs) was prepared by chemical impregnation/reduction and evaluated for the electrolysis of coal to produce hydrogen. Characterization of the electrocatalyst was performed using X-ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy. The synthesized Pt–Fe particles were well dispersed on the surface of the CFs. The addition of Fe to the catalyst enhanced the electrooxidation of coal when compared to Pt alone. PtFe (1:1) supported on carbon fibers exhibited superior catalytic activity towards the conversion of coal than PtFe (7:3) and PtFe (3:7). [ABSTRACT FROM AUTHOR]

A series of Pt-Sn/C catalysts used as anodes during ethanol oxidation are synthesized by a deposition process using NaBH4 as the reducing agent. The order in which the precursors are added affects the electrocatalytic activity and physical-chemical characteristics of the bimetallic catalysts, where the Pt-Sn catalyst prepared by co-precipitation of both metals functions best below a potential of 0.5 V and the catalyst prepared by sequential deposition of Sn and Pt (drying after Sn addition) is most active above a potential of 0.5 V. The electrochemical behavior of catalysts during ethanol oxidation in an acidic medium are characterized and monitored in a half-cell test at room temperature by cyclic voltammetry, chronoamperometry and anode potentiostatic polarization. Catalyst structure and chemical composition are investigated by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This behavior presented for best Pt-Sn catalyst can be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. [ABSTRACT FROM AUTHOR]

Abstract: The design of active and durable catalysts for formic acid (FA) electrooxidation requires controlling the amount of three neighboring platinum atoms in the surface of Pt-based catalysts. Such requirement is studied by preparing Pt decorated Pd/C (donated as Pt–Pd/C) with various Pt:Pd molar ratios via galvanic displacement making the amount of three neighboring Pt atoms in the surface of Pt–Pd/C tunable. The decorated nanostructures are confirmed by XPS, HS-LEIS, cyclic voltammetry and chronoamperometric measurements, demonstrating that Pt–Pd/C (the optimal molar ratio, Pt:Pd = 1:250) exhibits superior activity and durability than Pd/C and commercial Pt/C (J-M, 20%) catalysts for FA electrooxidation. The mass activity of Pt–Pd/C (Pt:Pd = 1:250) (3.91 A mg−1) is about 98 and 6 times higher than that of commercial Pt/C (0.04 A mg−1) and Pd/C (0.63 A mg−1) at a given potential of 0.1 V vs SCE, respectively. The controlled synthesis of Pt–Pd/C lead to the formation of largely discontinuous Pd and Pt sites and inhibition of CO formation, exhibiting unprecedented electrocatalytic performance toward FA electrooxidation while the cost of the catalyst almost the same as Pd/C. These findings have profound implications to the design and nanoengineering of decorated surfaces of catalysts for FA electrooxidation. [Copyright &y& Elsevier]

Pt colloidal nanoparticles were synthesized by simultaneous chemical reduction of metallic salts in presence of poly (N-vinyl-2-pyrrolidone) as protecting agent. The uniform and highly ordered Pt colloidal nanoparticles were associated to well dispersed particles ranging in particle size distribution around 4.5 ± 1.9 nm. The nanoparticles were deposited onto multiwalled carbon nanotubes (MWCNT). MWCNT were synthesized by chemical vapor deposition (CVD) method. Before the metal impregnation, the MWCNT were treated with HNO3 in reflux. Prepared Pt catalyst were characterized by various physical and electrochemical techniques, that is, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and cyclic voltammetry (CV). Raman spectroscopy reveals changes intensity ratio IG′/IG in the samples, after the cleaning process and Pt loading, indicating changes in the crystallinity of the materials. HRTEM showed Pt particles between 6.1 ± 0.9 nm and 6.5 ± 1.5 nm are well dispersed along the carbon nanotubes. XRD patterns show characteristics peaks corresponding to graphite and metallic Pt. The electrochemical properties of the MWCNT supported Pt nanoparticles were investigated by analyzing the response of the nanostructured catalyst for cyclic voltammetry and compared with a commercial material. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on the application of hydroxide ion conducting layered double hydroxides (LDHs) to the catalyst layer in an alkaline fuel cell for the improvement of the oxygen reduction reaction (ORR) at the triple phase boundary (TPB) in the catalyst layer. Ni–Al LDH intercalated with (Ni–Al LDH) and Mg–Al LDH were used in this study. Ni–Al LDH showed higher ionic conductivity than Mg–Al LDH under R.H. of 80%. The catalyst layers with and without hydroxide ion conducting LDHs was prepared, and a half-cell using the prepared catalyst layers was fabricated. The addition of LDHs to the catalyst layer increased the reduction current for ORR, indicating that hydroxide ion conducting LDHs introduced OH− conducting paths and increased TPB region within the catalyst layer. Above all, the addition of Ni–Al LDH to the catalyst layer more effectively increased the reduction current for ORR than the addition of Mg–Al LDH. The performance of the alkaline-type direct ethanol fuel cell was also improved. These experimental results indicate that high hydroxide ion conducting Ni–Al LDH effectively increased TPB region within the catalyst layer. [Copyright &y& Elsevier]

