Co/N-Doped hierarchical porous carbon as an efficient oxygen electrocatalyst for rechargeable Zn–air battery

Developing efficient electrocatalysts for ORR/OER is the key issue for the large-scale application of rechargeable Zn–air batteries. The design of Co and N co-doped carbon matrices has become a promising strategy for the fabrication of bi-functional electrocatalysts. Herein, the surface-oxidized Co nanoparticles (NPs) encapsulated into N-doped hierarchically porous carbon materials (Co/NHPC) are designed as ORR/OER catalysts for rechargeable Zn–air batteries via dual-templating strategy and pyrolysis process containing Co²⁺. The fabricated electrocatalyst displays a core–shell structure with the surface-oxidized Co nanoparticles anchored on hierarchically porous carbon sheets. The carbon shells prevent Co NP cores from aggregating, ensuring excellent electrocatalytic properties for ORR with a half-wave potential of 0.82 V and a moderate OER performance. Notably, the obtained Co/NHPC as a cathode was further assembled in a zinc–air battery that delivered an open-circuit potential of 1.50 V, even superior to that of Pt/C (1.46 V vs. RHE), a low charge–discharge voltage gap, and long cycle life. All these results demonstrate that this study provides a simple, scalable, and efficient approach to fabricate cost-effective high-performance ORR/OER catalysts for rechargeable Zn–air batteries.

The surface-oxidized Co nanoparticles incorporated in N-doped hierarchically porous carbon materials are designed as ORR/OER catalyst for rechargeable Zn–air batteries via dual-templating strategy and pyrolysis process.     

Mn substituted MnxZn1−xCo2O4 oxides synthesized by co-precipitation; effect of doping on the structural,electronic and magnetic properties

Mn substituted Mn_xZn_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C. The presence of manganese ions causes appreciable changes in the structural and magnetic properties of the Mn-substituted ZnCo₂O₄. The morphologies, structures, and electronic properties of Mn–Zn–Co oxide microspheres were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The X-ray diffraction and Fourier transform infrared spectroscopy results confirmed the formation of spinel Mn_xZn_1−xCo₂O₄. It was shown that the Mn–Zn–Co oxide microspheres increase in size and become regular in shape with increasing Mn concentration with the crystal size lying in the range from 19.1 nm to 51.3 nm. Magnetization measurements were carried out using a vibrating sample magnetometer at room temperature and 10 K. The saturation magnetization is observed to increase with increasing Mn concentration from x = 0 to x = 1.

Mn substituted Mn_xZn_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C.     

Synthesis of nanoscale CuO via precursor method and its application in the catalytic epoxidation of styrene

Nanoscale CuO with diameters in the range of 7–8 nm has been synthesized via a two-step precipitation–calcination method using copper(ii) isonicotinate tetrahydrate as the precursor. The first step involves the room temperature stirring of an alkaline ethanolic solution of the precursor which gives a non-crystalline CuO species, while the second step involves the calcination of the product of the first step at 180 °C to form nanocrystalline CuO which has been characterized by PXRD, TEM, SEM, H₂-TPR and Raman spectroscopy, etc. The CuO material has shown excellent catalytic activity in the oxidation of styrene using TBHP as the oxidizing agent leading to complete styrene conversion with more than 95% styrene oxide selectivity at the end of 6 h. The oxide catalyst can be reused for at least 6 successive runs without significant loss in activity.

Nanoscale CuO with diameters in the range of 7–8 nm has been synthesized via a two-step precipitation–calcination method using copper(ii) isonicotinate tetrahydrate as the precursor.     

