Ni-rich Surface Research Articles

Coupling phyllosilicate and NiCo alloy nanoparticles on sepiolite to enhance stability for hydrogen production by ethanol steam reforming

For hydrogen production from ethanol steam reforming (ESR), The NiCo alloy immobilized on sepiolite (SEP) support by a phyllosilicate precursor was deemed as an effective strategy to improved catalyst stability. The Ni/Co ratio was regulated to optimized the ESR reactivity of the bi-metallic catalysts prepared by the NH4F assisted urea hydrothermal method. The synergy effect of NiCo alloy with a Ni-rich surface on ESR reactivity and anti-deactivation was investigated. The 5Ni10Co/SEP catalyst presented the highest conversion (99.4 %) and H2 yield (68.2 %) at 700 °C, which was benefited from the downsized nanoparticle size and strong metal-support interaction. The proposal structure-activity relationship suggested that the NiCo alloy was exsolved from the phyllosilicate precursor grafted on SEP framework, providing an excellent mitigation for metal sintering. In addition, the synergy of NiCo alloy was elaborated by a combination of enhanced ethanol adsorption/dissociation on Ni sites and restrained methanation on Co sites, offering a 50 h catalyst stability during ESR consisting of the ethanol dehydration route. The developed NiCo alloy catalyst based on SEP support with phyllosilicate precursor provided a prospect on the application to H2 production from ESR over the bimetallic catalysts with simple preparation, high economy and structure stability.

Efficient solvent-free hydrodeoxygenation of bio-lipids over bifunctional NiW catalyst: Manipulations of surface-active sites by thermal pretreatment

The effect of thermal pretreatment on the bifunctional NiW catalyst and its hydrodeoxygenation (HDO) performance on oleic acid were investigated. Increasing the calcination temperature (CT) not only led to the growth of NiW particles, but caused the migration of Ni to the surface that resulted in the segregation of W. The reduction temperature (RT) was also able to tune the catalyst surface composition. A lower RT (600 °C) led to a W-rich surface, while a higher one (700 °C) interestingly resulted in a Ni-rich surface. To this end, the ratio of surface-active sites, i.e., the partially reduced W species (Wδ+) to Ni0 ones (Wδ+/Ni0), was manipulated. The highest Wδ+/Ni0 ratio of 2.6 was reached at the CT and RT of 550 °C and 700 °C, respectively, which contributed to an impressively high solvent-free deoxygenation of 95.1% at only 300 °C. The deoxygenation rate (rdeoxy.) was much higher than that of the reported non-precious catalysts, even comparable to the precious ones. Additionally, a high catalyst durability was found on non-acid feedstocks like triglycerides, long-chain alcohols, etc., but an acidic substrate like oleic acid tended to leach the loaded metals that eventually lessened the HDO activity.

The growth mechanism of diffused multilayer between electroplated nickel coating and nickel-aluminum bronze alloy

• 1. The calculated results of Fick’s second law prove the relationship: D Ni > D Cu > D Al . • 2. The larger D Ni and D Cu than D Al cause the preferential formation of Ni-Cu layer. • 3. The physicochemical approach is used to explain the ternary interdiffusion process. • 4. The formation of Ni-Al-Cu layer is at the expense of the depletion of Ni-Cu layer. The Ni-rich surface alloying modification has been implemented to enhance the corrosion resistance of nickel-aluminum bronze (NAB) alloy used in the marine environment, while the growth behavior of the Ni-rich diffused multilayer is still unclear. Herein, the theoretical analysis and morphological observation were applied to disclose the growth mechanism of the diffused multilayer, the results manifested that the diffusion coefficients of Ni and Cu were higher than that of Al, leading to the preferential interdiffusion process of Ni and Cu to generate the Ni-Cu solid solution gradient layer at the interface of the diffusion couple. With extending the heat treatment time, the Al diffused into the Ni-Cu layer to form the Ni-Al-Cu intermetallic layer between the Ni-Cu layer and NAB matrix, and the formation of Ni-Al-Cu layer was at the expense of the depletion of Ni-Cu layer.

