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Molybdenum disulfide (MoS2) is considered as a promising candidate to Pt-based catalysts. Literatures report the active centers of MoS2 locate at its edges, while the perfect in-plane domains are not active. In this study, a simple Co Mo S precursor decomposition approach is used to synthesize Co-doped MoS2 in-situ grown graphite paper (GP) substrate. Electrochemical analyses reveal the Co-doped MoS2 possesses excellent electrocatalytic activity comparable to Pt. Density functional theory (DFT) calculations indicate the inert in-plane S atoms neighboring the doped Co atoms become active towards triiodide reduction, as revealed by the adsorption energies (Ead) of iodine atom decreasing from 0.36 eV to −0.52 eV, identical with value obtained from Pt (−0.52 eV). Due to increased active sites, highly conductive of GP, and excellent electrical connection between Co-doped MoS2 and GP substrate, the dye-sensitized solar cell fabricated using Co-doped MoS2/GP as counter electrode (CE) shows higher photoelectric conversion efficiency (7.26%) than those based on MoS2/GP CE (6.57%) and platinized F-doped tin oxide (Pt/FTO) electrode (6.87%).

Water splitting associated with the conversion and storage of renewable energy is considered to be the most significant strategy to create hydrogen. Herein, an efficient self-supported electrode was developed by in-situ growth of interlayer expanded lamellar cobalt diselenide (CoSe2) nanosheets (NS) on carbon paper (CP) substrate (CoSe2 NS@CP). The analyses of TEM, SEM and XRD confirmed that the CP is homogeneously coated by few stacking layers of interlayer expanded lamellar structured CoSe2. This rationally designed nanostructure can provide more active sites for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The bifunctional electrode exhibits high electrocatalytic performance with −128 mV vs. RHE onset potential for the HER in 0.5 mol dm−3 H2SO4 and +1521 mV vs. RHE for the OER in 1.0 mol dm−3 KOH. Besides, small electrolysis potentials of −201.1 mV vs. RHE and +1636 mV vs. RHE are needed to drive the HER and OER at current density of 100 mA cm−2. Finally, a small overall cell voltage (ca. +1.75 V) was used to drive the water splitting reaction in 1.0 mol dm−3 KOH. The CoSe2 NS@CP electrode showed both excellent catalytic activity with overall current density of 100 mA cm−2 at 2.13 V and tremendous durability with negligible decrease in potential at a constant current of 20 mA cm−2 for more than 30 hours. Thus this rationally designed electrode material can be readily applied for large-scale water splitting process.

The self-standing electrode materials with large surface area and high electronic conductivity have attracted intensive attention in energy storage devices. Herein, the expanded graphite paper (EGP) is fabricated via a controlled cathodic expansion in acetonitrile with tetrabutylammonium bromide at 10 V. The as-prepared EGP exhibits a three-dimensional porous structure with large specific surface area and high electronic conductivity, which is a favorable support for in situ growing nickel cobalt carbonate hydroxide (NiCo-CH) nanowires via a simple hydrothermal method. The as-prepared NiCo-CH@EGP composite achieves high areal capacity of 2.55 C cm−2 at 0.5 mA cm−2, and still remains 1.38 C cm−2 even at 60 mA cm−2. The assembled NiCo-CH@EGP//activated carbon asymmetric supercapacitor exhibits the maximum energy density of 0.30 mWh cm−2 at a power density of 0.92 mW cm−2, and a suitable cyclic stability with the capacity retention of 78.1 % after 10,000 cycles at 20 mA cm−2. The results indicate that the self-standing NiCo-CH@EGP is a potential electrode material for energy storage devices.

Efficient and low cost reduced graphene oxide (rGOV) is prepared by chemical reduction of graphene oxide (GO) using vitamin C. Detailed characterization by XRD, SEM and Raman techniques confirm the successful reduction of GO. Thin films of rGOV with various thickness are deposited by spin coating on FTO glass substrates and are used as counter electrodes (CEs) in dye-sensitized solar cells (DSCs) incorporating the organic sensitizer D35 dye and the Co(bpy) 3 3+ /Co(bpy) 3 2+ redox couple. These devices present high photocurrent density ( j sc ) and open-circuit voltage ( V oc ) values resulting in enhanced photovoltaic performance in comparison with the Pt catalyst. The novel rGOV electrodes constitute an excellent, low-cost and environmentally friendly alternative solution to the costly platinum-based cathodes.

