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Cobalt manganese hydroxides with well-defined nanowire morphology (CoMn-HW) is scalable fabricated by adjusting solution contents, Mn/Co ratio and alkaline species. To further improve the conductivity of CoMn-HW, GO is introduced during fabrication process and reduced to rGO according to the high temperature and alkali atmosphere. By optimizing the adding mass of rGO, CoMn-HW/rGO with sandwiched like structure is successfully synthesized for supercapacitor electrode. The composite delivers a high specific capacitance of 784 F g−1 at current density of 0.5 A g−1, good rate capability (84.2% capacitance retention after current density increase 10 times). Moreover, an asymmetric supercapacitor with CoMn-HW/rGO10 as the positive electrode and active carbon as the negative electrode, is assembled and delivers a maximum energy density of 38.3 Wh kg−1 and power density of 8000 W kg−1, representing its potential in energy storage and conversion systems. • Co, Mn-hydroxides with nanowire morphology is scalable fabricated. • CoMn-HW/rGO with sandwiched like structure is synthesized under optimal synthesis condition. • An asymmetric supercapacitor based on CoMn-HW/rGO and AC is assembled with high energy and power densities. [ABSTRACT FROM AUTHOR]

In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (Ni–Al,Co–Al LDH) are developed via scalable method. Two materials all display core–shell hierarchical structure. High specific capacitance of 2041 F g−1 and 1586 F g−1 are obtained for ZnCo 2 O 4 @Co–Al LDH and ZnCo 2 O 4 @Ni–Al LDH,respectively. Combining with active surface and synergistic effect, the role of hierarchical structure in enhancing performance is revealed. Moreover, two all solid state supercapacitors based on fabricated materials as positive electrodes, activated carbon as negative electrodes and PVA–KOH as polymer electrolyte are assembled. The maximum power and energy densities of ZnCo 2 O 4 @Co–Al LDH//AC are 6200 W kg−1 and 50.1 Wh kg−1, respectively. While the power and energy densities of ZnCo 2 O 4 @Ni–Al LDH//AC are 3400 W kg−1 and 27.8 Wh kg−1. At last, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor ZnCo 2 O 4 @Co–Al LDH//AC as output device, is integrated as a self–sustaining power device, indicating its potential in practical applications. In this article, ZnCo 2 O 4 nanowires deposited with two kinds of typical layered double hydroxides (LDHs) are developed via scalable method. Combining with active surface and synergistic effect, the role of hierarchical structure of each material in enhancing performance is revealed. Moreover, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor as output device, is integrated as a self–sustaining power device, further indicating its potential in practical applications. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Herein, we present the synthesis of oxygen vacancies-rich α -MoO 3- x nanobelts through a novel defect-engineering strategy. The oxygen-vacancies could not only greatly increase the interlayer spacing and the electrical conductivity of MoO 3 , but also significantly enhance the electrochemical activity, which promotes faster charge storage kinetics. Meanwhile, to further facilitate the electron transfer and ion transport, a graphene nanomesh-carbon nanotube/MoO 3- x (GC/MoO 3- x) nanocomposite with three-dimensional sandwiched structure was fabricated, which displays high specific capacity up to 306 C g−1 as well as high volumetric capacity of 692 C cm−3. Our fabricated asymmetric supercapacitor (ASC) with the GC/MoO 3- x and GC/MnO 2 nanocomposites as anode and cathode, respectively, exhibits an ultrahigh energy of 150 Wh kg−1, corresponding to an impressive volumetric energy density of 319 Wh L−1. Notably, both the gravimetric and volumetric energy densities are much higher than most of the previously reported metal oxide based ASCs in aqueous electrolytes. Furthermore, the ASC displays an ultra-long lifespan with 101% retention ratio after 30,000 cycles. The outstanding performances of GC/MoO 3- x composite render it a highly promising candidate for next-generation supercapacitors with both high energy and power densities in future applications, especially in greatly limited space. Graphical abstract fx1 Highlights • Oxygen vacancies-rich MoO 3- x is prepared through a novel defect-engineering strategy. • Oxygen-vacancies greatly increase the interlayer spacing, electrical conductivity and electrochemical activity of MoO 3. • High specific capacity up to 306 C g−1 (692 C cm−3) is obtained. • An ultrahigh volumetric energy density of 319 Wh L−1 is obtained, the highest value for aqueous supercapacitors up to date. • ASC displays an ultra-long lifespan with 101% retention ratio after 30,000 cycles. [ABSTRACT FROM AUTHOR]