Role of Graphene on Ni/NiO for the Hydrogen Evolution Reaction

The hydrogen evolution reaction (HER) in alkaline electrolytes is an effective and environmentally friendly strategy for producing H2; however, challenges relating to catalyst efficiency and longevity remain. Herein, density functional theory (DFT) is used to help explain why a protective graphitic layer on Ni0/NiOx nanoparticles helps prevent surface oxidation at ambient and anodic conditions and reduction (NiOx → Ni0) at the cathodic potential. We find that the work of adhesion of the graphitic layer to nickel-terminated surfaces is 2–3 times stronger than that to oxygen- or hydroxylated-terminated surfaces. Furthermore, we determined the additional energy required to remove a surface group/atom (O, OH and Ni) when protected by a graphitic layer. Our findings lead us to conclude that the graphitic layer will limit oxidation, help minimize the reduction of NiOx and favor the formation of Ni-rich surfaces. These findings provide a plausible explanation of how an ideal Ni0/NiOx ratio is maintained during HER, which is crucial for enhanced device performance and stability.

Mechanistic insights into hydrogen evolution reaction on Ni2B(001) facet using first-principle calculations

In this paper, first-principle calculations based on density functional theory (DFT) were used to investigate the performance and mechanism of the hydrogen evolution reaction (HER) on the typical active (001) facet of the novel electrocatalyst Ni2B. There were two types of atomic distribution on the Ni2B (001) surface, namely the B-rich surface and the Ni-rich surface. The investigation of the reaction mechanism revealed that the Volmer-Heyrovsky mechanism was easier to be realized on this Ni2B (001) facet, and the Heyrovsky reaction was the reaction rate-determining step. The Gibbs free energy(ΔGH) on the B-rich surface was - 0.02 eV, which was closer to 0 eV than that on the Ni-rich surface of Ni2B (001). The HER reactivity on the Ni-rich surface was increased by Cr-doping (ΔGH = - 0.01 eV), which indicated that the introduction of other transition metal atoms might effectively increase the HER electrocatalysis activity of Ni2B (001) surface. This work paves a new avenue for exploring efficient and durable non-precious metal electrocatalysts for HER in acidic medium.

Facet and d-band center engineering of CuNi nanocrystals for efficient nitrate electroreduction to ammonia.

Electrocatalytic nitrate reduction offers a sustainable route to ammonia synthesis and wastewater treatment. However, the nitrate-to-ammonia conversion remains inefficient due to the sluggish kinetics and diverse side reactions. Herein, well-faceted CuNi nanocrystals with Ni-rich surfaces and favorable d-band centres were synthesized with the assistance of γ-cyclodextrin via a solvothermal process. When used as catalysts for nitrate electroreduction, they delivered an ammonia yield of 1.374 mmol h-1 mg-1 (0.5496 mmol h-1 cm-2) at -0.3 V with the faradaic efficiency and selectivity reaching 94.5% and 65.0%, respectively, surpassing pure Cu or Ni nanocrystals and most reported catalysts. Such excellent performances originated from the optimal geometric and electronic structures and special element distribution, which optimized the adsorption behaviors and accelerated the reaction kinetics. A NO3--NO2--NH3 pathway was proposed with the chemical process following the initial electron transfer process as the rate-determining step. This work sheds light on the design of efficient catalysts to achieve carbon neutrality through simultaneous geometric and electronic structure modulation.

Electrochemical preparation of porous ZnCuNi by electrodeposition in ethaline deep eutectic solvent followed by anodic or cathodic dealloying in alkaline aqueous solutions for higher nitrate reduction activity

Abstract Electrodeposition of zinc-rich ternary ZnCuNi alloys were potentiostatically studied from an Ethaline deep eutectic solvent (DES) (having a molar ratio of 1:2 choline chloride-ethylene glycol) containing ZnCl2, CuCl2 and NiCl2. Voltammetry was conducted to understand the cathodic deposition and anodic stripping occurred in this system as a function of potential before the deposition of the ternary alloys. Selective anodic dissolution of Zn from the as-deposited alloys in a NaOH aqueous solution produced porous structures; however, Cu was also dissolved from the alloys if the alloys are overoxidized. Alternatively, porous structures were also produced via cathodic dealloying of the Zn when the as-deposited alloy was subjected to the electroreduction of NaNO3. When used as electrode, both kinds of porous structure showed enhanced activities towards nitrate reduction. Because the cathodic dealloying did not consume Cu, the electrodes produced by cathodic dealloying exhibited activity and stability superior to the electrodes produced by anodic dealloying. More importantly, because the dealloying process and electrode activation could be simultaneously achieved in one step during the cathodic electrolysis of nitrate, the term “self-enhancing electrode formed by in-situ cathodic dealloying” was used in this study. The XPS analysis indicated that Ni-rich surfaces of ZnCuNi electrodes were produced with the anodic dealloying in contrast to the Cu-rich surfaces produced with the cathodic dealloying. This study demonstrates a facile approach to control the electrode surface compositions in dealloying zinc alloys. Although the application of the porous electrodes prepared in this study was tested for electroreduction of nitrate, this approach can be extended to the electrocatalysis of other systems.