Facile preparation of porous sheet–sheet hierarchical nanostructure NiO/Ni–Co–Mn–Ox with enhanced specific capacity and cycling stability for high performance supercapacitors

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination. The thermodynamic behavior was observed by TG/DTA. The chemical structure and composition, phase structure and microstructures were tested by XPS, XRD, FE-SEM and TEM. The electrochemical performance was measured by CV, GCD and EIS. The mechanism for formation and enhancing electrochemical performance is also discussed. Firstly, the precursors such as NiOOH, CoOOH and MnOOH grow on nickel foam substrates from a homogeneous mixed solution via chemical bath deposition. Thereafter, these precursors are calcined and decomposed into NiO, Co₃O₄ and MnO₂ respectively under different temperatures in a muffle furnace. Notably, NiO/Ni–Co–Mn–O_x on nickel foam substrates reveals a high specific capacity with 1023.50 C g⁻¹ at 1 A g⁻¹ and an excellent capacitance retention with 103.94% at 5 A g⁻¹ after 3000 cycles in 2 M KOH, its outstanding electrochemical performance and cycling stability are mainly attributed to a porous sheet–sheet hierarchical nanostructure and synergistic effects of pseudo-capacitive materials and excellent redox reversibility. Therefore, this research offers a facile synthesis route to transition metal oxides for high performance supercapacitors.

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination.     

Metal–organic framework derived hollow porous CuO–CuCo2O4 dodecahedrons as a cathode catalyst for Li–O2 batteries

Herein, hollow porous CuO–CuCo₂O₄ dodecahedrons are synthesized by using a simple self-sacrificial metal–organic framework (MOF) template, which resulted in dodecahedron morphology with hierarchically porous architecture. When evaluated as a cathodic electrocatalyst in lithium–oxygen batteries, the CuO–CuCo₂O₄ composite exhibits a significantly enhanced electrochemical performance, delivering an initial capacity of 6844 mA h g⁻¹ with a remarkably decreased discharge/charge overpotential to 1.15 V (vs. Li/Li⁺) at a current density of 100 mA g⁻¹ and showing excellent cyclic stability up to 111 charge/discharge cycles under a cut-off capacity of 1000 mA h g⁻¹ at 400 mA g⁻¹. The outstanding electrochemical performance of CuO–CuCo₂O₄ composite can be owing to the intrinsic catalytic activity, unique porous structure and the presence of substantial electrocatalytic sites. The ex situ XRD and SEM are also carried out to reveal the charge/discharge behavior and demonstrate the excellent reversibility of the CuO–CuCo₂O₄ based electrode.

Metal–organic framework derived porous CuO–CuCo₂O₄ dodecahedrons as a cathode catalyst for Li–O₂ batteries with significantly enhanced rate and cyclic performance.     

Heterogeneous activation of persulfate by ZnCoxFe2−xO4 loaded on rice hull carbon for degrading bisphenol A

A new low-cost composite of ZnCo_xFe_2−xO₄ loaded on rice hull carbon (ZnCo_xFe_2−xO₄-RHC) was synthesized via waste ferrous sulfate (the industrial waste produced in the process of producing titanium dioxide) and rice hull as raw materials, which was applied for the degradation of bisphenol A (BPA) by heterogeneous activated peroxodisulfate (PS). A series of characterizations including XRD, SEM, FTIR, and BET analysis were carried out to analyze the structure and morphology of the materials. It is confirmed that the ZnCo_xFe_2−xO₄-RHC composites show better catalytic activity and performance than other control samples, which can be attributed to the synergistic effect of Fe and Co, ZnCo_xFe_2−xO₄ and RHC based on these analyses. The degradation rate of BPA by ZnCo_1.3Fe_0.7O₄-50%RHC reached 100% within 15 min, and it can still maintain good catalytic efficiency after 5 cycles. ESR test and XPS results showed that free radical and non-free radical processes were involved in BPA degradation. These findings offer a novel, low cost and simple strategy for rational design and modulation of catalysts for the industrial degradation of organic pollutants, and provide a new idea for the utilization of waste ferrous sulphate in titanium dioxide industry.

Mechanism of the activation on PS by ZnCo_1.3Fe_0.7O₄-RHC for the degradation of BPA.     