A novel and binder free Co@graphite/paper electrode is prepared by electrodeposition Co nano-sheet on the surface of a graphite layer modified paper substrate. The morphology and phase structure of the Co@graphite/paper electrode are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer, transmission electron microscope and X-ray diffractometer. The catalytic activity of the Co@graphite/paper electrode for H 2 O 2 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. The catalyst combines tightly with the paper and exhibits a good stability. The oxidation current density reaches to 580 mA cm −2 in 2 mol dm −3 NaOH and 0.5 mol dm −3 H 2 O 2 at 0.5 V. Besides, we illustrate the reaction mechanization of the H 2 O 2 electrooxidation on the Co film. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen peroxide (H2O2) replaced oxygen (O2) as oxidant has been widely investigated due to its faster reduction kinetics, easier storage and handling than gaseous oxygen. The main challenge of using H2O2 as oxidant is the chemical decomposition. In this article, by using different C2H5OH/H2O volume ratio as the solvent, Co3O4 with different morphologies (nanosheet, nanowire, ultrafine nanowire net, nanobelts, and honeycomb-like) direct growth on Ni foam are synthesized via a simple solvothermal method for the first time. Results show that the introduction of ethanol could obviously improve the catalytic performance toward H2O2 electroreduction. The sample prepared in the solution with the C2H5OH/H2O volume ratio of 1:2 shows the best catalytic performance among the five samples and a current density of 0.214 A cm−2 is observed in 3.0 mol L−1 KOH + 0.5 mol L−1 H2O2 at −0.4 V (vs. Ag/AgCl KCl), which is much larger than that on the other metal oxides reported previously, almost comparable with the precious metals. This electrode of Co3O4 directly grown on Ni foam has superior mass transport property, which combining with its low-cost and facile preparation, make it a promising electrode for fuel cell using H2O2 as the oxidant. [Copyright &y& Elsevier]

Highlights: [•] β-Ni(OH)2 was modified via a template-free method by using different nickel salt. [•] The effects on the morphology and electrochemical behaviors were investigated. [•] The β-Ni(OH)2–SO4 2−/Ni-foam electrode displays 1025.3Fg−1 at 1.0Ag−1. [ABSTRACT FROM AUTHOR]

Highlights: [•] Al-substituted β-Ni(OH)2 were prepared by a simple template-free growth method. [•] The effect of Al contents on the electrochemical performances was investigated. [•] The specific discharge capacity was greatly enhanced by the addition of Al. [Copyright &y& Elsevier]

Abstract: A novel three-dimensional electrode consisting of Pd doped porous Ni film supported on Ni foam (Pd-porous Ni/Ni) is successfully prepared. The porous Ni film is synthesized by electrodeposition of Ni nanoparticles using hydrogen bubbles as a dynamic template. Pd doping is carried out via a chemical replacement reaction between Ni film and Na2PdCl4 solution. The obtained electrode exhibits a three-dimensional (3D) porous structure allowing the full utilization of catalyst surface active sites. The morphology of the electrode and the distribution of Pd on Ni particle surfaces are characterized by scanning electron microscope and energy dispersive X-ray spectrometer. The structure is analyzed using an X-ray diffractometer. The catalytic performance of the porous 3D electrode is evaluated by voltammetry and chronoamperometry. Results show that the electrode displays high catalytic activity and good stability for NaBH4 electrooxidation. The oxidation current density of NaBH4 on the Pd-porous Ni/Ni in 3.0 mol L−1 NaOH containing 0.1 mol L−1 NaBH4 at −0.6 V reaches 2.2 A mg−1, which is about 22 times of that on Pd/C (0.1 A mg−1) reported previously. [Copyright &y& Elsevier]

