Kinetics and PEMFC performance of RuxMoySez nanoparticles as a cathode catalyst

Kinetics of Ru_xMo_ySe_z nanoparticles dispersed on carbon powder was studied in 0.5 M H₂SO₄ electrolyte towards the oxygen reduction reaction (ORR) and as cathode catalysts for a proton exchange membrane fuel cell (PEMFC). Ru_xMo_ySe_z catalyst was synthesized by decarbonylation of transition-metal carbonyl compounds for 3 h in organic solvent. The powder was characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Catalyst is composed of uniform agglomerates of nanocrystalline particles with an estimated composition of Ru₆Mo₁Se₃, embedded in an amorphous phase. The electrochemical activity was studied by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Tafel slopes for the ORR remain invariant with temperature at −0.116 V dec⁻¹ with an increase of the charge transfer coefficient in dα/dT = 1.6 × 10⁻³, attributed to an entropy turnover contribution to the electrocatalytic reaction. The effect of temperature on the ORR kinetics was analyzed resulting in an apparent activation energy of 45.6 ± 0.5 kJ mol⁻¹. The catalyst generates less than 2.5% hydrogen peroxide during oxygen reduction. The Ru_xMo_ySe_z nanoparticles dispersed on a carbon powder were tested as cathode electrocatalyst in a single fuel cell. The membrane-electrode assembly (MEA), included Nafion^® 112 as polymer electrolyte membrane and commercial carbon supported Pt (10 wt%Pt/C-Etek) as anode catalyst. It was found that the maximum performance achieved for the electro-reduction of oxygen was with a loading of 1.0 mg cm⁻² Ru_xMo_ySe_z 20 wt%/C, arriving to a power density of 240 mW cm⁻² at 0.3 V and 80 °C.     

Ruthenium cluster-like chalcogenide as a methanol tolerant cathode catalyst in air-breathing laminar flow fuel cells

This paper reports the incorporation of a cluster-like Ru_xSe_y as a methanol tolerant cathode catalyst in a laminar flow fuel cell. The effect on cell performance of several concentrations of methanol in the cathode stream was investigated for the Ru_xSe_y catalyst and compared to a conventional platinum catalyst. While the Pt catalyst exhibited up to ∼80% drop in power density, the Ru_xSe_y catalyst showed no decrease in performance when the cathode was exposed to methanol. At several methanol concentrations the Ru_xSe_y catalyst performed better than the Pt catalyst. This demonstration of a methanol tolerant catalyst in a laminar flow fuel cell opens up the way for further miniaturization of the cell design and simplification of its operation as the need for an electrolyte stream to prevent fuel crossover has been eliminated.     

Palladium/Cobalt Coated on Multi‐Walled Carbon Nanotubes as an Electro‐catalyst for Oxygen Reduction Reaction in Passive Direct Methanol Fuel Cells

This work reports the synthesis of Pd‐based alloy electrocatalysts of Co supported on multi‐walled carbon nanotubes (MWCNTs) and their evaluation as cathode materials in a passive direct methanol fuel cell (PDMFC). The X‐ray diffraction (XRD) analysis showed well‐defined reflections corresponding to a face centered cubic phase of palladium. As compared to the Pd/MWCNT electrocatalyst, the bimetallic alloy electrocatalysts with the different Pd_xCo atomic ratios showed highly enhanced mass activity (MA) for the oxygen reduction reaction (ORR); however, the significant enhancement in the specific activity (SA) by a factor of about 1.2–5.6 for the ORR was found on the Pd_xCo alloy electrocatalysts in the presence and absence of methanol electrolyte solution. This enhancement SA in of the Pd‐based electrocatalysts was correlated to the changes in the lattice parameter and Pd_xCo surface composition. Surface area changes of Pd‐based electrocatalysts supported on MWCNT were evaluated using an accelerated durability test (ADT). The results obtained using the ADT were correlated to the performance of the Pd‐based electrocatalysts in the PDMFC. A better performance was obtained for the cell using Pd₃Co/MWCNT (2.53 mW cm^–2) compared to Pd/MWCNT (1.64 mW cm^–2) and Pt/C‐Electrochem (1.20 mW cm^–2) as cathode in the PDMFC. In the presence and absence of methanol the impedance Bode spectra showed one time constant that associated to follow a four electron pathway.     