Abstract: A viscoelastic-plastic constitutive model is developed to characterize the time-dependent mechanical response of perfluorosulphonic acid (PFSA) membranes. This model is then used in finite element simulations of a representative fuel cell unit, (consisting of electrodes, gas diffusion layer and bipolar plates) subjected to standardized relative humidity (RH) cycling test conditions. The effects of hold times at constant RH, the feed rate of humidified air and sorption rate of water into the membrane on the stress response are investigated. While the longer hold times at high and low humidity lead to considerable redistribution of the stresses, the lower feed and sorption rates were found to reduce the overall stress levels in the membrane. The redistribution and reduction in stress magnitudes along with inelastic deformation during hydration eventually lead to development of residual tensile stresses after dehydration. Simulations indicate that these tensile stresses can be on the order of 9–10 MPa which may lead to mechanical degradation of the membrane. The simulation results show that time-dependent properties can have a significant effect on the in-plane stress response of the membrane. [Copyright &y& Elsevier]

Abstract: Mo-modified Co–Pd–B (Co–Mo–Pd–B) and Pd-modified Co–B (Co–Pd–B) catalyst powders are synthesized by chemical reduction of cobalt and molybdenum salt at ambient conditions. The resulting catalyst powders are characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-photoelectron spectroscopy (XPS) and BET surface area measurement. The study on the catalytic efficiency of amorphous Co–Mo–Pd–B catalyst powders is performed in hydrogen generation by hydrolysis of alkaline sodium borohydride (NaBH4). The Co–Mo–Pd–B powders show the highest hydrogen generation rate as compared to Co–B, Co–Mo–B, and Co–Pd–B catalyst powders. Kinetic studies on the hydrolysis reaction of NaBH4 with Co–Mo–Pd–B catalyst reveal that the concentrations of both NaBH4 and NaOH have essentially no evident effects on hydrogen generation rate. The promoting effect of Mo in Co–Mo–Pd–B catalyst results in lower activation energy for hydrogen production, which is 36.36kJmol−1 compared to 64.87kJmol−1 obtained with pure Co–B powder. [Copyright &y& Elsevier]

Abstract: The reduction and oxidation (redox) durability and reforming activity of MgO–NiO–YSZ composites were examined to evaluate the suitability of MgO–NiO–YSZ composites as support materials for segmented-in-series solid oxide fuel cell (SOFC) cell stacks. The MgO–NiO–YSZ composites were compared with NiO–YSZ composites. The MgO–NiO–YSZ composites showed minimal size and structural changes during redox operations at 800°C and a nearly equivalent reforming activity to NiO–YSZ composites at temperatures ranging from 600°C to 800°C in spite of their lower Ni content. MgO–NiO–YSZ composites are good candidates for the support materials in segmented-in-series (SIS)-type SOFC cell stacks. [Copyright &y& Elsevier]

