Morphology, structure and magnetic properties of cobalt–nickel films obtained from acidic electrolytes containing glycine

Co-deposition of Co-Ni alloy catalysts from an ethylene glycol system for the hydrogen evolution reaction

The preparation of active, stable and low-cost non-noble electrocatalysts for the hydrogen evolution reaction (HER) using the electrochemical water splitting process is crucial for the promotion of sustainable energy. In this study, Co-Ni alloys with various Co contents are prepared using a galvanostatic method and the co-deposition behavior of Co2+ and Ni2+ in ethylene glycol (EG) is reported. These results indicate that the presence of additional Ni2+ species can accelerate the Co-Ni co-deposition process and Co2+ species in the system can inhibit the reduction of Ni2+. Moreover, the two effects are improved with an increase in Ni2+ or Co2+ species concentration in the EG system, respectively. Chronoamperometry records show that the Co-Ni electro-crystallization mechanism is one of 3D instantaneous nucleation and growth. Moreover, the Co-Ni alloy with 59.46 wt% Co exhibits high electrocatalytic activity for HER with an overpotential of 133 mV at 10 mA cm-2 in 1 M KOH due to a high value of electrochemical active surface area (ECSA) (955.0 cm2). Therefore, the Co-Ni alloy electrocatalyst obtained from the EG system could be a promising candidate for practical hydrogen production.

Improvement in Cobalt Phosphate Electrocatalyst Activity toward Oxygen Evolution from Water by Glycine Molecule Addition and Functional Details

Electrochemical water splitting using renewable energy shows promise for the development of sustainable hydrogen production methods. The process requires a highly active electrocatalyst for oxygen evolution to improve the overall water splitting efficiency. The present study showed that oxygen evolution improved dramatically upon the addition of glycine to cobalt phosphate, when the glycine was added to the electrolyte solution during electrodeposition. The functionality of the organic molecules was investigated using in situ UV-vis absorption, in situ X-ray absorption fine structure, and in situ infrared (IR) absorption spectroscopy in the attenuated total reflection mode. The results demonstrated that the glycine molecules assembled cobalt oxide clusters composed of CoO₆ (CoOOH) octahedrons a few nanometers in diameter upon the electrodeposition of cobalt catalysts. This suggests that the cobalt-glycine catalyst can decompose water to oxygen gas efficiently, because the number of cobalt oxide clusters increased as active reaction sites upon the addition of glycine molecules.

Glycine-Induced Electrodeposition of Nanostructured Cobalt Hydroxide: A Bifunctional Catalyst for Overall Water Splitting

Herein, an interconnected α-Co(OH)₂ structure with a network-like architecture was used as a bifunctional electrocatalyst for the overall water splitting reaction in alkaline medium. The complexing ability of glycine with a transition metal was exploited to form [Co(gly)₃ ]^- dispersion at pH 10, which was used for the electrodeposition. High-resolution TEM, UV/Vis-diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy were used to confirm that the as-synthesized materials had an α-Co(OH)₂ phase. The electrocatalytic oxygen and hydrogen evolution activity of the glycine-coordinated α-Co(OH)₂ was found to be approximately 320 and 145 mV, respectively, at 10 mA cm^-2 . The material required approximately 1.60 V (vs. reversible hydrogen electrode; RHE) to achieve the benchmark of 10 mA cm^-2 for overall water splitting with a mass activity of approximately 63.7 A g^-1 at 1.60 V (vs. RHE). The chronoamperometric response was measured to evidence the stability of the material for overall water splitting for up to 24 h. Characterization of the catalyst after the oxygen and hydrogen evolution reactions was performed by XPS and showed the presence of a Co^II /Co^III oxidation state.

'Green' Cr(iii)-glycine electrolyte for the production of FeCrNi coatings: electrodeposition mechanisms and role of by-products in terms of coating composition and microstructure

The electrodeposition of stainless steel-like FeCrNi alloys for miniaturised devices is appealing as it would allow combining excellent material properties (e.g. corrosion resistance, hardness, biocompatibility) at low-cost. However, conventional baths often contain hazardous hexavalent chromium. Cr-based alloys electrodeposited from environmentally friendly trivalent chromium electrolytes are crucial for industrial application for facilitating the transition towards sustainable and ecological production and processing. Nevertheless, this process has not been comprehensively studied or understood in depth: especially the role of organic agents (common additives for improving Cr(iii)-based plating; e.g. glycine) in terms of material properties of the electrodeposits. The aim of this work was to investigate the electrodeposition of FeCrNi coatings from a ‘green’ Cr(iii)–glycine electrolyte. Novel information was attained by analysing films developed under various conditions and characterising them using a combination of advanced techniques. The evolution of microstructure (from amorphous to nanocrystalline) in correlation with film composition (i.e. metals ratio and presence of impurities) and elemental 3D spatial distribution was achieved for coatings produced from different anode materials and thermal post-treatment. The influence of Cr(iii) and glycine in terms of coating atomic contents (i.e. Fe–Cr–Ni–O–C–N–H) was evaluated for films in which both the applied current density and electrolyte composition were varied. These results, together with a thorough analysis on metals speciation/complexation allowed us to propose various Cr(iii)-based electroreduction mechanisms, and to observe, upon annealing, segregation and distribution of impurities, as well as of oxides and metals with respect to microstructure variation, providing an explanation for the amorphisation process.