Carbon supported Ru–Se as methanol tolerant catalysts for DMFC cathodes. Part I: preparation and characterization of catalysts

Carbon supported Ru _x Se _y O _z catalysts were prepared from Ru₃(CO)₁₂ and RuCl₃ · xH₂O as ruthenium precursors and H₂SeO₃ and SeCl₄ as the selenium sources. Highly active catalysts for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFC) were obtained via a multi-step preparation procedure consisting of a CO₂-activation of the carbon support prior to the preparation of a highly disperse Ru particles catalyst powder that is subsequently modified by Se. Ultimately, an excess of Se was removed during a final thermal annealing step at 800 °C under forming gas atmosphere. The morphology of the catalysts was analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD), which shows that the catalysts consist of crystalline Ru-particles with sizes ranging from 2 to 4 nm exhibiting a good dispersion over the carbonaceous support. The corresponding catalytic activity in the process of oxygen reduction was analyzed by cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements. The nature of the carbon support used for the preparation of RuSe cathode catalysts is of significant importance for the activity of the final materials. Catalysts supported on CO₂-activated Black Pearls 2000 gave the highest ORR-activity. Se stabilizes the Ru-particles against bulk oxidation and actively contributes to the catalytic activity. An exceptional property of the carbon supported Ru-particles modified with Se is their resistance to coalescence up to temperatures of 800 °C under inert or reducing conditions. Additional effects of Se-modification are the enhanced stability towards electrochemical oxidation of Ru and a lowering of the H₂O₂ formation in the ORR.     

Pr0.6Sr0.4CoO3−δ electrocatalyst for solid oxide fuel cell cathode introduced via infiltration

Effects of infiltrated Pr_0.6Sr_0.4CoO_3−δ (PSCo) electrocatalyst on SOFC cathode performance have been studied. Nano-sized particulate catalysts, deposited on surfaces of a composite cathode of Sm₂O₃ doped CeO₂ (SDC) and La_1−xSr_xCo_1−yFe_yO_3−δ (LSCF), are assumed to effectively widen active sites, or triple phase boundaries, for the oxygen reduction reaction. Area specific resistance of commercially available cells has been decreased by 36–40% with the addition of 23 wt% PSCo electrocatalyst on cathode. Analysis of the impedance spectra demonstrates that PSCo electrocatalyst plays a significant role in dissociation of oxygen molecules and adsorption of oxygen atoms into the cathode. A total of 200 h operation of the cells demonstrated that catalytic activity of PSCo has not been significantly degraded. Simultaneous operations of multiple cells using a parallel-cell testing system have made it possible to compare the performance of several cells with high reliability.     

Studies on the effect of solvent for the synthesis of low-cost and efficient Pt-Co/CAB cathode electrocatalyst to enhance the performance of a hydrogen-based PEMFC

Highly efficient and low-cost Pt-Co/C_AB bimetallic cathode electrocatalysts were synthesized for hydrogen-based proton exchange membrane fuel cell (PEMFC) using three different types of solvent, namely, dimethyl sulphoxide (DMSO), dimethylformamide (DMF), and ethylene glycol (EG). The physical characterization of synthesized cathode electrocatalysts Pt-Co/C_AB-DMSO, Pt-Co/C_AB-DMF and Pt-Co/C_AB-EG was performed by scanning electron microscope–energy-dispersive X-ray (SEM–EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques, whereas the electrochemical investigation of all three Pt-Co/C_AB electrocatalysts was performed by CV and EIS studies. The synthesized Pt-Co/C-EG electrocatalyst produced the highest power density of 19.61 mW/cm² at a room temperature of 33°C. The power density increased to 26.11 mW/cm², that is, 133%, when the cell operating temperature was raised from 33 to 70°C. The excellent performance of the Pt-Co/C_AB-EG cathode electrode proves that it can be recommended as a commercial electrocatalyst for PEMFC cathode. In addition, the EG/EG was identified as the best solvent for the synthesis of Pt-Co/C_AB cathode electrocatalysts.     

