Increase In Peak Current Density Research Articles

Iron-vanadium redox flow batteries electrolytes: performance enhancement of aqueous deep eutectic solvent electrolytes via water-tuning

Deep eutectic solvents (DES) are being recognized as a highly promising electrolyte option for redox flow batteries. This study examines the impact of modifying the molar ratio of water to a DES consisting of urea and choline chloride on important measures of electrolyte performance, such as viscosity, cyclic voltammetry, and impedance spectroscopy. According to the findings, when the molar ratio of water to DES is 1:3, the viscosity of the electrolyte falls by 75 %, the peak current density increases by 5–9.5 times, the ionic conductivity increases by 5–10 times, and the ohmic resistance decreases by 60–90 %. This approach greatly enhances the conductivity and diffusion coefficient of the electrolyte, resulting in a novel, cost-effective, and highly efficient electrolyte for iron-vanadium redox flow battery applications. This study enhances the efficiency of DESs at the molecular level, establishing the foundation for future extensive implementations.

Record peak current density of over 1500 kA/cm2 in highly scaled AlN/GaN double-barrier resonant tunneling diodes on free-standing GaN substrates

This work demonstrates high-performance AlN/GaN double-barrier resonant tunneling diodes (RTDs) with high peak current density grown by plasma-assisted molecular beam epitaxy on c-plane free-standing GaN substrates, featuring stable and repeatable negative differential resistance (NDR) characteristics at room temperature. By scaling down the barrier thickness of AlN barrier and the lateral mesa size of collector, the record peak current density of 1551 kA/cm2 is achieved along with a peak-to-valley current ratio (PVCR) of 1.24, which is attributed to the reduced resonant tunneling time under thinner AlN barrier and the suppressed external incoherent valley current by reducing the dislocation number contained in the RTD device with the smaller size of collector. By statistically analyzing the NDR performance of RTD devices with different thicknesses of AlN barrier, the average peak current density increases from 145.7 to 1215.1 kA/cm2, while the average PVCR decreases from 1.45 to 1.1, correspondingly, accompanying with a decreased peak voltage from 6.89 to 5.49 V, with downscaling the AlN barrier thickness from 1.5 to 1.25 nm. The peak current density obtained in this work is the highest value among all the reported nitride-based RTDs up until now while maintaining high PVCR value simultaneously, which illustrates that ultra-scaled RTD based on vertical quantum-well structure and lateral collector size is a valuable approach for the development of nitride-based RTDs with excellent NDR characteristics and reveals their great potential applications in high-frequency oscillation sources and high-speed switch circuits.

Numerical investigation of the impact of thermoelectric effect on electron beam welding of dissimilar materials

Electron beam welding of GH4169 and Ni is required in the manufacture of the regenerative cooling system of the liquid rocket motor. The thermoelectric effect is observed during the welding of dissimilar metals; however, there has been a lack of investigation into the influence of this effect on electron beam welding joint formation and its dependence on test plate thickness. The thermoelectric effect of electron beam welding between GH4169 and Ni with varying thicknesses, as well as the influence of induced magnetic fields on electron beam trajectories, are investigated through the establishment of a numerical model incorporating thermal-electric-magnetic coupling.The results show that when the test plate increases from 2.5 mm to 10 mm the peak current density increases from 5.1 × 106 A/m2 to 7.6 × 106 A/m2, and the maximum magnetic flux density increases from 1.49× 10−2 T to 1.77 × 10−2 T. The increase in magnetic flux density results in a greater displacement of the electron beam spot away from the interface between the two materials, thereby causing incomplete fusion defects in the joints. This study elucidates the fundamental physical principles underlying the occurrence of incomplete fusion defects in electron beam welding joints, thereby furnishing essential theoretical underpinnings for enhancing the quality of dissimilar metal electron beam weld joints.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics.

The key issue in the 5-hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co-doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3-fold increase in peak current density. DFT calculations and in-situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+-O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+-O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+-O.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics

AbstractThe key issue in the 5‐hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co‐doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3‐fold increase in peak current density. DFT calculations and in situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+−O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+−O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+−O.

Ethanol Electrooxidation at 1-2 nm AuPd Nanoparticles.

