High Cobalt Content Research Articles

Pyrolysis of Metal Organic Frameworks (MOF): Transformations Leading to Formation of Transition Metal-Nitrogen-Carbon Catalysts

Metal Organic Framework (MOF) materials link inorganic and organic units by strong bonds, forming porous structures. Pyrolysis consists of heat treatment in inert or reductive atmosphere. Pyrolysis of MOFs, which uses MOFs as a template, is a promising way to synthesize carbon-based oxygen reduction reaction (ORR) catalysts. The size, shape and composition of the pyrolysis product is controllable by choosing MOF-based precursors and tuning the pyrolysis parameters. Two MOFs that are frequently used in the ORR catalysis are selected in this study: ZIF-8 and ZIF-67, both of which can be synthesized under ambient temperature and pressure. Co-based ZIF-67 is considered as a good precursor to highly active Co-N-C ORR catalysts due to its high content of nitrogen and cobalt. Zn-based ZIF-8 has isostructural structure to ZIF-67, but contains Zn instead of Co. Currently, pyrolysis process is highly empirical, where process parameters are optimized via trial-and-error. In this study we aim to demystify pyrolysis process and provide understanding on transformation of ZIF-based precursors during pyrolysis.Our team has investigated the pyrolytic synthesis of both ZIF-8 and ZIF-67 via in situ STEM, EDS and XRD and used electrochemical techniques to assess pyrolyzed materials activity towards ORR. The structures of both MOFs shrunk in size after pyrolysis to 1050 °C under high-vacuum environment, indicating that material evaporation and decomposition happened. However, the structure of the ZIF-8 remained, while that of ZIF-67 did not. The product of pyrolyzing ZIF-8 contains graphitic planes along with amorphous carbon phases. On the other hand, metal carbide covered by graphitized shell was formed during the pyrolysis of ZIF-67. Ex situ XPS was conducted on the precursor, product of pyrolysis and the product after acid etching. The nitrogen contained in the product of pyrolyzing ZIF-8 will not be removed after acid etching. A low content of nitrogen was observed on the surface and few nanometers beneath the surface of the pyrolysis product of ZIF-67. Most of the cobalt that remained after pyrolyzing the Co-based ZIF-67 will be removed by acid-etching. The degree of graphitization is the main difference between the process of pyrolyzing ZIF-8 and ZIF-67. The metal that remained at high temperature (1050 °C) might have catalyzed the graphitization process and thus destroyed the structure. The electrochemical activity of the pyrolysis products of ZIF-8 and ZIF-67 before and after acid etching was assessed with a rotating ring disk electrode setup. The halfwave potential of ZIF-67 was very low (~0.6 V), whereas the halfwave potential of ZIF-67 was higher, at 0.7 V. ZIF-67 showed very low surface area, as the structure of the MOF was not preserved during synthesis, whereas ZIF-8 did preserve structure and featured high electrochemical surface area.Figure. XPS, STEM characterization and electrochemical activity assessment. (a) XPS survey results of ZIF-8, its pyrolysis product, and the product after acid etching. ArE: Ar Etching. (b) STEM images of ZIF-8 after pyrolysis. (c) XPS survey results of ZIF-67, its pyrolysis product, and the product after acid etching. ArE: Ar Etching. (d) STEM images of ZIF-67 when pyrolyzing to 1050 °C. (e) ring current density and (f) disk current density in O2-saturated electrolyte. Red solid: ZIF-8 pyrolyzed to 975 under H2 atmosphere. Red dash: ZIF-8 pyrolyzed to 975 under H2 atmosphere with acid etching. Black solid: ZIF-67 pyrolyzed to 975 °C under H2 atmosphere. Black dash: ZIF-67 pyrolyzed to 975 °C under H2 atmosphere with acid etching. Figure 1

