Investigation on gaseous and electrochemical hydrogen storage performances of as-cast and milled Ti1.1Fe0.9Ni0.1 and Ti1.09Mg0.01Fe0.9Ni0.1 alloys

The AB-type Ti_1.1Fe_0.9Ni_0.1 (Mg₀ for short) and Ti_1.09Mg_0.01Fe_0.9Ni_0.1 (Mg_0.01 for short) alloys were fabricated by vacuum induction melting and mechanical milling. The effects of partly substituting Ti with Mg and/or mechanical milling on the structure, morphology, gaseous thermodynamics and kinetics, and electrochemical performances were studied. The results reveal that the as-cast Mg₀ alloy contains the main phase TiFe and a small number of TiNi₃ and Ti₂Ni phases. Substituting Ti with Mg and/or mechanical milling results in the disappearance of the secondary phases. The discharge capacities of the as-cast Mg₀ and Mg_0.01 alloys are 12.6 and 8.8 mAh g^?1, which increase to 52.6 and 80.4 mAh g^?1 after 5 h of mechanical milling. By milling the as-cast alloy powders with carbonyl nickel powders, they are greatly enhanced to 191.6 mAh g^?1 for the Mg₀+7.5 wt% Ni alloy and 205.9 mAh g^?1 for the Mg_0.01+5 wt% Ni alloy at the current density of 60 mA g^?1, respectively. The values of dehydrogenation enthalpy (ΔH_des) and dehydrogenation activation energy (E^des_(a)) are very small, meaning that the thermal stability and the desorption kinetics of the hydrides are not the key influence factors for the discharge capacity. The reduction of the particle size and the generation of the new surfaces without oxide layers have slight improvements on the discharge capacity, while the enhancement of the charge transfer ability of the surfaces of the alloy particles can significantly promote the electrochemical reaction of the alloy electrodes.     

Effect of Ti substitution on electrochemical properties of ZrNi alloy electrode for use in nickel-metal hydride batteries

Crystal structure and electrochemical properties of the Zr_1?xTi_xNi (0.05 ≤ x ≤ 0.5) alloys were investigated. X-ray diffraction spectra showed that the primary phase of all Zr_1?xTi_xNi alloys had the B33-type orthorhombic crystal structure, which was characteristic of ZrNi, and the unit cell volume of the primary phase linearly decreased with an increase in the x value. In the charge–discharge tests with the Zr_1?xTi_xNi alloy negative electrodes, the initial discharge curves for the alloys with x ≥ 0.3 had two plateaus. Both plateau potentials negatively shifted with an increase in the x value. The initial discharge capacity for the Zr_0.6Ti_0.4Ni alloy negative electrode was 349 mAh g^?1 at 25 mA g^?1 and 333 K, which was the highest in this study. The high-rate dischargeability and cycle performance were also improved by the partial replacement of Zr by Ti.     

Nickel-graphene nanocomposite with improved electrochemical performance for La0.7Mg0.3(Ni0.85Co0.15)3.5 electrode

A Ni-rGO nanocomposite was synthesized by a hydrothermal process and La_0.7Mg_0.3(Ni_0.85Co_0.15)_3.5, an AB_3.5-type hydrogen storage alloy, was prepared by magnetic levitation melting under argon atmosphere. The influences of the Ni-rGO nanocomposite on the hydrogen storage and electrochemical performance of the La_0.7Mg_0.3(Ni_0.85Co_0.15)_3.5 alloy were investigated via pressure composition isotherms (PCT) and electrochemical measurements. The PCT curves revealed that the addition of the Ni-rGO nanocomposite improved the reversibility of hydrogen absorption and desorption for the La_0.7Mg_0.3(Ni_0.85Co_0.15)_3.5 alloy. The electrochemical measurements showed that the electrochemical impedance of the La_0.7Mg_0.3(Ni_0.85Co_0.15)_3.5 alloy electrode was significantly reduced, the high rate dischargeability, HRD₁₂₀₀, increased from 60% to 86%, the limiting current density, I_L, increased from 1216.7 mA·g^?1 to 2287.6 mA·g^?1, and the hydrogen diffusion coefficient, D, increased with the added Ni-rGO nanocomposite. These improvements to the electrochemical performance are mainly attributed to the Ni-rGO framework, with the large specific surface area of the graphene, and to the high conductivity of metal nickel.     