We report a systematic study of the electrocatalytic properties and stability of a series of 1-2 nm Au, Pd, and AuPd alloy nanoparticles (NPs) for the ethanol oxidation reaction (EOR). Following EOR electrocatalysis, NP sizes and compositions were characterized using aberration-corrected scanning transmission electron microscopy (ac-STEM) and energy dispersive spectroscopy (EDS). Two main findings emerge from this study. First, alloyed AuPd NPs exhibit enhanced electrocatalytic EOR activity compared to either monometallic Au or Pd NPs. Specifically, NPs having a 3:1 ratio of Au:Pd exhibit an ~8-fold increase in peak current density compared to Pd NPs, with an onset potential shifted ~200 mV more to the negative compared to Au NPs. Second, the size and composition of AuPd alloy NPs do not (within experimental error) change following 1.0 or 2.0 h chronoamperometry experiments, while monometallic Au NPs increase in size from 2 to 5 nm under the same conditions. Notably, this report demonstrates the importance of post-catalytic ac-STEM/EDS characterization for fully evaluating NP activity and stability, especially for 1-2 nm NPs that may change in size or structure during electrocatalysis.

Numerical analysis of the performance of proton exchange membrane fuel cell with longitudinal vortex generators

To improve the performance of proton exchange membrane fuel cell (PEMFC), in this study the combination of longitudinal vortex generators (LVGs) and cathode channel is proposed to improve the power density performance and optimize the water-thermal management of PEMFC with a less pressure loss. The effects of the shape, spacing, angle of attack, and number of LVGs on the performance of PEMFC are investigated via numerical simulation. The results show that the current density of the PEMFC improved the most significantly by installing five groups of rectangular plane winglet with a 12 mm spacing and 45° angle of attack in the cathode channel, and that the peak current density increases by 33.3% with additional flow resistance loss of 164.64% than the initial design. The current density of the PEMFC increases with the increase of spacing, angle of attack, and number of vortex generator groups. Moreover, the vortex generator improves the distribution uniformity of temperature, water content, and oxygen content inside the PEMFC. Importantly, it is also observed that the secondary flow intensity of PEMFC channel is positively correlated with the current density of the PEMFC. When the angle of attack is 45°, the vorticity increases the most, i.e., 16.79% higher than that without a VG. Ultimately, the pressure drop and overall performance indicator of PEMFC with LVGs are demonstrated. Compared with the initial design, except the comprehensive performance of the 0° angle of attack has been improved, that of other schemes has been reduced. It is worth noting that, for other published optimization schemes, the research scheme proposed in this paper has certain advantages in terms of lifting current density with lower resistance loss. Therefore, it is still of great significance to improve the energy density of PEMFC.

Highly sensitive determination of doxorubicin hydrochloride antitumor agent via a carbon nanotube/gold nanoparticle based nanocomposite biosensor

A glassy carbon electrode modified with multi-walled carbon nanotubes (MWCNTs) decorated with gold nanoparticles has been investigated for the first time as an ultrasensitive electrochemical sensor for the determination of doxorubicin hydrochloride (DOX), an efficient antitumor agent. The developed nanocomposite has been characterized by scanning electron microscopy (SEM), besides cyclic and linear sweep voltammetry electrochemical techniques. An efficient catalytic activity for the reduction of DOX has been demonstrated, leading to a significant increase in peak current density and a remarkable decrease in reduction over-potential. Under the optimal condition, a wide linear DOX concentration range from 1×10-11 to 1×10-6 M with a very low detection limit of 6.5 pM was achieved with the modified electrode. Meanwhile, the functionalized MWCNTs/gold nanoparticles indicated an appropriate selectivity, reproducibility, and repeatability as well as long-term stability. The promising outcomes of this research approved the applicability of the developed nanocomposite sensor towards trace amounts of DOX in pharmaceutical and clinical preparations.