Influence of Pd and Au on electrochemical valorization of glycerol over Ni-rich surfaces

Herein we synthesized bi-metallic Pd@Ni and Au@Ni core-shell-like nanoparticles (NPs) for glycerol electrooxidation reaction (GEOR) in alkaline media. The morphological, structural and surface properties of the NPs were evaluated using a range of physicochemical techniques. The catalytic activity and stability were studied using the three-electrode electrochemical cell and 25 cm2- continuous electrolysis cell. Among different atomic ratios, Ni80Pd20 and Ni90Au10 nanoparticles showed the highest current densities which are ~4.5 and 4.2 times higher than spherical Ni, respectively. The addition of Pd and Au (<20 at.%) to Ni nanoparticles led to a remarkable glycerate selectivity of ~73.1% and 65.7% for Ni80Pd20 and Ni90Au10 catalysts at 1.3 V and 50 °C, respectively. Notably, after 6 h of electrolysis Pd@Ni and Au@Ni tend to suppress the C-C bond cleavage, compared to Ni at any applied potentials and temperatures. The DFT calculations predicted that the addition of Pd or Au to Ni reduces the work function of M@Ni NPs, which strengthens the OH adsorption and enhances the removal of GEOR intermediates.

Controlled contribution of Ni and Cr cations to stainless steel 304 electrode: Effect of electrochemical oxidation on electrocatalytic properties

The surface composition of a stainless steel 304 electrode, composed of Fe, Ni, and Cr, was adjusted through electrochemical oxidation under harsh anodizing conditions. As the electrochemical oxidation progressed, the Ni and Cr atoms in the Fe medium moved via the synergetic effect of electromigration and drag force, creating a Ni-rich surface on the electrodes with fast kinetics for the hydrogen evolution reaction. This study investigated the optimal duration of electrochemical oxidation affecting the cation contribution of Cr, which forms a passivation layer with high charge transfer resistance on the electrode. Electrochemical oxidation for 60 min induced a significant enhancement in the electrochemical catalytic activity as the cation contribution of Cr decreased.

The one-pot synthesis of CuNi nanoparticles with a Ni-rich surface for the electrocatalytic methanol oxidation reaction.

The use of fuel cells is one of the most promising renewable energy strategies, but they still suffer from many limitations. The high mass enthalpy of hydrogen as a fuel comes at the cost of inconveniences and risks associated with storage, transportation and utilization, while the high performance of Pt catalysts in commercial fuel cells is limited by their high cost, low earth abundance, and poor stability as a result of CO intermediate poisoning. To circumvent these dilemmas, direct methanol fuel cells (DMFCs) were developed, using methanol as a fuel and Ni as the anode catalyst. Thanks to the condensed form of the fuel, DMFCs are considered as the most promising fuel-cell solution for portable electronic devices. Usually, other elements have to be introduced into Ni-based catalysts to modify the active sites to provide better alternatives to pristine Ni metal in terms of activity and stability. In this study, we provide a mild synthetic method for the preparation of CuNi alloy nanoparticles. The proper alloying ratio leads to the suitable modification of the electronic structure of Ni, which promotes the MOR catalytic reaction on the NiCu alloy. The NiCu alloy catalyst exhibits a mass current density of 1028 mA mgmetal-1 for the MOR at 1.55 V (vs. RHE), which is among the best values obtained from similarly prepared Ni-based catalysts.

Facile one-pot synthesis of hollow NiCoP nanospheres via thermal decomposition technique and its free-standing carbon composite for supercapacitor application

Development of electrode materials with faster charge kinetics and high electrical conductivity are a major challenge to achieve high-performance supercapacitor. In this work, a novel bimetallic nickel cobalt phosphide hollow nanospheres of different Ni/Co molar ratios were synthesized via one-pot thermal decomposition method. Uniform presence of both Ni and Co species was confirmed by energy dispersive spectroscopy (EDS). In particular, a sample with the Ni: Co molar ratio of 1:9 exhibits the most optimized performance, i.e., high specific capacitance of 160 Fg−1 at 0.8 Ag−1, which might be attributed to the strong synergistic effect between Ni and Co species and rich surface electroactive sites in the sample. Besides, the sample also showed low charge transfer resistance (Rct), which in turn gives high electrical conductivity in comparison with other nickel cobalt phosphide (NiCoP) samples. The hollow nanospheres were incorporated into carbon nanofibers to form a free-standing carbon composite that exhibits excellent capacitance retention of 88.5% even after 5000 charge/discharge cycles. The strategy outlined here presents a facile synthesis technique of nickel-cobalt phosphide hollow nanostructures, a promising electrode material which can be explored for a wide variety of electrochemical energy storage applications.

