Effects of Zr addition on electrochemical characteristics of MgTiMnNi hydrogen storage alloys

The electrochemical hydrogen storage properties of 25 h milled Mg_0.80Ti_0.175Mn_0.025Zr_xNi_1-x (x = 0, 0.025, 0.05, 0.1) quinary alloys were investigated. The substitution of Zr for Mg or Ni leads to an increase in structural disorder and amorphization. Thus, the maximum discharge capacity and the cycling stability of MgNi-based alloys can be enhanced. The x-ray diffraction patterns indicate that all additive elements are entirely dissolved in the synthesized alloys, and amorphous structure was successfully obtained by 25 h milling. Among the milled alloys, the Mg_0.80Ti_0.175Mn_0.025Zr_0.10Ni_0.90 alloy exhibited the best discharge capacity of 604 mA h g⁻¹ at the initial charge/discharge cycle. The obtained results demonstrate that using multi-component compositions is beneficial for enhancing the structural and cyclic stability of MgNi-based alloys. Therefore, substituting additive elements for Mg or Ni may offer impressive performance for efficient hydrogen storage applications.     

Effect of substituting Mn for Ni on the hydrogen storage and electrochemical properties of ReNi2.6−xMnxCo0.9 alloys

ReNi_2.6−xMn_xCo_0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloys were prepared by induction melting. The effects of partially substituting Mn for Ni on the phase structure and electrochemical properties of the alloys were investigated systematically. In the alloys, (La, Ce)₂Ni₇ phase with a Ce₂Ni₇-type structure, (Pr, Ce)Co₃ phase with a PuNi₃-type structure, and (La, Pr)Ni₅ phase with a CaCu₅-type structure were the main phases. The (La,Pr)Ni phase appeared when x increased to 0.45, and the (La, Pr)Ni₅ phase disappeared with further increasing x (x > 0.45). The hydrogen-storage capacity of the ReNi_2.6−xMn_xCo_0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloys initially increased and reached a maximum when Mn content was x = 0.45, and then decreased with further increasing Mn content. The ReNi_2.6−xMn_xCo_0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloy exhibited a hydrogen-storage capacity of 0.81, 0.98, 1.04, 0.83 and 0.53 wt.%, respectively. Electrochemical studies showed that the maximum discharge capacity of the alloy electrodes initially increased from 205 mAh/g (x = 0.0) to 352 mAh/g (x = 0.45) and then decreased to 307 mAh/g (x = 90). The hydrogen absorption rate first increased and then decreased with addition of Mn element. The ReNi_2.15Mn_0.45Co_0.9 alloy showed faster hydrogen absorption kinetics than that of the other alloys. The presence of Mn element slowed hydrogen desorption kinetics.     

Optimization of anode performance in the ethanol electrochemical reforming for clean hydrogen production

Carbon-based fuel electrochemical reforming is considered as a promising hydrogen production method. Ethanol is one of the most appropriate carbon-based fuels. In this work, anode performance, especially the flow, ethanol electro-oxidization and energy consumption in the ethanol electrochemical reforming is numerically studied and experimental verified. Take the straight serpentine channel with square cross-section as a base structure in the electrochemical cell (EC), the effects of channel geometry and operating parameters are analyzed. Another five different configurations of flow channels, as well as another three different cross-sections are designed and explored. Results indicate that at the same cross-section area, the wider channel provides the higher effective area for proton transfer, and thereby improves the electrode reactions. The appropriate decrease of inlet velocity or increase of input voltage promotes the anode reaction and reduces the pressure drop in channel, while the operating temperature has the opposite effects on ethanol conversion and pressure drop. The arc channel is found optimal considering its highest ethanol conversion, although its pressure drop is a bit higher. The sector cross-section with uniform flow field distribution is found most favorable for the straight serpentine channel considering the ethanol electro-oxidization. These findings will favor the improvement of EC.     