Abstract: In phosphoric acid fuel cell (PAFC) stack, reduction of the phosphoric acid that is impregnated in the cell is a major factor to restrict the operating life. In this paper, the phosphoric acid reduction by the evaporative and condensational dissipation on the effect of liquid phase migration was evaluated by numerical analysis. The calculations that include the behavior of evaporation, condensation, and liquid phase migration for the phosphoric acid, and the behavior of gas flow and heat transfer were conducted for the model cell with conditions that correspond to an on site stack. The diffusion coefficient of liquid phase migration was derived from the activation energy and frequency factor based on the experimental results. The phosphoric acid distributions in the vapor phase and liquid phase at the process gas and electrode were calculated for the duration of 3136h, and as a result of those, the exhausting and remaining amount of phosphoric acid for the cell were evaluated. The effects of liquid phase migration on the phosphoric acid dissipation were evaluated by analysis for various diffusion coefficients, and the analysis results were compared with the experimental results for the model cell. [Copyright &y& Elsevier]

Abstract: PtAg/C nanoparticles were synthesized by chemical reduction and evaluated for the oxygen reduction reaction (ORR) in the absence and presence of glucose. PtAg/C catalyst formed onion-like layered structures, which are uniformly distributed on the support. PtAg/C showed activity comparable to that of Pt/C ETEK for ORR. Further, the catalyst exhibited high selectivity for ORR in the presence of glucose. PtAg/C was evaluated as cathode in a microfluidic fuel cell operated with high concentration of glucose (100mM) as fuel. The results demonstrated that the use of PtAg/C as cathode electrode achieved higher selectivity and better performance compared with Pt/C catalyst. [Copyright &y& Elsevier]

Abstract: The primary objective of this work is to develop alternative electrocatalysts to Pt-based materials for the oxygen reduction reaction (ORR) in alkaline fuel cells. We synthesized a bicore CuFe/C composite electrocatalyst by impregnation of iron and copper phthalocyanine-based complexes into a carbon support, followed by pyrolysis at 800–900°C in an Ar atmosphere. This novel composite catalyst exhibits electrochemical performance for ORR in 0.1M KOH similar to a commercial Pt/C (BASF Fuel Cell, 30%) catalyst at 6-fold lower CuFe loading. High resolution X-ray photoelectron spectroscopy (HR-XPS) results indicate that coordination bonding between Fe and N atoms still remains and show that a mixed Cu(I)/Cu(II) valency exists in the CuFe/C catalyst after high temperature heat treatment. The Cu(I)/Cu(II) redox mediator adjacent to Fe atoms is crucial to provide electrons to the NxFe–O2 adduct and maximize the overall rate of the reduction reaction. The results of this study may offer a new approach to development of efficient catalysts for oxygen reduction to water in alkaline media. [Copyright &y& Elsevier]

Abstract: Co based catalyst were evaluated for oxygen reduction (ORR) in liquid KOH and alkaline anion exchange membrane fuel cells (AAEMFCs). In liquid KOH solution the catalyst exhibited good performance with an onset potential 120mV more negative than platinum and a Tafel slope of ca. 120mVdec−1. The hydrogen peroxide generated, increased from 5 to 50% as the electrode potential decreased from 175 to −300mV vs. SHE. In an AAEMFC environment, one catalyst (GP2) showed promising performance for ORR, i.e. at 50mAcm−2 the differences in cell potential between the stable performance for platinum (more positive) and cobalt cathodes with air and oxygen, were only 45 and 67mV respectively. The second catalyst (GP4) achieved the same stable power density as with platinum, of 200 and 145mWcm−2, with air at 1bar (gauge) pressure and air (atm) cathode feed (60°C), respectively. However the efficiency was lower (i.e. cell voltage was lower) i.e. 40% in comparison to platinum 47.5%. [Copyright &y& Elsevier]

Abstract: Palladium–platinum nanoalloys with a core–shell and nano-network structure were successfully synthesized by a hydrogen sacrificial protective method in an aqueous solution directly using a perfluorinated sulfonic acid (PFSA) ionomer as a protecting agent. The structure, local composition and electrocatalytic activity for the oxygen reduction reaction of the Pd/Pt/PFSA nanoalloys were investigated by transmission electron microscopy (TEM), aberration corrected scanning transmission electron microscopy (Cs-STEM), energy-dispersive X-ray spectrometry (EDS) and voltammetry. The core–shell structure was completed without contaminating reducing agents, organic solvents, useless protecting agents and a mediator. The Pd/Pt/PFSA core–shell nanoalloys realized a high electrochemical surface area and better electrocatalytic mass-activity for the oxygen reduction reaction than the Pt/PFSA nanoparticles. [Copyright &y& Elsevier]