Dynamic Structure Evolution of Composition Segregated Iridium-Nickel Rhombic Dodecahedra toward Efficient Oxygen Evolution Electrocatalysis.

The anodic oxygen evolution reaction (OER) is central to various energy conversion devices, but the investigation of the dynamic evolution of catalysts in different OER conditions remains quite limited, which is unfavorable for the understanding of the actual structure-activity relationship and catalyst optimization. Herein, we constructed monodispersed IrNi x nanoparticles (NPs) with distinct composition-segregated features and captured their structural evolution in various OER environments. We decoded the interesting self-reconstruction of IrNi x NPs during the OER, in which an Ir-skin framework is generated in an acidic electrolyte, while a Ni-rich surface layer is observed in an alkaline electrolyte owing to Ni migration. Benefiting from such self-reconstruction, considerable OER enhancements are achieved under both acidic and alkaline conditions. For comparison, IrNi x nanoframes with Ir skins prepared by chemical etching show a similar structural evolution result in the acidic electrolyte, but a total different phenomenon in the alkaline electrolyte. By tracking the structural evolution of IrNi x catalysts and correlating them with OER activity trajectories, the present work provides a significant understanding for designing efficient OER catalysts with controlled compositional distributions.

Performance Improvement of V-Fe-Cr-Ti Solid State Hydrogen Storage Materials in Impure Hydrogen Gas.

Two approaches of engineering surface structures of V-Ti-based solid solution hydrogen storage alloys are presented, which enable improved tolerance toward gaseous oxygen (O2) impurities in hydrogen (H2) gas. Surface modification is achieved through engineering lanthanum (La)- or nickel (Ni)-rich surface layers with enhanced cyclic stability in an H2/O2 mixture. The formation of a Ni-rich surface layer does not improve the cycling stability in H2/O2 mixtures. Mischmetal (Mm, a mixture of La and Ce) agglomerates are observed within the bulk and surface of the alloy when small amounts of this material are added during arc melting synthesis. These agglomerates provide hydrogen-transparent diffusion pathways into the bulk of the V-Ti-Cr-Fe hydrogen storage alloy when the remaining oxidized surface is already nontransparent for hydrogen. Thus, the cycling stability of the alloy is improved in an O2-containing hydrogen environment as compared to the same alloy without addition of Mm. The obtained surface-engineered storage material still absorbs hydrogen after 20 cycles in a hydrogen-oxygen mixture, while the original material is already deactivated after 4 cycles.

Tuning the Electrocatalytic Oxygen Reduction Reaction Activity and Stability of Shape-Controlled Pt-Ni Nanoparticles by Thermal Annealing - Elucidating the Surface Atomic Structural and Compositional Changes.

Shape-controlled octahedral Pt-Ni alloy nanoparticles exhibit remarkably high activities for the electroreduction of molecular oxygen (oxygen reduction reaction, ORR), which makes them fuel-cell cathode catalysts with exceptional potential. To unfold their full and optimized catalytic activity and stability, however, the nano-octahedra require post-synthesis thermal treatments, which alter the surface atomic structure and composition of the crystal facets. Here, we address and strive to elucidate the underlying surface chemical processes using a combination of ex situ analytical techniques with in situ transmission electron microscopy (TEM), in situ X-ray diffraction (XRD), and in situ electrochemical Fourier transformed infrared (FTIR) experiments. We present a robust fundamental correlation between annealing temperature and catalytic activity, where a ∼25 times higher ORR activity than for commercial Pt/C (2.7 A mgPt-1 at 0.9 VRHE) was reproducibly observed upon annealing at 300 °C. The electrochemical stability, however, peaked out at the most severe heat treatments at 500 °C. Aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (EDX) in combination with in situ electrochemical CO stripping/FTIR data revealed subtle, but important, differences in the formation and chemical nature of Pt-rich and Ni-rich surface domains in the octahedral (111) facets. Estimating trends in surface chemisorption energies from in situ electrochemical CO/FTIR investigations suggested that balanced annealing generates an optimal degree of Pt surface enrichment, while the others exhibited mostly Ni-rich facets. The insights from our study are quite generally valid and aid in developing suitable post-synthesis thermal treatments for other alloy nanocatalysts as well.