Pt/Rh/Pt and Pt/Ru/Pt multilayers for the electrochemical oxidation of methanol and ethanol

The study of metallic multilayers (MM) has presented interesting highlights to understand electrocatalytic properties for organic molecules oxidation. This work reports the preparation and characterization of MM using rhodium or ruthenium as an intermediate layer, Ptpc/Rh/Pt and Ptpc/Ru/Pt, aiming to evaluate the electrocatalytic activity toward methanol and ethanol oxidation in acid medium. For methanol electro-oxidation, the evaluated MM presented higher current density than Ptpc, especially Ptpc/Rh2/Pt1 and Ptpc/Ru5/Pt2, where the increase in peak current density was 283% and 422% compared to Ptpc. By in situ infrared spectroscopy (FTIR in situ), it was observed that in MM the CO2 formation from methanol oxidation occurred in lower potentials compared to Ptpc. In the ethanol oxidation, Ptpc/Rh2/Pt1 and Ptpc/Ru5/Pt2 increase in peak current density 32% and 67% compared to Ptpc, respectively. The bands referring to the acetaldehyde, acetic acid and CO2 were observed first to MM than for Ptpc. The better electroactivity of the metallic multilayers in the electro-oxidation of alcohols could be explained by the changes in the electronic interaction between the exposed platinum surface and the rhodium or ruthenium intermediate layer, which facilitated the oxidation of intermediates at lower potentials, and thus, increasing of the electrocatalytic activity of these materials.

Effect of pulsed current on AZ31B magnesium sheets during annealing

Abstract The annealing tests heated by pulsed current (PC) or furnace for AZ31B magnesium sheets were carried out, and the effects of PC on the microstructure and dislocation density of the alloy were analyzed. The results show that PC strengthens the migration of boundaries, and then the twin grains, most of which distribute in the coarse grains, “spheroidize” to equiaxed grains, thus separating the coarse grains and refining the microstructure. This process homogenizes the initial microstructure and eliminate the typically lamellar twin grains. Moreover, PC also strengthens the dislocation annihilation. When the specimens were annealed by PC at 300 °C for 4 min, the dislocation density was even lower than that annealed by furnaces at 400 °C for 3 h before deformation. Furthermore, dislocation annihilation is enhanced with the increase of peak current density and the decrease of pulsed frequency.

RoDSE Synthesized Fine Tailored Au Nanoparticles from Au(X)4– (X = Cl–, Br–, and OH–) on Unsupported Vulcan XC-72R for Ethanol Oxidation Reaction in Alkaline Media

An electrosynthesis method to obtain Au nanoparticles dispersed on carbon Vulcan XC-72R support material was done using AuX4– (X = Cl–, Br–, and OH–) as molecular precursors and different electrolyte media. The Au surface structure was significantly enhanced using KOH as an electrolyte as opposed to KBr and H2SO4. Cyclic voltammetry was used as a surface sensitive technique to illustrate the Au/Vulcan XC-72R catalytic activity for the ethanol oxidation reaction (EOR). The Au electroactive surface areas obtained were 1.88, 5.83, and 13.96 m2 g–1 for Au/C–H2SO4, Au/C–KBr, and Au/C–KOH, respectively. The latter compares to chemically reduced Au/C–spheres that had an electroactive surface area of 15.0 m2 g–1. The electrochemical Au electrodeposition, in alkaline media (Au/C–KOH), exhibited the highest catalytic activity for the EOR with a 50% increase in peak current density when compared with Au nanoparticles prepared by the chemical reduction route. Raman and X-ray photoelectron spectroscopies analyses of t...

Abstract 16901: Utilizing In Silico Pathogenicity Prediction Tools and Heterologous Expression Patch Clamp Studies to Identify Bona Fide Pathogenic KCNH2 Variants Among Publically Available Exomes Derived From Subjects Without Evidence for Either Type 2 Long QT Syndrome or Type 1 Short QT Syndrome