MnO2/ZnCo2O4 with binder-free arrays on nickel foam loaded with graphene as a high performance electrode for advanced asymmetric supercapacitors

ZnCo₂O₄ nanosheets were successfully arrayed on a Ni foam surface with graphene using a hydrothermal method followed by annealing treatment; then MnO₂ nanoparticles were electrodeposited on the ZnCo₂O₄ nanosheets to obtain a synthesized composite binder-free electrode named MnO₂/ZnCo₂O₄/graphene/Ni foam (denoted as MnO₂/ZnCo₂O₄/G/NF). After testing the binder-free composite electrode of MnO₂/ZnCo₂O₄/G/NF via cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy testing, we found that it exhibited ultrahigh electrochemical properties, with a high specific areal capacitance of 3405.21 F g⁻¹ under a current density of 2 A g⁻¹, and wonderful cycling stability, with 91.2% retention after 5000 cycles. Moreover, an asymmetric supercapacitor (ASC) based on MnO₂/ZnCo₂O₄/G/NF//G/NF was successfully designed. When tested, the as-designed ASC can achieve a maximum energy density of 46.85 W h kg⁻¹ at a power density of 166.67 W kg⁻¹. Finally, the ASC we assembled can power a commercial red LED lamp successfully for more than 5 min, which proves its practicability. All these impressive performances indicate that the MnO₂/ZnCo₂O₄/graphene composite material is an outstanding electrode material for electrochemical capacitors.

Schematic illustration of formation process of MnO₂/ZnCo₂O₄/G/NF composite electrode.     

Controllable synthesis of nanostructured ZnCo2O4 as high-performance anode materials for lithium-ion batteries

Nanostructured ZnCo₂O₄ anode materials for lithium-ion batteries (LIBs) have been successfully prepared by a two-step process, combining facile and concise electrospinning and simple post-treatment techniques. Three different structured ZnCo₂O₄ anodes (nanoparticles, nanotubes and nanowires) can be prepared by simply adjusting the ratio of metallic salt and PVP in the precursor solutions. Charge–discharge tests and cyclic voltammetry (CV) have been conducted to evaluate the lithium storage performances of ZnCo₂O₄ anodes, particularly for ZnCo₂O₄ nanotubes obtained from a weight ratio 2 : 4 of metallic salt and PVP polymer in the precursor solution. Remarkably, ZnCo₂O₄ nanotubes exhibit high specific capacity, good rate property, and long cycling stability. Reversible capacity is still maintained at 1180.8 mA h g⁻¹ after 275 cycles at a current density of 200 mA g⁻¹. In case of rate capability, even after cycling at the 2000 mA g⁻¹ current density, the capacity could recover to 684 mA h g⁻¹. The brilliant electrochemical properties of the ZnCo₂O₄ anodes make them promising anodes for LIBs and other energy storage applications.

ZnCo₂O₄ nanoparticles, nanotubes, and nanofibers can be controllably prepared by simply tuning the weight ratios of metallic salts and PVP polymer in the precursor solution.     

Self-template formation of porous Co3O4 hollow nanoprisms for non-enzymatic glucose sensing in human serum

A novel type of porous Co₃O₄ hollow nanoprism (HNP) was successfully prepared using tetragonal cobalt acetate hydroxide [Co₅(OH)₂(OAc)₈·2H₂O] as precursor by a facile solvothermal process and a subsequent calcination treatment. The morphology and structure of the Co₃O₄ HNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and N₂ adsorption–desorption measurements. An enzyme-free glucose sensor was constructed based on the Co₃O₄ HNPs, and the electrochemical performance was tested by cyclic voltammetry (CV) and chronoamperometry. The as-prepared sensor exhibited a good electrocatalytic activity for glucose oxidation at the applied potential of 0.6 V in alkaline solution, with a high sensitivity of 19.83 μA mM⁻¹ cm⁻² and a high upper limit of 30 mM, which provide the potential for direct determination of blood glucose without any dilution pretreatment. The Co₃O₄ HNPs had a porous and tubular structure with a large amount of accessible active sites, which enhanced the mass diffusion and accelerated the electron transfer. Moreover, the sensor also demonstrated a desirable stability, selectivity and reproducibility, and could verify the non-enzymatic analysis of glucose in real samples.

