Effect of catalytic Pd coating on the hydrogen storage performances of ZrCo alloy by electroless plating method

The effects of Pd coating with different deposition concentration (PdCl₂ 0.2 g L^?1, 0.6 g L^?1, 1.0 g L^?1) on the surface morphology, microstructure and hydrogen storage performances of ZrCo alloy have been investigated. Results show that spherical Pd particles have been deposited on the surface of ZrCo alloy successfully, which transfer from sparse arrangement to continuous and compact film with increasing deposition concentration of PdCl₂. The hydriding kinetic property of all Pd coated alloys is improved compared with the bare alloy, which is due to the catalyst effect of Pd coating. The hydriding rate of the samples firstly increases and then decreases with increasing deposition concentration, which is closely related to the surface morphology and thickness of Pd coating. The hydriding kinetic property of the samples is greatly improved after 5 cycles, although Pd particles on the alloy surface peel off to some extent. This phenomenon indicates that the accumulated fresh surface during cycling makes a greater contribution to the improved hydriding kinetic property and the catalyst effect of Pd coating is weakened during cycling.     

Effect of CuO addition on electrochemical properties of AB3-type alloy electrodes for nickel/metal hydride batteries

In order to improve overall electrochemical properties of AB₃-type hydrogen storage alloy electrodes, especially the cycling stability, CuO was added to the electrode. Electrochemical properties of the electrodes with and without additives were studied. Cyclic voltammetry and SEM results show that CuO is reduced to Cu during the charging process and the fine Cu particles deposit at surface of the alloy particles. The as-deposited Cu particles form a protective layer to increase electronic and heat conductivity of the electrodes and thus improve maximum discharge capacity, high rate dischargeability, cycling stability and dischargeability at high temperature of the electrodes. The maximum discharge capacity increases from 314 mAh g⁻¹ (blank electrode) to 341 mAh g⁻¹ (3.0 wt.% CuO) and the capacity retention rate at the 200th cycle increases from 71.6% to 77.2% (2.5 wt.% CuO).     

Electrochemical investigations on cobalt-microencapsulated MmNi2.38Al0.82Co0.66Si0.77Fe0.13Mn0.24 hydrogen storage alloys for Ni–MH batteries

Cobalt coatings were applied over lanthanum process-rich MmNi_2.38Al_0.82Co_0.66Si_0.77Fe_0.13Mn_0.24 alloy particles by an autocatalytic electroless deposition process. Electrode characteristics such as electrochemical capacity and cycle life were studied for the uncoated and coated alloys. The structure and morphology of the surface modified samples were characterized with XRD and SEM/EDAX techniques. The cobalt coating forms a thin layer on the surface of the core material and the coated alloys exhibit a 15% improvement in performance over the bare alloy. A comparison of the electrochemical impedance behaviour of the bare and cobalt-coated metal hydride electrodes at different states-of-charge reveals that the relaxation period is distinct for different SOCs. The cobalt microencapsulations influence the apparent activation energy of the dehydriding process. The calculated equivalent rate constant (k_eq) values confirm the improvement in reversibility for the cobalt-coated alloy as compared to the bare alloy.     

Long-life Ni-MH batteries with high-power delivery at lower temperatures: Coordination of low-temperature and high-power delivery with cycling life of low-Al AB5-type hydrogen storage alloys

Although a low-Al or an Al-free design is an efficient way to develop low-temperature and high-rate metal hydride alloys, the cycling life of these alloys is poor. Our strategy is to employ B-side anti-corrosion elements (e.g., Fe, Si, Sn, Cu) to coordinate the low-temperature and high-power delivery with cycling life. We confirmed that excellent electrochemical kinetics (i.e., surface catalytic and bulk H-diffusion ability) is the primary condition for low-temperature and high-rate delivery, while it reverses with anti-corrosion ability. As a result, the low-temperature dischargeability (LTD), high-rate dischargeability (HRD) and peak power (P_peak) progressively decrease with Ni, Si, Cu, Fe, Sn and Al substitution, but the cycling stability successively increases with Ni, Si, Fe, Sn, Cu and Al substitution. Based on the thermodynamics and the coordination of the LTD, the HRD and P_peak with the cycling life, the (LaCe)_1.0(NiCoMn)_4.85Al_0.05Cu_0.1 alloy presents the best overall electrochemical properties. Notably, when using an as-designed Cu-doped anode, the assembled commercial 100 Ah prismatic Ni-MH batteries present excellent power delivery at ?40 °C.     