Novel alloys to improve the electrochemical behavior of zinc anodes for zinc/air battery

In our continued efforts for improving the performance of zinc anodes for a Zn/air battery, we now report the preparation of three alloys and improved performances of anodes made up with these alloys. The alloys contained zinc, nickel, and indium with different weight percentages and were calcined at two different temperatures. Out of the six alloys, the alloy which has a composition of zinc 90%, nickel 7.5% and Indium 2.5% and fired at 500 °C is found to be the best. In the case of the hydrogen evolution reaction, this alloy had its potential shifted to a more negative potential. As far as the cyclic voltammograms were concerned, the difference between the anodic and cathodic part was minimal when compared with other alloys. Surprisingly, this alloy had reversibility even after 100 cycles of the cyclic voltammogram. This is a clear indication that dendrite formation was reduced to a considerable extent. Images taken with a scanning electron microscope also indicated reduced dendrite formation.     

First-principles analysis of electrochemical hydrogen storage behavior for hydrogenated amorphous silicon thin film in high-capacity proton battery

Silicon material electrodes as proton carriers for high-capacity proton battery have only been proposed for such a short period of time that their physicochemical properties and electrochemical hydrogen storage behavior during charge and discharge processes remain nearly uncharted territory. Herein, the hydrogenated amorphous silicon (a-Si:H) thin film electrodes are prepared by radio frequency sputtering followed by ex-situ hydrogenation. The electrochemical properties of a-Si:H electrodes are tested experimentally, and the electrochemical hydrogen storage behaviors of a-Si:H electrodes are analyzed by first-principles calculations. The results show that the hydrogenation process significantly increases the electrochemical capacity of the electrodes and reduces the band gap of the electrode structure. The electrode exhibits weak conductivity during the initial charging, but the instability of the electrode electronic structure during the later charging results in a slight fluctuation of the electrochemical charging process. The a-Si:H electrode have better electrochemical hydrogen storage/release reversibility than non-hydrogenated electrodes, but this reversibility is weakened by oxygen atoms covered on the electrode surface. The electrochemical hydrogen storage process is easier to accomplish than the electrochemical desorption process of hydrogen evolution reaction for the a-Si:H electrodes. The a-Si:H thin film electrode is more stable on the Ni(111) substrate surface and the good conductivity of the electrode/substrate interface provides convenient conditions for the free transport of electrons in the electrochemical charge/discharge processes. We believe that these results perfectly explain the microscopic mechanisms responsible for the electrode reaction and electrochemical behavior of a-Si:H electrodes in this type of proton battery, and have a certain reference value in understanding the physicochemical properties and electrochemical hydrogen storage behavior of silicon material electrodes applied to other types of batteries during charge/discharge processes.     

Improvement of the electrochemical hydrogen storage performance of magnesium based alloys by various additive elements

Mg_1.5Ti_0.3Zr_0.1M_0.1Ni (M = Al, B, C, Fe, Pd) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. While Al deteriorated the alloy initial discharge capacity, it improved the alloy cyclic stability. The reversibility in the presence of B was very poor. Addition of B increased the alloy initial discharge capacity but reduced the alloy capacity retention rate. The cyclic stability of Fe-including alloy was much better than that of C-including alloy, although both of them have almost the same initial discharge capacities. Both the alloy initial discharge capacity and the alloy cyclic stability were improved significantly in the presence of Pd. The analysis by the electrochemical impedance spectroscopy revealed that Fe increased the corrosion resistance of the alloy without degrading the capacity retention rate. The hydroxide barrier layer in the presence of Al was predicted to be more porous due to the possible high rate selective dissolution of the disseminated Al-oxides.     

Effect of composition on the reactivity of Al-rich alloys with water

Fe-bearing Al–Ga–In–Sn alloys were prepared by using arc melting under high purity argon atmosphere. Their microstructures were investigated by means of XRD, SEM/EDX, and the eutectic reaction of Al with grain boundary phase Ga–In–Sn (GIS) was measured using DSC. Fe dendrites were found to present on columnar Al grain surfaces. As the amount of low melting point metals (Ga, In and Sn) is 6 wt.% with a ratio of In:Sn of 15:7, these alloys just consist of Al(Ga) and In₃Sn two phases. InSn₄ was found in an alloy as its weight ratio of In:Sn approaches 1:1 with an extra addition of Sn (1 wt.%). The reactions of Al alloys with water were performed at different water temperatures ranging from 0.5 to 50 °C. Al reacted with water at a lower water temperature of 0.5 °C, but the reaction suspended within tens of minutes. Once water was heated to a higher temperature of about 15 °C, Al reacted with water again. The H₂ generation rates measured at a water temperature of 50 °C depend on the compositions of alloys. Reasons concerning the reactivity of Al–water at different temperatures are discussed.     