Surface composition changes of CuNi-ZrO2 during methane decomposition: An operando NAP-XPS and density functional study

Bimetallic CuNi nanoparticles of various nominal compositions (1:3, 1:1, 3:1) supported on ZrO2 were employed for operando spectroscopy and theoretical studies of stable surface compositions under reaction conditions of catalytic methane decomposition up to 500°C. The addition of Cu was intended to increase the coke resistance of the catalyst. After synthesis and (in situ) reduction the CuNi nanoparticles were characterized by HR-TEM/EDX, XRD, FTIR (using CO as probe molecule) and NAP-XPS, all indicating a Cu rich surface, even when the overall nanoparticle composition was rich in Ni. Density functional (DF) theory modelling, applying a recently developed computational protocol based on the construction of topological energy expressions, confirmed that in any studied composition Cu segregation on surface positions is an energetically favourable process, with Cu preferentially occupying corner and edge sites. Ni is present on terraces only when not enough Cu atoms are available to occupy all surface sites.When the catalysts were applied for methane decomposition they were inactive at low temperature but became active above 425°C. Synchrotron-based operando NAP-XPS indicated segregation of Ni on the nanoparticle surface when reactivity set in for CuNi-ZrO2. Under these conditions C 1s core level spectra revealed the presence of various carbonaceous species at the surface. DF calculations indicated that both the increase in temperature and especially the adsorption of CHx groups (x=0-3) induce the segregation of Ni atoms on the surface, with CH3 providing the lowest and C the highest driving force.Combined operando and theoretical studies clearly indicate that, independent of the initial surface composition after synthesis and reduction, the CuNi-ZrO2 catalyst adopts a specific Ni rich surface under reaction conditions. Based on these findings we provide an explanation why Cu rich bimetallic systems show improved coke resistance.

In situ development of highly concave and composition-confined PtNi octahedra with high oxygen reduction reaction activity and durability

Controlled syntheses of PtNi metal nanocrystals with unique structures for catalyzing oxygen reduction reactions (ORRs) have attracted great interest. Here, we report the one-step synthesis of single-crystal PtNi octahedra with in situ-developed highly concave features and self-confined composition that are optimal for ORR. Detailed studies revealed that the Pt-rich seeding, subsequent Pt/Ni co-reduction, and Pt–Ni interfusion resulted in uniform single-crystal PtNi octahedra, and that the combination of Ni facet segregation and oxygen etching of a Ni-rich surface led to the concavity and confined Ni content. The concave PtNi nanocrystals exhibited much higher ORR performance than the commercially available Pt/C catalyst in terms of both specific activity (29.1 times higher) and mass activity (12.9 times higher) at 0.9 V (vs. reversible hydrogen electrode (RHE)). The performance was also higher than that of PtNi octahedra without concavity, confirming that the higher activity was closely related to its morphology. Moreover, the concave octahedra also exhibited remarkable stability in ORR (93% mass activity remained after 10,000 cycles between 0.6 and 1.1 V vs. RHE) owing to the passivation of the unstable sites.

Tuning Pt-skin to Ni-rich surface of Pt3Ni catalysts supported on porous carbon for enhanced oxygen reduction reaction and formic electro-oxidation

Controlling surface composition of bimetallic catalysts is of significance in energy conversion and storage. Here, we controlled thermal treatment to synthesize different surface composition of bimetallic catalysts with average diameter <4nm. We report the synthesis of Pt3Ni catalyst with Pt-skin surface directly supported on porous graphitic carbon (PC), which showed over 300% increase in mass activity compared with Pt/C for the oxygen reduction reaction (ORR). The high activity and stability are attributed to the Pt-skin structure and the morphology of PC. When we tuned the surface composition to Ni-rich, it showed 300% increase in mass activity when compared with Pt/C towards oxidizing of HCOOH. Our approach to control surface composition can be used to design nanocatalysts for different reaction and are simple, effective and promotional to be industrialized.

