Influence of temperature on corrosion behavior of PbCaSnCe alloy in 4.5 M H2SO4 solution

The temperature effect on corrosion behaviors of PbCaSnCe alloy in 4.5 M H₂SO₄ solution was investigated by using potentiodynamic curve, electrochemical impedance spectra (EIS), Mott-Schottky plot and photocurrent response methods. It was found that PbCaSnCe alloy was in passive state in sulfuric acid solution, a passive film can be formed on alloy surface. The compositions of passive films formed at 0.9 V for 2 h under different temperatures were detected by X-ray photoelectron spectroscopy (XPS). The results showed that the film resistance and the transfer resistance decreased with the increment of the solution temperature. Mott-Schottky analysis and the photocurrent response revealed that the passive film exhibited n-type semi-conductive character, the donor density of the passive film decreased with increasing the solution temperature. Photocurrent response revealed that the photocurrent increased with increasing temperature. XPS results indicated that the PbO₂ content in passive films may increase with increasing the solution temperature.     

Electrochemical investigation of the anodic corrosion of Pb–Ca–Sn–Li grid alloy in H2SO4 solution

The steady-state and anodic corrosion of Pb–0.17 wt.% Ca–0.88 wt.% Sn, and Pb–0.17 wt.% Ca–0.88 wt.% Sn–0.06 wt.% Li alloys in 4.5 M H₂SO₄ at 25 °C were studied using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The experimental results show that the lithium added to Pb–Ca–Sn alloy increases corrosion resistance in equilibrium potential and inhibits the growth of the anodic corrosion layer.     

Cyclic voltammetry and electrochemical impedance of MmNi3.6Co0.7Mn0.4Al0.3 alloy electrode before and after treatment with a hot alkaline solution containing reducing agent

The hydrogen storage alloy (MmNi_3.6Co_0.7Mn_0.4Al_0.3, Mm=Ce-rich mischmetal) electrodes were treated in an alkaline solution containing a reducing agent (KBH₄ or NaH₂PO₂). Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were applied to characterize the electrochemical properties of the alloy electrodes before and after surface treatment. The results show that the charging efficiency and electrochemical reaction activity of metal hydride (MH) electrode were markedly improved by the treating. The reaction of the untreated MH electrode was chiefly controlled by the charge transfer process at the interface of electrode/electrolyte, or by the mixture of the charge transfer and hydrogen diffusion processes, but the reaction of the treated electrode was mainly controlled by hydrogen atom's diffusion in the alloy bulk. The results of EIS measurements indicate that the charge transfer resistance of MH electrode was reduced and its specific surface area augmented after treatment.     

Study of Pt electrode dissolution in H2O2-containing H2SO4 solution using an electrochemical quartz crystal microbalance

Pt electrode dissolution has been investigated using an electrochemical quartz crystal microbalance (EQCM) in H₂O₂-containing 0.5 mol dm⁻³ H₂SO₄. The Pt electrode weight-loss of ca. 0.4 μg cm⁻² is observed during nine potential sweeps between 0.01 and 1.36 V vs. RHE. In contrast, the Pt electrode weight-loss is negligible without H₂O₂ (<0.05 μg cm⁻²). To support the EQCM results, the weight-decrease amounts of a Pt disk electrode and amounts of Pt dissolved in the solutions were measured after similar successive potential cycles. As a result, these results agreed well with the EQCM results. Furthermore, the H₂O₂ concentration dependence of the Pt weight-decrease rate was assessed by successive potential steps. These EQCM data indicated that the increase in H₂O₂ accelerates the Pt dissolution. Based on these results, H₂O₂ is known to be a major factor contributing to the Pt dissolution.     