Abstract: The growth of CuO nanosheet arrays on Cu foil was demonstrated. The morphology and structure of the CuO were examined by scanning electron microscopy and X-ray diffraction spectroscopy. The catalytic performance of the obtained CuO/Cu electrode for hydrogen peroxide electroreduction in 3.0moldm−3 KOH was evaluated by means of cyclic voltammetry and chronoamperometry. The CuO/Cu electrode shows an onset potential for H2O2 electroreduction comparable to Co3O4 nanowire arrays grown on Ni foam and around 100mV more negative than precious metal catalysts, such as Pt and Pd, demonstrating its good catalytic activity for H2O2 electroreduction. The stabilized mass current density for H2O2 electroreduction on the CuO/Cu electrode at −0.3V reached about 57% of that on Co3O4 nanowire arrays grown on nickel foam. Compared to conventional fuel cell electrodes fabricated by mixing active materials with conducting agents and polymer binders, this electrode of CuO nanosheet arrays directly grown on Cu has superior mass transport property, which combining with its low-cost and facile preparation, make it a promising electrode for fuel cell using H2O2 as the oxidant. [Copyright &y& Elsevier]

Abstract: Spherical clusters of Ni(OH)2 nanosheets are directly grown on skeletons of nickel foam via a facile template-free spontaneous growth method. The obtained electrode (β-Ni(OH)2/Ni-foam) is characterized by X-ray diffractometry, scanning and transmission electron microscopy and thermal analysis. Results show that Ni(OH)2 has a β-phase structure and presents on the nickel foam skeleton mostly as spherical clusters with a diameter of ∼10μm. The spheres are composed of nanosheets with thickness of ∼60nm, width of ∼230nm and length up to ∼2μm, and the nanosheets are assembled by nanoparticles with diameter of ∼20nm. The electrochemical performance of the β-Ni(OH)2/Ni-foam electrode is evaluated by cyclic voltammetry and galvanostatic charge–discharge tests. The difference between the oxygen evolution reaction onset potential and the anodic peak potential for this electrode (∼100mV) is larger than that for β-Ni(OH)2 nanosheets and nanotubes powder electrode (∼65–77mV) and much larger than that for commercial spherical β-Ni(OH)2 powder electrode (∼25–47mV), indicating that the β-Ni(OH)2/Ni-foam electrode can be fully charged. The specific discharge capacity of β-Ni(OH)2 in the β-Ni(OH)2/Ni-foam electrode reaches 275mAhg−1, which is close to the theoretical value, lower than that of β-Ni(OH)2 nanotubes (315mAhg−1), but higher than that of nanosheets (219.5mAhg−1), commercial micrometer grade spherical powders (265mAhg−1) and microtubes (232.4mAhg−1). [Copyright &y& Elsevier]

Abstract: Nanowire arrays of mixed oxides of Co and Ni freely standing on Ni foam are prepared by a template-free growth method. The effects of Ni content on the morphology, structure and catalyst performance for oxygen evolution reaction are investigated by scanning electron microscopy, X-ray diffraction spectroscopy and electrochemical techniques including cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. A transformation from nanowire arrays to nanoplate arrays is found with the increase of the atomic ratio of Ni to Co in the preparation solution. The NixCo3−xO4 electrode obtained at 1:1 of Ni:Co in the preparation solution exhibits nanowire array structure and has better catalytic performance for oxygen evolution reaction than other NixCo3−xO4 and Co3O4 electrodes. The catalytic activities of the NixCo3−xO4 and Co3O4 electrodes are correlated with their surface roughness. Superior stability of the NixCo3−xO4 nanowire array electrode is demonstrated by a chronopotentiometric test. The reaction orders with respect to OH− on the NixCo3−xO4 electrode are close to 2 and 1 at low and high overpotentials, respectively. [Copyright &y& Elsevier]

Abstract: Direct carbon fuel cells are promising power sources using solid carbon directly as fuel. Their performances significantly depend on the electrooxidation activity of carbon fuel. Electrooxidation of activated carbon particulates in molten Li2CO3–K2CO3 was investigated by potentiodynamic and potentiostatic method. Results indicated that the electrooxidation performance of activated carbon was significantly enhanced by pre-soaking with Li2CO3–K2CO3 and by treatment with HF, HNO3 and NaOH, respectively. The onset potential negatively shifted by around 100 mV and the current density increased by around 50 mA cm−2 after pre-soaking. The non-oxidant acids (HF) treatments are more effective than oxidant acid (HNO3) and base (NaOH) treatments. HF treated activated carbon exhibited the highest activity among all the samples. The enhancement in electrooxidation performance can be closely correlated with the increase in surface area and porosity caused by acid and base treatments. [Copyright &y& Elsevier]