Introduction: Loss-of-function (LOF) and gain-of-function (GOF) pathogenic variants in the KCNH2 -encoded Kv11.1 potassium channel cause type 2 long QT syndrome(LQT2) and type 1 short QT syndrome (SQT1), respectively. Given the prevalence of KCNH2- mediated heart disease (1 in 8000 for LQT2,1 in 100,000 for SQT1) and the reduced penetrance/variable expressivity seen in LQTS and SQTS, large databases such as the Genome Aggregation Database (gnomAD, n=141,352 individuals) might harbor subjects with unidentified LQT2/SQT1-causative mutations. Objective: To determine which “ultra-rare” KCNH2 missense variants (MVs) in gnomAD are most likely to be LQT2- or SQT1-causative. Methods: A list of gnomAD-derived MVs in KCNH2 was compiled. The frequency of each MV in gnomAD was assessed. Each MV was analyzed by 8 in silico pathogenicity prediction tools. MVs that were seen once in gnomAD and predicted damaging by all 8 tools were considered possible LQT2/SQT1-causative MVs worthy of functional validation via whole-cell patch clamp. Results: Overall, 233/474 (49%) of gnomAD KCNH2 MVs were seen in just 1 of >140,000 subjects. Of these, 2 (0.4%) MVs (S320W, S379Y) were predicted damaging by 8 in silico tools. Both S320W and S379Y localize to the N-terminus of the Kv11.1 potassium channel. There was no significant change in peak or tail current density between heterozygously expressed KCNH2-S320W (n=13, p=NS) and KCNH2-WT (n=13). However, heterozygous KCNH2-S379Y (n=12) produced a marked increase in peak current density across the range -30 mV to +20 mV and shifted the V 1/2 of activation by -17 mV (p < 0.001). Also, tail current density of S379Y channels significantly increased across the range -20 mV to +20 mV and the V 1/2 of deactivation shifted by -26 mV (p < 0.001). Conclusion: With this stringent requirement of ultra-rarity, universal prediction of damaging impact, and functionally abnormal electrophysiological properties, one SQT1-causative pathogenic variant in gnomAD was identified consistent with the predicted frequency of SQTS. The search continues among the remaining 32 ultra-rare MVs in KCNH2 where at least 75% of the in silico tools predicted deleterious impact of the MV to find the 15-20 subjects in gnomAD’s population who ought to have an LQT2-causative MV.

CACHD1 is an α2δ-Like Protein That Modulates CaV3 Voltage-Gated Calcium Channel Activity.

The putative cache (Ca2+ channel and chemotaxis receptor) domain containing 1 (CACHD1) protein has predicted structural similarities to members of the α2δ voltage-gated Ca2+ channel auxiliary subunit family. CACHD1 mRNA and protein were highly expressed in the male mammalian CNS, in particular in the thalamus, hippocampus, and cerebellum, with a broadly similar tissue distribution to CaV3 subunits, in particular CaV3.1. In expression studies, CACHD1 increased cell-surface localization of CaV3.1, and these proteins were in close proximity at the cell surface, consistent with the formation of CACHD1-CaV3.1 complexes. In functional electrophysiological studies, coexpression of human CACHD1 with CaV3.1, CaV3.2, and CaV3.3 caused a significant increase in peak current density and corresponding increases in maximal conductance. By contrast, α2δ-1 had no effect on peak current density or maximal conductance in CaV3.1, CaV3.2, or CaV3.3. A comparison of CACHD1-mediated increases in CaV3.1 current density and gating currents revealed an increase in channel open probability. In hippocampal neurons from male and female embryonic day 19 rats, CACHD1 overexpression increased CaV3-mediated action potential firing frequency and neuronal excitability. These data suggest that CACHD1 is structurally an α2δ-like protein that functionally modulates CaV3 voltage-gated calcium channel activity.SIGNIFICANCE STATEMENT This is the first study to characterize the Ca2+ channel and chemotaxis receptor domain containing 1 (CACHD1) protein. CACHD1 is widely expressed in the CNS, in particular in the thalamus, hippocampus, and cerebellum. CACHD1 distribution is similar to that of low voltage-activated (CaV3, T-type) calcium channels, in particular to CaV3.1, a protein that regulates neuronal excitability and is a potential therapeutic target in conditions such as epilepsy and pain. CACHD1 is structurally an α2δ-like protein that functionally increases CaV3 calcium current. CACHD1 increases the presence of CaV3.1 at the cell surface, forms complexes with CaV3.1 at the cell surface, and causes an increase in channel open probability. In hippocampal neurons, CACHD1 causes increases in neuronal firing. Thus, CACHD1 represents a novel protein that modulates CaV3 activity.