Double-doped YFeO3 as new electrodes for protonic ceramic fuel cells

Mixed ionic-electronic conductors (MIECs) based on YFeO3 are positioned as one of the promising cathode materials for intermediate-temperature solid oxide fuel cells (so-called protonic ceramic fuel cells or PCFCs) based on proton-conducting electrolytes. Simultaneous modification of both basic cationic sublattices of YFeO3 by calcium and iron was used to tailor the functionality of the obtained Y0.9Ca0.1Fe1–хСoхO3–δ (x = 0.2, 0.3, 0.4 and 0.5) compounds. Following the successful synthesis of these oxides, such functional characteristics as structural, thermal, transport properties and electrochemical activity were extensively studied taking the composition (i.e. cobalt concentration, x) into account. The complex analysis carried out on the obtained data shows that Co-doping results in improved electrical conductivity and electrochemical polarisation resistance with no adverse effects on their thermal expansion, even at the highest cobalt content (x = 0.5). The performance of a single SOFC with the selected Y0.9Ca0.1Fe0.5Сo0.5O3–δ electrode confirms the prospects of Y0.9Ca0.1Fe1–хСoхO3–δ phases as modernized MIECs having good thermal properties and acceptable electrochemical activity.

Effects of magnetic field and particles content on rheology and resistivity behavior of magnetorheological elastomer with embedded cobalt particles

In most studies, carbonyl iron particles were merged with carbon-based particles such as graphite or carbon black particles as fillers to enhance the electrical properties of magnetorheological elastomers (MREs). These combined fillers can be replaced by using a single material in order to reduce brittleness due to the high amount of composition. Therefore, in this research, cobalt particles having dual properties, magnetic and electrical, have been employed as a filler in MRE. A total of three anisotropic MREs containing 53, 60, and 67 wt% of cobalt were fabricated through the mixing process method. The characterization related to morphological and magnetic properties of MRE samples was analyzed by using field emission scanning electron microscopy and vibrating sample magnetometer. Then, the rheological properties of the MRE in various strengths of magnetic field intensity between 0 and 0.8 T were conducted by using a rheometer. Afterward, the effect of the cobalt on the electrical properties was investigated and compared with different applied forces towards the MRE. The outcome showed that the rheological and electrical properties of MRE were improved with the increase of cobalt content embedded in the silicone matrix. Higher cobalt content in MRE contributed to a higher magnetorheological (MR) effect and simultaneously lower the electrical resistivity. Therefore, the addition of cobalt particles as a filler in MRE is a great potential to be applied as sensors.

Superintending Scenedesmus and Chlorella sp. with lead and cobalt tolerance governed via stress biomarkers

Abstract In this study, Scenedesmus sp. and Chlorella sp. were exposed to 100, 150, 200 mg/L of lead and 10, 50, 100 mg/L of cobalt for 10 days. The chlorophyll content at Pb (200 mg/L) was found to be 2.35 ± 0.15 μg/mL in Scenedesmus sp. and 2.58 ± 0.02 μg/mL in Chlorella sp. on the 10th day. Scenedesmus sp. and Chlorella sp. exposed to Co (100 mg/L) showed a decline in chlorophyll content (0.83 ± 0.09 μg/mL and 0.74 ± 0.08 μg/mL) respectively. Furthermore, Scenedesmus sp. and Chlorella sp. exposed to 100 mg/L of lead showed the highest lipid peroxidation measured using malonaldehyde (MDA) (10.60 μmol/g and 6.24 μmol/g), superoxide dismutase (SOD) (49.04 U/mL and 49.32 U/mL) and catalase (CAT) (237.74 nmol/min/mL and 373.48 nmol/min/mL) activity, respectively. Scenedesmus sp. and Chlorella sp. exposed to 200 mg/L of lead showed elevated MDA (4.89 μmol/g and 5.14 μmol/g), SOD (32.05 U/mL and 37.80 U/mL) and CAT (121.78 nmol/min/mL and 160.46 nmol/min/mL) activity, respectively. Scenedesmus sp. and Chlorella sp. showed a high tolerance for 100 mg/L of lead and 10 mg/L of cobalt. As the concentration of lead and cobalt was increased, cell growth declined and elevated levels of stress biomarkers were observed. This study helps to understand plant tolerance levels and presents their candidature for treating wastewater with high lead and cobalt content.