Fabrication of Mg–Ni–Sn alloys for fast hydrogen generation in seawater

Mg-2.7Ni-x wt.% Sn(x = 0–2) alloys were fabricated to promote hydrogen generation kinetics of Mg-2.7Ni alloy. The Sn in Mg-2.7Ni-Sn alloys exists as Mg₂Sn phase at the grain boundary and solid solution at the Mg matrix. The Mg₂Sn at the grain boundary acts as the initiation site for pitting corrosion and the dissolved Sn in the alloy causes pitting corrosion by locally breaking the surface oxide film in the Mg matrix in seawater. The Mg-2.7Ni-1Sn alloy showed an excellent hydrogen generation rate of 28.71 ml min^?1 g^?1, which is 1700 times faster than that of pure Mg due to the combined action of galvanic and intergranular corrosion as well as pitting corrosion in seawater. As the solution temperature was increased from 30 to 70 °C, the hydrogen generation rate from the hydrolysis of the Mg-2.7Ni-1Sn alloy was dramatically increased from 34 to 257.3 ml min^?1 g^?1. The activation energy for the hydrolysis of Mg was calculated to be 43.13 kJ mol^?1.     

Elaboration and electrochemical characterization of Mg–Ni hydrogen storage alloy electrodes for Ni/MH batteries

Mg–Ni hydrogen storage alloy electrodes with composition of Mg–33, 50, 67 Ni at. % in amorphous phase were prepared by means of mechanical alloying (MA) process using a planetary ball mill. The electrochemical hydrogen storage characteristics and mechanisms of these electrodes were investigated by electrochemical measurements, X–ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The relationship between alloy composition and electrochemical properties was evaluated. In addition, optimum milling time and composition of Mg–Ni hydrogen storage alloy with acceptable electrochemical performance were determined. XRD results show that the alloys exhibit dominatingly amorphous structures after milling of 20 h. The electrochemical measurements revealed that the discharge capacity of Mg₃₃Ni₆₇ and Mg₆₇Ni₃₃ alloy electrodes reached a maximum when alloys were prepared after 20 h of milling time (260 and 381 mAhg^?1, respectively). The maximum discharge capacity of Mg₅₀Ni₅₀ alloy was observable after 40 h milling (525 mAhg^?1). It was also found that the cyclic stability of the alloys increased with increasing Ni content. Among these alloys, the amorphous Mg₅₀Ni₅₀ alloy presents the best overall electrochemical performance. In this paper, electrode process kinetics of Mg₅₀Ni₅₀ alloy electrode was also studied by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The impedance spectra of electrodes were measured at different depths of discharge (DODs). The observed spectra were fit well with the equivalent circuit model used in the paper. The electrochemical parameters calculated from electrochemical impedance were also compared. The electrochemical discharge and cyclic performance of 20, 40 and 60 h milled Mg₅₀Ni₅₀ alloy electrodes were demonstrated by the fitted charge transfer resistance and Warburg impedance obtained at various DODs. It was further observed that the controlling-step of the discharge process changed from a mixed rate-determining process at lower DODs to a mass-transfer controlled process at higher DODs. The fitted results demonstrated that charge–transfer resistance (R_ct) increased with DOD. The R_ct of 40 h milled Mg₅₀Ni₅₀ alloy (29.27 Ω) was lower than that of 20 h (41.89 Ω) and 60 h milled alloys (92.43 Ω) at fully discharge state.     

Old-loofah-derived hard carbon for long cyclicity anode in sodium ion battery

Hard carbon was prepared via the carbonization of the old loofah sponge at 800 °C for 1 h in the inert N₂ atmosphere for sodium ion battery (SIB) anode. The resultant old-loofah-derived hard carbon was investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Raman, galvanostatic charge/discharge, cyclic voltammetry (CV) and alternating current (AC) impedance. The results suggested that the old-loofah-derived hard carbon powders consisted of many irregular micro-particles with the mean particle size of 12 μm. Furthermore, the old-loofah-derived hard carbon anode also delivered satisfactory electrochemical performances in SIB. For example, the initial discharge specific capacity was as high as about 695 mAh g^?1 at 25 mA g^?1, and the reversible discharge specific capability after 1000 cycles was still about 171 mAh g^?1 even at 1000 mA g^?1, indicating long cycle stability and the promising feasibility of the old-loofah-derived hard carbon anode. The disordered micro-structure and large interlayer distance may jointly contribute into the satisfactory electrochemical performances.     

