Synthesis of catalytic filamentous carbon on a nickel/graphite catalyst and a study of the resulting carbon-carbon composite materials in microbial fuel cells

The carbon-carbon composite materials obtained via the synthesis of catalytic filamentous carbon (CFC) on a Ni/graphite supported catalyst in the process of the pyrolysis of C₃–C₄ alkanes in the presence of hydrogen were systematically studied. The effects of the following conditions on the catalytic activity expressed as the yield of carbon (g CFC)/(g Ni) and on the character of CFC synthesis on graphite rods were studied: procedures for supporting Ni(II) compounds (impregnation and homogeneous precipitation), the concentrations of impregnating compouds (nickel nitrate, urea, and ethyl alcohol) in solution, graphite treatment (oxidation) conditions before supporting Ni(II) compounds, and the pyrolysis temperature of C₃–C₄ alkanes in the range of 400–600°C. Optimum conditions for preparing CFC/graphite composite materials, which are promising for use as electrodes in microbial fuel cells (MFCs), were chosen. The electrochemical characteristics of an MFC designed with the use of a CFC/graphite electrode (anode) and Gluconobacter oxydans glycerol-oxidizing bacteria were studied. The morphology of the surfaces of graphite, synthesized CFC, and also bacterial cells adhered to the anode was studied by scanning electron microscopy.     

Synthesis of nanostructured carbon on Ni catalysts supported on mesoporous silica,preparation of carbon-containing adsorbents,and preparation and study of lipase-active biocatalysts

This work continues a series of our studies on the synthesis of nanostructured carbon (NSC) by the pyrolysis of H₂ + C₃–C₄ alkane mixtures on nickel and cobalt metal catalysts supported on chemically diverse inorganic materials (aluminosilicates, alumina, carbon) having different textural characteristics (mesoporous and macroporous supports) and shapes (granules, foamed materials, and honeycomb monoliths). Here, we consider Ni catalysts supported on granular mesoporous silica (SiO₂). It has been elucidated how the yield of synthesized carbon depends on the Ni/SiO₂ catalyst preparation method (homogeneous precipitation or impregnation) and on the composition of the impregnating solution, including the molar ratio of its components—nickel nitrate and urea. The morphology of catalytic NSC and Ni distribution in the silica granule have been investigated using a scanning electron microscope with an EDX analyzer. Carbon-containing composite supports (NSC/SiO₂) have been employed as adsorbents for immobilizing microbial lipase. The enzymatic activity and stability of the resulting biocatalysts have been estimated in transesterification reactions of vegetable (sunflower and linseed) oils involving methyl or ethyl acetate, esterification, and synthesis of capric acid–isoamyl alcohol esters in nonaqueous media.     

Voltammetry of Formaldehyde at Mechanically Renewable Solid Electrodes

The electrochemical behavior of formaldehyde (CH₂O) at solid electrodes made of platinum, gold, silver, cobalt, nickel, copper, and graphite was studied. The working surface of the electrodes was renewed by cutting a thin layer (0.5 m) immediately in the test solution. It was found that, in alkaline solutions, CH₂O was oxidized at all electrodes other than cobalt and graphite ones while scanning the potential to the anode and cathode regions. The peaks of CH₂O oxidation at platinum and gold electrodes using potential scanning in the anode and cathode directions, as well as at nickel, copper, and silver electrodes using potential scanning in the anodic direction, are suitable for analytical purposes.     

Improved performances of E. coli-catalyzed microbial fuel cells with composite graphite/PTFE anodes

The composite graphite/PTFE electrodes with a variety of PTFE contents were tested as anodes in microbial fuel cell (MFC) based on the biocatalysis of bacteria Escherichia coli (E. coli). It is shown that the PTFE content in the composite electrodes can significantly influence the efficiency of current generation of the MFCs. The composite electrodes with optimized PTFE contents, e.g., 24% to 36% (w/w), are well-suited to serve as anode of E. coli-catalyzed MFCs. In the absence of exogenous electron mediators, E. coli-catalyzed MFC with the composite anode containing 30% PTFE and a conventional air cathode exhibited a power density of 760 mW m⁻², which is even much higher than those reported in the literature so far for E. coli MFCs using efficient electron mediators. These results show significant prospects for developing low cost and effective anode of MFCs.     