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.     

Preparation and electrochemical hydrogen storage properties of Ti49Zr26Ni25 alloy covered with porous polyaniline

A facile saturated solution synthesis method is used to obtain the porous polyaniline (P-PANI). The materials exhibit unique sea urchin-like morphology and special porous structure. Ti₄₉Zr₂₆Ni₂₅ quasicrystal is fabricated via mechanical alloying followed by annealing treatment. Different amounts of P-PANI are coated on the surface of hydrogen storage alloy by ball milling. For comparison, Ti₄₉Zr₂₆Ni₂₅ alloy doped with conventional PANI (C-PANI) is also prepared. The electrochemical characterizations of the composites are conducted in the standard tri-electrode system. Ultimately, the P-PANI coated Ti₄₉Zr₂₆Ni₂₅ electrode shows preferable performance compared with the C-PANI modified alloy (230.6 mAh/g) and original alloy (209.3 mAh/g). As the additive content of P-PANI is 6 wt%, a maximum discharge capacity of 258.7 mAh/g is obtained. Furthermore, the cycle stability and high-rate dischargeability of the electrodes are also enhanced. The P-PANI materials with distinctive morphology and unique porous structure can not only improve the electrocatalytic activity of polyaniline but also increase the specific surface area of Ti₄₉Zr₂₆Ni₂₅ alloy. The P-PANI can further facilitate the hydrogen diffusion, expedite the charge transfer in/on the alloy and improve the corrosion resistance, thus enhancing the electrochemical performance and reaction kinetics of the hydrogen storage alloys.     

Crystal structure and electrochemical characteristics of non-AB5 type La–Ni system alloys

The La–Ni system compounds have been prepared by arc-melting method under Ar atmosphere. X-ray diffraction analysis reveals that the as-prepared alloys consist of different phases. The electrochemical properties, including activation, maximum discharge capacity, high rate chargeability (HRC), and high rate dischargeability (HRD) of these alloy electrodes have been studied through the charge–discharge recycle testing at different temperatures and charge (or discharge) currents. Among the La–Ni alloy electrodes studied, LaNi_2.28 alloy has the most excellent high rate charging performance, and La₂Ni₇ alloy exhibit the highest high rate dischargeability, while La₇Ni₃ alloy is capable of discharging at low temperature.     

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.     

Effect of carbon coating on the electrochemical properties of La–Y–Ni-based hydrogen storage alloys

The A₂B₇-type (LaSmY) (NiMnAl)_3.5 alloys were prepared by induction melting, and then the alloy samples coated with different contents of nano-carbon were prepared by the mixing and sintering method using pitch as carbon source. The effects of the contents and structure of the coated-carbon on the electrochemical properties of alloy samples were investigated. With the carbon content increase from 0.1 to 1.0 wt%, the cyclic stability is improved and the high-rate dischargeabilitiy (HRD) of the alloy electrodes first increase and then decrease. The kinetic results show that the carbon coating improves the electrocatalytic activity and electrical conductivity of the alloy electrodes. The alloy electrode with 0.5 wt% carbon coating exhibits the best electrochemical properties. The maximum discharge capacity (C_max) is 345.7 mAh·g⁻¹, the HRD₁₂₀₀ is 72.49%, and the capacity retention rate (S₃₀₀) is 79.44%.     

Enhanced high-rate discharge properties of La11.3Mg6.0Sm7.4Ni61.0Co7.2Al7.1 with added graphene synthesized by plasma milling

In order to improve the high-rate discharge properties of La_11.3Mg_6.0Sm_7.4Ni_61.0Co_7.2Al_7.1 (AB_3.0) alloy electrodes, the effects of plasma milling (PM) and graphene addition on their electrochemical properties and kinetics have been investigated. It was found that the discharge capacity of AB_3.0 at a high discharge current density was significantly improved after the addition of graphene followed by PM for only 10 min. Moreover, the high-rate dischargeability (HRD) and the exchange current density I₀ of the alloy electrodes were also increased. The PM technique exhibits obvious advantages for improving the high-rate discharge properties of hydrogen-storage alloys.     