Co₃O₄ hollow nanoprisms based non-enzymatic glucose sensor were prepared by a self-template process, exhibiting wide linear range, good selectivity and stability, which can directly monitoring blood glucose without any dilution pretreatment.     

Enhancing the thermoelectric power factor of nanostructured ZnCo2O4 by Bi substitution

Bi_xZnCo_2−xO₄ (0 ≤ x ≤ 0.2) nanoparticles with different x values have been prepared by the sol–gel method; the structural, morphological, thermal and thermoelectric properties of the prepared nanomaterials are investigated. XRD analysis confirms that Bi is completely dissolved in the ZnCo₂O₄ lattice till the x values of ≤0.1 and the secondary phase of Bi₂O₃ is formed at higher x value (x > 0.1). The synthesized nanomaterials are densified and the thermoelectric properties are studied as a function of temperature. The electrical resistivity of the Bi_xZnCo_2−xO₄ decreased with x value and it fell to 4 × 10⁻² Ω m for the sample with x value ≤ 0.1. The Seebeck coefficient value increased with the increase of Bi substitution till the x value of 0.1 and decreased for the sample with higher Bi content (x ≤ 0.2) as the resistivity of the sample increased due to secondary phase formation. With the optimum Seebeck coefficient and electrical resistivity, Bi_0.1ZnCo_1.9O₄ shows the high-power factor (α²σ_{550 K}) of 2.3 μW K⁻² m⁻¹ and figure of merit of 9.5 × 10⁻⁴ at 668 K respectively, compared with other samples. The experimental results reveal that Bi substitution at the Co site is a promising approach to improve the thermoelectric properties of ZnCo₂O₄.

Nanostructuring and Bi substitution have considerably increased the thermoelectric power factor and ZT of Bi_xZnCo_2−xO₄; Bi_1.9ZnCo_1.9O₄ shows a higher power factor than that of other Bi substituted samples.     

Comparison on the immersion corrosion and electrochemical corrosion resistance of WC–Al2O3 composites and WC–Co cemented carbide in NaCl solution

WC–15 wt% Al₂O₃ composites were prepared via hot pressing sintering technology. The corrosion behaviors of WC–Al₂O₃ composites and traditional WC–Co cemented carbide in NaCl solution were studied by immersion corrosion and electrochemical technique. The impedance value of the WC–Al₂O₃ composite increased more rapidly than WC–Co cemented carbide during the 24 hours, which indicated that WC–Al₂O₃ composites had a more compact passivation film than WC–Co cemented carbide. The results confirmed that the corrosion resistance of WC–Al₂O₃ composites was higher than that of WC–Co cemented carbide in NaCl solution. The corrosion mechanisms of WC–Al₂O₃ composites and WC–Co cemented carbide in NaCl solution were also revealed by SEM, EDS, XPS and Raman. The corrosion products of WC–Al₂O₃ composites mainly contain WO₃, while for WC–Co cemented carbide they are Co(OH)₂, Co₃O₄ and WO₃. The different corrosion mechanism of the two materials is attributed to the Al₂O₃ phase instead of the Co binder, which avoids the galvanic corrosion between the WC phase and the Co binder.

WC–Al₂O₃ composites possess higher corrosion resistance compared with WC–Co cemented carbide. The main corrosion mechanism for WC–Al₂O₃ composites is the oxidation of the WC phase.     