The origin of the gold and uranium ores of the Black Reef Formation, Transvaal Supergroup, South Africa

The Black Reef Formation is a laterally extensive sedimentary succession at the base of the Transvaal Supergroup. The quartz-pebble conglomerates host erratic concentrations of gold and uranium; however, in areas that are located spatially above the gold and uranium-bearing reefs of the Witwatersrand Supergroup, the concentrations can reach ore-grade. Although the depositional environment was similar to that of the Witwatersrand Supergroup, the processes that lead to the high gold and uranium concentrations in the Black Reef were quite different. The Black Reef experienced intense, post-depositional hydrothermal alteration by circulating aqueous and hydrocarbon fluids (oils) that deposited large volumes of native gold, uranium minerals and pyrobitumen. The gold, which is filamentous, is concentrated along As–Ni-rich surfaces of pyrite, and with uraninite in pyrobitumen. In both environments, the gold is interpreted to be the product of chemically-triggered precipitation from hydrothermal fluid(s). The uraninite occurs either as precipitates in pyrobitumen or is “invisible” in the pyrite, occurring as nanoparticles in this mineral. This indicates that conditions were sufficiently oxidizing for the hydrothermal transport of uranium, and contrasts with the case for the Witwatersrand reefs where much of the uranium is detrital. Luminescent radiation damage associated with vein quartz and pyrobitumen, as well as the diffuse distribution pattern of uranium in the pyrobitumen may indicate that some uranium was transported by liquid hydrocarbons. Pyrite in the Black Reef (sedimentary, detrital and hydrothermal pyrite) is highly enriched in gold, uranium and other redox-sensitive trace elements. Provenance analyses using the trace element compositions of the pyrite show that it was not the result of erosional reworking of the underlying Witwatersrand Reefs. However, the close spatial association of high gold and uranium concentrations in the Black Reef with ore-bearing Witwatersrand reefs suggests strongly that gold and uranium, whether in pyrite or occurring as native gold and uraninite, were hydrothermally recycled (uranium may have been recycled by hydrocarbon fluids) from the Witwatersrand Reefs.

Fischer–Tropsch synthesis over alumina supported bimetallic Co–Ni catalyst: Effect of impregnation sequence and solution

The effect of Ni substitution on the Fischer–Tropsch (FT) synthesis activity and selectivity of alumina supported cobalt (Co/Al2O3) catalyst was investigated with a continuous stirred tank reactor at 230°C and 1MPa. Bimetallic Co–Ni/Al2O3 catalysts were prepared by an impregnation method. Total amount of supported metal was fixed at 20wt%. Influence of the Co/Ni ratio, impregnation sequences and solutions on the structure and activity of Co–Ni/Al2O3 catalyst was systematically studied. Low Ni-loading slightly increased CO conversion rate at nearly constant C5+ selectivity, but excess Ni-loading largely decreased CO conversion rate and C5+ selectivity. The catalytic activity did not depend on impregnation sequence, when Ni-loading amount was low. However, when Co was substituted with large amount of Ni, catalysts prepared by sequential impregnation method (Ni first and then Co) showed higher activity than those prepared by co-impregnation method and reverse sequential impregnation method (Co first and then Ni). These results indicate that catalysts with a Co-rich surface would be better than those with a Ni-rich surface. Impregnation solution also influenced the catalytic activity. Co–Ni/Al2O3 catalysts prepared by co-impregnation method using aqueous NH3 solution (Co+Ni/Al2O3-A) showed higher activity than those prepared using pure water or aqueous HNO3 solution. The best catalyst was Co(19wt%)+Ni(1wt%)/Al2O3-A, which exhibited 1.6 times as high activity as Co(20wt%)/Al2O3 catalyst prepared by a conventional impregnation method. The variation of catalytic activity with the kind of impregnation solution would be attributed to the differences in CO adsorption amount and/or electron density of surface Co metal sites.

Fabrication and evaluation of nickel cobalt alloy electrocatalysts for alkaline water splitting

Abstract As a catalyst for the hydrogen evolution reaction (HER) in alkaline water splitting, NiCo alloys of various compositions were prepared through electrodeposition onto Cu substrates. The composition of each alloy catalyst was varied by controlling the molar ratio of Co 2+ ions in the electrolyte. With an increase in the Co content, the morphologies of the NiCo alloys were progressively changed from a round to polygonal shape. The NiCo alloys all exhibited a Ni rich surface, as confirmed by the bulk-to-surface compositional ratio and degree of alloying. The catalytic activities of the NiCo alloys toward the HER of water splitting were electrochemically tested in a KOH electrolyte, and the specific activities were characterized by considering the electrochemical surface areas of Ni and Co. The effect of alloying was demonstrated to be a significant enhancement of HER activity, resulting from a change in the electronic structures of Ni and Co.