Proteolytic cleavage of the hydrophobic domain in the CaVα2δ1 subunit improves assembly and activity of cardiac CaV1.2 channels

Voltage-gated L-type CaV1.2 channels in cardiomyocytes exist as heteromeric complexes with the pore-forming CaVα1, CaVβ, and CaVα2δ1 subunits. The full complement of subunits is required to reconstitute the native-like properties of L-type Ca2+ currents, but the molecular determinants responsible for the formation of the heteromeric complex are still being studied. Enzymatic treatment with phosphatidylinositol-specific phospholipase C, a phospholipase C specific for the cleavage of glycosylphosphatidylinositol (GPI)-anchored proteins, disrupted plasma membrane localization of the cardiac CaVα2δ1 prompting us to investigate deletions of its hydrophobic transmembrane domain. Patch-clamp experiments indicated that the C-terminally cleaved CaVα2δ1 proteins up-regulate CaV1.2 channels. In contrast, deleting the residues before the single hydrophobic segment (CaVα2δ1 Δ1059-1063) impaired current up-regulation. CaVα2δ1 mutants G1060I and G1061I nearly eliminated the cell-surface fluorescence of CaVα2δ1, indicated by two-color flow cytometry assays and confocal imaging, and prevented CaVα2δ1-mediated increase in peak current density and modulation of the voltage-dependent gating of CaV1.2. These impacts were specific to substitutions with isoleucine residues because functional modulation was partially preserved in CaVα2δ1 G1060A and G1061A proteins. Moreover, C-terminal fragments exhibited significantly altered mobility in denatured immunoblots of CaVα2δ1 G1060I and CaVα2δ1 G1061I, suggesting that these mutant proteins were impaired in proteolytic processing. Finally, CaVα2δ1 Δ1059-1063, but not CaVα2δ1 G1060A, failed to co-immunoprecipitate with CaV1.2. Altogether, our data support a model in which small neutral hydrophobic residues facilitate the post-translational cleavage of the CaVα2δ1 subunit at the predicted membrane interface and further suggest that preventing GPI anchoring of CaVα2δ1 averts its cell-surface expression, its interaction with CaVα1, and modulation of CaV1.2 currents.

Effects of peak current density on the structure and property of PbO2–CeO2 nanocomposite electrodes prepared by pulse electrodeposition

PbO2–CeO2 nanocomposite electrodes were prepared by pulse electrodeposition method in the lead nitrate solution containing CeO2 nanoparticles with different peak current density. The content of CeO2 nanoparticles in the electrodes increase with the increase of peak current density. The effects of peak current density on the morphology and structure of PbO2–CeO2 nanocomposite electrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the increase of peak current density can make the morphology finer and more compact, and the crystal size decreases with the increase of peak current density. The oxygen evolution overpotential and stability of PbO2–CeO2 nanocomposite electrodes enhance with the increase of peak current density. The electrocatalytic property of PbO2–CeO2 nanocomposite electrodes was examined for the electrochemical oxidation of rhodamine B (RhB). The results show that the RhB removal efficiency on PbO2–CeO2 nanocomposite electrodes increase with the increase of peak current density, which can be attributed to the higher oxygen evolution overpotential and CeO2 content in the composite electrodes.

Electrodeposition of Aluminum onto Copper-Coated Printed Circuit Boards

The electrodeposition of aluminum thin films onto copper-coated printed circuit boards from aluminum chloride-trimethylphenylammonium chloride ionic liquids is studied. Various electrodeposition methods with different surface pretreatment procedures were investigated and compared to optimize the deposited aluminum morphology and properties. For the same amount of charge, a pulse current deposition approach applied at a low duty cycle of 10% allowed the use of higher deposition current densities, leading to finer and more compact aluminum deposits compared with those produced by constant potential and constant current deposition techniques. Pulse current deposition with various peak current densities of −25 mA/cm2 to −65 mA/cm2 was conducted over a temperature range of 20°C to 60°C. At a moderate temperature of 40°C, the electrodeposited aluminum layer was the most adherent. An increase of peak current density did not have an obvious effect on the deposit morphology, but it led to an increased amount of both deposited aluminum and incorporated impurities (oxygen and chloride). At room temperature, the electrical resistivity of the copper-coated printed circuit boards with deposited aluminum decreased as the peak current density for aluminum deposition increased.