Chalcogenide metal centers for oxygen reduction reaction: Activity and tolerance

This mini-review summarizes materials design methods, oxygen reduction kinetics, tolerance to small organic molecules and fuel cell performance of chalcogenide metal catalysts, particularly, ruthenium (Ru_xSe_y) and non-precious transition metals (M_xX_y: M = Co, Fe and Ni; X = Se and S). These non-platinum catalysts are potential alternatives to Pt-based catalysts because of their comparable catalytic activity (Ru_xSe_y), low cost, high abundance and, in particular, a high tolerance to small organic molecules. Developing trends of synthesis methods, mechanism of oxygen reduction reaction and applications in direct alcohol fuel cells as well as the substrate effect are highlighted.     

Effect of Fe Doping on Layered GdBa0.5Sr0.5Co2O5+δ Perovskite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Layered perovskite cathode materials have received considerable attention for intermediate temperature solid oxide fuel cells (IT‐SOFCs) because of their fast oxygen ion diffusion through pore channels and high catalytic activity toward the oxygen reduction reaction (ORR) at low temperatures. In this study, we have investigated the effects of Fe substitution for the Co site on electrical and electrochemical properties of a layered perovskite, GdBa_0.5Sr_0.5Co_2?xFe_xO_5+δ (x = 0, 0.5, and 1.0), as a cathode material for IT‐SOFCs. Furthermore, electrochemical properties of GdBa_0.5Sr_0.5CoFeO_5+δ–yGDC (y = 0, 20, 40, and 50 wt%) cathodes were evaluated to determine the optimized cell performance. At a given temperature, the electrical conductivity and the area‐specific resistances (ASRs) of GdBa_0.5Sr_0.5Co_2?x Fe_xO_5+δ decrease with Fe content. The lowest ASR of 0.067 Ω·cm² was obtained at 873 K for the GdBa_0.5Sr_0.5CoFeO_5+δ. The GdBa_0.5Sr_0.5CoFeO_5 + δ composite with 40 wt% GDC was identified as an optimum cathode material, showing the highest maximum power density (1.31 W/cm²) at 873 K, and other samples also showed high power density over 1.00 W/cm².     

Study of IrxRu1−xO2 oxides as anodic electrocatalysts for solid polymer electrolyte water electrolysis

Electrocatalysts of the general formula Ir_xRu_1−xO₂ were prepared using Adams’ fusion method. The crystallite characterization was examined via XRD, and the electrochemical properties were examined via cyclic voltammetry (CV) in, linear sweep voltammetry (LSV) and chronopotentiometry measurements in 0.5 M H₂SO₄. The electrocatalysts were applied to a membrane electrode assembly (MEA) and studied in situ in an electrolysis cell through electrochemical impedance spectroscopy (EIS) and stationary current density–potential relations were investigated. The Ir_xRu_1−xO₂ (x = 0.2, 0.4, 0.6) compounds were found to be more active than pure IrO₂ and more stable than pure RuO₂. The most active electrocatalyst obtained had a composition of Ir_0.2Ru_0.8O₂. With an Ir_0.2Ru_0.8O₂ anode, a 28.4% Pt/C cathode and the total noble metal loading of 1.7 mg cm⁻², the potential of water electrolysis was 1.622 V at 1 A cm⁻² and 80 °C.     

Oxygen and water vapor gas barrier poly(ethylene naphthalate) films by deposition of SiOx plasma polymers from mixture of tetramethoxysilane and oxygen

SiO_x films were deposited from a mixture of tetramethoxysilane (TMOS) and oxygen on poly(ethylene 2,6‐naphthalate) film using ion‐assisted plasma polymerization technique (Method II) and conventional plasma polymerization technique (Method I), and were compared in chemical composition and gas barrier properties. Methods I and II were different in electrical circuit between electrodes (anode and cathode) and electric power supply. In Method I, the anode electrode was grounded, and the cathode electrode was coupled to the discharge power supply. In Method II, the anode electrode was connected with the discharge power supply, and the cathode electrode was grounded. There was not large difference in SiO_x deposition rate between the plasma polymerizations by Methods I and II. Plasma polymers deposited from TMOS/O₂ mixtures by Method II possessed smaller C/Si and O/Si atomic ratios than those deposited by Method I and showed advantage in gas barrier properties. The oxygen and water vapor permeation rates were 0.08–0.13 cm³ m^?2 day^?1 atm^?1 at 30°C at 90% RH and 0.244–0.276 g m^?2 day^?1 at 40°C at 90% RH, respectively. From these results, it can be concluded that the ion‐assisted plasma polymerization is a useful technique for deposition of gas barrier SiO_x thin films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 915–925, 2007     