Researches on the recovery of useful metals from spent Li-Ion batteries

The present and future importance of Li-Ion batteries is immeasurable; this is evidenced by the awarding of the Nobel Prize in chemistry in 2019, to the team of John Goodenough - director, M Stanley Whittingham and Akita Yashino, who developed the technology to make this type of rechargeable battery. Used at the beginning (1990-2000) in applications such as portable electronic equipments (mobile phones, laptops, electric tools, energy storage systems, etc.), these batteries are considered the most suitable battery for powering electric vehicles. Today the number of electric cars in the world has exceeded 4 million units and the future estimates are among the most optimistic. Recycling of Li-Ion batteries is mainly done in China and South Korea, countries that have a large share in their production, but things can change. Intense research for the recovery and reuse of useful metals contained in these batteries is carried out in many research laboratories. The paper presents the current state of the research undertaken for the recovery of the cathodic paste with high content of Cobalt of waste LIBs, by ultrasonography in lactic acid solution. The hydrometallurgical method uses a non-polluting organic (lactic) acid. The working technique, the results obtained and the investigations carried out on the recovered materials are presented (analysis of optical and electron microscopy, EDX, X-ray diffraction). The paper also includes data regarding the optimization of the separation process of the active cathode paste from the aluminium foil using the orthogonal central-compositional programming of the second order.

Electrodeposition and properties of Со-Re alloys

The present paper considers the electrodeposition of CoRe alloys from a citrate and a citrate-pyrophosphate electrolyte. It has been shown that coatings containing up to 67 at.% Re are deposited from a citrate electrolyte with a current efficiency of 20–40%, and that the use of a citrate-pyrophosphate electrolyte allows the current efficiency for the alloy to be increased, but the coating contains a smaller amount of rhenium – 13.5 аt.%. The corrosion tests carried out in solutions of 3.5% NaCl and 1 M KOH show that the optimal deposition current density in a citrate electrolyte is 30–40 mА·сm−2, at which the most fine-crystalline coatings is formed, which has a corrosion resistance of 3.0 and 1.6 kΩ·сm2 for corrosive solutions. The coating deposited from a citrate-pyrophosphate electrolyte is an interstitial solid solution of rhenium in cobalt, which allows a high corrosive resistance to be achieved, with the high cobalt content giving soft magnetic properties to alloys. The CoRe alloys show electrocatalytic activity in the hydrogen evolution reaction and allow one to reduce by an order of magnitude the exchange current density and by 220 mV the hydrogen overpotential relative to cobalt.

Highly efficient hydrogenation reduction of aromatic nitro compounds using MOF derivative Co–N/C catalyst

A unique MOF derivative core–shell Co–N/C catalyst exhibits porous structure with high specific area, high cobalt content (23%) and high nitrogen content (3%), resulting in the excellent hydrogenation reduction of nitro compounds.

ИЗУЧЕНИЕ СОДЕРЖАНИЯ НЕКОТОРЫХ ТЯЖЕЛЫХ МЕТАЛЛОВ В МЯГКИХ ТКАНЯХ ЖИВОРОДКИ ОБЫКНОВЕННОЙ (VIVIPARUS VIVIPARUS L.), ОБИТАЮЩЕЙ В Р. СОЖ В РАЙОНЕ Г. ГОМЕЛЯ

The soft tissues of molluscs are the components that make it possible to establish the degree of influence of the urban agglomeration on the pollution of the components of the aquatic ecosystem, which do not have a visible anthropogenic load, with compounds of heavy metals. The content of the heavy metals under investigations (except for nickel) decreased in comparison with the data obtained in 2002, which indicates a decrease in anthropogenic load on the aquatic ecosystems of the Sozh. The high content of copper, cobalt and nickel before the city’s wastewater is received confirms the influx of pollutants with the surface runoff of agro-residential areas and settlements located upstream of the city along the river. Unidirectional decrease in copper concentration downstream of the Sozh testifies to the course of ecosystem self-cleaning processes. Confirmation of these processes is a significant decrease in the content of lead and chromium in the area outside the city, in comparison with the section of the river within the city limits. The abnormally high concentration of lead and chromium in the soft tissues of Viviparus viviparus L. in the river section within the city limits, nickel and cobalt below the city limits, indicates the flow of metals into the river with the surface runoff of the city. The high level of metal content in the old complex shows the need to conduct a study on the content of pollutants in aquatic ecosystems that do not have a visible anthropogenic load, but are used by the population for recreational purposes.

