Electro-oxidation of glycerol on platinum dispersed in polyaniline matrices

Films of polyaniline (PAni) were electrosynthesized on gold and glassy carbon substrates. The morphology of the films was verified using scanning electron microscopy (SEM) and, as expected, the PAni film formed on glassy carbon presented fibrillar morphology, while that formed on gold presented fibrils on top of a more compact structure. Different amounts of platinum were electrodeposited into the polymer matrices at constant potential and the electrocatalytic activities of the electrodes were evaluated for glycerol electro-oxidation in acidic medium. Furthermore, the active areas of such modified electrodes were determined from the charges involved in the electro-oxidation of an adsorbed carbon monoxide monolayer. Considering the real active areas, the modified electrode with the gold substrate presents higher electrocatalytic activity for glycerol oxidation than that with the glassy carbon substrate. This difference is mainly related to their morphological characteristics and platinum particle sizes.     

Miniaturization limits for single-chamber micro-solid oxide fuel cells with coplanar electrodes

Single-chamber solid oxide fuel cells with coplanar microelectrodes were operated in methane–air mixtures (R_mix = 2) at 700 °C. The performance of cells with one pair of NiO–YSZ (yttria stabilized zirconia) anode and (La_0.8Sr_0.2)_0.98MnO₃–YSZ cathode, arranged parallel on a YSZ electrolyte substrate, was found to be significantly dependent on the electrode width. For an interelectrode gap of 250 μm, cells with average electrode widths exceeding 850 μm could establish a stable open circuit voltage (OCV) of 0.8 V, while those with widths less than 550 μm could not establish any OCV. In the intermediate range, the cells exhibited significant fluctuations in voltage and power under our testing conditions. This behavior suggests that a lower limit to electrode dimensions exists for cells with single electrode pairs, below which neither a stable difference in oxygen partial pressure, nor an OCV, can be established. Conversely, increasing the electrode width imposes a penalty in the form of an increase in the cell resistance. However, both size limits can be circumvented by employing multiple pairs of microscale electrodes in an interdigitated configuration.     

Corrosion study of single crystal Ni–Mn–Ga alloy and Tb<Subscript>0.27</Subscript>Dy<Subscript>0.73</Subscript>Fe<Subscript>1.95</Subscript> alloy for the design of new medical microdevices

Once placed in a magnetic field, smart magnetic materials (SMM) change their shape, which could be use for the development of smaller minimally invasive surgery devices activated by magnetic field. However, the potential degradation and release of cytotoxic ions by SMM corrosion has to be determined. This paper evaluates the corrosion resistance of two SMM: a single crystal Ni–Mn–Ga alloy and Tb_0.27Dy_0.73Fe_1.95 alloy. Ni–Mn–Ga alloy displayed a corrosion potential (E _corr) of −0.58 V/SCE and a corrosion current density (i _corr) of 0.43 μA/cm². During the corrosion assay, Ni–Mn–Ga sample surface was partially protected; local pits were formed on 20% of the surface and nickel ions were mainly found in the electrolyte. Tb_0.27Dy_0.73Fe_1.95 alloy exhibited poor corrosion properties such as E _corr of −0.87 V/SCE and i _corr of 5.90 μA/cm². During the corrosion test, this alloy was continuously degraded, its surface was impaired by pits and cracks extensively and a high amount of iron ions was measured in the electrolyte. These alloys exhibited low corrosion parameters and a selective degradation in the electrolyte. They could only be used for medical applications if they are coated with high strain biocompatible materials or embedded in composites to prevent direct contact with physiological fluids.     

A methanol – Tolerant carbon supported Pt–Sn cathode catalysts

Carbon supported Pt–Sn bimetallic electrocatalysts with a Pt:Sn 90:10 atomic ratio were prepared by impregnation method and then heat treated at 300 and 500 °C under Helium atmosphere. The purpose of this work is to investigate the effect of tin addition to platinum for methanol tolerant oxygen reduction reaction. In this sense, structure and morphological properties of supported bimetallic catalysts were correlated to the catalytic performance. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations confirm the formation of Pt–Sn bimetallic electrocatalysts with a Pt single-phase material alloy and revealed an increase in the average particle size after heat treatment. The electrocatalytic activities of these samples for the oxygen reduction reaction (ORR) were examined in acidic medium using both a rotating disk (RDE) and a rotating ring disk (RRDE) electrodes. Compared with the Pt/C, Pt–Sn/C bimetallic catalysts show superior electrocatalytic activity towards ORR with an approaching four electron pathway leading to water formation. The specific and mass activity for ORR follow the order of Pt–Sn/C-500 ≈ Pt–Sn/C-300 > Pt–Sn/C > Pt/C. Furthermore, it is found that among the three Pt–Sn samples, Pt–Sn/C-500 exhibits the highest methanol tolerance. These experimental observations indicate that the addition of Sn into Pt is favorable to maximize the ORR performances of platinum and further the heat treatment is beneficial to improve the methanol tolerance behavior. On this basis, the novel Pt–Sn catalysts can be considered as potential candidates to be used as cathodes in Direct Methanol Fuel Cells.     