Abstract: The construcal tree-shaped network is introduced into the design of a methanol steam microreactor in the context of optimization of the flow configuration. A three-dimensional model for methanol steam reaction in this designed microreactor is developed and numerically analyzed. The methanol conversion, CO concentration in the product and the total pressure drop of the gases in the microreactor with constructal tree-shaped network are evaluated and compared with those in the serpentine reactor. It is found that the reaction of methanol steam reforming is enhanced in the constructal tree-shaped microreactor, since the tree-shaped reactor configuration, which acts an optimizer for the reactant distribution, provides a reaction space with larger surface-to-volume ratio and the reduction of reactant velocities in the branches. Compared with the serpentine microreactor, the constructal reactor possesses a higher methanol conversion rate accompanied with a higher CO concentration. The conversion rate of the constructal microreactor is more than 10% over that of serpentine reactor. More particularly, the reduction of flow distance makes the constructal microreactor still possess almost the same pressure drop as the corresponding serpentine reactor, despite that the bifurcations induce extra local pressure loss, and the reduction of channel size in branches also causes pressure losses. [Copyright &y& Elsevier]

Abstract: Co-B amorphous alloy powders have been synthesized by chemical reduction of cobalt chloride with potassium borohydride in an aqueous solution. We find that this alloy can be used as an anode catalyst for a direct borohydride fuel cell (DBFC). This catalyst exhibits excellent electrocatalytic activity. An essential power output of 220mWcm−2 has been achieved at 15°C, and a life test last for 160h with no attenuation has been observed. The amorphous structure of the CoB alloy is still stable after the life test. [Copyright &y& Elsevier]

Abstract: Au and AuAg electrocatalysts were prepared by chemical reduction and supported on Vulcan XC-72 for their application in a laminar membraneless microfluidic fuel cell that operates with glucose as fuel in basic media. Average particle size and lattice parameters were determined by X-ray diffraction technique, resulting in 4 and 21nm for Au and AuAg respectively. The composition ratio of Au and Ag in the mixture was estimated by X-ray fluorescence. X-ray photoelectron spectroscopy measurements were used to determinate oxidation states. The electrocatalytic activity of Au/C and AuAg/C materials was investigated in terms of glucose electrooxidation in 0.3M KOH. The results obtained by electrochemical studies in a half cell configuration showed that the onset potential for glucose oxidation on AuAg/C presented a negative shift ca. 150mV compared with Au/C. AuAg/C was evaluated in a microfluidic fuel cell operated with glucose as fuel showing good stability and higher performance when was compared with Au/C. [Copyright &y& Elsevier]

Abstract: Unitized regenerative fuel cells (URFCs) have become more attractive for some time due to its potentially wide energy storage application such as in fields of space and renewable energy. In this study, TiC supported Pt–Ir electrocatalysts (Pt–Ir/TiC) for oxygen electrode in URFCs were synthesized, respectively, by chemical reduction process and plasma reduction process. Their physical and electrochemical properties are characterized and compared using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), cyclic voltammogram (CV), potentiostatic technique, and electrochemical impedance spectroscopy (EIS). The results from XRD, XPS and TEM demonstrate that the plasma process gives a finer metal crystals and higher metal dispersion on the TiC support. The CV, polarization, potentiostatic and EIS results show that the Pt–Ir/TiC electrocatalyst prepared by the plasma reduction process is obviously more active than that by the chemical reduction process, in agreement with the above metal-dispersion observations. The plasma process is a promising way for the preparation of supported electrocatalysts. [Copyright &y& Elsevier]

Abstract: A direct hydrazine fuel cell using H2O2 as the oxidizer has been developed. The N2H4/H2O2 fuel cell is assembled by using Ni–Pt/C composite catalyst as the anode catalyst, Au/C as the cathode catalyst, and Nafion membrane as the electrolyte. Both anolyte and catholyte show significant influences on cell voltage and cell performance. The open-circuit voltage of the N2H4/H2O2 fuel cell reaches up to 1.75V when using alkaline N2H4 solution as the anolyte and acidic H2O2 solution as the catholyte. A maximum power density of 1.02Wcm−2 has been achieved at operation temperature of 80°C. The number of electrons exchanged in the H2O2 reduction reaction on Au/C catalyst is 2. [Copyright &y& Elsevier]

