Synthesis and characterization of GO-PpPDA/Ni–Mn nanocomposite as a novel catalyst for methanol electrooxidation

The graphene oxide-poly (p-phenylene diamine) (GP) composite is synthesized through in-situ polymerization of p-phenylene diamine on GO sheets and used as an efficient support material for electrodeposition of Ni and Mn. The resulting GP/Ni–Mn catalyst shows high catalytic activity, stability and durability for methanol electrooxidation. The surface area of GP composite is calculated to be about 28% and 36% higher than GO and PpPDA, respectively. In addition, combining Ni and Mn demonstrated some synergetic effect for methanol electrooxidation. The electrochemical active surface area of GP/Ni–Mn is about 1.625 cm², which is much higher than GP/Ni and GP/Mn. GP/Ni–Mn nanocomposite presented 87.3% of the peak current after 5 h and almost 83.16% of the maximum current for 500 cycles. The excellent characteristics of this composite are attributed to high surface area, high electrochemical active surface area and fine distribution of metallic particles on the support material.     

Synthesis and characterization of macroporous Ni,Co and Ni–Co electrocatalytic deposits for hydrogen evolution reaction in alkaline media

In this work, macroporous Ni, Co and Ni–Co electrodes have been developed by co-deposition at high current density on stainless steel (AISI 304) substrates. The obtained materials were characterized both morphologically and chemically by confocal laser scanning microscopy, and SEM coupled with EDX analysis. The activity for hydrogen evolution reaction (HER) on the obtained layers was assessed by using pseudo-steady-state polarization curves and electrochemical impedance spectroscopy (EIS) in alkaline solution (30 wt.% KOH). The electrochemical results show that HER on these electrodes takes place by the Volmer–Heyrovsky mechanism. The synthesized coatings present higher catalytic activity for HER than commercial smooth Ni electrode. As the Co content increases in the electrodeposition bath the obtained structures show lower surface roughness factors. Ni–Co deposit with a Co content of 43 at.% manifests the highest intrinsic activity for HER as a consequence of the synergetic combination of Ni and Co.     

Carbon-ceramic supported bimetallic Pt–Ni nanoparticles as an electrocatalyst for electrooxidation of methanol and ethanol in acidic media

The electrooxidation of methanol and ethanol was investigated in acidic media on the platinum–nickel nanoparticles carbon-ceramic modified electrode (Pt–Ni/CCE) via cyclic voltammetric analysis in the mixed 0.5 M methanol (or 0.15 M ethanol) and 0.1 M H₂SO₄ solutions. The Pt–Ni/CCE catalyst, which has excellent electrocatalytic activity for methanol and ethanol oxidation than the Pt–Ni particles glassy carbon modified electrode (Pt–Ni/GCE), Pt nanoparticles carbon-ceramic modified electrode (Pt/CCE) and smooth Pt electrode, shows great potential as less expensive electrocatalyst for these fuels oxidation. These results showed that the presence of Ni in the structure of catalyst and application of CCE as a substrate greatly enhance the electrocatalytic activity of Pt towards the oxidation of methanol and ethanol. Moreover, the presence of Ni contributes to reduce the amount of Pt in the anodic material of direct methanol or ethanol fuel cells, which remains one of the challenges to make the technology of direct alcohol fuel cells possible. On the other hand, the Pt–Ni/CCE catalyst has satisfactory stability and reproducibility for electrooxidation of methanol and ethanol when stored in ambient conditions or continues cycling making it more attractive for fuel cell applications.     