Tailoring of RuO2 nanoparticles by microwave assisted “Instant method” for energy storage applications

RuO₂ nanoparticles are synthesized by Instant method using Li₂CO₃ as stabilizing agent, under microwave irradiation at 60 °C and investigated for the anodic oxygen evolution reaction (OER) and for their supercapacitance properties in 0.5 M H₂SO₄ medium. Structural and morphological characterizations of RuO₂ are investigated by in situ X-ray diffraction (XRD), thermogravimetric analysis (TG-DTA), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDS) and Raman spectroscopy. The TEM images of as prepared material show the uniform distribution of RuO₂ nanoparticles with mean diameter of ca. 1.5 nm. Analysis on as prepared material indicates the structural formula as [RuO₂·2.6H₂O] 0.7H₂O with low crystallinity. The influence of annealing temperature on RuO₂ is studied in light of electrocatalytic activity for oxygen evolution reaction (OER) and capacitance. Electrochemical performances of RuO₂ electrodes are followed by current-potential curves, galvanostatic charge-discharge cycles and evolved oxygen measurements. The amount of oxygen gas evolved during the OER by the crystalline RuO₂ is found to be consistent with the electrical energy supplied to the catalyst. The cyclic voltammogram of RuO₂ exhibits the typical capacitance behavior with highly reversible nature. The specific capacitance of hydrous RuO₂ is found to be 737 F g⁻¹ at the scan rate of 2 mV s⁻¹, by the balanced transport of proton through the structural water and electron transport along dioxo bridges, which makes a suitable material for energy storage. The specific capacitance decreases with increase in the crystallinity of RuO₂. The present study shows the potential method to synthesize rapid and uniform nano particles of RuO₂ for water electrolysis and supercapacitors.     

Promising anode candidates for direct ethanol fuel cell: Carbon supported PtSn-based trimetallic catalysts prepared by Bönnemann method

To find an efficient anode catalyst for ethanol electrooxidation, several trimetallic PtSnM/C (M = Ni, Co, Rh, Pd) and their corresponding bimetallic PtX/C (X = Sn, Ni, Co, Rh, Pd) catalysts were synthesized by Bönnemann's colloidal precursor method and evaluated by comparing their electrocatalytic activity using conventional electrochemical techniques. For better understanding of the catalyst deactivation during the ethanol electrooxidation, chronoamperometric test was also combined to X-ray photoelectron spectroscopy (XPS) analysis. A significant finding is that trimetallic compositions PtSnCo/C and PtSnNi/C have enhanced activity compared to that of PtSn/C, with lower onset potential for ethanol electrooxidation and notably improved peak current densities. Thus the presence of Ni and Co heteroatom seems to promote C–C bond cleavage and facilitate the removal from the catalyst surface of adsorbed intermediates. These trends are satisfactorily confirmed by testing in a direct ethanol fuel cell (DEFC), since trimetallic PtSnNi/C and PtSnCo/C anode catalysts have significantly higher overall performance and peak power density than Pt/C, PtSn/C or other trimetallic catalyst compositions PtSnRh/C or PtSnPd/C. Furthermore, the presence of Ni or Co helps to improve the weak stability of PtSn/C by providing a stronger Pt–carbon support interaction. XPS results revealed that the surface Pt/Sn atomic ratio of PtSnNi/C catalyst only slightly decreased even after 12 h at 500 mV. On the other hand, a higher concentration of oxide species appeared on the treated PtSn/C surface as a result of a high degradation of carbon support.     