Conjugates of reduced phosphorus-nitrogen co-doped graphene oxide nanosheets (rPNDGONS), reduced phosphorus doped graphene oxide nanosheets (rPDGONS), reduced nitrogen doped graphene oxide nanosheets (rNDGONS), reduced pyrolised graphene oxide nanosheets (rpyGONS) with nanosized cobalt (II) phthalocyanine (CoPc NP ) or cobalt tetra amino phenoxy phthalocyanine (CoTAPhPc NP ) were characterised and tested for their electrocatalytic behaviour towards the detection of hydrogen peroxide. Cyclic and linear scan voltammetries, and chronoamperometry were used to evaluate the electrocatalytic nature of the designed probes. For hydrogen peroxide detection, CoPc NP -rPNDGONS-GCE oxidation gave sensitivity of 12.00 mA/M, limit of detection of 4.48 nM, a rate constant of 2.66 × 10 5 M −1 s −1 , adsorption equilibrium constant of 3.7 × 10 2 M −1 and Gibbs free energy −14.84 kJmol −1 . The lowest detection limit was obtained for CoTAPhPc NP -rPNDGONS-GCE at 1.21 nM.

Reduced graphene oxide nanosheets (rGONS), reduced boron doped graphene oxide nanosheets (rBDGONS) and reduced nitrogen doped graphene oxide nanosheets (rNDGONS) and their composites with cobalt tetra aminophenoxy phthalocyanine nanoparticles (CoTAPhPc NP) were employed towards the detection of hydrogen peroxide. The nanomaterials were characterized by absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, linear sweep voltammetry and cyclic voltammetry. rNDGONS showed excellent electrooxidation and electroreduction of hydrogen peroxide supported by superior surface coverage values. The inclusion of nanosized Pc significantly lowered the reduction overpotential. CoTAPhPc NP -rNDGONS-GCE gave a sensitivity of 39.30 mA/M, catalytic rate constant of 1 × 10 3 M −1 s −1 and a detection limit of 8.2 nM. An adsorption equilibrium constant and Gibbs free energy of 1.26 × 10 3 M −1 and −17.69 kJ mol −1 respectively were observed.

Zinc-air battery is considered as one of the promising energy storage devices due to their low cost, eco-friendly and safe. Here, we present a simple approach to the preparation of cobalt sulfide nanoparticles supported on a nitrogen and sulfur co-doped graphene oxide surface. Cobalt sulfide nanoparticles dispersed on graphene oxide hybrid was successfully prepared by solid state thermolysis approach at 400 °C, using cobalt thiourea and graphene oxide. X-ray diffraction study revealed that hybrid electrode prepared at 400 °C results in pure CoS 2 phase. The hybrid CoS 2 (400)/N,S-GO electrode exhibits low over-potential gap about 0.78 V vs. Zn after 70 cycles with remarkable and robust charge and discharge profile. And also the CoS 2 (400)/N,S-GO showing deep discharge behavior with stability up to 7.5 h.

Cobalt and Fe were co-electrodeposited as single crystal, faceted particles onto carbon paper to produce Co/Fe-oxyhydroxide oxygen evolution reaction (OER) catalysts with various Co/Fe ratios. Electron microscopy and Auger electron spectroscopy were used to investigate the morphology and composition of the electrodeposits. Iron content in the deposits increased with increasing Fe concentration in the electrolyte and Fe segregated to the particle surfaces. Electrochemical tests demonstrated that the deposit Co/Fe ratio influences OER activity by altering the electrochemically active surface area (ECSA) and charge transfer resistance. The OER activity increased with increasing Fe content up to ∼65 at% Fe, with a minimum overpotential of 0.33 V at 10 mA cm−2 in 1 M KOH. The fabricated OER catalysts were assembled into a Zn-air battery for discharge-charge cycling tests and showed lower charge potentials compared with bare carbon paper.