Study the effect of conductive fillers on a secondary Zn electrode based on ball-milled ZnO and Ca(OH)2 mixture powders

The active materials of the secondary Zn electrode containing a mixture powder of zinc oxide (ZnO) and calcium hydroxide (Ca(OH)₂) powders were prepared by a ball-milled method. The characteristic properties of active materials of ball-milled ZnO + Ca(OH)₂ mixture powders were examined by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) system, X-ray diffraction (XRD) analysis, and micro-Raman spectroscopy. The prepared Zn powder electrodes were by using the ball-milled active materials powder +2 wt.% highly electronic conductive fillers, i.e., nano-copper or carbon nanotubes (CNTs) powder. The electrochemical properties of the secondary Zn electrodes without and with the conductive fillers were studied by using cyclic voltammetry (CV) and galvanostatic charge/discharge tests. It was found that the charge/discharge properties of the secondary Zn electrode could be improved when the nano-sized conductive fillers were added into the electrode. In fact, it may be due to the formation of a better electronic conduction path in the electrode matrix. In particular, it was found that the best electrochemical properties were the secondary Zn electrode with 2 wt.% nano-copper fillers. According to the results, it is demonstrated here that the CV method is a quick technique to effectively evaluate the performance of a secondary Zn electrode.     

Influence of CO2, CH4, and initial temperature on H2/CO laminar flame speed

The objective of this study is to investigate the impact of syngas composition by varying the H₂/CO ratio (1:3, 1:1, and 3:1 by volume), the CO₂ dilution (0%–40%), and methane addition (0%–40%) on laminar flame speed. Thus, laminar flame speeds of premixed syngas–air mixtures were measured for different equivalence ratios (0.8–2.2) and inlet temperatures (295–450 K) using the Bunsen-burner method. It was found that laminar flame speed increases with increasing H₂/CO ratio, while CO₂ dilution or CH₄ addition decreased it. The location of the maximum flame speed shifts to richer mixtures with decreasing H₂/CO ratio, while it shifts to leaner mixtures with the addition of CH₄ due to its inherent slower flame speed. The location of the maximum flame speed is also shifted towards leaner mixtures with the addition of CO₂ due to the preponderance of the reduction of the adiabatic flame temperature with increasing dilution. Comparison between experimental and numerical results shows a better agreement using a modified mechanism derived from GRI-Mech 3.0. A correlation, based on the experimental results, is proposed to calculate the laminar flame speed over a wide range of equivalence ratios, inlet temperatures, and fuel content.     

Performance and stability characteristics of MEAs with carbon-supported Pt and Pt1Ni1 nanoparticles as cathode catalysts in PEM fuel cell

Polarization curves of membrane electrode assemblies (MEAs) containing carbon-supported platinum (Pt/C) and platinum-nickel alloy (Pt₁Ni₁/C) as cathode catalysts were obtained for durability test as a function of time over 1100 h at constant current. Charge transfer resistance was measured using electrochemical impedance spectroscopy and postmortem analysis such as X-ray diffraction and high-resolution transmission electron microscopy was conducted in order to elucidate the degradation factors of each MEA. Our results demonstrate that the reduced performance of MEAs containing Pt₁Ni₁/C as a cathode catalyst was due to decreased oxygen reduction reaction caused by the corrosion of Ni, whereas that of MEAs containing Pt/C was because of reduced electrochemical surface area induced by increased Pt particle size.     

Studies on cerium (Ce/Ce)–vanadium(V/V) redox flow cell—cyclic voltammogram response of Ce/Ce redox couple in H2SO4 solution

A novel Ce⁴⁺/Ce³⁺–V²⁺/V³⁺ redox flow cell has been designed. The electrochemical responses of higher concentration Ce⁴⁺/Ce³⁺ couple in H₂SO₄ solution were investigated via cyclic voltammetry. The normal potential and the kinetic parameters for anodic oxidation of Ce³⁺ and cathodic reduction of Ce⁴⁺ were measured. The results showed the surface of platinum electrode was fully covered with type I oxide that inhibited the reduction of Ce⁴⁺. The reversibility of the Ce⁴⁺/Ce³⁺ couple improved with the increase of H₂SO₄ concentration. Different electrochemically active substances existed at various state of charge (SOC) and the reversibility of the Ce⁴⁺/Ce³⁺ couple at the carbon electrode was superior to platinum.     