Synthesis of interconnected mesoporous ZnCo2O4 nanosheets on a 3D graphene foam as a binder-free anode for high-performance Li-ion batteries

Interconnected mesoporous sheet-like ZnCo₂O₄ nanomaterials directly grown on a three-dimensional (3D) graphene film (GF) coated on Ni foam (NF) have been successfully synthesized via an effective chemical vapor deposition (CVD) method combined with a subsequent hydrothermal route. When the ZnCo₂O₄@3DGF@NF composite material with a high surface area of 46.06 m² g⁻¹ is evaluated as a binder-free anode material for lithium ion batteries, it exhibits a superior electrochemical performance with a high discharge capacity (1223 mA h g⁻¹ at a current density of 500 mA g⁻¹ after 240 cycles), and an excellent reversibility (coulombic efficiency of 97–99%). Such an outstanding electrochemical performance may be attributed to its unique mesoporous sheet-like nanostructure with a 3DGF supporting, which can facilitate the electrolyte penetration and accelerate the ion/electron transport, as well as buffer the volume variation during charge/discharge processes.

Mesoporous ZnCo₂O₄ nanomaterials grown on a three-dimensional (3D) graphene film (GF) coated on Ni foam (NF) have been synthesized via an effective chemical vapor deposition (CVD) method combined with a subsequent hydrothermal route.     

Porous niobia spheres with large surface area: alcothermal synthesis and controlling of their composition and phase transition behaviour

Submicron-sized niobia (Nb₂O₅) porous spheres with a high specific surface area (300 m² g⁻¹) and nano concave–convex surfaces were synthesized via a rapid one-pot single-step alcothermal reaction. Prolonged reaction time or high reaction temperatures resulted in a morphology change of Nb₂O₅ from amorphous sphere to rod crystals with hexagonal crystal phase. A similar alcothermal reaction yielded TiO₂–Nb₂O₅ composite porous spheres, whose Ti : Nb molar ratio was controlled by changing the precursor solution component ratios. A simple thermal treatment of amorphous TiO₂–Nb₂O₅ porous spheres consisting of 1 : 2 (molar ratio) Ti : Nb at 600 °C for 2 h induced crystal phase transfer from amorphous to a monoclinic crystal phase of submicron-sized TiNb₂O₇ porous spheres with a specific surface area of 50 m² g⁻¹.

Nb₂O₅, TiO₂–Nb₂O₅, and TiNb₂O₇ porous spheres with large surface area were synthesized by alcothermal reaction and calcination.     

Thermally reduced mesoporous manganese MOF @reduced graphene oxide nanocomposite as bifunctional electrocatalyst for oxygen reduction and evolution

Oxygen electrocatalysis plays a crucial role in harnessing energy from modern renewable energy technologies like fuel cells and metal–air batteries. But high cost and stability issues of noble metal catalysts call for research on tailoring novel metal–organic framework (MOF) based architectures which can bifunctionally catalyze O₂ reduction and evolution reactions (ORR & OER). In this work, we report a novel manganese MOF @rGO nanocomposite synthesized using a facile self-templated solvothermal method. The nanocomposite is superior to commercial Pt/C catalyst both in material resource and effectiveness in application. A more positive cathodic peak (E_pc = 0.78 V vs. RHE), onset (E_onset = 1.09 V vs. RHE) and half wave potentials (E_1/2 = 0.98 V vs. RHE) for the ORR and notable potential to achieve the threshold current density (E_{@10 mA cm⁻²}= 1.84 V vs. RHE) for OER are features promising to reduce overpotentials during ORR and OER. Small Tafel slopes, methanol tolerance and acceptable short term stability augment the electrocatalytic properties of the as-prepared nanocomposite. Remarkable electrocatalytic features are attributed to the synergistic effect from the mesoporous 3D framework and transition metal–organic composition. Template directed growth, tunable porosities, novel architecture and excellent electrocatalytic performance of the manganese MOF @rGO nanocomposite make it an excellent candidate for energy applications.

Oxygen electrocatalysis plays a crucial role in harnessing energy from modern renewable energy technologies like fuel cells and metal–air batteries.     