Properties of polyamide 6,10/poly(vinyl alcohol) blends and impact on oxygen barrier performance

The oxygen transmission rate, average volume of free‐volume cavities (V_f) and fractional free volume (F_v) of polyamide 6,10 (PA610)/poly(vinyl alcohol) (PVA) (i.e. PA610_xPVA⁰⁵_y, PA610_xPVA⁰⁸_y and PA610_xPVA¹⁴_y) blend films reduced to minimum values when their PVA contents reached corresponding optimal values. Oxygen transmission rate, V_f and F_v values obtained for optimal PA610_xPVA^z_y blown films were reduced considerably with decreasing PVA degrees of polymerization. The oxygen transmission rate of the optimal bio‐based PA610₈₀PVA⁰⁵₂₀ blown film was only 2.4 cm³ (m²·day·atm)^?1, which is about the same as that of the most often used high‐barrier polymer, ethylene–vinyl alcohol copolymer. Experimental findings from dynamic mechanical analysis, differential scanning calorimetry, wide‐angle X‐ray diffraction and Fourier transform infrared spectroscopy of the PA610_xPVA^z_y blends indicate that PA610 and PVA in the blends are miscible to some extent at the molecular level when the PVA contents are less than or equal to the corresponding optimal values. The considerably enhanced oxygen barrier properties of the PA610_xPVA^z_y blend films with optimized compositions are attributed to the significantly reduced local free‐volume characteristics. © 2017 Society of Chemical Industry     

Effect of support type and synthesis conditions on the oxygen reduction activity of RuxSey catalyst prepared by the microwave polyol method

Ru_xSe_y nanoparticles supported on different carbon substrates were synthesized by microwave heating of ethylene glycol solutions of Ru(III) chloride and sodium selenite at different pH and Ru/Se mole ratios. The resulting catalysts were used for the electrochemical oxygen reduction reaction (ORR) in acidic solution. The electrochemical activity was highest for the supported catalyst synthesized at pH 8. Increasing the Se concentration of the catalyst up to 15 mol% increased the catalytic activity for the ORR; at this Se concentration, the activity of the catalyst was considerably higher than that observed for pure Ru catalyst synthesized at exactly the same conditions. The influence of the type of carbon support on the activity of the electrocatalyst was also investigated. Among the different supports, including carbon black (Vulcan XC-72R) (C1), and nanoporous carbons synthesized from resorcinol- (C2) and phloroglucinol-formaldehyde (C3) resins, the Ru_xSe_y catalyst supported on C3 exhibited highest activity for ORR.     

Benzene electro-oxidation in a PEMFC for phenol and electricity cogeneration

In the present investigation, the electrochemically-assisted oxidation of benzene in a H₂–O₂ proton exchange membrane fuel cell (PEMFC), for electricity and phenol cogeneration is studied. Experiments were carried out in a PEMFC electrochemical reactor using Pd black as cathode electrocatalyst at 60 and 80 °C, respectively and 1 atm back pressure. Indeed, it was found that the only product detected under the examined experimental conditions was phenol. The online GC product analysis revealed that it is impossible to produce phenol when the fuel cell circuit is open (I = 0) under all the examined experimental conditions. When the fuel cell circuit was closed, however, the phenol yield was found to follow a volcano-type dependence on the current of the external circuit. It was found that the maximum phenol yield was 0.35% at 100 mA/cm² at 80 °C. At the same time, the PEMFC performance was also investigated during the phenol generation process. Furthermore, experiments with the rotating ring disc electrode (RRDE) technique showed that the intermediate oxidation product, i.e. H₂O₂ existed during the oxygen electro-reduction process. The cyclic voltammograms showed that benzene was strongly adsorbed on the Pd surface, leading to a degradation of the PEMFC performance.     

