Anodic electrodeposition of conducting cobalt oxyhydroxide films on a gold surface. XPS study and electrochemical behaviour in neutral and alkaline solution

Electroless Cobalt Deposition on Dealloyed Nanoporous Gold Substrate: A Versatile Technique to Control Morphological and Magnetic Properties

The connection of multidisciplinary and versatile techniques capable of depositing and modeling thin films in multistep complex fabrication processes offers different perspectives and additional degrees of freedom in the realization of patterned magnetic materials whose peculiar physical properties meet the specific needs of several applications. In this work, a fast and cost-effective dealloying process is combined with a fast, low-cost, scalable electroless deposition technique to realize hybrid magnetic heterostructures. The gold nanoporous surface obtained by the dealloying of an Au₄₀Si₂₀Cu₂₈Ag₇Pd₅ ribbon is used as a nanostructured substrate for the electrodeposition of cobalt. In the first steps of the deposition, the Co atoms fill the gold pores and arrange themselves into a patterned thin film with harder magnetic properties; then they continue their growth into an upper layer with softer magnetic properties. The structural characterization of the hybrid magnetic heterostructures is performed using an X-ray diffraction technique and energy-dispersive X-ray spectroscopy, while the morphology of the samples as a function of the electrodeposition time is characterized by images taken in top and cross-section view using scanning electron microscopy. Then, the structural and morphologic features are correlated with the room-temperature magnetic properties deduced from an alternating-gradient magnetometer's measurements of the hysteresis loop and first order reversal curves.

Cobalt-Doped Iron Phosphate Crystal on Stainless Steel Mesh for Corrosion-Resistant Oxygen Evolution Catalyst

We report an oxygen evolution reaction (OER) catalyst prepared by the incorporation of cobalt-doped iron phosphate on stainless steel mesh (SSM) through a one-step hydrothermal method. Compared to the catalytic property of bare SSM, our OER catalyst (0.84-CoFePi) showed a 42% improvement in current density at the potential of 1.9 V vs. RHE, and the onset potential was decreased by 26.5 mV. Furthermore, the loss in current density of bulk electrolysis after 12 h in 1 M KOH (pH 14) solution and 0.0441 wt% H2SO4 (pH ≈ 3) containing 0.1 M NaCl solution was negligible (3.1% and 3.2%, respectively). Moreover, our cobalt-doped iron phosphate on SSM exhibits the dramatic improvement in corrosion resistance to a basic, mild acidic solution and chloride ions compared to bare SSM.

Green Synthesis of Iron-Doped Cobalt Oxide Nanoparticles from Palm Kernel Oil via Co-Precipitation and Structural Characterization

In this study, a bio-derived precipitating agent/ligand, palm kernel oil, has been used as an alternative route for the green synthesis of nanoparticles of Fe-doped Co3O4 via the co-precipitation reaction. The palm oil was extracted from dried palm kernel seeds by crushing, squeezing and filtration. The reaction of the palm kernel oil with potassium hydroxide, under reflux, yielded a solution containing a mixture of potassium carboxylate and excess hydroxide ions, irrespective of the length of saponification. The as-obtained solution reacts with an aqueous solution containing iron and cobalt ions to yield the desired metallo-organic precursor, iron cobalt carboxylate. Characterization of the precursors by IR and gas chromatography (GC) attests to the presence of carboxylate fatty acids in good agreement with the proportion contained in the oil, and ICP confirms that the metallic ratios are in the proportion used during the synthesis. Analysis of the products thermally decomposed between 400 °C and 600 °C by XRD, EDX, TEM and ToF-SIMS, established that cobalt iron oxide nanoparticles (Co(1-x)Fex)3O4 were obtained for x ≤ 0.2 and a nanocomposite material (Co(1-x)Fex)3O4/Fe3O4 for x ≥ 0.2, with sizes between 22 and 9 nm. ToF-SIMS and XRD provided direct evidence of the progressive substitution of cobalt by iron in the Co3O4 crystal structure for x ≤ 0.2.

Boosting Hole Transfer in the Fluorine-Doped Hematite Photoanode by Depositing Ultrathin Amorphous FeOOH/CoOOH Cocatalysts

The charge transfer is a key issue in the development of efficient photoelectrodes. Here, we report a method using F-doping and dual-layer ultrathin amorphous FeOOH/CoOOH cocatalysts coupling to enable the inactive α-Fe₂O₃ photoanode to become highly vibrant for the oxygen evolution reaction (OER). Fluorine doping is revealed to increase the charge density and improve the conductivity of α-Fe₂O₃ for rapid charge transfer. Furthermore, ultrathin FeOOH was deposited on F-Fe₂O₃ to extract photogenerated holes and passivate the surface states for accelerated charge carrier transfer. Moreover, CoOOH as an excellent cocatalyst was coated onto FeOOH/F-Fe₂O₃ with the photoassisted electrodeposition method remarkably expediting OER kinetics through an optional pathway of holes utilized by Co species. Ultimately, the CoOOH/FeOOH/F-Fe₂O₃ photoanode exhibits a satisfactory photocurrent density (3.3-fold higher than pristine α-Fe₂O₃) and a negatively shifted onset potential of 80 mV. This work showcases an appealing maneuver to activate the water oxidation performance of the α-Fe₂O₃ photoanode by an integration strategy of heteroatom doping and cocatalyst coupling.