Electrodeposition mechanisms of a ‘green’ FeCrNi Cr(iii)–glycine electrolyte and their correlation with coatings' composition (metals/impurities), microstructure and elemental distribution variations.

Formation of uniform magnetic C@CoNi alloy hollow hybrid composites with excellent performance for catalysis and protein adsorption

C@CoNi hollow composites are fabricated via an extended Stöber method, mussel chemistry and subsequent carbonization treatment, which can be used as a catalyst for the reduction of 4-nitrophenol and histidine-rich protein separation.

High-Throughput Structural and Functional Characterization of the Thin Film Materials System Ni-Co-Al

High-throughput methods were used to investigate a Ni-Co-Al thin film materials library, which is of interest for structural and functional applications (superalloys, shape memory alloys). X-ray diffraction (XRD) measurements were performed to identify the phase regions of the Ni-Co-Al system in its state after annealing at 600 °C. Optical, electrical, and magneto-optical measurements were performed to map functional properties and confirm XRD results. All results and literature data were used to propose a ternary thin film phase diagram of the Ni-Co-Al thin film system.

Magnetometry of Individual Polycrystalline Ferromagnetic Nanowires

Ferromagnetic nanowires are finding use as untethered sensors and actuators for probing micro- and nanoscale biophysical phenomena, such as for localized sensing and application of forces and torques on biological samples, for tissue heating through magnetic hyperthermia, and for microrheology. Quantifying the magnetic properties of individual isolated nanowires is crucial for such applications. Dynamic cantilever magnetometry is used to measure the magnetic properties of individual sub-500 nm diameter polycrystalline nanowires of Ni and Ni₈₀ Co₂₀ fabricated by template-assisted electrochemical deposition. The values are compared with bulk, ensemble measurements when the nanowires are still embedded within their growth matrix. It is found that single-particle and ensemble measurements of nanowires yield significantly different results that reflect inter-nanowire interactions and chemical modifications of the sample during the release process from the growth matrix. The results highlight the importance of performing single-particle characterization for objects that will be used as individual magnetic nanoactuators or nanosensors in biomedical applications.

Insights into size-dominant magnetic microwave absorption properties of CoNi microflowers via off-axis electron holography

In this study, CoNi flower-like hierarchical microstructures with different sizes were obtained via a one-step solvothermal method by simply adjusting the concentration of precursors and surfactant. The obtained CoNi microflowers possess uniform and tunable size, good monodispersity, and remarkable magnetic microwave absorption properties as well as electron holography phase images. Characterization results have demonstrated the dependency of properties of CoNi microflowers on their morphologies and sizes. The microflowers exhibit different stray magnetic fields that might be determined by whether the pristine nanoflakes on the flowers' surface was parallel or perpendicular to grid plane. And as the size of microflowers increased, the coercive force (Hc) value decreased while saturation magnetization (Ms) value gradually increased, and it can be also observed that the values of Ms and Hc at 5 K are higher than those at 300 K. In addition, the blocking temperature decreased when size increased. Typically, the 2.5 μm CoNi microflowers achieve the maximum reflection loss (RL) value of -28.5 dB at 6.8 GHz with a thickness of 2 mm, while on the other hand, the 0.6 μm flowers achieved a broader absorption bandwidth below -10 dB of 6.5 GHz. Therefore, it is believable that the CoNi flowers with different sizes and hierarchical structures in this work have great potential for high performance magnetic microwave absorption applications.

Dependency of magnetic microwave absorption on surface architecture of Co20Ni80 hierarchical structures studied by electron holography

To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as -33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<-10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g(-1) for urchin-like and 96.41 emu g(-1) for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ''(μ')(-2)(f)(-1) is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.

One-pot electrosynthesis of multi-layered magnetic metallopolymer nanocomposites

Researchers have been investigating various methodologies for fabricating well-defined, homogenous composites consisting of nanoparticles (NPs) dispersed in a matrix. The main challenges are to prevent particle agglomerations during fabrication and to obtain nanoparticles whose size distribution could be tuned on demand. One of the methods that can provide these features is electrodeposition. We report for the first time the fabrication of a thin magnetic multilayer nanocomposite film by electrodeposition from one bath containing both a monomer and metal salts. Cobalt and cobalt-nickel NPs were deposited on conductive polymer polypyrrole thin films using different electrodeposition potentials and times. Multilayer nanocomposite films were fabricated by subsequent electrodeposition of polymer and nanoparticle layers. Scanning electron microscopy analysis showed that a wide range of NPs (70-230 nm) could be synthesized by manipulating growth potentials and times. The cobalt-nickel NPs were found to contain hexagonal close-packed (hcp) and face-centered cubic (fcc) phases based on X-ray diffraction and selected area electron diffraction. Magnetic measurements proved that both the single and the multi-layered nanocomposites were magnetic at room temperature.