Synthesis and characterization of g/Ni–SiO2 composite for enhanced hydrogen storage applications

Hydrogen is considered as one of the most important clean energy carriers for the future. Many experimental and theoretical investigations have focused on the adsorption and activation of H₂ on the metal surfaces. Metal oxides and semiconductors are suitable materials for this purpose. Gelatin assisted Ni loaded SiO₂ (g/Ni–SiO₂) was prepared and its structural properties, morphology, composition and surface properties were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), Elemental mapping and energy dispersive spectrum (EDS), High resolution transmission electron microscopy (HR-TEM) and Brunauer-Emmett-Teller (BET) surface area measurements. The prepared material was effectively utilized for H₂ storage applications at room temperature. The H₂ storage capacity of g/Ni–SiO₂ was twice that of pristine SiO₂. This may be due to large change in pore volume and pore diameter of g/Ni–SiO₂, which may enhances the H₂ storage capacity of the sample. The H₂ storage capacity of other materials such as ZnO, anatase TiO₂, g/TiO₂, g/ZnO, g/TiO₂–SO₄^2-, Sb doped TiO₂, Ag₂S/TiO₂, Sb₂O₃, CdS and SiO₂/CdS also studied and compared with g-Ni/SiO₂.     

Nickel–palladium electrocatalysts for methanol,ethanol, and glycerol oxidation reactions

Carbon-supported Pd and PdNi electrocatalysts with different Ni contents were prepared by metal ion chemical reduction with borohydride. XRF analyses showed that the actual compositions of the materials were close to the nominal compositions. XRD measurements revealed that the materials were crystalline, with small peak displacements when Ni and Pd ions were reduced on carbon support, and suggested a segregated phase and not a Ni incorporation into the Pd lattice. HRTEM micrographs showed homogeneous particle distributions on the carbon, with a narrow particle size distribution and few agglomerations of nanoparticles. All the materials presented electrochemical activity for the oxidation of methanol, ethanol, and glycerol in KOH, and the oxidation current peak increased as a function of the Ni content in the catalyst.     

Enhancement of catalytic properties and durability in Ni–B–P/Ni foam for hydrazine electrooxidation

Hydrazine is a promising energy carrier of high power density, high theoretical cell voltage, and zero carbon emission to replace fossil fuel-dominated energy sources. Herein, we present a new Ni–B–P/NF catalyst for hydrazine electrooxidation by a facile electroless plating process. The Ni–B–P/NF catalyst exhibits remarkable catalytic activity (290 mA cm⁻² at 0.3 V) by combining merits of high intrinsic activity, large specific surface area, satisfactory conductivity, and lattice dislocation. Meanwhile, the Ni–B–P/NF catalyst provides excellent long-term durability (5000 s, 94.4%), which is at the leading level among the reported Ni-based electrocatalysts for hydrazine electrooxidation to date. It is found that the phosphorus-containing coating and its tight binding to the substrate contribute to the long-term durability of Ni–B–P/NF. XPS results and electron models are used to elucidate the electron transition mechanism of the Ni–B–P coating. This work presents a novel catalyst for hydrazine electrooxidation and demonstrates its promising application in energy storage and fuel cell systems.     

Optimization of the Pd–Sn–GNS nanocomposite for enhanced electrooxidation of methanol

Highly dispersed Pd nanoparticles with varying loadings (15–40 wt%) and (20 − x)%Pd–x%Sn (where x = 1, 2, 3 and 5) nanocomposites are obtained on graphene nanosheets (GNS) by a microwave-assisted ethylene glycol (EG) reduction method for methanol electrooxidation in alkaline solution. The electrocatalysts were characterized by XRD, SEM, TEM, cyclic voltammetry, and chronoamperometry. The study shows that the Pd nanoparticles on GNS are crystalline and follow the face centered cubic structure. Introduction of a small amount of Sn (1–5 wt%) shifts the characteristic diffraction peaks for Pd slightly to a lower angle. The electrocatalytic performance of the Pd/GNS electrodes has been observed to be the best with 20 wt% Pd loading; a higher or lower loading than 20 wt% Pd produces an electrode with relatively low catalytic activity. The apparent catalytic activity of this active electrode at E = −0.10 V is found to improve further by 79% and CO poisoning tolerance by 40% with introduction of 2 wt% Sn. Among the electrodes investigated, the 18%Pd–2%Sn/GNS exhibited the greatest electrocatalytic activity toward methanol electrooxidation.     