In this paper, amorphous Ni-B nanoparticles doped with cobalt are successfully prepared by simple chemical reduction to investigate the mechanism by which cobalt enhances the electroactivity. Transmission electron microscopy (TEM) images indicate that the morphology of the Ni-B-(Co) amorphous nanoparticles is uniformly spherical, and that the particle size is about 10–15 nm. X-ray photoelectron spectra (XPS) show that Co electrons shifted to B and Ni. Subsequently, the electrocatalytic characteristics were investigated by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The results show that the methanol electro-oxidation current of Ni-B-(Co) amorphous nanoparticles initially increased and decreased as the Co content increased. Ni-B-Co0.05 nanoparticles exhibited the best electrocatalytic activity for methanol oxidation. It is proposed that the role of cobalt in methanol catalysis on the surface of amorphous Ni-B-Co nanoparticles is initially to promote the generation of NiOOH by preferentially forming CoOOH. Meanwhile Co could increase the absorption ability of Ni 3d orbit toward the methanol and intermediates, and thus improve the catalytic activity toward methanol. Our study provides a theoretical guide concerning doped atoms raising the electroactivity of the methanol oxidation on amorphous Ni-B nanoparticles.

Most reported non-precious-metal catalysts for oxygen evolution reaction (OER) are composed of iron, cobalt, or nickel. Copper, on the other hand, is relatively neglected despite its versatility. In this paper, we describe a series of steps to enhance the OER efficiency of copper-based catalyst, including metal organic framework (MOF)-guided structure control, secondary metal doping, and nitridation. In particular, the effect of growth solvent on coordination kinetics and morphology of the precursor MOFs was studied in detail. The optimal MOF structure was further engineered with Fe doping followed by rapid microwave-assisted nitridation, resulting in CuFeN/CNT composite. Experimental results showed that all three engineering steps have significant impact on the enhanced OER efficiency. CuFeN/CNT composite with optimal Fe doping derived from urchin-shaped CuFeMOF exhibited a greatly enhanced OER performance comparable to that of precious metal catalyst, affording a current density as high as 236.3 mA at an overpotential of 420 mV (RuO2, 215.3 mA). Furthermore, excellent stability in alkaline media was observed during 1000 cycles and chronopotentiometric analysis for over 20 hours. We highlight that the entire synthesis protocol is environmentally benign and sustainable by employing microwave to enable rapid formation and conversion of the precursors with minimal energy consumption.

Currently, it is still a big challenge to develop highly active and robust trifunctional non-noble electrocatalysts to meet the practical application of renewable energy storage and conversion devices including metal-air batteries and water electrolyzers. N and O co-doped helical carbon nanotubes encapsulated with CoFe alloy (CoFe@NO CNT) were prepared in situ on carbon paper using ZIF67 as precursor through ion exchange and chemical vapor deposition (CVD) pyrolysis methods. Comparative studies found that the heterogeneous catalysis of CoFe alloy produced spiral carbon nanotubes, which had a much higher N and O doping content than conventional carbon nanotubes containing monometallic cobalt particles. On the basis of the advantages of in situ growth and 3D open structure of catalytic electrode, the helical carbon nanotubes with abundant N catalytic species, C = O functional groups and core-shell structure exhibit superior electrocatalytic activity for ORR/OER/HER. The zinc-air battery (ZAB) and water electrolysis device based on CoFe@NO CNT electrodes showed peak power density (142 mW/cm2), specific capacity (819 mAh/gZn), low overall water splitting voltage (1.57 v @ 10 mA/cm2) and good stability. Two CoFe@NO CNT based ZABs in serial connection can efficiently drive the electrolyzer with two same CoFe@NO CNT/CFP electrodes to split water and two quasi-solid state ZABs in series provide a peak power of 212 mW to light a red light-emitting diode (LED) indicator.