Abstract: In this study, a novel core–shell structured Pd3Fe@Pt/C electrocatalyst, which is based on Pt deposited onto carbon supported Pd3Fe nanoparticles, is prepared for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The carbon supported Pd3Fe nanoparticles act as seeds to guide the growth of Pt. The formation of the core–shell structured Pd3Fe@Pt/C is confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical characterization. The higher surface area of the synthesized catalyst suggests that the utilization of Pt in the Pd3Fe@Pt/C catalyst is higher than that in Pt/C. Furthermore, better electrocatalytic performance than that of Pt/C and Pd3Fe/C catalyst is observed in the ORR which follows a four-electron path. Consequently, the results indicate that the Pd3Fe@Pt/C catalyst could be used as a more economically viable alternative for the ORR of PEMFCs. [Copyright &y& Elsevier]

Abstract: We proposed and tested a new and novel arrangement for a direct methanol fuel cell consisting of one inlet for a methanol solution and four outlets for oxidant gas (air), in both the anode and cathode flow fields. It utilizes different operating temperatures of 40°C and 60°C, and different methanol solution flow rates of 5mlmin−1, 10mlmin−1, and 20mlmin−1. Test results indicate a significant reduction in produced CO2 gas in the anode flow channels and product water in the cathode flow channels; consequently, cell performance can be greatly improved. Furthermore, methanol crossover can also be avoided and reduced. [Copyright &y& Elsevier]

Abstract: Carbon-supported bimetallic palladium–lead (Pd–Pb/C) catalysts with different amounts of lead are prepared using a co-reduction method. The catalysts are characterized by various techniques, which reveal the formation of an alloy nanoparticle structure. The electrochemical activities of the catalysts towards ethanol oxidation in alkaline media are examined by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods. The results show that the Pd–Pb(4:1)/C catalyst exhibits a better catalytic activity than the Pd/C catalyst. From carbon monoxide (CO) stripping results, the addition of lead also facilitates the oxidative removal of adsorbed CO. The promoting effect of lead is explained by a bi-functional mechanism and d-band theory. [Copyright &y& Elsevier]

Abstract: A solution-phase synthesis method was studied to prepare carbon supported Pt-Co alloy catalysts. The organic precursors of Pt acetylacetonate and Co acetylacetonate were reduced in a high boiling point solvent of octyl ether in the presence of oleic acid (OAc) and oleylamine (OAm) to produce fine Pt-Co nanoparticles, which were subsequently deposited on carbon support to obtain Pt-Co/C catalysts. Thermogravimetric analysis suggests that the stabilizers (OAc and OAm) can be removed by copious ethanol washing and subsequent moderate temperature heat-treatment (250°C, under Argon atmosphere). X-ray diffraction patterns indicate that the average particle size is around 2.3nm, and the lattice parameter is 3.868Å for the heat-treated Pt-Co/C (40wt%). Transmission electron microscopy images show very small Pt-Co alloy nanoparticles homogeneously dispersed on the carbon support with a particle size distribution of 2–4nm for all Pt-Co/C samples. The elements composition of Pt and Co in the final Pt-Co/C catalyst can be well controlled, as evidenced by inductively coupled plasma atomic emission spectroscopy and energy dispersive spectroscopy analyses. Proton exchange membrane fuel cell tests show the heat-treated Pt-Co/C cathode catalyst has higher mass activity of oxygen reduction reaction than Pt/C at an operation voltage of 0.9V, this can be attributed to its smaller particle size and reduced lattice parameter. [Copyright &y& Elsevier]