Preparation and electrochemical hydrogen storage properties of Co9S8 alloy coated with cobalt/graphene composite

A facile one-pot reduction process is used to obtain the cobalt/graphene composite (CoRGO). The CoRGO materials exhibit unique reticular globular morphology. Co₉S₈ hydrogen storage alloy is fabricated via mechanical alloying method. Different amounts of CoRGO are coated on the surface of Co₉S₈ alloy by ball milling. The electrochemical characterizations of the composites are conducted in the standard tri-electrode system. Ultimately, the CoRGO coated Co₉S₈ electrode shows preferable performance than the RGO modified alloy (603.6 mAh/g) and original alloy (577.3 mAh/g). As the additive content of CoRGO is 6 wt%, a maximum discharge capacity of 637.5 mAh/g is obtained. Furthermore, the cycle stability and high-rate dischargeability of the electrode are also enhanced. The Co particles in the CoRGO participate in the reversible redox reactions and the graphene provides high conductivity. The CoRGO with distinctive structure and morphology can not only improve the electrocatalytic activity but also increase the specific surface area of Co₉S₈ alloy. The cobalt and graphene species in the CoRGO composite serve a synergistic effect in further facilitating the hydrogen diffusion, expediting the charge transfer in/on the alloy and improving the corrosion resistance, thus enhancing the electrochemical performance and reaction kinetics of Co₉S₈ alloy.     

Investigation of MnCu0.5Co1.5O4 spinel coated SUS430 interconnect alloy for preventing chromium vaporization in intermediate temperature solid oxide fuel cell

The MnCu_0.5Co_1.5O₄ spinel coating is proposed as a protective coating for SUS430 alloy to improve its oxidation resistance and prevent chromium vaporization. The coated alloy is exposed to dual atmosphere (Air/H₂–3%H₂O) at 750 °C for 200 h, exhibiting a stable spinel structure on the air side, but reduced to MnO, Cu and Co on the fuel side. The coating layer could maintain integrated and dense with a thickness of 13–14 μm. The experiment results shown that the MnCu_0.5Co_1.5O₄ coating is an effective diffusion barrier that can inhibit oxidation and chromium vaporization of metallic interconnect. The relatively low amount of Cr deposition on LSM cathode on coated condition is considered associating with the stable electrochemical performance under current density of 400 mA cm^?2. The above results indicate that MnCu_0.5Co_1.5O₄ spinel is a promising coating for interconnect alloy of solid oxide fuel cell.     

Effect of temperature on the discharge capacity of the Laves phase alloy used in nickel/metal-hydride batteries

The discharge capacity, the high-rate dischargeability and the self-discharge characteristics of negative electrodes consisting of the Zr-based, modified AB₂ type alloys of ZrV_0.1Mn_0.7Ni_1.2 alloy and ZrV_0.1Mn_0.5Mo_0.2Ni_1.2 alloy, the latter having the form of partially substituted Mo for Mn sites in the former alloy, are investigated in 6 M KOH solution at 30, 40 and 60°C. It is found that the discharge capacities obtained at 30 and 40°C are almost the same in both alloys, but they decrease at 60°C. The activation process becomes faster in both alloys with increasing temperature. The high-rate dischargeability increases slightly from 85% at 30°C to 90% at 60°C. At the very high discharge current of 5 A g⁻¹, however, the discharge capacity at 60°C was increased by 7× and 17× more than that at 30°C in ZrV_0.1Mn_0.7Ni_1.2 alloy and ZrV_0.1Mn_0.5Mo_0.2Ni_1.2 alloy, respectively. The addition of Mo improved the self-discharge characteristics, especially at 60°C.     