Synthesis and characterization of bimetallic Cu–Ni/ZrO2 nanocatalysts: H2 production by oxidative steam reforming of methanol

Cu/ZrO₂, Ni/ZrO₂ and bimetallic Cu–Ni/ZrO₂ catalysts were prepared by deposition–precipitation method to produce hydrogen by oxidative steam reforming of methanol (OSRM) reaction in the range of 250–360 °C. TPR analysis of the Cu–Ni/ZrO₂ catalyst showed that the presence of Cu facilitates the reduction of the Ni at lower temperatures. In addition, this sample showed two reduction peaks, the former peak was attributed to the reduction of the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich phase, and the second was assigned to the remaining Ni atoms forming bimetallic Ni-rich nanoparticles. Transmission Electron Microscopy revealed Cu or Ni nanoparticles on the monometallic samples, while bimetallic nanoparticles were identified on the Cu–Ni/ZrO₂ catalyst. On the other hand, Cu–Ni/ZrO₂ catalyst exhibited better catalytic activity than the monometallic samples. The difference between them was related to the Cu–Ni nanoparticles present on the former catalyst, as well as the bifunctional role of the bimetallic phase and the support that improve the catalytic activity. All the catalysts showed the same selectivity toward H₂ at the maximum reaction temperature and it was ∼60%. The high selectivity toward CO is associated to the presence of the bimetallic Ni-rich nanoparticles, as evidenced by TEM–EDX analysis, since this behavior is similar to the one showed by the monometallic Ni-catalyst.     

Comparison study of electrocatalytic activity of reduced graphene oxide supported Pt–Cu bimetallic or Pt nanoparticles for the electrooxidation of methanol and ethanol

Pt–Cu bimetallic nanoparticles supported on reduced graphene oxide (Pt–Cu/RGO) were synthesized through the simple one-step reduction of H₂PtCl₆ and CuSO₄ in the presence of graphene oxide (GO) at room-temperature. The Pt–Cu/RGO was characterized with UV–vis spectrophotometer, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy and its catalytic behavior for the direct oxidation of methanol was investigated. Compared to Pt/RGO and Pt/C catalysts, Pt–Cu/RGO hybrids exhibited markedly superior catalytic activity for the electrocatalytic oxidation of methanol and ethanol. This improved catalytic activity can be attributed to the dendritic structure of the Pt–Cu bimetallic nanoparticles.     

The effect of the absence of Ni,Co, and Ni–Co catalyst pretreatment on catalytic activity for hydrogen production via oxidative steam reforming of ethanol

This article presents a study of the catalytic performance of Ni, Co, and Ni–Co–Mg–Al mixed oxides obtained from hydrotalcite precursors for the oxidative steam reforming of ethanol (OSRE) when no pretreatment (pre-reduction) is accomplished. Two catalysts (a Ni-based monometallic and an equimolar Ni–Co-based catalyst) achieve in situ reduction over shorter time periods compared with the other bimetallic catalysts and also, exhibit the best catalytic activity. On the contrary, the monometallic Co catalyst did not exhibit good catalytic performance, likely because of the existence of resistant spinel phases to soft reduction processes and/or to the re-oxidation of Co. The equimolar presence of Ni and Co generates a synergistic effect evidenced by the increase in the reducibility, basicity, and mobility of electrophilic oxygen species of the solid. The results yield important information for better understanding the catalytic system under study.     