Properties of mesoporous carbon modified carbon felt for anode of all-vanadium redox flow battery

A novel anode material for all-vanadium redox flow battery was synthesized by dispersion coating of sol-gel processed (resorcinol-furaldehyde) mesoporous carbon (MPC) onto the surface of polyacrylonitrile carbon felt (CF). The coated samples were then annealed at 900°C and 1100°C and the subsequent morphology, surface chemistry, and electrochemical properties of the MPC coated CF were characterized and compared with an uncoated CF. Addition of the MPC coating is shown to dramatically increase surface area while also increasing the number of active surface oxygen groups particularly for samples annealed at 1100°C. MPC coating shows a mixed effect on electrochemical properties. Characterization with cyclic voltammetry reveals the introduction of MPC coating provides roughly 30% increase in peak current density for the oxidation and reduction reactions of the V(IV)/V(V) redox couple, which is attributed to the significantly increased number of active reaction sites. However, MPC coating seems to be accompanied by a reduction in conductivity as demonstrated by increased redox peak separation and charge transfer resistance. This negative effect on conductivity can be mitigated by heat treatment (at or above 1100°C) which improves surface graphitization reducing redox peak separation and charge transfer resistance such that it is comparable with uncoated samples.

Electrocatalytic performance of Ni-Ti-O nanotube arrays/NiTi alloy electrode annealed under H2 atmosphere for electro-oxidation of methanol

In the present study, Ni-Ti-O nanotube arrays (Ni-Ti-O NTs) were fabricated by anodizing NiTi alloy in a mixed solution consisted of ethylene glycol and glycerol. Then the Ni-Ti-O NTs were suffered annealing treatment under hydrogen atmosphere, leading to the significant improved electrocatalytic performance. The morphologies, the phases and the surface electronic states of Ni-Ti-O NTs samples before and after annealing were characterized by SEM, XRD and XPS, respectively. And their electrocatalytic properties for methanol oxidation were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the alkaline media. Results show that electrocatalytic activity of the Ni-Ti-O NTs samples annealed under H2 exhibits a significant improvement because of the increases of the conductivity and the active sites provided by reduction of Ni3+. The Ni-Ti-O NTs samples with lower crystallinity annealed at 500 °C for 2 h have better electrocatalytic performance for methanol electro-oxidation in alkaline medium. The peak current density increases after a consecutive sweep for 1000 times and varies indistinctively after placing in the air for 30 days, indicating the excellent long-term electrocatalytic stability. The in situ formation of Ni-base material catalyst in Ni-Ti-O nanotube benefits improvement of the catalytic properties during long-term operation. The Ni-Ti-O NTs/Ni-Ti alloy is a desirable substitute of catalysts support material or it is also a promising electrocatalytic electrode for direct methanol fuel cells.

Ultrafine FePd Nanoalloys Decorated Multiwalled Cabon Nanotubes toward Enhanced Ethanol Oxidation Reaction

Ultrafine iron-palladium (FePd) nanoalloys deposited on γ-Fe2O3, FePd-Fe2O3, further anchored on carboxyl multiwalled carbon nanotubes (MWNTs-COOH), FePd-Fe2O3/MWNTs, were successfully synthesized by a facile one-pot solution based method as thermally decomposing palladium acetylacetonate (Pd(acac)2) and iron pentacarbonyl (Fe(CO)5) in a refluxing dimethylformamide solution in the presence of MWNTs-COOH. A 3.65 fold increase of peak current density was observed in cyclic voltammetry (CV) for ethanol oxidation reaction (EOR) compared with that of Pd/MWNTs after normalizing to Pd mass. The greatly enhanced tolerance stability toward poisoning species and largely reduced charge transfer resistance were also obtained in chronoamperometry and electrochemical impedance spectroscopy due to the downward shifted d-band center of FePd alloy, easily formed oxygen containing species on Fe2O3, and the stabilizing role of the MWNTs.

Multiwalled Cabon Nanotubes Functionalized Magnetic Fepd Alloy with Enhanced Activity for Ethanol Oxidation Reaction