3D SnO2/sulfonated graphene composites with interpenetrating porous structure as anode material for lithium-ion batteries

Combine SnO₂ nanoparticles with some conductive carbonaceous materials has been regarded as one of the most effective strategies to solve the problems of poor conductivity and volume change. In this work, a SnO₂/sulfonated graphene composite with 3D interpenetrating porous structure (3D SnO₂/SG) was synthesized. The elaborate designed 3D SG structure not only generates an excellent electronic conductivity, but also buffers the volume expansion of the SnO₂ particles. As a result, the desirable 3D possesses enhanced performance when used as anode material in lithium battery. For example, the electrochemical results showed that the 3D SnO₂/SG presents a high reversible specific capacity (928.5 mA h g^?1 at the current density of 200 mA g^?1). Even after 120 cycles, the specific capacity of 679.7 mA h g^?1 (at the current density of 400 mA g^?1) are still maintained.     

Electrochemical properties of Ti2Ni hydrogen storage alloy

In this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti₂Ni alloy used as negative electrode in nickel-metal hydride batteries have been studied by different electrochemical techniques. Several methods, such as, galvanostatic charge and discharge, the constant potential discharge and the potentiodynamic polarization are applied to characterize electrochemically the studied alloy. The studied electrodes are observed before and after electrochemical tests at different temperatures by scanning electron microscopy.The amorphous Ti₂Ni is activated after five cycles and the achieved maximum discharge capacity is about 67 mAh g^?1 at ambient temperature. Despite the low values of the maximum discharge capacity and the cycling stability (17%) and the steep decrease of the discharge capacity after activation, this alloy conserves a good stability lifetime during a long cycling. A good correlation is observed between the evolution of the discharge capacity and those of the redox parameters during a long cycling.The enthalpy change, the entropy change and the activation energy of the formation reaction of the Ti₂Ni metal hydride are evaluated electrochemically. The found values of the enthalpy change, the entropy change and the activation energy are about ?43.3 kJ mol^?1, 51.7 J K^?1 mol^?1 and 34.9 kJ mol^?1, respectively.     

Effects of annealing temperature on the structure and properties of the LaY2Ni10Mn0.5 hydrogen storage alloy

The effects of annealing at 1123, 1148, 1173 and 1198 K for 16 h on the structure and properties of the LaY₂Ni₁₀Mn_0.5 hydrogen storage alloy as the active material of the negative electrode in nickel–metal hydride (Ni–MH) batteries were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy linked with an energy dispersive X-ray spectrometer (SEM–EDS), pressure-composition isotherms (PCI) and electrochemical measurements. The quenched and annealed LaY₂Ni₁₀Mn_0.5 alloys primarily consist of Ce₂Ni₇- (2H) and Gd₂Co₇-type (3R) phases. The homogeneity of the composition and plateau characteristics of the annealed alloys are significantly improved, and the lattice strain is effectively reduced. The alloys annealed at 1148 K and 1173 K have distinctly greater hydrogen storage amounts, 1.49 wt% (corresponding to 399 mAh g^?1 in equivalent electrochemical units) and 1.48 wt%, respectively, than the quenched alloy (1.25 wt%, corresponding to 335 mAh g^?1 in equivalent electrochemical units). The alloys annealed at 1148 K and 1173 K have relatively good activation capabilities. The annealing treatment slightly decreases the discharge potentials of the alloy electrodes but markedly increases their discharge capacity. The maximum discharge capacities of the annealed alloy electrodes (372–391 mAh g^?1) are greater than the extreme capacity of the LaNi₅-type alloy (370 mAh g^?1). The cycling stability of the annealed alloy electrodes was improved.     