Electrochemical reduction of silver vanadium phosphorous oxide, Ag2VO2PO4: Silver metal deposition and associated increase in electrical conductivity

This report details the chemical and associated electrical resistance changes of silver vanadium phosphorous oxide (Ag₂VO₂PO₄, SVPO) incurred during electrochemical reduction in a lithium based electrochemical cell over the range of 0-4 electrons per formula unit. Specifically the cathode electrical conductivities and associated cell DC resistance and cell AC impedance values vary with the level of reduction, due the changes of the SVPO cathode. Initially, Ag⁺ is reduced to Ag⁰ (2 electrons per formula unit or 50% of the calculated theoretical value of 4 electrons per formula unit) accompanied by significant decreases in the cathode electrical resistance, consistent with the formation of an electrically conductive silver metal matrix within the SVPO cathode. As Ag⁺ reduction progresses, V⁵⁺ reduction initiates; once the SVPO reduction process progresses to where the reduction of V⁵⁺ to V⁴⁺ is the dominant process, both the cell and the cathode electrical resistances then begin to increase. If the discharge then continues to where the dominant cathode reduction process is the reduction of V⁴⁺ to V³⁺, the cathode and cell electrical resistances then begin to decrease. The complex cathode electrical resistance pattern exhibited during full cell discharge is an important subject of this study.     

Effects of H2 on the number concentration of particulate matter in diesel engines using a low-pressure loop exhaust-gas recirculation system

We investigated the effects of H₂ on the number concentration of particulate matter (PM) emissions from a diesel engine fitted with a low-pressure loop exhaust gas recirculation system. We used a 2.2-L four-cylinder direct-injection diesel engine satisfying EURO V regulations, and converted this engine to include an H₂ feed. The air/fuel (A/F) ratio was varied in the range of 21.9–45.5 and the brake mean effective pressure was varied in the range of 2–6 bars to control the O₂ concentration and in-cylinder temperature, both of which are significant for PM emissions. The number concentration of the emitted PM was measured using a scanning mobility particle sizer. We found that the emitted PM decreased by the addition of H₂ which caused the unburned gas temperature increased. Furthermore, the degree of reduction was larger as the A/F ratio, load, and H₂ energy fraction increased. However, with A/F ratios of less than 21.9, the addition of H₂ increased the number concentration of emitted PM which was attributed to the small O₂ concentration at these A/F ratios.     

Effect of biomass leaching on H2 production,ash and tar behavior during high temperature steam gasification (HTSG) process

The effect of biomass water leaching on H₂ production, as well as, prediction of ash thermal behavior and formation of biomass tar during high temperature steam gasification (HTSG) of olive kernel is the main aim of the present work. Within this study raw olive kernel samples (OK₁, OK₂) and a pre-treated one by water leaching (LOK₂) were examined with regard to their ash fouling propensity and tar concentration in the gaseous phase. Two temperatures (T = 850 and 950 °C) and a constant steam to biomass ratio (S/B = 1.28) were chosen in order to perform the steam gasification experiments. Results indicated that considering the samples' ash thermal behavior, it seemed that water leaching improved the fusibility behavior of olive kernel; however, it proved that water leaching does not favour tar steam reforming, while at the same time decreases the H₂ yield in gas product under air gasification conditions, due to possible loss of the catalytic effect of ash with water leaching.     