Co/N co-doped carbonaceous polyhedron as efficient peroxymonosulfate activator for degradation of organic pollutants: Role of cobalt

• Synthesized a novel Co,N co-doped carbon material with Core-shell MOFs. • Co@N-C-2 showed superb catalytic performance and low cobalt leaching. • Nonradical way including 1 O 2 and electron transfer dominated oxidation process. • Co species regulated the structure and determined the activation mechanism. • Co@N-C-2/PMS system is resistant to the inorganic anions and NOM. In this study, Co/N co-doped polyhedron carbonaceous catalyst (Co@N-C-2) with abundant mesoporous, high graphitization degree and cobalt content was synthesized via the pyrolysis of core–shell MOFs composite (ZIF-8@ZIF-67). The two cobalt species (Co NPs and Co-N x ) coexisted in Co@N-C-2 were unveiled to play different role in PMS activation. Concretely, the Co-N x served as active sites for 1 O 2 evolution pathway, while Co NPs greatly improved the graphitization degree and thus enhanced the electron transfer pathway. Owing to the novel structure, the as-prepared Co@N-C-2 presented superior catalytic performance upon PMS activation for the removal of several organic pollutants in comparison with the catalysts derived from single MOFs (ZIF-8 and ZIF-67) and the transition metal oxides. Moreover, Co@N-C-2 could be recovered by thermal treatment, and the Co@N-C-2/PMS system also showed high resistance to inorganic anions and natural organic matter (NOM). This study reveals the crucial role of cobalt species in regulating the structure of catalyst and determining the PMS activation pathway.

Investigating Abuse Tolerance and Improved Cycle Life in Si Anode Systems with Novel Electrolyte Design

Si has emerged as the most promising successor to graphite as an anode material in Lithium-ion batteries. Known to have nearly ten times the capacity of graphite, Si is increasingly being used to partially replace traditional graphite to raise the overall energy density of a cell. High nickel cathode chemistries such as NMC811 are also of particular interest due to its high specific capacity and low cobalt content, which drives down cost. Pairing these active materials is an obvious design choice, however it results in combining their respective drawbacks. Relative to lower nickel NMCs, NMC811 has been shown to be more reactive with carbonate electrolyte components and is known to be more violently reactive upon thermal decomposition. Si based materials swell dramatically upon lithiation, causing the SEI layer to break and reform with repeated cycling, consuming the electrolyte in the process. In combination, high energy density also implies increased safety concerns. To overcome these problems new electrolyte additives are needed.We report a new family of electrolyte additives designed to improve the robustness of the SEI and overall stability of the electrolyte system, which carries significance in improving cycle life and abuse tolerance in higher energy density cells. This is a tunable, drop-in solution to addressing the need for improving battery performance as well as safety. We demonstrate the effect of these additives on the SEI via analytical characterizations (SEM, XPS) and how it relates to improved long-term cycle life. The effect of additives on thermal decomposition at the material level is investigated via DSC and on the cell level via ARC, presenting a relationship between electrolyte design and inhibited electrode-electrolyte decomposition reactions. Novel electrolyte additives are thus shown to be a promising approach to resolving future high energy demand without compromising safety.

Surface quality of cemented tungsten carbide finished by direct cutting using diamond-coated carbide end mill