Synergetic catalyst effect of Ni/Pd dual metal coating accelerating hydrogen storage properties of ZrCo alloy

Aimed at enhancing the hydrogen absorption/desorption performances of ZrCo system, Ni/Pd dual metal coating is employed on ZrCo alloy combined with the electroless plating and displacement plating. The effects of Ni/Pd dual metal coating on the microstructure, hydrogen storage performance of ZrCo alloys were investigated systematically. The results show that Ni/Pd dual metal coating deposits on the surface of ZrCo sample successfully with the thickness of 500 nm. The hydrogen absorption kinetic property is substantially enhanced for ZrCo alloy after Ni/Pd dual metal coating, which is owing to the catalytic effect of Ni/Pd coating. Further, the activation energies (E_a) for hydrogen absorption and desorption are calculated using the Arrhenius Equation and Kissinger method, respectively. Compared with the bare ZrCo, the activation energies of the Ni/Pd coated samples for hydriding/dehydriding process decrease which facilitate the hydrogenation/dehydrogenation reaction. This work introduces a rational approach by building new catalytic coating on the hydrogen storage materials to improve the hydriding/dehydriding kinetic performance.     

Carbon support hydrogenation in Pd/C catalysts during reductive thermal treatment

The resistance of the Pd/C samples towards hydrogenation of the carbon support was studied in the temperature-programmed and isothermal regimes. Carbonaceous graphite-like material Sibunit was used as a carbon support. Pristine Sibunit was additionally graphitized via high temperature treatment (1900 °C) in an inert atmosphere. Both initial and graphitized supports were subjected to oxidative treatment in order to increase the amount of surface functional oxygen-containing groups. Palladium (1 wt%) was supported using an aqueous solution of H₂PdCl₄. All the samples were characterized by a low-temperature adsorption of nitrogen, transmission electron microscopy, and Raman spectroscopy. The graphitization procedure was found to decrease significantly the specific surface area of the support, while the oxidative treatment affects this parameter negligibly. Testing the Pd-containing samples in a hydrogen flow revealed the following order in accordance with amount of methane released: Pd/iSib » Pd/iSib-ox > Pd/gSib > Pd/gSib-ox.     

Enhancing sinterability and electrochemical properties of Ba(Zr0.1Ce0.7Y0.2)O3-δ proton conducting electrolyte for solid oxide fuel cells by addition of NiO

The influence of NiO on the sintering behavior and electrical properties of proton conducting Ba(Zr_0.1Ce_0.7Y_0.2)O_3-δ (BZCY7) as an electrolyte supporter for solid oxide fuel cells is systematically investigated. SEM images and shrinkage curve demonstrate that the sinterability of the electrolyte pellets is dramatically improved by doping NiO as a sintering aid. The sintering aid amount and sintering temperature are optimized by analyzing the linear shrinkage, grain size and morphology for a series of sintered BZCY7 electrolyte pellets. Almost full dense electrolyte pellets are successfully formed by using 0.5–1.0 wt% NiO loading after sintering at 1400 °C for 6 h. The linear shrinkage of 0.5 wt% NiO modified BZCY7 sample is about 14.25% higher than that without NiO addition (4.81%). Energy dispersive X-ray spectroscopy analysis indicate that partial NiO might dissolve into the perovskite lattice structure and the other NiO react with BZCY7 to form BaY₂NiO₅ secondary phase as a sintering aid. Excessive NiO is especially detrimental to the electrical properties of BZCY7 and thus lower the open circuit voltage. The electrochemical performance for a series of single cells with different concentration NiO modified BZCY7 electrolyte are measured and analyzed. The optimized composition of 0.5 wt% NiO modified BZCY7 as an electrolyte support for solid oxide fuel cell demonstrates a high electrochemical performance.     

A simple and fast method for the preparation of super active Pd/CNTs catalyst toward ethanol electrooxidation

For the first time, galvanic reduction by zinc sheet is used as a new strategy to prepare modified electrodes. In this work, glassy carbon electrode (GCE) was modified by decoration of Pd nanostructures on carbon nanotubes (Pd/CNTs). In this method, deposited PdCl₂ on CNTs was directly reduced to metallic Pd nanostructure using a zinc sheet in HCl (2% w/w) solution. This approach offers a number of advantages including being very fast, simple and green; and modified electrodes show high activity. The prepared catalyst is characterized by Field Emission Scanning Electron Microscopy, X-Ray Diffraction and energy-dispersive X-ray and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). In addition, electrochemical measurements show that the performance as well as the stability of the as-prepared catalyst for ethanol oxidation is outstanding. The Pd/CNTs catalyst shows higher mass current density, which is 7.9 times as high as that of commercial Pd/C.     