Electrochemical Response of Cobalt(II) in the Presence of Ammonia

The electrochemical oxidation of cobalt(II) at gold, boron‐doped diamond, basal and edge plane pyrolytic graphite, and highly oriented pyrolytic graphite electrodes in aqueous solutions containing NH₃ has been studied using cyclic voltammetry, with subsequent chemical and electrochemical processes explained in detail. Furthermore, the electro‐reduction of [Co(NH₃)₆]³⁺ in the presence of different electrolytes has also been studied to obtain a better understanding of the oxidation pathway of the Co(II)‐ammine complexes. In aqueous solution the mechanism can be described by the following scheme:     

Layered Al‐substituted Cobalt Hydroxides/GO Composites for Electrode Materials of Supercapacitors

In this work, Al‐substituted α‐Co(OH)₂/GO composites with supercapacitive properties were prepared by chemical co‐precipitated method in which cobalt nitrate and aluminum nitrate were used as the raw material, and graphite oxide was employed as carrier. The as‐prepared materials were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and fourier transform infrared spectroscopy (FT‐IR). Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements showed that the Al‐substituted α‐Co(OH)₂/GO electrode material had excellent electrochemical capacitance. The specific capacitance of 1137 F·g⁻¹ was achieved in 6 mol/L KOH solution at a current density of 1 A·g⁻¹ within a potential range of 0–0.5 V. Moreover, only 12% losses of the initial specific capacitance were found after 500 cycles at a current density of 1 A·g⁻¹.     

Effect of support and cobalt precursors on the activity of Co/AlPO4 catalysts in Fischer–Tropsch synthesis

Cobalt supported on amorphous aluminum phosphate (Co/AlPO₄) catalysts were prepared by the impregnation method using three different cobalt precursors such as cobalt nitrate, acetate and chloride to elucidate the activity of Fischer–Tropsch synthesis. The use of AlPO₄ as a support for cobalt-based catalysts exhibits better catalytic performance during FTS reaction than the corresponding Co/Al₂O₃ catalyst. TPR results also suggest that the reducibility of the catalysts varies with the nature of cobalt precursors employed during the impregnation on AlPO₄ support. The Co/AlPO₄ catalyst prepared from cobalt nitrate shows higher CO conversion and C₈+ selectivity than the others due to the facile formation of homogeneous cobalt particles with proper electronic characters and high reducibility. Interestingly, all Co/AlPO₄ showed a growth of filamentous carbon initiated from the large mobile cobalt particles during the reaction. The differences in catalytic properties of Co/AlPO₄ are mainly attributed to the cobalt particle size, reducibility with different electronic states of metallic cobalt, pore diameter of AlPO₄ and formation of filamentous carbon.     

Redox behaviour of the dicobalt cofacial porphyrin Co2FTF4 and related complexes adsorbed on graphite electrodes

Adsorbed on graphite electrodes, Co₂FTF4 in a potent catalyst for O₂ reduction by a four-electron mechanism. The two observable redox surface waves have been previously assigned to the two cobalt centres. Using differential pulse polarography (DPP), the behaviour of this dicobalt cofacial dimer was re-examined at different pH values in aqueous solutions and in the presence of potential axial ligands for cobalt. From these observations and from a comparison with other adsorbed porphyrins it can be concluded that (a) the porphyrins are probably adsorbed by strong interactions between graphite and the aromatic rings, and (b) the more negative surface wave is cobalt-based but the more positive one is instead a porphyrin ring oxidation. This implies that the catalyst is in the Co^IICo^IIIFTF4 state when catalytic oxygen reduction begins.     

Graphene-supported cobalt nanoparticles used to activate SiO2-based anode for lithium-ion batteries

Although SiO₂-based anode is a strong competitor to supersede graphite anode for lithium-ion batteries, it still has problems such as low electrochemical activity, enormous loss of active lithium, and serious volume expansion. In order to solve these problems, we used a graphene network loaded with cobalt metal nanoparticles (rGO–Co) to coat SiO₂ porous hollow spheres (SiO₂@rGO–Co). The construction of porous hollow structure and graphene network can shorten the lithium-ion (Li⁺) diffusion distance and enhance the conductivity of the composite, which improves the electrochemical activity of SiO₂ effectively. They also alleviate the volume expansion of the anode in the cycling process. Moreover, nano-scale cobalt metal particles dispersed on graphene catalyze the conversion reaction of SiO₂ and activate the locked Li⁺ in Li₂O through a reversible reaction, which improves the charge and discharge capacity of the anode. The capacity of SiO₂@rGO–Co reaches 370.4 mAh/g after 100 cycles at 0.1 A/g, which is 6.19 times the capacity of pure SiO₂ (59.8 mAh/g) under the same circumstance. What is more, its structure also exhibits excellent cycle stability, with a volume expansion rate of only 13.0% after 100 cycles at a current density of 0.1 A/g.     

Cobalt Hydroxide Nanosheets and Their Thermal Decomposition to Cobalt Oxide Nanorings

We demonstrate herein that single‐crystalline β‐cobalt hydroxide (β‐Co(OH)₂) nanosheets can be successfully synthesized in large quantities by a facile hydrothermal synthetic method with aqueous cobalt nitrate as the cobalt source and triethylamine as both an alkaline and a complexing reagent. This synthetic method has good prospects for the future large‐scale production of single‐crystalline β‐Co(OH)₂ nanosheets owing to its high yield, low cost, and simple reaction apparatus. Single‐crystalline porous nanosheets and nanorings of cobalt oxide (Co₃O₄) were obtained by a thermal‐decomposition method with single‐crystalline β‐Co(OH)₂ nanosheets as the precursor. A probable mechanism of formation of β‐Co(OH)₂ nanosheets, porous Co₃O₄ nanosheets, and Co₃O₄ nanorings was proposed on the basis of the experimental results.     