Abstract: Au/Ni-foam electrodes with three dimensional network structures are prepared by simple spontaneous deposition of nano-sized Au particles onto nickel foam surface in an aqueous solution of AuCl3. Their morphology and catalytic performance for NaBH4 electrooxidation and H2O2 electroreduction in NaOH solution are investigated. Au particles with diameters smaller than 100nm are uniformly deposited on the whole surface of all skeletons of the nickel foam substrate. The onset potential for NaBH4 electrooxidation and H2O2 electroreduction is about −1.2V and −0.1V, respectively. A direct liquid feed alkaline NaBH4–H2O2 fuel cell is constructed using Au/Ni-foam electrode as both the anode and the cathode. The effects of the concentration of NaBH4 and H2O2 and operation temperature on the fuel cell performance are investigated. The fuel cell exhibits an open circuit voltage of about 1.07V and a peak power density of 75mWcm−2 at a current density of 150mAcm−2 and a cell voltage of 0.5V operating on 0.2moldm−3 NaBH4 and 0.5moldm−3 H2O2 at 40°C. [Copyright &y& Elsevier]

Abstract: A high performance alkaline direct borohydride–hydrogen peroxide fuel cell with Pt–Ru catalyzed nickel foam as anode and Pd–Ir catalyzed nickel foam as cathode is reported. The electrodes were prepared by electrodeposition of the catalyst components on nickel foam. Their morphology and composition were analyzed by SEM–EDX. The effects of concentrations of NaBH4 and H2O2 as well as operation temperature on the cell performance were investigated. The cell exhibited an open circuit voltage of about 1.0V and a peak power density of 198mWcm−2 at a current density of 397mAcm−2 and a cell voltage of 0.5V using 0.2moldm−3 NaBH4 as fuel and 0.4moldm−3 H2O2 as oxidant operating at room temperature. Electrooxidation of NaBH4 on Pt–Ru nanoparticles was studied using a rotating disk electrode and complete 8e− oxidation was observed in 2moldm−3 NaOH solution containing 0.01moldm−3 NaBH4. [Copyright &y& Elsevier]

Abstract: Spinel structure Co3O4 nanoparticles with an average diameter of around 17nm were prepared and evaluated as electrocatalysts for H2O2 reduction. Results revealed that Co3O4 exhibits considerable activity and good stability for electrocatalytic reduction of H2O2 in 3M NaOH solution. The reduction occurs mainly via the direct pathway when H2O2 concentration is lower than 0.5M. An Al-H2O2 semi fuel cell using Co3O4 as cathode catalyst was constructed and tested at room temperature. The fuel cell displayed an open circuit voltage of 1.45V and a peak power density of 190mWcm−2 at a current density of 255mAcm−2 operating with a catholyte containing 1.5M H2O2. This study demonstrated that Co3O4 nanoparticles are promising cathode catalysts, in place of precious metals, for fuel cells using H2O2 as oxidant. [Copyright &y& Elsevier]

A series of prototype direct methanol fuel cells (DMFCs) were constructed and operated under identical procedures and conditions except for the surface compositions of the anode electrocatalysts. The cathode electrocatalyst was Pt black (loading 2 mg/cm2, specific surface area: ca. 27 m2/g), the electrolyte membrane was Nafion™ 117, and the anode electrocatalysts were a series of Pt–Ru adatom (Pt–Ruad) nanoparticles (loading 2 mg/cm2, specific surface area: ca. 27 m2/g) prepared by a direct surface reductive deposition of Ruad onto Pt black. The optimum surface coverage of Pt by Ruad was ca. 33% for DMFCs operating at 60 °C. The optimum ranged from ca. 30 to 60% at 90 °C. A DMFC using Pt–Ruad nanoparticles supported on carbon (Vulcan XC-72™) as anode electrocatalyst was operated for 20 days at 8 h each day without loss of activity. These results, combined with those from an in situ cyclic voltammetry study, indicate that no significant Ruad dissolution and/or redistribution occurred during fabrication and operation of the prototype DMFCs. [Copyright &y& Elsevier]