• Superiority of direct cutting of cemented carbide with diamond-coated tool was shown. • Surface quality in direct cutting, electrical machining, and polishing was compared. • Specularity of finished surface similar to polishing was obtained via direct cutting. • Large compressive residual stress can also be obtained via direct cutting. • Higher transverse rupture strength can be achieved compared with polishing. This study addresses the finished surface quality of cemented tungsten carbide obtained via direct cutting with a diamond-coated carbide end mill under ultrasmall feed rates. The surface appearance, composition distribution, profile, roughness, residual stress, and transverse rupture strength were experimentally investigated. The finished surfaces obtained via electric discharge machining with two types of machining conditions and mechanical polishing processes were also evaluated to compare the surface quality. Two types of cemented tungsten carbide materials, TAS VC-70 and VM-40, were applied as the workpiece materials. A mirror surface can be obtained via direct cutting and mechanical polishing with both materials. The microstructure morphologies of the finished surface obtained via direct cutting were different from those obtained via mechanical polishing. In the case of VC-70 which has larger tungsten carbide grain size and higher cobalt content, the flat cross-section of the tungsten carbide grain under ductile mode cutting was conspicuous in direct cutting under small feed rate and depth of cut. In contrast, an extremely thin layer composed of fine grains of tungsten carbide and cobalt was observed on the finished surface in direct cutting under comparatively large feed rate and depth of cut. The surface roughness and profile of the finished surface resulting from direct cutting were comparatively rougher than those resulting from mechanical polishing, although the finished surface was significantly smoother than that resulting from electric discharge machining. The residual stress of the subsurface obtained via direct cutting showed larger compressive stress than that obtained via electric discharge machining and mechanical polishing under all cutting conditions and materials. Moreover, satisfactory transverse rupture strength can be obtained via direct cutting in both materials compared with other processes, and two times more transverse rupture strength can be achieved via direct cutting compared with the case of electric discharge machining in VM-40 cutting.

New alloy development from modified cast Ni-base superalloy GTD-111 with additions of Al, Ni and/or Co prepared by vacuum arc melting process

Abstract The aim of this research is to study and evaluate the effects of cobalt and nickel additions on heat-treated and thermal-exposed microstructures in cast nickel-base superalloy grades based on GTD-111 with cobalt and nickel modifications. In the study, 1 wt.-% aluminium, as well as various cobalt and nickel contents, was added to all the modified alloy. After standard heat treatment, it was found that increasing the 1 wt.-% aluminium content affected the morphology of gamma prime particles, causing them to become more cuboidal in shape and larger in size. On the other hand, the size of gamma prime in all modified alloys decreased slightly with increasing cobalt contents. However, cobalt and nickel additions did not strongly affect the shape of the gamma prime particles. After long-term exposure at temperatures of 1173 K and 1273 K for 1440 ks, these gamma prime particles were much larger in size than those of heat-treated ones. The higher temperature caused extreme increases in the average size of thermal-exposed gamma prime particles. Also, the gamma prime particles became nearly spherical in shape and had lower coarsening rate with higher cobalt and lower nickel contents. Moreover, the addition of cobalt reduced the coalescence of gamma prime particles. Samples with cobalt content higher than 13.1 wt.-% were able to maintain the cubic shape of the particles even after long-term exposure at a temperature of 1273 K for 1440 ks. No topologically close-packed phase was found in any analyzed specimens.

Heterogeneous activation of peroxymonosulfate for bisphenol A degradation using CoFe2O4 derived by hybrid cobalt-ion hexacyanoferrate nanoparticles

A facile coprecipitation-thermal method is reported to prepare spinel cobalt ferrites CoFe2O4 nanoparticles (NPs) with a well-defined mesoporous dominated structure using hybrid cobalt-ion hexacyanoferrate (CoFeHCF) NPs as a template. The properties of the synthesized catalysts are evidenced by various characterization methods. And the effects of time, pH, catalyst/oxidant/BPA dosage, coexisting ions and natural organic matter (NOM) on catalytic degradation of bisphenol A (BPA) are investigated. The as-prepared CoFe2O4 shows a high catalytic performance of 97% elimination for 45 μM BPA in 40 min. The excellent catalytic performance could be attributed to the large specific surface area (66.18 m2/g) and high content of cobalt (the atomic ratio of Fe/Co is 1.86) of CoFe2O4 NPs. Slightly alkaline pH, higher catalyst dosage and anions including Cl− and CO32−/HCO3− are favorable for BPA degradation. Especially, 81.57% mineralization of BPA could be achieved in 60 min under the optimization system. The catalytic capacity of CoFe2O4 could be regenerated by simple washing and drying at 200℃, which is much lower than the crystal temperature. SO4∙− and HO∙ are the primary reactive species responsible for BPA oxidation while SO4∙− might play a dominant role. This work provides a novel method to produce CoFe2O4 nanocatalysts for contaminant degradation and encourage the extended application of CoFeHCF in the environment.