Exfoliated Single Layers of Layered Cobalt Hydroxide for Ultrafine Co3O4 Nanoparticles on Graphene Nanosheets as an Efficient Electrocatalyst for Oxygen Reduction

A highly effective way to produce an oxygen reduction electrocatalyst was developed through the self-assembly of exfoliated single layers of cobalt hydroxide (Co(OH)₂) and graphene oxide (GO). These 2D materials have complete contact with one another because of their physical flexibility and the electrostatic attraction between negatively charged GO and positively charged Co(OH)₂ layers. The strong coupling induces transformation of the Co(OH)₂ single layer into a discrete nanocrystal of spinel Co₃O₄ with an average size of 8 nm on reduced GO (RGO) during calcination, which could not be obtained with bulk-layered cobalt hydroxide because of its rapid layer collapse. The ultrafine Co₃O₄/RGO hybrid exhibited not only comparable performance in the oxygen reduction reaction but also higher durability compared with the commercial 20 wt % Pt/C catalyst.     

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C₅₊) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C₅₊ yield, for the catalyst containing 10 wt % Co.     

Direct Growth of Cobalt Hydroxide Rods on Nickel Foam and Its Application for Energy Storage

The present work reports synthesis of cobalt hydroxide (Co(OH)₂) rods on nickel foam and its supercapacitor application. Hierarchical Co(OH)₂ rods with length of approximately 3.5 μm and diameter of approximately 400 nm were prepared by one‐step, simple, and inexpensive chemical‐bath‐deposition method. The direct growth of Co(OH)₂ rods on the Ni foam gave three dimensional (3D) structure for easy access of electrolyte throughout material surface. Also, well‐adhered interface between Co(OH)₂ rods and Ni‐foam surface gave better conduction channels. Detailed electrochemical study was performed by using cyclic voltammetry and galvanostatic charge/discharge measurements. The results demonstrate that Co(OH)₂ rods on Ni foam are efficient electrodes for supercapacitor application.     

Nanoflake-like cobalt hydroxide/ordered mesoporous carbon composite for electrochemical capacitors

Nanocomposites consisting of mesoporous carbon CMK-3 and cobalt hydroxide nanoflakes are synthesized by a chemical precipitation method. The successful growth of nanometer-sized Co(OH)₂ flakes on the surface of CMK-3 is confirmed by scanning electron microscopy. The Co(OH)₂/CMK-3 composite electrodes are investigated for its use in the electrochemical capacitors with cyclic voltammograms, chronopotentiometric measurements, and electrochemical impedance spectroscopy. Experimental studies reveal that the Co(OH)₂/CMK-3 composite electrode with the 20 wt.% CMK-3 presents excellent electrochemical performance with specific capacitance of 750 F/g (or 910 F/g after being corrected for the weight percentage of the Co(OH)₂ phase). The overall improved electrochemical behavior accounts for the unique structure design in the Co(OH)₂/CMK-3 composite in terms of porous nanostructure, large specific surface area, and good electrical conductance. The Co(OH)₂/CMK-3 composite electrode also shows better rate capability and cyclic stability, suggesting its potential applications as the electrode materials for electrochemical capacitors.     

May 3D nickel foam electrode be the promising choice for supercapacitors?

The manganese oxide (MnO₂) nanowires and cobalt hydroxide (Co(OH)₂) nanosheets are successfully electrodeposited on nickel foam (NF), respectively (referred to as MnO₂/NF and Co(OH)₂/NF electrode hereinafter). Both electrodes show higher specific capacitance (C _s) and more excellent rate performance than that of most reported corresponding materials. In addition, our previous study of Ni(OH)₂/NF electrodes also exhibited conspicuous results. Combined with the outstanding properties of NF, it is noticeable that the NF electrodes may be a promising choice for supercapacitors.     

Electrochemical characterization of cobalt cordierites attached to paraffin-impregnated graphite electrodes

The electrochemistry of , and cobalt-containing cordierites (Co₂Al₄Si₅O₁₈) attached to paraffin-impregnated graphite electrodes has been studied by linear scan and cyclic voltammetries in HCl+NaCl and NaOH electrolytes. This electrochemistry is compared with that of vitreous cobalt cordierite, cobalt(II) oxide and cobalt spinel aluminate (CoAl₂O₄), the two last taken as reference materials. Electrochemical processes involve the site-characteristic reduction of Co(II) species to cobalt metal near to –0.5 V vs. SCE and their oxidative dissolution near +0.3 V, accompanied by solid state interconversion between Co(II) and Co(III) at potentials above +0.45 V. Cordierite-modified electrodes display a significant site-dependent catalytic effect on the electrochemical oxidation of mannitol in 0.10 M NaOH.     