The bimetallic sulfides hold great promise for achieving high-performance supercapacitors. A facile unipolar pulse electrodeposition (UPED) method is developed to prepare nickel cobalt sulfides/polypyrrole (PPy) nanocomposites on carbon paper as electrode for supercapacitors, in which the crystalline structure, morphology and electrochemical performance of Co-Ni sulfides can be readily manipulated by simply changing the Co/Ni molar ratio in the electrodeposition electrolyte. It is demonstrated that the optimal CNS-3 electrode delivers the highest specific capacitance (2004 F g−1 at 1 A g−1), excellent rate capability and superior cycling stability. The outstanding electrochemical capacitive behavior can be ascribed to the synergistic effect of the Co-Ni sulfides, the 3D integrated porous structure of the electrode, as well as the conductivity and adhesion of PPy. Furthermore, an asymmetric supercapacitor (ASC) fabricated by the CNS-3 as positive electrode and activated carbon as negative electrode also displays remarkable electrochemical performance with ultralong cycle life and high energy density. These results manifest the great potential of CNS-3 in the development of high-performance supercapacitor electrode materials. Theoretically, the green and efficient UPED technology could also allow preparing other bimetallic or polymetallic sulfides with controllable composition, crystal structure and morphology.

In this paper, we show that magnesium and cobalt doped SnO2 (Mg-SnO2 and Co-SnO2) nanostructures have profound influence on the discharge capacity and coulombic efficiency of lithium ion batteries (LIBs) employing pure SnO2 and zinc doped SnO2 (Zn-SnO2) as benchmark materials. The materials were synthesized via sol-gel technique. The structural, chemical and morphological characterization indicates that the Zn, Mg and Co dopants were effectively implanted into the SnO2 lattice and that Co doping significantly reduced the grain growth. The electrochemical performances of the nanoparticles were investigated using galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The Co-SnO2 electrode delivered a reversible capacity of around 575 mAh g−1 at the 50th cycle with capacity retention of ∼83% at 60 mA g−1current rate. A capacity of ∼415 mAh g−1 when cycling at 103 mA g−1and >60% improvement in coulombic efficiency compared to the pure compound clearly demonstrate the superiority of Co-SnO2 electrodes. The improved electrochemical properties are attributed to the reduction in particle size of the material up to a few nanometers, which efficiently reduced the distance of lithium diffusion pathway and reduction in the volume change by alleviating the structural strain caused during the Li+ intake/outtake process. The EIS analyses of the electrodes corroborated the difference in electrochemical performances of the electrodes: the Co-SnO2 electrode showed the lowest resistance at different voltages during cycling among other electrodes.

Glycine (GLY), potassium tartrate (PT), and hydroxyethylidene diphosphonic acid (HEDP) have been used as effective complexing agents for chemical mechanical polishing (CMP) of a cobalt (Co) barrier layer, but the most suitable of these three complexing agents is still unclear. In this paper, the density functional theory (DFT) method is employed to predict the complexing capability of the three complexing agents to Co ions. The prediction results show that the complexing capability of the three complexing agents is in the order of: HEDP > GLY > PT. Then, electrochemical experiments, static corrosion tests, UV-Vis spectra, and XPS analysis successfully prove the effectiveness of the DFT method for molecular activity prediction. The experimental results show that regardless of the presence or absence of H2O2, PT has the weakest complexing capability, which results in sufficient Co removal rate without causing unnecessary Co dissolution. In addition, the complexation capability of HEDP is stronger than that of GLY when the oxidation of the Co surface is not a limiting factor.

Exploring earth-abundant and extremely active bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential and challenging for practical application of overall water splitting. Enriching edge defects is proven a remarkably effective strategy to enhance the exposure of active sites and thus improve the electrocatalytic performance. This paper reports an edge-rich Mo-doping cobalt iron oxide nanomeshes (NMs) vertically supported on nickel foam (NF) by means of the straightforward hydrothermal synthesis technique. The synthesized Co1Fe1Mo1.8O NMs@NF exhibits an outstanding OER performance with super low overpotential of 210 mV and HER activity with low overpotential of 157 mV to reach the current density of 10 mA cm−2, as well as long-term cycle durability after 24 h. Significantly, as a bifunctional electrode, Co1Fe1Mo1.8O NMs@NF displays a low potential of 1.68 V to reach 10 mA cm−2 coupled with a long-term water splitting stability in an alkaline electrolyte. This work may pave the way to a rational design of prospective bifunctional electrocatalysts for practical applications of electrochemical process.