Synthesis and regeneration of mesoporous Ni–Cu/Al2O4 catalyst in sub-kilogram-scale for methanol steam reforming reaction

A green template-free method is proposed for the synthesis of mesoporous Ni–Cu/Al₂O₄ catalyst in sub-kilogram scale. In the convenient synthetic method, an intermediate is formed via electrostatic forces and hydrogen bonding interactions between the aluminate ions and the metal ions and/or metal hydroxides under suitable pH conditions. The desired Ni–Cu/Al₂O₄ composites, with Ni/Cu molar ratios of 10%, 20% and 30% of Cu at Cu/Al molar ratio of 10.0%, respectively, are then obtained from calcination. The nitrogen adsorption-desorption isotherms show that the Ni–Cu/Al₂O₄ composites have specific surface areas of 136–170 m²g^-1. The Ni–Cu/Al₂O₄ products are used as catalyst materials in the methanol steam reforming (MSR) of hydrogen and are shown to have a high conversion efficiency (>99%), a low methane concentration, good stability, and a high hydrogen yield (H₂/methanol molar ratio ≈ 3.0) at low reaction temperatures in the range of 200–300 °C. In addition, the coke formation on the catalyst surface is less than 1.0 wt% even after a reaction time of 30 h. Notably, the Ni–Cu/Al₂O₄ catalyst can be regenerated by calcination at 800 °C and retains a high methanol conversion efficiency of close to >99% when reused in MSR.     

Solvothermal synthesis of Pd10–Ni45–Co45/rGO composites as novel electrocatalysts for enhancement of the performance of DBFC

In this research, three Pd decorated Ni and Co catalyst nanoparticle were synthesized on reduced graphene oxide (rGO) supports are synthesized through a facile solvothermal procedure. Borohydride oxidation reaction (BOR) activity and performance of prepared electrocatalysts respect to NaBH₄ oxidation is evaluated by various electrochemical techniques in the three-electrode and the fuel cell configuration. Among the prepared catalysts, Pd₁₀–Ni₄₅–Co₄₅/rGO exhibits the highest BOR activity. The cyclic voltammograms showed that the measured current at 0.5 V for the electrode of Pd₁₀–Ni₄₅–Co₄₅/rGO is as much as 108 mA cm⁻² higher than Pd₁₀–Ni₉₀/rGO and 185 mA cm⁻² higher than Pd₁₀Co₉₀/rGO. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra were employed to study the morphology and crystal structure of the prepared catalyst. The results of DBFC test show that the Pd₁₀–Ni₄₅–Co₄₅/rGO nanoparticles as anodic catalyst, enhanced power density to 50.4 mW cm⁻² which is 10.5% and 45.2% higher than power density of DBFCs with Pd₁₀–Ni₉₀/rGO (45.6 mW cm⁻²) and Pd₁₀Co₉₀/rGO (34.7 mW cm⁻²) anode catalysts, respectively. These results indicate that the competency of operating procedure for assembling nickel alloys electrodes can improve the activity of the prepared catalysts for BOR considerably.     

Pd–Ni–Cu–P metallic glass nanowires for methanol and ethanol oxidation in alkaline media

We demonstrate that Pd₄₃Ni₁₀Cu₂₇P₂₀ bulk metallic glass (BMG) nanowires, prepared by a facile, scalable top-down nanomolding approach, can be used as high surface area electrocatalysts for alkaline alcohol fuel cell applications. These nanowires exhibit higher activity for methanol and ethanol oxidation in alkaline media compared to pure Pd, quantified by cyclic voltammetry. Furthermore, the Pd-BMG nanowire electrocatalyst has a 300 mV lower onset potential for CO oxidation suggesting improved poisoning resistance beyond pure Pd. The Pd-BMG electrocatalyst activation energies for methanol and ethanol oxidation of 22 and 17 kJ mol⁻¹ are lower than the pure Pd values of 38 and 30 kJ mol⁻¹, respectively. Unique properties of BMGs (homogeneity, viscosity, surface tension) facilitate the formability into high surface area electrocatalysts at low processing temperatures. The high electrical conductivity and chemical/physical stability suggest that these materials are ideal candidates for widespread commercial use including energy conversion/storage, hydrogen production, and sensors.     