Recent advances in electrochemical non-enzymatic glucose sensors - A review

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.

MeOx/Al2O3 and MeOx/CeO2 (Me = Fe, Co, Ni) catalysts for high temperature N2O decomposition and NH3 oxidation

Efficient oxygen transfer through Me–CeO₂ interface explains higher activity of MeO_x/CeO₂ (Me = Fe, Co, Ni) samples in deN₂O and NH₃ oxidation compared with MeO_x/Al₂O₃ ones.

Interface controlled oxidation states in layered cobalt oxide nanoislands on gold

Layered cobalt oxides have been shown to be highly active catalysts for the oxygen evolution reaction (OER; half of the catalytic "water splitting" reaction), particularly when promoted with gold. However, the surface chemistry of cobalt oxides and in particular the nature of the synergistic effect of gold contact are only understood on a rudimentary level, which at present prevents further exploration. We have synthesized a model system of flat, layered cobalt oxide nanoislands supported on a single crystal gold (111) substrate. By using a combination of atom-resolved scanning tunneling microscopy, X-ray photoelectron and absorption spectroscopies and density functional theory calculations, we provide a detailed analysis of the relationship between the atomic-scale structure of the nanoislands, Co oxidation states and substrate induced charge transfer effects in response to the synthesis oxygen pressure. We reveal that conversion from Co(2+) to Co(3+) can occur by a facile incorporation of oxygen at the interface between the nanoisland and gold, changing the islands from a Co-O bilayer to an O-Co-O trilayer. The O-Co-O trilayer islands have the structure of a single layer of β-CoOOH, proposed to be the active phase for the OER, making this system a valuable model in understanding of the active sites for OER. The Co oxides adopt related island morphologies without significant structural reorganization, and our results directly demonstrate that nanosized Co oxide islands have a much higher structural flexibility than could be predicted from bulk properties. Furthermore, it is clear that the gold/nanoparticle interface has a profound effect on the structure of the nanoislands, suggesting a possible promotion mechanism.

Magnetic properties of corrosion-resistant CoW films

CoW films with different compositions have been prepared by an electrochemical deposition method.

An oxygen evolution Co–Ac catalyst – the synergistic effect of phosphate ions

When Co–Ac was used for electrolysis in phosphate solution, a hybrid Co–Pi–Ac was formed, resulting in enhanced catalytic activity towards OER.

Transition metal-rich mesoporous silicas and their enhanced catalytic properties

Transition metal-rich mesoporous silica was obtained using ammonia complex ions, which exhibited excellent catalytic efficiency for carbon dioxide hydrogenation.

Nanomolar detection of hydrogen peroxide on glassy carbon electrode modified with electrodeposited cobalt oxide nanoparticles

The electrochemical detection of H2O2 was investigated on a cobalt oxide nanoparticles modified glassy carbon electrode in phosphate buffer solution (pH 7). Cyclic voltammetry at potential range -1.1 to 1.1 V from CoCl2 natural aqueous solution produced well defined cobalt oxide nanoparticles deposited on the surface of glassy carbon electrode. The surface of resulting electrode was characterized with SEM. The formation of cobalt oxyhydroxide film was investigated by cyclic voltammetry in alkaline and natural aqueous solution. The modified electrode showed well defined and stable redox couples in both alkaline and natural aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response to H2O2 on the modified electrode was examined using cyclic voltammetry and amperometry. The amperometric detection of hydrogen peroxide is carried out at 0.75 V versus Ag/AgCl reference electrode in phosphate buffer solution with pH 7.4. The detection limit (S/N=3) was 0.4 nM with linearity up to 6 orders of magnitude and sensitivity of 4.86 microA microM(-1) cm(-2). The response time of the electrode to achieve 95% of the steady-state current is <2 s. No measurable reduction in analytical performance of the modified electrode was found by storing the electrode in ambient conditions for 20 days. This modified electrode recedes many advantages such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability of signal response during hydrogen peroxide oxidation. The immobilization of cobalt oxide nanoparticles on the surface of GC electrode appears to be a highly efficient method for the development of a new class of sensitive, stable and reproducible hydrogen peroxide electrochemical sensor.

Preparation and Characterization of Copper-Doped Cobalt Oxide Electrodes

Cobalt oxide (Co3O4) and copper-doped cobalt oxide (CuxCo(3-x)O4) films have been prepared onto titanium support by the thermal decomposition method. The electrodes have been characterized by different techniques such as cyclic voltammetry, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The effect on the electrochemical and crystallographic properties and surface morphology of the amount of copper in the oxide layer has been analyzed. The XPS spectra correspond to a characteristic monophasic Cu-Co spinel oxides when x is below 1. However, when the copper content exceeds that for the stoichiometric CuCo2O4 spinel, a new CuO phase segregates at the surface. The analysis of the surface cation distribution indicates that Cu(II) has preference for octahedral sites.