In this paper, three dimensional reduced graphene oxide skeleton onto nickel foam (3D RGO NF) was fabricated by a facile dip-coating method combined with alkaline reduction. The as-prepared skeleton was used as a substrate to immobilize Ni-Co layered double hydroxide (Ni-Co LDH) with special morphology of nanowires to effectively prevent the agglomeration of material. The Ni-Co LDH/3D RGO NF electrode exhibited an enhanced specific capacitance of 1054 F g −1 compared with Ni-Co LDH/NF, excellent rate capability (60% capacitance retention with a ten-fold increase in current density) as well as long cyclic life (95% capacity retention after 2000 cycles). In addition, an aqueous asymmetric supercapacitor was composed of Ni-Co LDH/3D RGO NF as positive electrode and activated carbon as negative electrode, which exhibited a specific capacitance of 108.7 F g −1 at 2 mA cm −2 in a potential range from 0 to 1.6 V; it showed maximum energy density of 38.6 Wh kg −1 at 69.5 W kg −1 . Moreover, the Ni-Co LDH/3D RGO NF//AC has an outstanding cycling stability (about 70% capacitance retention after 4000 cycles), which makes it a potential candidate for electrochemical energy storage devices.

In this paper, we report a synthetic route for cobalt sulfides nanoparticles embedded in porous carbon fibers (Co9S8@C) by carbonizing polydopamine (PDA)-coated metal coordination polymers (MCPs) and subsequent sulfidation process. This material serves as an anode for lithium-ion batteries, which exhibits high capacity and good rate capability. At a rate of 0.1C, a high reversible capacity of 1565 mA h g−1 is being obtained. In addition, the battery maintains a stable reversible capacities of 606 mA h g−1 for 300 cycles at 1C. The improvement of lithium-storage performance is mainly attributed to the smart design of carbon-wrapped mesoporous Co9S8 fibers, which not only prevents aggregation and volume change of the Co9S8 particles, but also enables good conductivity, and thus enhances electrochemical stability.

This paper reports on the peculiarities of the metal-centered redox activity in a polymeric cobalt(II) complex of a sterically hindered tetradentate N2O2 Schiff base (salen type) ligand. A Co(III)/Co(II) redox process in the polymer film during its formation on the electrode and subsequent electrochemical switching in a monomer-free electrolyte has been characterized by cyclic voltammetry, electrochemical quartz crystal microbalance, and electrochemical impedance spectroscopy. The obtained results indicate that cobalt ions in the polymer can effectively function as independent redox sites. The metal-centered redox activity largely governed by the unique features of a sterically hindered salen type ligand is time-dependent and sensitive to the presence of coordinating species in the electrolyte. In relatively fast potentiodynamic scans, the Co(III)/Co(II) redox switching in an acetonitrile solution exhibits a high degree of chemical and electrochemical reversibility and stability and can be considered as a quasi-equilibrium process. A novel analytical solution for modeling quasi-equilibrium voltammetric curves accounting for the existence of short-range interactions within redox polymer films is proposed and used to estimate the attraction constant in the cobalt-salen type polymer. The study findings contribute to a better understanding of the prospects of using electrodes modified with the investigated polymeric complex in energy storage and catalytic applications.