Fabrication and testing of coplanar single-chamber micro solid oxide fuel cells with geometrically complex electrodes

Coplanar single-chamber micro solid oxide fuel cells (SC-μSOFCs) with curvilinear microelectrode configurations of arbitrarily complex two-dimensional geometry were fabricated by a direct-write microfabrication technique using conventional fuel cell materials. The electrochemical performance of two SC-μSOFCs with different electrode shapes, but comparable electrode and inter-electrode dimensions, was characterized in a methane–air mixture at 700 °C. Both cells exhibited stable open circuit voltage and peak power density of 0.9 V and 2.3 mW cm⁻², respectively, indicating that electrode shape did not have a significant influence on the performance of these fuel cells.     

Electroactivity of RuO2–IrO2 mixed nanocatalysts toward the oxygen evolution reaction in a water electrolyzer supplied by a solar profile

Pure crystalline ruthenium–iridium oxide materials were synthesized with high surface area by co-precipitation method in ethanol medium. Cyclic and linear scan voltammetries were then undertaken to evaluate the effect of mixing iridium and ruthenium oxides on the oxygen evolution reaction (OER). The activity of these anode catalysts was evidenced through the determination of their capacitances, surface charges and Tafel slopes. It was found that the Ru_0.9Ir_0.1O₂ catalyst presented catalytic properties close to those of RuO₂, in particular for low overpotentials. The proposed synthesis method was also shown to be suitable for recovering large catalyst amount for O₂ production in a large surface proton exchange membrane water electrolyzer (PEMWE). Polarization measurements were therefore performed in a single PEMWE cell and the durability of the catalytic materials was evaluated by supplying a solar power profile. The efficiency loss at 1 A cm⁻² and 80 °C was only 90 μV h⁻¹ for 1000 h under galvanodynamic operating conditions for Ru_0.9Ir_0.1O₂ as anode, while the cell voltage varied between 1.75 and 1.85 V.     

Synthesis of LaB<Subscript>6</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powders via ball milling-assisted annealing

In this study, LaB₆–Al₂O₃ nanocomposite powders were synthesized via ball milling-assisted annealing process starting from La₂O₃–B₂O₃–Al powder blends. High-energy ball milling was conducted at various durations (0, 3, 6 and 9 h). Then, the milled powders were annealed at 1200 °C for 3 h under Ar atmosphere in order to obtain LaB₆ and Al₂O₃ phases as reaction products. X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM) techniques were utilized to carry out microstructural characterization of the powders. No reaction between the reactants was observed in the XRD patterns of the milled powders, indicating that high-energy ball milling did not trigger any chemical reactions even after milling for 9 h. LaAlO₃ and LaBO₃ phases existed in the annealed powders which were milled for 0, 3 and 6 h. LaBO₃ phase was removed after HCl leaching. 9-h milled and annealed powders did not exhibit any undesired phases such as LaAlO₃ and LaBO₃ after leaching step, and pure nanocrystalline LaB₆–Al₂O₃ composite powders were successfully obtained. TEM analyses revealed that very fine LaB₆ particles (~?100 nm) were embedded in coarse Al₂O₃ (~?500 nm) particles.     

Microstructural characterizations and mechanical properties of NbB2 and VB particulate-reinforced eutectic Al-12.6 wt% Si composites via powder metallurgy method

Mechanical alloying of elemental Al, Si, NbB₂ and VB powder mixtures constituting the matrix alloy composition of Al-12.6?wt% Si and particulate-reinforced compositions of Al-12.6?wt% Si-x NbB₂ and Al-12.6?wt% Si-x VB (x?=?1, 2 and 5?wt%) were carried out for 2, 4 and 8?h in a high-energy ball mill. Mechanically alloyed (MA’d) powders were subjected to cold pressing (450?MPa), cold isostatic pressing (400?MPa) and pressureless sintering (570?°C/2?h) processes. Powder particle morphologies changed from flaky to equiaxed shape after the optimum MA duration of 4?h. 1?wt% NbB₂ and 1?wt% VB particulate-reinforced Al-12.6?wt% Si based composites exhibited better mechanical properties than the Al-12.6?wt% Si matrix alloy and Al-12.6?wt% Si-x NbB₂ and Al-12.6?wt% Si-x VB (x?=?2 and 5?wt%) composite samples. In particular, Al-12.6?wt% Si-1?wt% NbB₂ had the highest yield strength (378?MPa), compressive strength (491?MPa) and hardness (1.86?GPa) values. Investigations on the wear behaviors of the composites revealed that significant amount of wear loss occurred as a result of debris formation due to pull-outs of reinforcing boride (NbB₂ and VB) and oxidized Al (Al₂O₃) particles.