Lithium ion intercalation in partially crystalline TiO2 electrodeposited on platinum from aqueous solution of titanium(IV) oxalate complexes

Starting from the aqueous solution of titanium(IV) oxalate complexes and controlling electrochemical conditions using a cyclic voltammetry (CV) method, the thin layers of TiO₂ on platinum were obtained, which after additional heat treatment, at 450 °C, were still of amorphous nature. The amorphous state of the samples, containing an admixture of crystalline anatase, was confirmed by Raman spectroscopy and by a variety of electrochemical techniques. The new electrochemical procedure allows preparing the oxide with different morphologies. By the comparison with the peroxotitanium route, the oxalate precursor method offers the possibility of the synthesis of amorphous TiO₂ at higher temperatures that is the essential key for the cycling stability of the oxide if one is used as an anode material in lithium ion batteries. The results from cycling voltammetry revealed that electrodeposited TiO₂ reversibly and fast intercalates lithium ions due to its high internal surface area. Therefore, the nanostructural morphology facilitates lithium ion intercalation which was monitored and confirmed in all electrochemical testing. The specific capacity of the TiO₂ approaches the value of 145 mAh g⁻¹ at 8 C-rate in the best case. From the electrochemical impedance spectroscopy (EIS) measurements in connection with SEM investigations, it was concluded that Li⁺ diffusion is the finite space process and its rate is depending on the size of the crystallites building the oxide films. Evaluated values of the D-coefficients are of the order of 10⁻¹⁴ cm² s⁻¹.     

Improvement in the hydrogen storage properties of Mg by mechanical grinding with Ni, Fe and V under H2 atmosphere

Mg-5wt%Ni-2.5wt%Fe-2.5wt%V (named Mg-5Ni-2.5Fe-2.5V) powder was prepared by reactive mechanical grinding using a planetary ball mill. The activation process, the changes in phase and microstructure with hydriding-dehydriding cycling, and the variations in the hydriding and dehydriding rates with temperature were investigated. The rate-controlling step for the dehydriding reaction of Mg-5Ni-2.5Fe-2.5V was analyzed by using a spherical moving boundary model. As the temperature increased from 473 K through 623 K, the initial hydrogen absorption rate under 12 bar H₂ decreased, while the hydrogen desorption rate under 1.0 bar H₂ increased.     

Microscopic magnetism in lithium insertion materials of LiNi1−xCoxO2 (x = 0, 1/4, 1/2, 3/4, and 1)

The magnetic nature of lithium insertion materials of LiNi_1−xCo_xO₂ (x = 0, 1/4, 1/2, 3/4, and 1) were investigated by means of positive muon-spin rotation/relaxation (μ⁺SR) spectroscopy combined with X-ray diffraction (XRD) analyses and susceptibility measurements. Zero field μ⁺SR spectra for all the samples below 300 K were well fitted by a dynamic Kubo–Toyabe function, indicating the existence of randomly oriented magnetic moments even at 2 K, i.e., disordered state. The field distribution width Δ due to magnetic Ni³⁺ ions decreases exponentially with increasing x, suggesting that the Co substitution is likely to simply dilute Ni moments. This also supports that cobalt and nickel ions are homogeneously distributed in a solid matrix even in a muon-scale (microscopically), which is consistent with the results of macroscopic measurements.     

The role of Li and Ni metals in the adsorbate complex and their effect on the hydrogen storage capacity of single walled carbon nanotubes coated with metal hydrides,LiH and NiH2

In this first principles study based on density functional theory, we report the hydrogen storage capability of (5, 5) single walled carbon nanotubes coated with Lithium hydride and Nickel hydride. The paper brings out the role of lightweight Li atom and heavy Ni atom in binding the respective hydrides and hydrogen molecules with the single walled carbon nanotubes. The investigation is carried out for half and full coverage of the adsorbates (metal hydrides) on the sidewalls of the carbon nanotubes. The clustering of the adsorbates is observed in full coverage case of both the systems and its effect on hydrogen storage capacity and binding energy is reported. The clustering patterns are different in each of the systems and dependent on the nature of the metal atom in the metal hydride. The storage capacity of single walled carbon nanotubes coated with heavy transition metal hydride is around 3 wt.% whereas it is around 6 wt.% in their counterparts coated with lightweight metal hydride.