Results reported in this research paper are related to the photo-oxidation of water into molecular oxygen, using n-type photoelectrodes operated with the support of an external electric bias. These photoanodes are made of 1 cm2 rectangular glass substrates, surface-covered by thin films of conductive fluorine-doped tin oxide (FTO). Thin mats of titanium dioxide nanorods (TDNRs) have been deposited over the FTO surfaces. The TDNRs have then been sensitized by surface deposition of cobalt dodecahedral Zeolitic Imidazolate Framework (ZIF-67) metal organic framwork (MOF). ZIF-67 has been deposited using a two-step process: (i) deposition of cobalt hydroxide by chronoamperometry; (ii) in-situ transformation of cobalt hydroxide into ZIF-67 by chemical reaction with a solution of 2-methylimidazol. The amount of ZIF-67 has been adjusted by monitoring the duration of the electro-reduction step. The photoanodes have been characterized by scanning electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and UV–Vis absorption spectroscopy. The photoelectrochemical responses of the different photoanodes have been measured under chopped illumination conditions. Dark currents as high as 100–150 μA/cm2 and photocurrents of only 10–15 μA/cm2 have been measured on fresh samples with large MOF contents, at an operating potential of +1.0 V vs. saturated calomel electrode, 25 °C, under UV–Vis irradiation. No dark current and photocurrents close to 40 μA/cm2 have been measured on samples with low MOF contents. The dynamics of charge transfer leading to the formation of molecular oxygen has been analyzed by photoelectrochemical impedance spectroscopy to understand the interplay between the OER electroactivity and photoelectroactivity. It is shown that large MOF contents induce two contradictory effects: the first one (faster charge transfer kinetics) is desirable while the second one (faster charge recombination kinetics) is not desirable. Only limited MOF contents are beneficial to maximize the photocurrent density.

Cobalt oxides are attractive alternative anode materials for next-generation lithium-ion batteries (LIBs). To improve the performance of conversion-type anode materials such as cobalt oxides, well dispersed and nanosized particulate morphology is typically required. In this study, we describe the in situ electrochemical generation of cobalt oxide nanosheets from commercial micrometer-sized LiCoO 2 oxide as an anode material for LIBs. The electrode material as prepared was analyzed by XRD, FE-SEM and TEM. The electrochemical properties were investigated by cyclic voltammetry and by a constant current galvanostatic discharge–charge test. The material shows a high tap density and promising anode performance in terms of capacity, rate performance and cycling stability. A capacity of 560 mA h g −1 is still achieved at a current density of 1000 mA g −1 by increasing the amount of additives in the electrode to 40 wt%. This paper provides a new technique for developing a high-performance conversion-type anode for LIBs.

This paper focuses on electroless deposition of different Re-Me alloys, where Me is Co, Fe or Ni. The possibility to form high-quality Re-Ni films by this process has been demonstrated recently. In the current research we study and compare the influence of the iron-group metals on process kinetics, alloy composition and surface morphology. Alloys of Re-Ni (78 at.%), Re-Co (65 at.%) and Re-Fe (55 at.%) were prepared. Open-circuit potential measurements, as well as a polarization studies, were performed to investigate the induced co-deposition of Re with Ni, Co and Fe. It was shown that for Re-Co and Re-Ni alloys this process is controlled by a mixed-control reaction rather than by mass transport. Good agreement between the calculated and experimentally determined film deposition rates was obtained. Of the three iron-group metals, Ni was found to have the highest catalytic activity for reduction of R e O 4 − and formation of the Re-Me alloys.

Electroactive materials with hollow nanostructures received great attractiveness due to large surface area, low density and superior structure permeablity. The paper reported a new template synthesis of nickel/cobalt layered double hydroxides (Ni/Co-LDH) without any adscititious alkali source, oxidant and step for removal of the template. Nickel nitrate, cobalt nitrate and SiO 2 nanosphere were dispersed in an ethanol solution. Then, the mixed soution was heated at 160 °C for 6 h to obtain Ni/Co-LDH product. During the process, ethanol and nitrate underwent a redox reaction releasing hydroxide ions, which will react with nickel and cobalt ions to form ultrathin Ni/Co-LDH nanoflakes. Meanwhile, SiO 2 template was gently dissolved by hydroxide ions. Interestingly, perfect match between generation rate of Ni/Co-LDH nanoflakes and removal rate of the template creates an elaborate three-dimensional structure with well-defined hollow interior and hydrangea-like exterior. The unique structure will greatly improve electron and mass transfer during the faradic redox reaction. The Ni/Co-LDH electrode exhibits excellent electrochemical performance for supercapacitors. Its specific capacitance is up to 2158.7 F g −1 at the current density of 1 A g −1 and 1965.6 F g −1 at the current density of 5 A g −1 . The capacitance can keep at least 97.5% of initial value after 1500 cycles. The study also provides prominent approach for the fabrication of hollow nanomaterials with three-dimensional structure for supercapacitors, Li-ion batteries, catalyst and sensors.