Abstract: We report a durable electrocatalyst support, highly graphitized mesoporous carbon (GMPC), for oxygen reduction in polymer electrolyte membrane (PEM) fuel cells. GMPC is prepared through graphitizing the self-assembled soft-template mesoporous carbon (MPC) under high temperature. Heat-treatment at 2800°C greatly improves the degree of graphitization while most of the mesoporous structures and the specific surface area of MPC are retained. GMPC is then noncovalently functionalized with poly(diallyldimethylammonium chloride) (PDDA) and loaded with Pt nanoparticles by reducing Pt precursor (H2PtCl6) in ethylene glycol. Pt nanoparticles of ∼3.0nm in diameter are uniformly dispersed on GMPC. Compared to Pt supported on Vulcan XC-72 carbon black (Pt/XC-72), Pt/GMPC exhibits a higher mass activity towards oxygen reduction reaction (ORR) and the mass activity retention (in percentage) is improved by a factor of ∼2 after 44h accelerated degradation test under the potential step (1.4–0.85V) electrochemical stressing condition which focuses on support corrosion. The enhanced activity and durability of Pt/GMPC are attributed to the graphitic structure of GMPC which is more resistant to corrosion. These findings demonstrate that GMPC is a promising oxygen reduction electrocatalyst support for PEM fuel cells. The approach reported in this work provides a facile, eco-friendly promising strategy for synthesizing stable metal nanoparticles on hydrophobic support materials. [Copyright &y& Elsevier]

Abstract: Carbon-supported PdNi catalysts for the ethanol oxidation reaction in alkaline direct ethanol fuel cells are successfully synthesized by the simultaneous reduction method using NaBH4 as reductant. X-ray diffraction characterization confirms the formation of the face-centered cubic crystalline Pd and Ni(OH)2 on the carbon powder for the PdNi/C catalysts. Transmission electron microscopy images show that the metal particles are well-dispersed on the carbon powder, while energy-dispersive X-ray spectrometer results indicate the uniform distribution of Ni around Pd. X-ray photoelectron spectroscopy analyses reveal the chemical states of Ni, including metallic Ni, NiO, Ni(OH)2 and NiOOH. Cyclic voltammetry and chronopotentiometry tests demonstrate that the Pd2Ni3/C catalyst exhibits higher activity and stability for the ethanol oxidation reaction in an alkaline medium than does the Pd/C catalyst. Fuel cell performance tests show that the application of Pd2Ni3/C as the anode catalyst of an alkaline direct ethanol fuel cell with an anion-exchange membrane can yield a maximum power density of 90mWcm−2 at 60°C. [Copyright &y& Elsevier]

Abstract: The performance of the positive electrode composed of a mixture of nickel hydroxide (Ni(OH)2) and a small amount of manganese dioxide (MnO2) was investigated for the positive electrode of Fuel Cell/Battery (FCB) system. It was found that the positive electrode can function not only as an active material of secondary batteries when it is charged but also as a catalyst of fuel cells when oxygen is supplied, which was confirmed by the following characterization: electrochemical characterization was performed with cyclic voltammetry (CV) and galvanostatic discharge curve in oxygen and oxygen-free atmosphere. CV of Ni(OH)2/MnO2 positive electrode exhibited the redox reaction of Ni(OH)2 as well as oxygen reduction reaction. It was observed that the discharge curves of positive electrode had two working potentials in half cell test when the electrode was charged and oxygen was supplied: one from the reactions of nickel oxyhydroxide (NiOOH); the other from the fuel cell reactions of manganese dioxide (MnO2). It was also observed that the discharge curves had two working voltages in full cell test when the cell was fully charged and oxygen was supplied: one at 1.2V from the battery reactions of NiOOH; the other at 0.8V from the fuel cell reactions of MnO2. In particular, the discharge capacity of overcharged cell was improved approximately 2 times compared with a battery of the same electrode quantity due to the additional function of this system as a fuel cell by using oxygen generated by water electrolysis. XRD analysis showed that there was no crystal structure change before and after (over)charge–discharge cycles. In summary, these experimental results showed that the novel bi-functional FCB system could provide an improved overall energy density per weight compared with conventional secondary batteries. [Copyright &y& Elsevier]

Abstract: A core–shell structured low-Pt catalyst, PdPt@Pt/C, with high performance towards both methanol anodic oxidation and oxygen cathodic reduction, as well as in a single hydrogen/air fuel cell, is prepared by a novel two-step colloidal approach. For the anodic oxidation of methanol, the catalyst shows three times higher activity than commercial Tanaka 50wt% Pt/C catalyst; furthermore, the ratio of forward current I f to backward current I b is high up to 1.04, whereas for general platinum catalysts the ratio is only ca. 0.70, indicating that this PdPt@Pt/C catalyst has high activity towards methanol anodic oxidation and good tolerance to the intermediates of methanol oxidation. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The core–shell structure of the catalyst is revealed by XRD and TEM, and is also supported by underpotential deposition of hydrogen (UPDH). The high performance of the PdPt@Pt/C catalyst may make it a promising and competitive low-Pt catalyst for hydrogen fueled polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) applications. [Copyright &y& Elsevier]