The surface of Pt nanoparticles was cleaned and saturated with hydrogen by treatment first with a 3% aqueous solution of H2O2 and then with hydrogen gas under water at room temperature. Reaction between the surface hydrogen and aqueous RuCl3 deposited 0.18 surface equivalents of Ruad onto the Pt nanoparticles. The deposition was repeated several times, with each reaction depositing ∼0.18 surface equivalents more Ruad onto the Pt–Ruad nanoparticles. The resulting Pt–Ruad nanoparticles were analysed using cyclic voltammetry, CO stripping voltammetry, and as catalysts for electrooxidation of MeOH in three-electrode experiments and in prototype direct methanol fuel cells. The optimum surface coverage (θRu) for electrooxidation of MeOH was ∼0.33 under these conditions. [Copyright &y& Elsevier]

To improve the structure stability and accelerate electrochemical reaction kinetics, oxygen vacancies-enriched sub-7 nm Bi 2.88 Fe 5 O 12- x nanoparticles with high electrochemical activity have been elaborately anchored on two-dimensional MXene nanosheets through a facile electrostatic assembly approach for electrochemical energy storage. MXene nanosheets could not only effectively buffer the serious volume change of Bi 2.88 Fe 5 O 12- x nanoparticles but also facilitate fast electron transfer as a flexible, well-conductive but robust substrate in the fast charge/discharge processes. Owing to the three-dimensional distinct structure and the strong synergistic effects between MXene and Bi 2.88 Fe 5 O 12- x nanoparticles, the obtained composite exhibits impressive electrochemical performances. The composite electrode possesses high gravimetric specific capacity of 176 mAh g−1 with ultrahigh volumetric specific capacity of 476 mAh cm−3 at 0.5 A g−1 in an aqueous electrolyte, superior to those of the so-far reported Bi 2 O 3 -based electrode materials. In addition, our fabricated asymmetric device displays a high volumetric energy density of 177 Wh L−1 and remarkable cycling performance with 93.3% retention ratio after 10,000 cycles. Moreover, the resultant MXene/Bi 2.88 Fe 5 O 12- x composite presents high reversible specific capacity of 805 mAh g−1 for Li-ion storage, corresponding to the volumetric specific capacity of 2176 mAh cm−‍3. Image 1 • Ultrasmall oxygen vacancies-rich Bi 2.88 Fe 5 O 12- x /MXene composite have been prepared. • Supercapacitive charge storage mechanism has been revealed by ex - situ XRD and XPS. • The composite shows high volumetric capacity of 476 mAh cm−3 in 3 M KOH solution. • Our ASC device exhibits an ultrahigh volumetric energy density of 177 Wh L−1. [ABSTRACT FROM AUTHOR]

The need for safe, cost-effective aqueous magnesium ion batteries has led to high electrochemical performance designs of materials and structures to meet strict requirements. A composite of manganese dioxide and carbon molecular sieves (δ -MnO 2 @CMS) with a core-shell structure is used as the cathode in the aqueous magnesium ion battery, which not only solves the inherent deficiencies of low conductivity from manganese dioxide but also maximizes its specific capacities via a hierarchical structure. In addition, the anode material, nanowire VO 2 (formed via a solvothermal reaction) is rarely investigated in this system. Interestingly, this material can form new electrodes with more stable structures after the first charged process and avoids the formation of MgO, thereby providing insertion/extraction of magnesium ions into/from the host anode material. An aqueous rechargeable magnesium ion battery can be successfully assembled using the two electrodes designed above. This device shows high rate properties and delivers reversible capacities of 112.2, 94.6, 78.7, 69.5, and 59.1 mAh g−1 at current densities of 50, 100, 200, 300, and 500 mA g−1. Image 1 • δ -MnO 2 @CMS with core-shell structure is synthesized by hydrothermal method. • The nanowire VO 2 as anode is obtained by simple one-step hydrothermal process. • The Mg2+ insertion/deinsertion mechanism of two electrodes is explored. • Assembled aqueous magnesium-ion battery exhibits excellent rate property. [ABSTRACT FROM AUTHOR]