Hydrogenolysis of Dimethyl Disulfide to Methanethiol in the Presence of Cobalt Sulfide Catalysts

The hydrogenolysis of dimethyl disulfide to methanethiol at T = 180–260°C and atmospheric pressure in the presence of supported cobalt sulfide catalysts has been studied. Cobalt sulfide on aluminum oxide exhibits a higher activity than that on a carbon support or silicon dioxide. The maximum reaction rate per gram of a catalyst is observed on an 8% Co/Al₂O₃ catalyst. At temperatures of up to 200°C and conversions up to 90%, methanethiol is formed with nearly 100% selectivity regardless of the cobalt content, whereas the selectivity for methanethiol under more severe conditions decreases because of its condensation to dimethyl sulfide.     

Liquid Phase Hydrogenolysis of Biomass‐derived Lactate to 1,2‐Propanediol over Silica Supported Cobalt Nanocatalyst

Liquid phase hydrogenolysis of ethyl lactate to 1,2‐propanediol was performed over silica supporting cobalt catalysts prepared by two different methods: precipitation‐gel (PG) technique and deposition‐precipitation (DP) procedure. The cobalt species (Co₃O₄/cobalt phyllosilicate) present in the corresponding calcined PG and DP catalysts were different as a consequence of the preparation methods, and Co OH Co olation and Si O Co oxolation molecular mechanisms were employed to elucidate the chemical phenomena during the different preparation procedures. In addition, the texture (BET), reduction behavior (TPR and in‐situ XRD), surface dispersion and state of cobalt species (XPS), and catalytic performance differ greatly between the samples. Because of small particle size, high dispersion of cobalt species and facile reducibility, the Co/SiO₂ catalyst prepared by precipitation‐gel method presented a much higher activity than the catalyst prepared by deposition‐precipitation method. Metallic cobalt is assumed to be the catalytically active site for the hydrogenolysis reaction according to the catalytic results of both cobalt samples reduced at different temperatures and the structure changes after reaction.     

Preparation of CoSe nanoparticles by microwave-assisted polyol method: effect of Se/Co ratio, support type and synthesis conditions on oxygen reduction activity

Highly methanol-tolerant CoSe nanoparticles supported on different carbon substrates were synthesized by microwave heating of glycerol solutions of cobalt(II) acetate and sodium selenite at different Se/Co mole ratios in the presence of different concentrations of acetic acid and ammonia. The resulting CoSe catalysts were used for the electrochemical oxygen reduction reaction (ORR) in acidic solution in the presence of methanol. The ORR activity of the catalyst was increased by increasing its Se content up to 50?mol%. The presence of acetic acid or ammonia in the synthesis solution significantly affects the electrocatalytic performance of the CoSe catalyst; highest activity was observed when the catalyst was synthesized at NH₃/Co(II) mole ratio of 6. Among the catalysts prepared on different supports including carbon black (Vulcan XC-72R), and nanoporous carbons synthesized from resorcinol-formaldehyde and phloroglucinol-formaldehyde resins, the one supported on the carbon prepared from the last resin exhibited highest electrocatalytic activity for ORR.     

Cobalt‐based Catalysts Modified Cathode for Enhancing Bioelectricity Generation and Wastewater Treatment in Air‐breathing Cathode Microbial Fuel Cells

To seek an efficient way to enhance the power output and wastewater treatment of microbial fuel cell (MFC), several cobalt‐based composites are successfully synthesized by a facile hydrothermal method under different pyrolysis temperature, and these composites are used as electrocatalyst in air‐breathing cathode of MFC. Different species of nitrogen atom are successfully grafted on the cobalt‐based composites and confirmed by physical and electrochemical analyses. In MFC tests, the maximum power density increases from 577.8 mW m^?2 to 931.1 mW m^?2 with pyrolysis temperature (except for 1000 °C). These electrochemical tests and high COD removal show that Co/N/C‐900 can rapidly transfer electron via a 2×2 e^? transfer pathway, mainly due to the exposure of large electrochemical active area and introduction of the defects of pyridinic?N and abundant oxygen vacancies. Although the power density of MFC with Co/N/C‐900 is 81.1 % of that of commercial Pt/C, the MFC with Co/N/C‐900 is more stable than that of Pt/C, and the power density for Co/N/C‐900 has only a 2.8 % decrease during 25‐cycles operation. The great electrocatalytic activity of the novel Co/N/C‐900 composite exhibits a superior outlook for scale‐up application of MFC in the future.