Design,elaboration and characterization of a Ni–MH battery prototype

This paper shows advances achieved in the design and construction of a nickel–metal hydride (Ni–MH) battery prototype. The requirements of the design were to characterize the new variables appearing in a commercially assembled battery, such as limited physical space, electrical contact resistance, the behaviour of the system as a function of the gas evolution during fast charge and overcharge, and others. The electrochemical characterization was performed using laboratory equipment.     

Synthesis and characterization of high-density non-spherical Ni(OH)2 cathode material for Ni–MH batteries

Positive electrode active materials of non-spherical nickel hydroxide powders with a high tap-density for alkaline Ni–MH batteries have been successfully synthesized using a polyacrylamide (PAM) assisted two-step drying method. The tap-density of the powders reaches 2.32 g cm⁻³, which is significantly higher than that of nickel hydroxide powders obtained by the conventional co-precipitation method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG-DTA), Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge–discharge test were used to characterize the physical and electrochemical properties of the synthesized material. The results show that the as-prepared nickel hydroxide materials have an irregular tabular shape, a high density of structural disorder, and a high specific surface area. The charge–discharge tests indicate that nickel hydroxide powders synthesized by the new method have better electrochemical performance than those obtained by the conventional co-precipitation method. This performance improvement could be attributable to a more compact electrode microstructure, a lower amount of intercalated anions, better reaction reversibility, a higher proton diffusion coefficient, and lower electrochemical impedance, as indicated by TG-DTA, CV, and EIS. The results clearly show that better electrochemical activity can be achieved using nickel hydroxide that has a higher tap-density. Moreover, the new synthesis process is simple, cost-effective, and facile for large-scale production.     

Electrocatalytic activity for the hydrogen evolution of the electrodeposited Co–Ni–Mo,Co–Ni and Co–Mo alloy coatings

The electrocatalytic activity for the HER of the ternary Co–Ni–Mo and the binary Co–Ni and Co–Mo alloy coatings is investigated in 1 M KOH solution. The surface morphology and the structure of the studied coatings is characterized by SEM and XRD analysis. The electrocatalytic activity for the HER is evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, cathodic polarization and chronopotentiometry techniques. XRD analysis reveals that all studied coatings are composed of the Co hcp structure. However, alloy deposits with Mo is characterized by more nanocrystalline structure. Electrochemical experiments reveal superior electrocatalytic activity of coatings with Mo in comparison to Co–Ni alloy. This is the results of larger real surface area of Co–Mo and Co–Ni–Mo alloys, which is confirmed by the higher surface roughness factors (R_f) calculated based on the EIS results. The ternary alloy coating is characterized by the highest R_f parameter and the highest catalytic activity for the HER.     

Synthesis of a novel Co–B/CuNWs/CTAB catalyst via chemical reaction at room temperature for hydrolysis of ammonia-borane

Co–B has good catalytic activity in the hydrogenation reaction of unsaturated groups and has been widely studied and applied. Co–B catalysts were usually prepared by reducing cobalt salts with reducing agents. However, the high surface energy and magnetic properties of Co–B catalysts made the particles easily agglomerate. Then, agglomeration increased the particle size of the sample and reduced the effective surface area of the catalyst powder, which limited the catalytic activity of the Co–B catalysts. A new type of Co–B/copper nanowires/cetyl trimethyl ammonium bromide (Co–B/CuNWs/CTAB) catalyst with high catalytic activity was prepared by a chemical reduction in this work. The performance of Co–B/CuNWs/CTAB was studied in the hydrolysis of ammonia-borane (AB) and CuNWs inserted into the Co–B interlayer could avoid particle agglomeration, thereby effectively increasing the specific surface areas of the catalysts. Furthermore, the insertion of CuNWs facilitated the transportation of electrons and improved catalytic activity. The BET analysis shows that the maximum surface area of the sample is 148.9 m²/g. Meanwhile, the hydrogen generation rate of 13.46 L min^?1·g^?1 at 30 °C was obtained by using the synthesized Co–B/CuNWs/CTAB catalyst with a low activation energy of 8.771 kJ mol^?1.     