CNF-grafted carbon fibers as a binder-free cathode for LithiumOxygen batteries with a superior performance

In this work, we report the significant enhancement of the electrochemical performance and flexibility of a lithium–oxygen battery by introducing a free-standing, binder-free carbon nano-fibers (CNF) grafted carbon paper cathode with a bimodal pore architecture. The small pore structures (～100 nm) accommodated Li₂O₂, and the large pore structures (～10 μm) enabled effective oxygen diffusion without clogging the pores. This kind of cathode overcame some troubles of the cathode prepared by spraying coating method, such as the low utilization of substrate surface, the unreasonable aperture structure and the aggregation of active carbon material. As a result, this electrode structure imparted stability to active sites during the recovery of discharge products to the initial state, providing long-term cyclability of more than 800 cycles in a 1 M LiTFSI/TEGDME electrolyte system. In addition, the battery output a discharge capacity as high as 20000 mAh g^?1 at 468 mA g^?1 and exhibited a charge/discharge rate as high as 1136 mA g^?1 (0.57 mA cm^?2). The test results suggest that these CNF-grafted carbon papers have the potential to be used for oxygen/air electrodes for next-generation lithium-oxygen batteries, though the present results need to be improved to achieve performance of practical significance, namely with regard to (i) cathode mass loading to get higher areal capacity, and (ii) cycling performance at higher current density.     

Direct-current electrodeposition of Ni–S–Fe alloy for hydrogen evolution reaction in alkaline solution

Ni–S–Fe alloy has been successfully fabricated on a copper foil substrate through direct-current electrodeposition as an electrocatalyst for hydrogen evolution reaction (HER) in alkaline solution. The Ni–S–Fe alloy is characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The electrocatalytic performance of Ni–S–Fe alloy for HER is studied in 30 wt% KOH solution. The results show that the Ni–S–Fe alloy exhibits much higher catalytic activity for HER relative to Ni–S alloy, as manifested by smaller overpotential of 222 mV at 10 mA cm^?2 and higher exchange current density of 1.60 × 10^?2 mA cm^?2. The Tafel slope of 84.5 mV·dec^?1 implies an underlying Volmer-Heyrovsky mechanism. The outstanding catalytic performance of the Ni–S–Fe alloy may originate from the synergistic effects of Ni and Fe, refined grain, and enlarged surface area of Ni–S–Fe alloy upon Fe doping. In addition, the Ni–S–Fe alloy has better anti-corrosion property than Ni–S alloy as a result of the poorer crystallinity of Ni–S–Fe alloy.     

Trimetallic PtNiCo nanoflowers as efficient electrocatalysts towards oxygen reduction reaction

Nanostructures of PtNiCo alloy have been prepared using a simple solvothermal process followed by annealing at higher temperature and studied for electrochemical oxygen reduction reaction (ORR) kinetics. PtNiCo/C catalyst has demonstrated an interesting trend of enhancement in the ORR activity along with long-term durability. The specific activity of 2.47 mA cm^?2 for PtNiCo-16h/C (PtNiCo/C prepared at reaction time of 16 h) is ～12 times higher than that of Pt/C (0.2 mA cm^?2). Further, X-ray diffraction, transmission electron microscopy and X-ray photo electron spectroscopy studies have been carried out systematically to understand the phase formation, morphology along with surface defects and elemental analysis respectively. The durability of the catalyst was evaluated over 10,000 potential cycles using standard triangular potential scan in the lifetime regime. Interestingly, after 10k durability cycles, PtNiCo-16h/C electrocatalyst showed enhanced ORR activity (32% higher activity; Im@10k cycles = 0.716 A mg_Pt^?1) and stability compared to commercial Pt/C signifying the retention of Ni and Co due to higher lattice contraction in PtNiCo alloy electrocatalyst.     

Sulfur/alumina/polypyrrole ternary hybrid material as cathode for lithium-sulfur batteries