Abstract: Two kinds of Pt–Au/CNT catalysts with different structures are prepared by synthesizing the formerly separated Pt/Au (Au separating Pt) in separate solutions, and PtAu nanoparticles in mixed solution using the borohydride reduction method with trisodium citrate as the stabilizing agent, and then depositing the metal colloid nanoparticles on the carbon nanotubes supporting material. The structural information and particle size are characterized by UV–vis absorption spectra, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results confirm the formation of Pt–Au nanoparticles with PtAu and separated Pt/Au structures. The catalytic activities for methanol oxidation reaction and oxygen reduction reaction are examined by electrochemical measurements. Compared with the Pt/CNT catalyst, the two Pt–Au/CNT catalysts show a lower overpotential for the oxygen reduction reaction in the presence of methanol, indicating a higher methanol tolerance on Au-modified Pt nanoparticles. Particularly, the Pt/Au/CNT catalyst with Au separating Pt nanoparticles structure exhibits the significantly higher methanol tolerance than PtAu/CNT catalyst. The enhanced methanol tolerance may be attributed to less methanol adsorption on Pt surface due to the effect of Au nanoparticles. [Copyright &y& Elsevier]

Abstract: Direct-oxidation fuel cells (DOFC) are promising electrochemical devices for various applications. In addition to methanol (MeOH), alternative fuels are being tested in a search for lower toxicity, safer handling, and higher energy density. Ethylene glycol (EG) was employed as one of such fuels. However, DOFCs face several problems, such as fuel crossover through the membrane during its operation. This not only lowers the cell potential but also poisons the catalyst for the oxygen-reduction reaction (ORR). Experiments were performed on the poisoning of Pt and Pt-alloy ORR catalysts (both commercial and homemade, by electroless deposition), by fuels and their oxidation by-products. At 25°C, methanol poisoning was found to be reversible and the catalytic activity measured afterwards in a fuel-free solution and the electrochemical surface area (ECSA) were enhanced. The effect of poisoning by methanol and ethylene glycol and their oxidation intermediates is reported here for the first time. The severity of poisoning was found to be MeOH≪formaldehyde

Abstract: The activity for the oxygen reduction reaction (ORR) on carbon supported Pt–Ni electrocatalysts prepared by reduction of Pt and Ni precursors with NaHB4 was investigated in sulphuric acid both in the absence and in the presence of methanol and compared with that of a commercial Pt/C electrocatalyst. In methanol-free sulphuric acid solution the Pt70Ni30/C alloy electrocatalyst showed a lower specific activity towards oxygen reduction compared to Pt/C. In O2-free H2SO4 the onset potential for methanol oxidation on Pt70Ni30/C was shifted to more positive potentials, which indicates a lower activity for methanol oxidation than platinum. In the methanol containing electrolyte the higher methanol tolerance of the Pt70Ni30/C electrocatalyst for the ORR was ascribed to the lower activity of the binary electrocatalyst for methanol oxidation, arising from a composition effect. [Copyright &y& Elsevier]

Abstract: A new plating process has been developed for the formation of the cathode catalyst of a micro tubular direct methanol fuel cell. By using this method, a thin porous layer of Pt electrocatalyst was firstly bonded onto a tubular polymer electrolyte membrane by chemical reduction of Pt complex impregnated in the membrane. Electroplating was further made to control the loading amount and size of the Pt catalyst particles. The deposited Pt catalyst layer is around 12μm in thickness with the Pt particles size of 10nm. The micro tubular DMFC with a 6mg–Ptcm-2 cathode exhibited a peak power density of 2mWcm-2 under passive and air breathing conditions at ambient temperature and pressure. [Copyright &y& Elsevier]