Effect of Ce on electrochemical properties of the TiVNi quasicrystal material as an anode for Ni/MH batteries

In order to investigate effect of Ce on electrochemical properties of the Ti_1.4V_0.6Ni quasicrystal, (Ti_1.4V_0.6Ni)_99.4Ce_0.6 alloy ribbon is prepared by arc melting and subsequent melt-spinning technique. The electrochemical properties of the Ti_1.4V_0.6Ni and (Ti_1.4V_0.6Ni)_99.4Ce_0.6 are studied as negative electrode for nickel–metal hydride batteries in aqueous KOH solution. The structures of the alloys were characterized by XRD and TEM. Phase structure investigations of the (Ti_1.4V_0.6Ni)_99.4Ce_0.6 show that alloy mainly consist of the icosahedral quasicrystal (I-phase) and face centered cubic (FCC) phase with Ti₂Ni-type structure. The electrochemical measurements demonstrated that the negative electrode made by (Ti_1.4V_0.6Ni)_99.4Ce_0.6 alloy showed an improved electrochemical reversibility and a considerably higher charge–discharge capacity when compared to the Ce-free base alloy. Its maximum discharge capacity is about 300 mAh/g, which is higher than that of Ti_1.4V_0.6Ni, and remains 270 mAh/g after 30 cycles at a current density of 30 mA/g. The discharge process is also characterized by electrochemical impedance spectroscopy.     

In-situ patterned intra-anode triple phase boundary in SOFC electroless anode: An enhancement of electrochemical performance

Co-existence of intra-anode and conventional triple phase boundary (TPB) is reported for the first time in core (YSZ)-shell (Ni) electroless anode cermet. A mathematical model is proposed for determination of intra-anode TPB length and has been validated experimentally. Retention of longer intra-anode TPB even after repeated redox cycling is responsible for relatively lower conductivity degradation of such cermets. Existence of intra-anode TPB in electroless anode results in significant improvement of electrochemical performance. Single cells with electroless anode exhibit a current density of 2.5 A cm⁻² compared to cells with conventional anode (1.7A cm⁻²) at 800 °C, 0.7 V.     

Effect of minor nickel alloying with zinc on the electrochemical and corrosion behavior of zinc in alkaline solution

The electrochemical and corrosion behavior of pure zinc and Zn-0.5Ni alloy in strong alkaline solution (7 M KOH) was investigated by Tafel plot, potentiodynamic, potentiostatic and electrochemical impedance spectroscopy (EIS) methods, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Measurements were conducted under different experimental conditions. The results of both Tafel plot extrapolation and the electrochemical impedance spectroscopy (EIS) measurements exhibited the same trend, which the cathodic and anodic processes on the alloy surface are less significant compared with those on the pure zinc. The results revealed that, the shift in steady state of open-circuit potential (E_corr) to more negative potential in the case of the studied alloy compared with that of pure zinc has a positive effect on both charge efficiency and self-discharge.The anodic potentiodynamic measurements demonstrated that the polarization curves exhibited active/passive transition. The active dissolution of both pure zinc and its alloy increases with increasing temperature and scan rate. The activation energy (E_a) value of active region and peak current (I_AI) of the two studied electrodes in the investigated alkaline solution is calculated and compared. In the case of alloy, the results obtained at certain positive potential (+425 mV vs. SCE), exhibited high current density indicating that the most passive layer was destroyed. This indicates that the addition of small amount from Ni to Zn promotes the electrochemical reaction (in the passive region), acting as so-called self catalysis. Accordingly, one can conclude that, the electrochemical behavior of the investigated alloy in strong alkaline solution contributes to suppression of hydrogen gas evolution and increases the corrosion resistance. In addition, reactivation of the alloy surface takes place in the passive region.     