Recently, lithium-sulfur batteries (LSBs) have received extensive attention due to its high energy density of 2600 Wh kg^?1. At the same time, sulfur is earth-abundant, economical and non-poisonous. Nevertheless, the poor electrochemical performance restricts its commercial application, including the inferior cycling stability caused by the significant dissolution of lithium polysulfides and the low specific capacity because of the poor electrical conductivity of sulfur. In this work, we adopt a simple and amicable process to prepare sulfur/alumina/polypyrrole (S/Al₂O₃/PPy) ternary hybrid material to overcome these defects. In this strategy, each composition of the ternary hybrid material plays an essential role in cathode: alumina and PPy can provide strong adsorption for the dissolved intermediate polysulfides. Meanwhile, PPy also works as a conductive and flexible additive to expedite electron transport, and is coated on the surface of the as-prepared SAl₂O₃ composite by in situ chemical polymerization. The sulfur is encapsulated uniformly and perfectively by the two components, which is confirmed by field emission scanning electron microscope. The ternary hybrid material manifests good electrochemical performance as expected, and displays high initial discharge capacity of 1088 mA h g^?1 and a discharge capacity of 730 mA h g^?1 after 100 cycles at a current density of 200 mA g^?1. Besides, S/Al₂O₃/PPy also shows good rate capability. The synergy between alumina and PPy is the decisive factor, which gives rise to good electrochemical performance of cathode for high-performance LSBs.     

Highly efficient,large surface area and spherically shaped Pt particles deposited electrolytically synthesized graphene for methanol oxidation with impedance spectroscopy

Graphene was synthesized via electrochemical exfoliation technique of graphite rod in Poly (sodium 4-styrenesulfonate) solution. Laser Raman and X-ray Diffraction Spectroscopies were used to confirm the defects and crystal nature of graphene. The surface wettability studies based on water contact angle, further differentiates the affinity of as-prepared graphene and pristine graphite towards water. Modified Glassy carbon (GC) electrodes were prepared by electro-deposition of Platinum (Pt) on bare and graphene coated GC, denoted as GC/Pt and graphene/Pt modified GC respectively. The morphology and chemical composition of the thus synthesized graphene and graphene/Pt modified electrodes were investigated by High resolution transmission electron microscopy, Scanning electron microscopy and Energy dispersive spectroscopy. The electrochemically active surface area of the electro-deposited spherically shaped Pt particles was calculated to be 63.96 m² g^?1 and 25.10 m² g^?1 on graphene/Pt and GC/Pt, respectively. The electro-catalytic performance of modified electrodes for methanol oxidation was envisaged by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. Graphene/Pt modified GC electrode showed higher oxidation peak current (42.90 mA cm^?2) than GC/Pt modified electrode (16.24 mA cm^?2) in forward scan of methanol oxidation because of the uniform distribution of spherically shaped Pt particles on graphene. The reaction path for methanol oxidation at different potentials was elucidated by means of Electrochemical Impedance Spectroscopy.     

One-step synthesis of amorphous Ni–Fe–P alloy as bifunctional electrocatalyst for overall water splitting in alkaline medium

Design of inexpensive and highly efficient bifunctional electrocatalyst is paramount for overall water splitting. In this study, amorphous Ni–Fe–P alloy was successfully synthesized by one-step direct-current electrodeposition method. The performance of Ni–Fe–P alloy as a bifunctional electrocatalyst toward both hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) was evaluated in 30 wt% KOH solution. It was found that Ni–Fe–P alloy exhibits excellent HER and OER performances, which delivers a current density of 10 mA cm^?2 at overpotential of ～335 mV for HER and ～309 mV for OER with Tafel slopes of 63.7 and 79.4 mV dec^?1, respectively. Moreover, the electrolyzer only needs a cell voltage of ～1.62 V to achieve 10 mA cm^?2 for overall water splitting. The excellent electrocatalytic performance of Ni–Fe–P alloy is attributed to its electrochemically active constituents, amorphous structure, and the conductive Cu Foil.     

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.     

Facile preparation of nanoporous TiO2/MoOx composite and its high lithium storage performances as an anode material

Nanoporous TiO₂/MoO_x composite is easily fabricated via one-step mild dealloying of well-designed TiMoAl ternary alloy in alkaline solution. Selectively leaching the Al atom from the precursor alloy resulted in the formation of nanoporous TiO₂/MoO_x composite accompanied with the natural oxidation of Ti and Mo atoms. The TiO₂/MoO_x composite is comprised of interconnected nanoscaled network backbone and hollow channels with the ligament size around 40 nm and the pore size around 90 nm. Owing to the rich porosity and the incorporation of MoO_x, the as-made nanocomposite exhibits markedly enhanced lithium storage performances with superior reversible capacity, outstanding rate capability, and prominent cycling stabilities compared with the pure TiO₂. Especially, the reversible capacity remains about 321.6 and 167.5 mA h g^?1 at the rate of 300 and 1000 mA g^?1, respectively, after long cycling up to 500 times. Benefitting from the unique performance and facile preparation, the TiO₂/MoO_x composite holds promising application potential as an anode material in lithium-ion batteries.     