The effect of an immobilized diffusion layer on the catalyst layer and the oxygen reduction reaction in polymer electrolyte fuel cells (PEMFCs) have been studied. Since, the oxygen reduction reaction is an inhibitive reaction, much effort has been devoted to the improvement of this reaction in PEMFCs. In this work, the effect of an immobilised hydrophobe carbon layer as the diffusion layer in the gas diffusion electrode has been evaluated. The study of various electrochemical methods in this research, as well as the evaluation of cell polarisation curves showed that the efficiency of electrodes with the diffusion layer in the high current density regions is higher than the electrodes with no diffusion layer. While in the lower current density region the electrodes without the diffusion layer are more efficient than the other type. [Copyright &y& Elsevier]

Development of high-performance electrode materials is critical to the commercial realization of solid oxide fuel-cell (SOFC) technology. The material development process is, however, very complex and requires understanding of the fundamental issues of the materials and the electrochemistry that is involved. An interesting example is the (La,Sr)MnO3 (LSM) cathode material. This paper discusses some important issues in the development and optimization of LSM cathode materials for SOFCs. The relationship between the microstructure, interfacial properties and the electrochemical behaviour of the cathode material is not a static one. Rather, it changes and evolves constantly under fuel-cell operation conditions. Such dynamic relationship between the properties and the electrochemical behaviour is important for the fundamental understanding of the mechanism and kinetics of the oxygen reduction at LSM cathodes, and for the development of high-performance cathodes for SOFCs that operate at intermediate temperatures (600–800 °C). [Copyright &y& Elsevier]

Oxygen reduction processes at a yttria stabilized zirconia|doped lanthanum manganite (LSM|YSZ) interface are investigated by ac impedance spectroscopy. Three semi-arcs are clearly observed at an oxygen partial pressure (pO2) of 0.001 atm. The constant-phase element of frequency arc and the pO2-dependence of 1/R (R: resistance) are correlated to interpret the reaction processes associated with the frequency arcs. It is found that at least five elementary steps are involved in oxygen reduction at the LSM|YSZ interface. Three of these steps are identified as the rate-determining steps, namely: (i) gas diffusion through the porous LSM electrode from the bulk to the reaction sites; (ii) surface diffusion of oxygen intermediate species along the LSM surface; (iii) incorporation of oxygen ions from the three phase boundary into the YSZ electrolyte lattice. The pO2-dependent exchange current density of the rate-determining step predicted by model is consistent with the experimental data, which further confirms the validity of the proposed oxygen reduction processes at the LSM|YSZ interface. [Copyright &y& Elsevier]

In direct borohydride fuel cell (DBFC), there is a contradiction between catalytic activity and specific discharge capacity (SDC) owing to the dual catalytic effects of most anode catalysts on both borohydride oxidation reaction (BOR) and borohydride hydrolysis reaction (BHR). To overcome this problem, a facile method to fabricate an ultrathin tin dioxide (SnO 2) supported cobalt oxide (Co 3 O 4) composite material (u-SnO 2 /Co 3 O 4) as DBFC anode catalyst was developed. Both catalytic ability for BOR and specific discharge capacity of the DBFC using the u-SnO 2 /Co 3 O 4 (DBFC-u-SnO 2 /Co 3 O 4) with 5–10 nm thick two-dimensional (2D) SnO 2 were improved. The maximum power density (52.5 mW cm−2) and SDC (1380 mAh g−1) of DBFC-u-SnO 2 /Co 3 O 4 were respectively increased by 105% and 1740% in comparison with those of DBFC with Co 3 O 4 as anode catalyst (DBFC-Co 3 O 4). The u-SnO 2 /Co 3 O 4 has higher specific surface area, electron donation ability, and the rate of desorption of intermediate product (such as BH 3 OH−, H ads) which may account for the excellent catalytic performance of u-SnO 2 /Co 3 O 4 for BOR. Image 1 • Ultrathin SnO 2 supported Co 3 O 4 (u-SnO 2 /Co 3 O 4) is synthesized by chemical reduction. • Direct borohydride fuel (DBFC) uses u-SnO 2 /Co 3 O 4 as anode catalyst is developed. • DBFC-u-SnO 2 /Co 3 O 4 has superior specific discharge capacity contrast to DBFC-Co 3 O 4. [ABSTRACT FROM AUTHOR]