Oxygen reduction on Ru-oxide pyrochlores bonded to a proton-exchange membrane

Oxygen reduction at a gas-fed, porous, ruthenium-pyrochlore electrode attached to a Dow Developmental Fuel Cell Membrane was measured in solutions of various pH. Electrode assemblies containing high surface area Pb₂Ru_2–x Pb _x O_7–y or Bi₂Ru_2–x Bi _x O_7–y with different amounts of Teflon content with/without the incorporation of Dow gel in the active part of the electrode with/without a CO₂-treated Vulcan XC-72 carbon substrate were tested. The oxide pyrochlores were found to be chemically stable and to show their lowest overpotential if separated from a 2.5 M H₂SO₄ proton reservoir by the membrane. Interesting oxygen reduction activity at room temperature was obtained with the Pb₂Ru_1.74Pb_0.26O_7–y electrode bonded with 22% by weight Teflon and incorporating 5% by weight Dow gel. The performance of the oxides against B-site Pb concentration and a measurement of the surface charge on the particles indicate that, in this configuration, the active sites for the oxygen reduction reaction are OH^– species at the O-site positions of the A₂B₂O₆O_1–y pyrochlores, especially the bridging oxygen with one Ru and one Pb near neighbour, i.e. Pb–O_b–Ru. Evidence that oxide particles precipitated on CO₂-treated carbon transfer electrons to the substrate is also presented.     

The oxygen reduction reaction on Pt/TiO x N y -based electrocatalyst for PEM fuel cell applications

Titanium oxy-nitride was developed for the first time as Pt electrocatalyst support for the ORR in PEM fuel applications. The conditions of the support preparation and the Pt/TiO _x N _y -based electrodes’ elaboration by chemical reduction method were determined. Comparison of the polarization curves of the carbon and the TiO _x N _y supported how clearly TiO _x N _y was more stable than the Vulcan XC-72R. It was found that the 40 wt% Pt/TiO _x N _y -based electrocatalyst is active for the ORR in acid medium, but the activity was less than that of Pt/C. The normalized electrochemical surface area degradation of Pt/TiO _x N _y was significantly less than that of Pt/C. The kinetics of the ORR on Pt/TiO _x N _y proceeded through a four-electron transfer process. The single-cell hydrogen/oxygen PEM fuel cell performances based on Pt/TiO _x N _y cathode electrocatalyst exhibited the same range of characteristics as those based on Pt/C.     

Oxygen barrier,free volume,and blending properties of fully bio-based polyamide 11/poly(vinyl alcohol) blends

Fully bio-based polyamide 11 (PA11) was melt-blended with poly(vinyl alcohol) (PVA) with varying degrees of polymerization (DP) to prepare PA11_xPVA^z_y. The PA11_xPVA^z_y films demonstrated the lowest oxygen transmission rates (OTR) and free volume characteristics, when PVA contents of each PA11_xPVA^z_y series reached a corresponding critical concentration. The minimum OTR and free volume characteristics obtained for the optimal PA11_xPVA^z_y films reduced significantly with decreasing PVA DPs. The OTR of the optimal PA11_xPVA^z_y blown film was 1.07 cm³ m⁻² day⁻¹ atm⁻¹, which is near to that of the ethylene-vinyl alcohol copolymer high-barrier polymer. The results of dynamical, mechanical, and other experimental characterizations demonstrated that PA11 and PVA are compatible to some extent when PVA concentrations are less-than or equal to the respective critical values. The enhanced oxygen permeation resistance and free volume characteristics for optimal PA11_xPVA^z_y films are at least partly ascribed to the improved hydrogen-bonded molecular interactions between PA11 CO groups and PVA O─H groups. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48562.     