Solvothermal synthesis of Li3VO4: Morphology control and electrochemical performance as anode for lithium-ion batteries

In this work, orthorhombic Li₃VO₄ with the controllable morphology has been synthesized by tuning the solvent composition (volume ratios of ethanol to deionized water) in a solvothermal approach. The resulting Li₃VO₄ samples with various morphologies (coral-shaped particle, self-assembled hierarchical microsphere, cube-like particle, sheet-like structure) show then different electrochemical performances when employed as anodes for Li-ion battery applications. The Li₃VO₄ with self-assembled hierarchical microsphere morphology (volume ratio of ethanol to deionized water at 15:15) exhibits the best electrochemical performance. The subsequent carbon coating process on microsphere samples is claimed to significantly improve both the capacities at both low (350–430 mAh g^?1 at 100 mA g^?1) and high current (180–350 mAh g^?1 at 2 A g^?1) conditions, and their excellent cycling stability.     

Electrochemical hydrogen storage properties of mechanically alloyed Mg0.8Ti0.2-xMnxNi (x = 0, 0.025, 0.05, 0.1) type alloys

Mechanical alloying was used in the synthesis of Mg_0.8Ti_0.2-xMn_xNi (x = 0, 0.025, 0.05, 0.1) quaternary alloys to analyze the effect of Mn substitution for Ti on the electrochemical performance of MgNi alloys. The milling was carried out for 25 h. By adding a small amount of Mn (x = 0.025) to the Mg_0.8Ti_0.2Ni alloy, a completely amorphous structure was obtained. The maximum discharge capacity of the Mg_0.8Ti_0.175Mn_0.025Ni alloy was observed as 543 mAh g^?1 at the initial charge/discharge cycle. When x = 0 and x = 0.05, the discharging performances of Mg_0.8Ti_0.2-xMn_xNi alloys were approximately the same. However, when x = 0.1, the lowest initial discharge capacity (401 mAh g^?1) and discharge capacity performance were observed. The capacity retention rates of Mg_0.8Ti_0.175Mn_0.025Ni, Mg_0.8Ti_0.2Ni, Mg_0.8Ti_0.05Mn_0.05Ni, and Mg_0.8Ti_0.1Mn_0.1Ni alloys were 81%, 68%, %67, and 47%, respectively, at the 20th cycle.     

Enhanced electrochemical and hydrogen storage properties of La–Mg–Ni-based alloy electrode using a Ni and N co-doped reduced graphene oxide nanocomposite as a catalyst

To enhance the electrochemical property of a La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy, a three-dimensional (3D) reduced graphene oxide (rGO)-supported nickel and nitrogen co-doped (Ni–N@rGO) nanocomposite is fabricated by an impregnation method and introduced into the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy. The results show that the reversible hydrogen storage property and the comprehensive electrochemical performance of the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy are enhanced effectively when it is modified by the Ni–N@rGO nanocomposite. The high-rate dischargeability values at a discharge current density of 1500 mA g⁻¹ for the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy and Ni–N@rGO-modified samples are 0.0% and 70.5%, respectively. Additionally, the anodic peak currents for the unmodified alloy electrode is 892 mA g⁻¹. Under the catalytic action of the Ni–N@rGO nanocomposite, the value increases to 2307 mA g⁻¹, which is 2.59 times larger than that of unmodified samples. The results also indicate that the diffusion ability of the hydrogen atom in the alloy electrode body enhances significantly when modified by the Ni–N@rGO nanocomposite. The hydrogen diffusion coefficient for the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy electrode increases from 3.93 × 10⁻¹⁰ cm² s⁻¹ to 6.15 × 10⁻¹⁰ cm² s⁻¹ when is modified by Ni–N@rGO nanocomposite. These improvements in the comprehensive electrochemical properties are mainly attributed to the excellent electrochemical activity and conductivity of the Ni–N@rGO nanocomposite.