Effect of surface reconstruction induced by different electrochemical methods on hydrogen evolution performance of Ni2P array catalysts

The design and development of electro-catalyts is of importance to the industrial hydrogen production through water splitting. Among various catalysts, nickel-based component has been widely applied due to its excellent catalytic performance. The activity of such catalyst could be improved relative chemical reactions, including Selenization, sulfurization, phosphating and hydroxylation, but their surface structure might be rebuilt, further affecting the catalytic performance. Herein, sheet-like phosphide-based material was synthesized on the nickel foam, and the phenomenon of surface rebuilding was investigated through three different electrochemical methods, chronoamperometry (It) and chronopotentiometry (CP), and Cyclic voltammetry (CV). Results showed the significantly difference in surface morphology due to the utilization of the three electrochemical methods. Crystal component could be completely transferred to amorphous after CP and It, with the reduction of overpotential by 44 and 49 mV respectively. Compared to these two electrochemical methods, CV could enable the occurrence of whole oxidative and reductive reactions on the surface, inducing the formation of heterostructure, crystal NiO and amorphous NiP, on the surface. This structure achieves 58 mV reduction of overpotential, which is 58 mV lower than precursor. And the stability test also showed only 0.08% of attenuation, indicating a better electrochemical performance.     

Description and characterization of an electrochemical hydrogen compressor/concentrator based on solid polymer electrolyte technology

Proton-exchange membrane (PEM) technology is commonly used for manufacturing water electrolysers, H₂/O₂ fuel cells and unitized regenerative fuel cells. It can also be used to develop electrochemical compressors, for the purpose of concentrating and/or pressurizing gaseous hydrogen. The aim of the work reported here was to evaluate the main operating characteristics of a laboratory scale (≈10 N liter/h) monocell compressor. The role of various operating parameters (current density, temperature of electrochemical cell, water vapor partial pressure in the hydrogen feed gas, anodic gas composition, etc.) has been evaluated and is discussed. It is shown that the relative humidity of hydrogen oxidized at the anode of the compressor should be adapted to the current density during operation to avoid mass transfer limitations or electrode flooding. A cell voltage of 140 mV is required at 0.2 A cm⁻² to compress hydrogen in one step from atmospheric pressure up to 48 bar, corresponding to an energy consumption of ca. 0.3 kW h/Nm³. Experiments have been performed up to 130 bar. Series connection of several compressors is recommended to reach output pressures higher than 50 bar. To reduce gas cross-permeation effects which can negatively impact the efficiency of the compressor, additional experiments have been made using Nafion membrane modified by addition of zirconyl phosphate. Finally, data related to the extraction of hydrogen from H₂-N₂ gas mixtures are also reported and discussed.     

Effects of surface coating with Cu-Pd on electrochemical properties of A2B7- type hydrogen storage alloy

La_0.75Mg_0.25Ni_3.2Co_0.2Al_0.1 hydrogen storage alloy, the nickel-metal hydride (MH/Ni) secondary battery negative electrode, was modified by CuSO₄ solution (3 wt% in Cu in contrast with alloy weight) and PdCl₂ solution varied from 1 wt% to 4 wt% in Pd in contrast with alloy weight with a simplified pollution-free replacement plating method, aiming at improving its comprehensive electrochemical properties. The XRD analysis and SEM images combined with EDS results reveal that Cu and Pd nanoparticles are uniformly plated on the pristine alloy surface. The relative amount of Pd on the Cu-Pd coated alloy surface increases notably as the PdCl₂ concentration increases in the plating solution. Electrochemical tests indicate that alloy electrodes modified by Cu-Pd composite coating show perfect activation performance, which achieve the maximum discharge capacity at the first charge-discharge cycle. Moreover, alloy electrodes coated with Cu-Pd perform dramatically enhanced high rate dischargeability (HRD). The enhancement increases firstly and then decreases as the content of Pd increases in the Cu-Pd coating. Meanwhile, the cycle life of modified alloys is also improved significantly. Among all the samples, the Cu-Pd coated alloy with 3 wt% Pd content in the PdCl₂ solution reinforces the comprehensive electrochemical properties most sufficiently, with dischargeability of 86.4% under 1500 mA/g and remaining capacity of 82.7% after 100 cycles.     