Palladium-ruthenium alloy nanoparticles dispersed on CoWO4-doped graphene for enhanced methanol electro-oxidation

Highly dispersed nanoparticles (NPs) of Pd and Pd-Ru alloys on the 10 wt% CoWO₄-doped GNS (graphene nano sheets) support have been obtained by a microwave-assisted polyol reduction and investigated for their application as efficient electrode materials for methanol oxidation reaction (MOR). Structural and electrocatalytic surface characterization of hybrid materials were carried out by XRD, TEM, XPS, cyclic voltammetry and chronoamperometry. Pure CoWO₄ and CoWO₄-doped GNS follow the monoclinic crystal structure and the Pd NPs (6–7 nm) dispersed on CoWO₄-doped GNS follow the face-centered cubic crystal structure. It is observed that with the increase of Pd loading from 5 to 20 mg on the support, the onset potential (E_op) for MOR shifts negatively and the MOR current density increases, the magnitude of shift in E_op and increase in the MOR peak current density being the greatest in the case of 15 mg Pd loading. Introduction of Ru from 0.6 to 2.0 mg into 15 mg Pd on the catalyst support, the apparent activity of the active catalyst, 15Pd/10 wt% CoWO₄-GNS improved further, the magnitude of improvement, however, being the greatest (≈50%) with 1.0 mg Ru. Thus, novel 15Pd-1.0Ru/10 wt%CoWO₄-doped GNS can be a promising electrode material for MOR in alkaline solutions.     

Synthesis of Pd/TiO2 nanotubes/Ti for oxygen reduction reaction in acidic solution

Highly ordered and uniformly distributed TiO₂ nanotubes on a pure titanium substrate (TNTs/Ti) are successfully fabricated by a pulse anodic oxidation method as the support for Pd electrocatalyst. Pd is electrochemically deposited onto TNTs/Ti support. The sensitization with SnCl₂ and activation with PdCl₂ are critical for the formation of highly dispersed Pd nanoparticles on the TNTs/Ti support. It has been found that both Pd/TNTs/Ti and Pt electrodes show the similar electrochemical behavior in H₂SO₄, implying the possibility to develop the Pt-free alternative electrocatalyst based on the Pd/TNTs/Ti system in acid medium. The preliminary results in this work show that the Pd/TNTs/Ti catalysts have an acceptable catalytic activity for the oxygen reduction reaction (ORR) in acid medium. The factors influencing the structure of TNTs and the catalytic activity of Pd/TNTs/Ti for the ORR are also studied in detail.     

Characteristics of A2B7-type LaYNi-based hydrogen storage alloys modified by partially substituting Ni with Mn

LaY₂Ni_10.5?xMn_x (x = 0.0, 0.5, 1.0, 2.0) alloys are prepared by a vacuum induction-quenching process followed by annealing. The structure, as well as the hydriding/dehydriding and charging/discharging characteristics, of the alloys are investigated via X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), pressure-composition isotherms (PCI), and electrochemical measurement. The alloys have multiphase structures mainly composed of Gd₂Co₇-type (3R) and Ce₂Ni₇-type (2H) phases. Partial substitution of Ni by Mn clearly increases the hydrogen storage capacity of the alloys. The x = 0.5 alloy exhibits a maximum hydrogen storage capacity of 1.40 wt % and a discharge capacity of 392.9 mAh g^?1, which are approximately 1.5 and 1.9 times greater than those of the x = 0.0 alloy, respectively. The high-rate dischargeability (HRD) of the x = 0.5 alloy is higher than that of the other alloys because of its large hydrogen diffusion coefficient D, which is a controlling factor in the electrochemical kinetic performance of alloy electrodes at high discharge current densities. Although the cyclic stability of the x = 0.5 alloy is not as high as that of the other alloys, its capacity retention ratio is as high as 56.3% after the 400th cycle. The thermodynamic characteristics of the x = 0.5 alloy satisfy the requirements of the hydride electrode of metal hydride–nickel (MH–Ni) batteries.