Assessment of physicochemical parameters and metal distribution in bog peat of the western segment of the North European part of Russia (Arkhangelsk region).

This article is devoted to the study of physicochemical parameters and the assessment of the accumulation and distribution of metals in peat deposits from the North European part of Russia (Arkhangelsk region). Peat profiles were selected both in the area with a high anthropogenic load and in a bog remote from industrial pollution. The determination of metals was carried out by using the methods X-ray fluorescence analysis and atomic absorption spectroscopy. It was determined that the studied bogs can be attributed to the low ash type, and the recorded pH and mineralisation values make it possible to attribute these deposits to the acid-oxidising facies of oligotrophic peatlands, characteristic of taiga landscapes. Assessment of metal accumulation showed a high content of titanium, chromium, lead, nickel, vanadium, cobalt, aluminium, silicon, and copper in peat, mainly caused by the burning of fossil fuels and industrial production, as well as the burning of urban and industrial waste. The peat profiles are characterised by significant fluctuations in the content of elements in different horizons. Studies have shown the need to monitor the content of metals in peatlands from the Arkhangelsk region to assess atmospheric pollution from industrial emissions, both at the moment and in the past.

Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition

Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), X-ray powder diffraction (XRD), N2 physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity.

Tuning magnetic order in the van der Waals metal Fe5GeTe2 by cobalt substitution

Fe5-xGeTe2 is a van der Waals material with one of the highest reported bulk Curie temperatures, $T_C$ ~ 310K. In this study, theoretical calculations and experiments are utilized to demonstrate that the magnetic ground state is highly sensitive to local atomic arrangements and the interlayer stacking. Cobalt substitution is found to be an effective way to manipulate the magnetic properties while also increasing the ordering temperature. In particular, cobalt substitution up to 30% enhances $T_C$ and changes the magnetic anisotropy, while approximately 50% cobalt substitution yields an antiferromagnetic state. Single crystal x-ray diffraction evidences a structural change upon increasing the cobalt concentration, with a rhombohedral cell observed in the parent material and a primitive cell observed for ~46% cobalt content relative to iron. First principles calculations demonstrate that it is a combination of high cobalt content and the concomitant change to primitive layer stacking that produces antiferromagnetic order. These results illustrate the sensitivity of magnetism in Fe5-xGeTe2 to composition and structure, and emphasize the important role of structural order/disorder and layer stacking in cleavable magnetic materials.

Oxygen Electrocatalysis with Mesoporous Co−N−C Catalysts: Towards Understanding the Active Site and Development of Rechargeable Zn‐Air Batteries

AbstractWe demonstrate the synthesis of two bifunctional electrocatalysts (Co−N−C‐TET and Co−N−C‐Phen) based on cobalt‐ and nitrogen‐doped mesoporous carbon derived from cobalt complexes and their bifunctional electrocatalytic activity towards oxygen electrocatalysis. Both catalysts are bifunctionally active towards the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in alkaline pH. Co−N−C‐TET has excellent OER activity and delivers the benchmark current density of 10 mA cm−2 at a remarkably low overpotential of 0.28 V. The Co−N−C‐Phen catalyst is superior in terms of overall bifunctional activity and durability. The nitrogen and cobalt content of the catalyst controls the overall oxygen electrocatalytic performance. The nitrogen content, and its chemical nature in the catalyst, decides the ORR activity, whereas the metal content of the catalyst regulates the OER activity. Cobalt‐rich Co−N−C‐TET has significantly high OER activity compared to Co−N−C‐Phen. The enhanced OER activity of the Co−N−C‐TET catalyst is ascribed to the presence of a high cobalt content. The graphitic‐N‐ and pyridinic‐N‐rich Co−N−C‐Phen catalyst has enhanced ORR activity. An aqueous rechargeable Zn‐air battery (ZAB) is fabricated using the Co−N−C‐Phen‐based air‐cathode. The ZAB shows an open‐circuit voltage of 1.40 V and power density of 128.2 mW cm−2 with >48 h of galvanostatic charge‐discharge cycling stability. It outperforms the reference ZAB made of Pt and IrO2 catalysts.