Enhanced electrochemical lithium storage performance of Mg2FeH6 anode with TiO2 coating

Light-weight metal hydrides are potential high-capacity conversion anode materials for lithium-ion batteries, but the poor reaction reversibility and cyclic stability of hydride anodes need to be improved. In this work, the ternary hydride Mg₂FeH₆ was composited with the graphite (G) by ball-milling, and the Mg₂FeH₆-G composite electrode was further coated with amorphous TiO₂ film by magnetron sputtering. The resultant Mg₂FeH₆-G/TiO₂ electrode exhibited a stable charge capacity of 412 mAh g^?1 over 100 cycles, which is much higher than 46 mAh g^?1 at 20th cycle for the pure Mg₂FeH₆ electrode, or 185 mAh g^?1 at 100th cycle for the Mg₂FeH₆-G electrode. There is only little capacity degradation after 20 cycles for the Mg₂FeH₆-G/TiO₂ electrode and the charge capacity retention is 84.7% after 100 cycles. The remarkable improvement in the cyclic stability of Mg₂FeH₆-G/TiO₂ electrode is mainly attributed to the dense TiO₂ coating that maintains the structural integrity of electrode during cycling. The TiO₂ coating also prevents the direct contact of high active LiH/MgH₂ with the liquid electrolyte, and thus ensures the high reversibility of conversion reaction of MgH₂ during cycling.     

Effect of La partial substitution for Zr on the Structural and electrochemical properties of Ti0.17Zr0.08-xLaxV0.35Cr0.1Ni0.3 (x = 0–0.04) electrode alloys

In order to elucidate the effects of metallic La addition on the performance of Ti–V-based hydrogen storage alloys as negative electrodes for nickel/metal-hydrides batteries, Ti_0.17Zr_0.08-xLa_xV_0.35Cr_0.1Ni_0.3 (x = 0, 0.01, 0.02, 0.03, 0.04) alloys were prepared and their structural and electrochemical properties were systematically investigated. X-ray powder diffraction (XRD) results showed that these alloys were mainly consisted of C14 Laves phase with a hexagonal structure, V-based solid solution phase with BCC structure and C15 Laves phase with a cubic structure. The electrochemical measurements indicated that the maximum discharge capacities of the alloy electrodes decreased from 337.3 mAh/g (x = 0) to 262.5 mAh/g (x = 0.04) and that the substitution of Zr with metallic La in the alloys had no obvious effect on the capacity retention rate (C₁₀₀/C_max, C₂₀₀/C_max). The high-rate dischargeability (HRD) of the alloy electrodes at the discharge current density of 800 mA/g first increased from 69.01% (x = 0) to 71.13% (x = 0.01) and then decreased to 65.35% (x = 0.04). In brief, the HRD was improved with an optimum La content in the alloy (x = 0.01). The electrochemical hydrogen kinetics of the alloy electrodes was further studied by means of electrochemical impedance spectroscopy, linear polarization, anodic polarization and potential-step measurements. The charge-transfer reaction resistance R_ct decreased for x = 0.01 with respect to x = 0 and then increased with the increase of x, while exchange current density I₀, limiting current density I_L and hydrogen diffusion coefficient D were all increased for x = 0.01 with respect to x = 0 and then decreased with the increase of x. The optimal content of La in Ti_0.17Zr_0.08-xLa_xV_0.35Cr_0.1Ni_0.3 alloys for negative electrodes in alkaline rechargeable secondary batteries is x = 0.01 in this study.     