The preparation and catalytic behavior of a shell–core Ni/Mg–Al catalyst for ethanol steam reforming

The structural “memory effect” of a hydrotalcite (HT)-derived mixed oxide is utilized to prepare a shell–core Ni/Mg–Al catalyst for ethanol steam reforming (ESR). The reconstruction proceeds rapidly in a Ni²⁺ nitrate solution on the outer layer of the Mg–Al mixed oxide particle, being accompanied with the growth of large flake-like sheets. A part of Ni²⁺ ions can incorporate into the reconstructed HT-like structure, leading to the formation of the shell-type Ni loading catalyst after calcination. At 700 °C, the shell–core catalysts with much lower Ni contents perform better activities than that of the bulk Ni/Mg–Al catalyst prepared directly via the calcination of the HT-like precursor. Further investigations reveal that temperature and space-time significantly affect the contribution of WGS, CH₄ reforming reactions to the product distribution in the ESR reaction. Most interestingly, C₂H₄ is observed in the reactions carried out at 700 °C and very low space-time.     

Core-shell structured tungsten–tungsten carbide as a Pt catalyst support and its activity for methanol electrooxidation

Tungsten carbide was synthesized by calcination of carbon cryogel containing tungsten in a form of metatungstate. Characterization by X-ray diffraction and transmission electron microscopy indicated core-shell structure of the particles with tungsten core and tungsten carbide shell, attached to graphitized carbon. Pt nanoparticles were deposited on this material and most of them were nucleated on tungsten carbide. Cyclic voltammetry of W-C support and Pt/W-C catalyst indicated hydrogen intercalation in surface hydrous tungsten oxide. Oxidation of CO_ads on Pt/W-C commences earlier than on Pt/C for about 100 mV. The onset potentials of MOR on Pt/W-C and Pt/C are the same, but at more positive potentials Pt/W-C catalyst is more active. It was proposed that promotion of MOR is based on bifunctional mechanism that facilitates CO_ads removal. Stability test was performed by potential cycling of Pt/W-C and Pt/C in the supporting electrolyte and in the presence of methanol. Pt surface area loss observed in the supporting electrolyte of both catalysts after 250 cycles was about 20%. Decrease in the activity for methanol oxidation was 30% for Pt/W-C, but even 48% for Pt/C. The difference was explained by the presence of hydrous tungsten oxide on Pt in Pt/W-C catalyst, which reduces accumulation of poisoning CO_ads.     

Catalytic performance of Ni–Al nanoparticles fabricated by arc plasma evaporation for methanol decomposition

The catalytic properties of Ni-25 at% Al (Ni25Al) nanoparticles fabricated by arc plasma evaporation toward methanol decomposition were studied at temperatures ranging from 513 to 753 K. The Ni25Al nanoparticles showed much higher activity than gas atomized Ni25Al powders. They showed a high degree of selectivity for methanol decomposition into H₂ and CO. Side reactions such as methanation and water-gas shift reaction were suppressed to a high temperature of 673 K, which is hardly achieved for common Ni catalysts. Detailed characterization of the Ni25Al nanoparticles showed that they were composed of Ni, Ni₃Al, and Al₂O₃ phases with Ni and Al oxides on the surface of the Ni and Ni₃Al phases. The Ni oxides were reduced to Ni phase by a hydrogen reduction prior to methanol decomposition, while the Al oxides remained unchanged. It is supposed that the Ni phase provided the active sites for methanol decomposition, and the Ni₃Al and Al₂O₃ phases acted as supports for the Ni phase. Probably the Ni₃Al and Al₂O₃ phases provided good resistance to agglomeration of the Ni phase during the reaction, which might contribute to maintain the high catalytic performance of the nanoparticles for methanol decomposition.