Tuning Cobalt‐Free Nickel‐Rich Layered LiNi0.9Mn0.1O2 Cathode Material for Lithium‐Ion Batteries

AbstractAs the demand for high‐energy‐density batteries becomes more and more urgent, cathode materials of high‐energy lithium‐ion batteries have received widespread attention. LiNixCoyMn1‐x‐yO2 (NCM) ternary materials with high nickel and low cobalt content as well as a high cut‐off voltage are continually pursued. Here, a nickel‐rich cobalt‐free cathode material, LiNi0.9Mn0.1O2, was synthesized by using a co‐precipitation method to achieve a stable structure and excellent electrochemical performance. It shows a discharge specific capacity of 190 mAhg−1 in the first cycle at a rate of 0.2 C, and a capacity retention of 93 % over 150 cycles at 2.7–4.3 V. It also exhibits excellent electrochemical performance under high cut‐off voltage. The initial discharge specific capacity reaches 197.5 mAhg−1 at 0.2 C within 2.7 to 4.5 V, and the capacity retains 188.9 mAhg−1 after 100 cycles. The work provides an alternative cathode material for high‐energy‐density and cost‐effective lithium‐ion batteries.

Enhanced proton conductivity of Gd–Co bi-doped barium cerate perovskites based on structural and microstructural investigations

Abstract Microstructural and electrochemical investigations of bi-doped (Gd and Co) barium cerate perovskites, with theoretical formula BaCe(0.85-x)CoxGd0.15O3-δ (x = 0.02; 0.03 and 0.05) were carried out by X-ray Diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), Raman, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy analysis (EIS). Based on the ionic radii of Co2+ (0.75 A) and Co3+ (0.55 A, six-fold coordination), Co ions did not substitute Ba ions on the A-sites of the ABO3 perovskite and therefore substituted Ce ions on the B-sites. The behavior was confirmed by Raman analysis where it was found that cobalt doping stabilized the perovskite arrangement favoring a higher symmetry structure. From the XPS analysis, an increase in oxygen vacancies as the surface defect for proton conduction was detected in the samples with higher cobalt content. These samples showed the highest proton conductivity of 4.81·10−3–4.36·10−2 S cm−1 in the temperature range 200–800 °C.

Fundamental research of applying tungsten carbide-cobalt as tool electrode material for sinking EDM

The manufacturing process milling is limited in machining specific geometries like inner contours with sharp edges, high aspect ratios or defined radii. Sinking EDM (S-EDM) is an appropriate process to machine complex features if the negative geometry is machinable. The tool electrode wear is a critical factor, because it affects machining accuracy and process efficiency. The tool electrode wear depends on S-EDM processing parameters, the geometry and material of the tool electrode. The material tungsten carbide-cobalt owns suitable thermophysical properties for the application as tool electrode material in EDM. Most applications of tungsten carbide-cobalt in EDM are limited to EDM drilling processes, where tungsten carbide tube electrodes are widely used. The advancements in milling of hard materials enable an economic manufacturing of tungsten carbide-cobalt form electrodes for sinking EDM applications. However, it is not investigated which composition of the material tungsten carbide-cobalt is the most appropriate for the application as tool electrode material in S-EDM. Additionally, there are no suitable EDM process parameters in order to benefit from the material characteristics of the respective tungsten carbide-cobalt. Focus of this work is the analysis of different tungsten carbide grades regarding the average grain size and the cobalt content in order to identify correlations between the material characteristics and the EDM process results. Therefore, eight different tungsten carbide grades with four different grain sizes and five different cobalt contents were applied in S-EDM experimental analysis. The experimental studies showed a general suitability of tungsten carbide-cobalt tool electrodes for EDM-processing, where the material removal rate is comparable to commonly used tool electrode materials. Nevertheless, the relative tool wear shows inferior results. It could be observed that higher cobalt content and coarser grain size of the applied tungsten carbide tool electrodes are advantageous for S-EDM.