Microstructural evolution and mechanical properties of WC–6CO cemented carbide prepared via SPS: incorporation of YSZ as a reinforcer

WC–Co based alloys are widely applied cemented carbide materials due to unique and outstanding properties. In this study, a series of WC–6Co cemented carbides are quickly prepared via SPS and the effects of Zr₂O₃-7 wt% Y₂O₃(YSZ) on the properties of the as-prepared samples are also investigated. The results show that with the increase of the YSZ amount, the density, flexural strength and fracture toughness of the samples were particularly improved to a certain extent, but the Vickers hardness was slightly reduced. Combined with the evolution of microstructure and analysis of property changes, it can be speculated that the mechanism of YSZ additive promoting sintering can be attributed to the formation of solid solution and subsequent activation sintering process. Consequently, YSZ was preliminarily proved to be a potential enhancer for the WC–Co based cemented carbides.

WC–Co based alloys are widely applied cemented carbide materials due to unique and outstanding properties.     

Facilely controlled synthesis of a core-shell structured MOF composite and its derived N-doped hierarchical porous carbon for CO2 adsorption

A new strategy for controlled synthesis of a MOF composite with a core–shell structure, ZIF-8@resorcinol–urea–formaldehyde resin (ZIF@RUF), is reported for the first time through in situ growth of RUF on the surface of ZIF-8 nanoparticles via an organic–organic self-assembly process by using hexamethylenetetramine as a formaldehyde-releasing source to effectively control the formation rate of RUF, providing the best opportunity for RUF to selectively grow around the nucleation seeds ZIF-8. Compared with the widely reported method for MOF composite synthesis, our strategy not only avoids the difficulty of incorporating MOF crystals into small pore sized materials because of pore limitation, but also effectively guarantees the formation of a MOF composite with a MOF as the core. After carbonization, a morphology-retaining N-doped hierarchical porous carbon characterized by its highly developed microporosity in conjunction with ordered mesoporosity was obtained. Thanks to this unique microporous core–mesoporous shell structure and significantly enhanced porosity, simultaneous improvements of CO₂ adsorption capacity and kinetics were achieved. This strategy not only paves a way to the design of other core–shell structured MOF composites, but also provides a promising method to prepare capacity- and kinetics-increased carbon materials for CO₂ capture.

New strategy for controlled synthesis of core–shell structured ZIF-8 composite and hierarchical N-doped carbon via an effective in situ self-assembly process.     

Coherent nanoscale cobalt/cobalt oxide heterostructures embedded in porous carbon for the oxygen reduction reaction

Cost-effective and efficient electrocatalysts for the oxygen reduction reaction (ORR) are crucial for fuel cells and metal–air batteries. Herein, we report the facile synthesis of a Co/CoO/Co₃O₄ heterostructure embedded in a porous carbon matrix by refluxing and annealing. This composite exhibits several structural merits for catalyzing the ORR: (1) the existence of metallic Co and graphitic carbon enhanced the electrical conduction; (2) the porous, loose carbon network facilitated the electrolyte permeation and mass transport; (3) more importantly, the nanosized coherent CoO/Co₃O₄ heterojunctions with structural defects and oxygen vacancies enhanced the charge transport/separation at the interface and adsorption affinity to O₂, thus promoting the ORR kinetics and lowering the reaction barrier. Consequently, the composite electrode manifests high electrocatalytic activity, attaining a current density of 6.7 mA cm⁻² at −0.8 V (vs. Ag/AgCl), which is superior to pure CoO nanoparticles (4.7 mA cm⁻²), and has good methanol tolerance. The present strategy based on heterostructure and vacancy engineering may pave the way for the exploration of more advanced, low-cost electrocatalysts for electrochemical reduction and evolution processes.

Cost-effective and efficient electrocatalysts for the oxygen reduction reaction (ORR) are crucial for fuel cells and metal–air batteries.     