Study on the microstructure and electrochemical properties of lead-calcium-tin-aluminum alloys

A detailed investigation of the effects on the microstructure and electrochemical properties of lead-calcium-tin-aluminum alloys of adding tin and calcium was undertaken. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) were used to study the anode electrochemical behavior (such as the growth of lead dioxide, a passive film and the evolution of oxygen) of the lead grid alloy in sulfuric acid solution. The structure and corrosion morphology of the lead alloy were observed and analyzed using a polarizing microscope, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The experimental results show that the grains gradually became smaller as the content of calcium increased, and the content of tin decreased, in the alloy. The size and shape of grains were related to the ratio of tin to calcium content in the alloys. The linear sweep voltammetry and AC impedance measurements suggested that the preferred ratio of tin to calcium content, r, is between 9 and 15, and the optimum range of tin content in the alloys is 0.8-1.1%.     

Synthesis of potential nanostructures based on strontium hexaferrite for electrochemical hydrogen storage

Today, the reduction of fossil fuel resources and the increase of their destructive environmental effects are important challenges. One strategy to this problem is application of new sources of energy supply. Hydrogen can play an important role in future energy supplies due to its unique properties such as clean combustion and high energy content relative to mass. In addition, hydrogen is considered as a green energy because it can be produced from renewable sources and is not polluting. The most important issue in hydrogen as a fuel is its storage. Hydrogen must be stored reversibly in a completely safe manner as well as with high storage efficiencies. One of the best ways to store hydrogen is using of new nanostructured adsorbents. In this study, first strontium hexaferrite (SrFe₁₂O₁₉) nanostructures are synthesized by sol-gel auto-combustion method. Then, the samples structure is studied using various techniques. Furthermore, the nanostructures are used as hydrogen storage materials. Using electrochemical techniques, the hydrogen storage properties of the materials are investigated in alkaline media. The obtained electrochemical results show that the maximum hydrogen storage capacity of SrFe₁₂O₁₉ nanostructures is about 3100 mAh/g.     

Study on the structure and hydrogen storage characteristics of as-cast La0.7Mg0.3Ni3.2Co0.35−XCuX alloys

In this paper, the structure, hydrogen storage performance, electrochemical discharge and cyclic characteristics of La_0.7Mg_0.3Ni_3.2Co_0.35−XCu_X alloys were investigated using X-ray diffraction (XRD), pressure composition isotherm (PCT) and electrochemical tests. XRD tests showed that all of the alloys were composed of La₂Ni₇ and LaNi phases. The ratio of LaNi phase in these alloys increased with increasing substitution of Cu for Co. PCT tests showed that increasing substitution of Cu for Co resulted in the decrease of hydrogen storage capacity and the increase of plateau pressure. Electrochemical discharge tests showed that the discharge capacity increased first and then decreased with increasing substitution of Cu for Co.     

Synergistic effects of 1T-2H MoS2 nanoflowers modified with Ag3PO4 nanoclusters for highly efficient electrochemical activity

The development of highly efficient binary heterostructures with enhanced electrocatalytic activities is vital for reducing the energy consumed by the hydrogen evolution reaction (HER). Herein, we successfully design and synthesize an eco-friendly Ag₃PO₄/1T-2H MoS₂ heterostructure to catalyze the HER process. Micromorphology and microstructure studies show that the Ag₃PO₄ nanoclusters are well dispersed with abundant catalytically active sites on the surface of the 1T-2H MoS₂ nanoflowers. X-ray photoelectron spectroscopy confirms the stable oxidation state and electronic interactions in the 2 wt% Ag₃PO₄/1T-2H MoS₂ nanostructure. Benefitting from the strong electronic interactions and advantages of abundant heterogeneous interfaces and catalytically active sites, the 2 wt% Ag₃PO₄/1T-2H MoS₂ heterostructure delivers excellent and durable electrochemical HER activity in alkaline solution, with a low overpotential of 149 mV for the HER at 10 mA cm⁻², in clear improvement over 1T-2H MoS_2. The enhanced electrocatalytic activity is ascribed to the abundant catalytically active sites, rapid charge transport, and Ag₃PO₄/1T-2H MoS₂ synergism. This study provides a novel strategy for exploring and synthesizing low-cost binary electrocatalysts that enhance the electrochemical HER performance in energy-conversion applications.