Ultrafine Palladium iron alloy (FePd) nanoparticles (NPs) deposited on gamma phased iron oxide (r-Fe2O3), FePd-Fe2O3, which were further anchored on Multi-walled carbon nanotubes (MWNTs), FePd-Fe2O3/MWNTs, was successfully synthesized by a facile one-pot solution based method as thermal decomposing palladium acetylacetonate (Pd(acac)2) and iron pentacarbonyl (Fe(CO)5) in a refluxing dimethylformamide (DMF) solution in the presence of carboxylic groups functionalized MWNTs (MWNTs-COOH). The formation of FePd alloy was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) through investigating the crystalline structures and verifying specific bonding energy. Transmission electron microscope (TEM) revealed that the ultrafine FePd NPs were uniformly deposited on the surface of superparamagnetic r-Fe2O3 NPs which were further evenly distributed on the MWNTs surface. A 3.65 increase of peak current density after normalizing to Pd mass was observed in cyclic voltammetry (CV) for ethanol oxidation reaction compared with that of Pd/MWNTs. Greatly enhanced tolerance stability towards poisoning species and largely reduced charge resistances were also obtained in chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) due to the formation of FePd alloy and the unique double deposited Pd structure. Experimental 100.0 mg MWNTs-COOH was first dispersed in 60 mL DMF solution undergoing 1h sonication, the solution was then transferred to a 250-mL 3-neck flask and heated to reflux (~160 °C) in ~ 20 min. For the synthesis of FePd-based nanocatalysts, 202.0 mg well dispersed Pd(acac)2 in 20 mL DMF was added to the refluxing MWNTs-COOH/DMF solution. Fe(CO)5 (130.2, 437.0, and 875.0 mg) was following added to the solution after boiling again in ~ 5 min, the products were donated as FePd-Fe3C/MWNTs, FePd-Fe2O3(3:5)/MWNTs and FePd-Fe2O3(3:10)/MWNTs, respectively(the composition was determined by Mössbauer spectrometer). For the control synthesis of Pd/MWNTs and Fe3O4/MWNTs, only 202.0 mg Pd(acac)2 or 875.0 mg Fe(CO)5 was added to the refluxing MWNTs-COOH/DMF solution. All the solutions were maintained refluxing for an additional 3 hours to complete the whole reaction. Finally, after cooling down to room temperature, the solid iron containing products were removed from the suspension using a permanent magnet and Pd/MWNTs were filtered under vacuum. All the final products were rinsed with acetone 3 times and collected after vacuum drying at 60 °C for 24 hours. Results and Discussion The Mössbauer spectrometer and XPS has successfully determined the compositions of catalysts with varying the amount of Fe(CO)5. Typical peaks of Fe2O3, Fe3O4 and FePd are clearly observed in XRD indicating the successful synthesis of FePd-Fe2O3/MWNTs. The interaction between NPs and MWNTs and the loading of catalysts was determined by Raman spectra and TGA. An greatly enhanced the peak current in CV and improved tolerance stability toward poisoning species are also demonstrated by CV, CV and EIS, which indicates the positive role of the FePd alloy and the Fe2O3 substrates. Conclusion Highly catalytic active and magnetic FePd-Fe2O3/MWNTs nanocatalysts have been prepared by simple thermal decomposing Pd(acac)2 and Fe(CO)5 in a refluxing dimethylformamide (DMF) solution in the presence of MWNTs-COOH. The formation of FePd alloy has been confirmed by the crystalline structures and composition investigation by XRD and XPS spectra. A unique structure as FePd NPs first deposited on Fe2O3 NPs which further uniformly dispersed on MWNTs was disclosed by TEM. Electro-characterizations as CV, CA and EIS demonstrated an enhanced catalytic performance compared with Pd/MWNTs towards EOR after the introduction of Fe. Modified electronic properties of Pd by Fe, easily proceeded poisoning species on γ-Fe2O3 and the optimal combination of promoter Fe2O3 and MWNTs substrate are mainly account for the greatly enhanced activity. This simple method is of great significance for the facile preparation of recyclable Pd catalysts with high catalytic activity. Acknowledgments The financial supports from University of Tennessee Knoxville are kindly acknowledged. Figure 1. CV of (a) Fe3O4/MWNTs, (b) Pd/MWNTs, (c) FePd-Fe2O3(3:10)/MWNTs, (d) FePd-Fe3C/MWNTs and (e) FePd-Fe2O3(3:5)/MWNTs in 1.0 M KOH solution containing 1.0 M ethanol with current density normalized to Pd mass at a scan rate of 50 mV/s. Background is the HRTEM of FePd-Fe2O3(3:5)/MWNTs. References 1 Y. Wang, Q. He, J. Guo, H. Wei, K. Ding et al, ChemElectroChem, 2(4) (2015) 559-570. 2. Z. Zhang, J. Ge, L. Ma, J. Liao, T. Lu, W. Xing, Fuel Cells, 9 (2) (2009) 114-120 Figure 1