Dynamic Simulation of Oxygen Transport Rates in Highly Ordered Electrodes for Proton Exchange Membrane Fuel Cells

Highly ordered Pt electrode has been recognized as an important technology for reducing Pt usage in fuel cells due to its improved oxygen transport capability. However, ordered Pt electrode can lead to the decrease in roughness of electrode, which in turn makes it unclear whether the improved oxygen transport can offset the decreased roughness of ordered electrode. Herein, we theoretically investigate the oxygen distribution, generated current, and minimum Pt loading of ordered Pt electrode based on kinetic model of oxygen transport. The results reveal that ordered Pt electrodes do not exhibit concentration polarization with the electrode thickness up to 100 μm. For ordered Pt electrode with diameter of nanorod of 60 nm, the limited current density reaches 110.2 A cm⁻² that is much higher than that for conventional electrode without considering Ohmic loss and mass transport loss outside electrode. To generate a current of 1.5 A cm⁻² at 0.67 V for fuel cell, the minimum Pt loading of cathode in PEMFC reaches 0.029 mg cm⁻² assuming that the electrocatalyst nanorods contain 1 nm Pt layer at the outmost surface.     

Fast preparation of Cu(In,Ga)Se2 and CuIn(S,Se)2 bulk materials by combustion synthesis

CuIn_1‐xGa_xSe₂ and CuIn(S_ySe_1‐y)₂ bulk materials with relative densities of 93.4%‐96.2% have been prepared by combustion synthesis, from elementary reactants and in a reaction time of a few seconds. The samples have a chalcopyrite lattice structure, and the lattice parameters decrease with increasing x and y. The substitution of In with Ga and Se with S in CuInSe₂ causes an increase in the bandgap. In combustion synthesis, the high temperature accelerates the reaction and results in fast densification, the high heating rate simplifies the reaction path and avoids the formation of intermediate compounds, and the gas pressure depresses the evaporation of reactants. As a fast, furnace‐free, and scalable technique, combustion synthesis may offer a low‐cost way to produce CuInSe₂‐based materials and bring new possibilities to their commercial applications.     

Activity and active sites of nitrogen-doped carbon nanotubes for oxygen reduction reaction

Nitrogen-doped carbon (CNx) nanotubes were synthesized by thermal decomposition of ferrocene/ethylenediamine mixture at 600–900 °C. The effect of the temperature on the growth and structure of CNx nanotubes was studied by transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. With increasing growth temperature, the total nitrogen content of CNx nanotubes was decreased from 8.93 to 6.01 at.%. The N configurations were changed from pyrrolic-N to quaternary-N when increasing the temperature. Examination of the catalytic activities of the nanotubes for oxygen reduction reaction by rotating disk electrode measurements and single-cell tests shows that the onset potential for oxygen reduction in 0.5 M H₂SO₄ of the most effective catalyst (CNx nanotubes synthesized at 900 °C) was 0.83 V versus the normal hydrogen electrode. A current density of 0.07 A cm^?2 at 0.6 V was obtained in an H₂/O₂ proton-exchange membrane fuel cell at a cathode catalyst loading of 2 mg cm^?2.     

Realizing the invariant electrostrain response and low hysteresis via multicomponent coordination in Pb-based ceramics

High-performance piezoelectric materials are essential in many piezoelectric devices. However, the composition of piezoelectric materials usually has a great influence on their performance. In this work, xBi(Mg_1/2Ti_1/2)O₃–yPbZrO₃–zPbTiO₃ (xBMT–yPZ–zPT; 0.2 ≤ x ≤ 0.4, 0.25 ≤ y ≤ 0.4, and 0.35 ≤ z ≤ 0.4) ternary ceramics with different compositions were synthesized and it was found that the strain response was not sensitive to the composition. The crystal structure, strain response, ferroelectric properties, and temperature stability of xBMT–yPZ–zPT ceramics were investigated in detail. X-ray diffraction patterns show that all the as-prepared xBMT–yPZ–zPT ceramics with x = 0.2, 0.3, 0.4, and 0.5 possess a perovskite structure. Under an external electric field of 6 kV mm⁻¹, the strain values of xBMT–yPZ–zPT ternary ceramics with x = 0.2, 0.3, 0.4, and 0.5 were 0.30%, 0.31%, 0.30%, and 0.27%, respectively. In addition, the strain hysteresis of these ternary ceramics is also almost the same and low. These merits make xBMT–yPZ–zPT piezoelectric ceramics have broad application prospects in the field of commercial actuators.