Co2O3/Co2N0.67 nanoparticles encased in honeycomb-like N,P, O-codoped carbon framework derived from corncob as efficient ORR electrocatalysts

It is essential to develop cost-effective rechargeable metal–air batteries, with high activity, stability, and efficiency, that use non-precious metals (NPMs)-based cathodic oxygen reduction reaction (ORR) catalysts. Here, by using earth-abundant corncob (CC) as the carbon source, Co(OH)₂, NaH₂PO₄, and melamine as the precursors, and KOH as the chemical activator, CoNP@bio-C-a is obtained and comparative studies are carried out with three other types of CC-derived carbon-based catalytic materials, namely, bio-C, CoP@bio-C, and CoNP@bio-C. Depending mainly on the formation of Co₂O₃/Co₂N_0.67 active sites (as p–n heterojunctions) and N, P, O-containing functional groups, the resultant CoNP@bio-C-a catalyst exhibits best electrocatalytic activity among the four types of catalysts; via a 4-electron pathway, it has good stability and good methanol tolerance. In addition, its unique honeycomb-like porous structure, high graphitization degree, and abundant oxygen-containing groups contribute to its excellent ORR activity. This study provides insights for exploring the application of heteroatom-doped biomass-derived carbon catalysts.

We develop a honey-comb-like N, P-codoped carbon framework derived from corncob as efficient ORR electrocatalysts.     

From spent alkaline batteries to ZnxMn3−xO4 by a hydrometallurgical route: synthesis and characterization

A series of Zn/Mn binary oxides with different molar ratios (1.4–11) were synthesized via co-precipitation from a solution obtained through the acidic (HCl) leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn–C batteries. The oxides obtained were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Magnetic properties of the samples were also investigated. The Raman spectroscopy results showed all the binary metallic oxides belong to the Zn_xMn_3−xO₄ (0.25 ≤ x ≥ 1.75) type. All showed a spinel crystalline structure. The saturation magnetization decreases with the Zn/Mn molar ratio; a maximum of 13.19 emu g⁻¹ was found for the molar ratio of 11 at the Curie temperature (25.5 K). XPS showed that all the synthesized compounds contained Mn²⁺, Mn³⁺ and Mn⁴⁺. Mn²⁺ was the most prominent at a molar ratio of 11, Mn³⁺ was most common at a molar ratio of 2, and Mn⁴⁺ at 1.4.

A series of Zn/Mn binary oxides with different molar ratios were synthesized via co-precipitation from a solution obtained through the leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn–C batteries.     

Nanostructured RuO2–Co3O4@RuCo-EO with low Ru loading as a high-efficiency electrochemical oxygen evolution catalyst

Electrochemical water splitting technology is considered to be the most reliable method for converting renewable energy such as wind and solar energy into hydrogen. Here, a nanostructured RuO₂/Co₃O₄–RuCo-EO electrode is designed via magnetron sputtering combined with electrochemical oxidation for the oxygen evolution reaction (OER) in an alkaline medium. The optimized RuO₂/Co₃O₄–RuCo-EO electrode with a Ru loading of 0.064 mg cm⁻² exhibits excellent electrocatalytic performance with a low overpotential of 220 mV at the current density of 10 mA cm⁻² and a low Tafel slope of 59.9 mV dec⁻¹ for the OER. Compared with RuO₂ prepared by thermal decomposition, its overpotential is reduced by 82 mV. Meanwhile, compared with RuO₂ prepared by magnetron sputtering, the overpotential is also reduced by 74 mV. Furthermore, compared with the RuO₂/Ru with core–shell structure (η = 244 mV), the overpotential is still decreased by 24 mV. Therefore, the RuO₂/Co₃O₄–RuCo-EO electrode has excellent OER activity. There are two reasons for the improvement of the OER activity. On the one hand, the core–shell structure is conducive to electron transport, and on the other hand, the addition of Co adjusts the electronic structure of Ru.

The optimized RuO₂/Co₃O₄–RuCo-EO electrode with Ru loading of 0.064 mg cm⁻² exhibits the excellent oxygen evolution activity with an overpotential of 220 mV at the current density of 10 mA cm⁻² and a Tafel slope of 59.9 mV dec⁻¹.