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Cobalt (Co) mainly exists in two allotropic forms: a low temperature hexagonal close-packed (HCP) structure and a high temperature face-centered cubic (FCC) structure. However, annealing at high temperature only induces the formation of FCC-Co on the surface of a bulk sample and fabrication of bulk FCC-Co is still a great challenge. In this work, nanoporous FCC-Co with a macroscopic dimension is successfully fabricated via a vapor phase alloying (VPA)–vapor phase dealloying (VPD) strategy using zinc (Zn) as the vapor source. Moreover, the thickness of the nanoporous layer could be modulated by adjusting the VPA time. The bulk nanoporous FCC-Co with different shapes and sizes can be fabricated owing to the flexibility and reactivity of the Zn vapor. Both the temperature effect and the size influence contribute to the formation of bulk FCC-Co during the VPD process. In addition, nanoporous FCC-Co shows different magnetic properties as benchmarked with pristine HCP-Co. Our findings provide a new methodology for the preparation of bulk nanoporous FCC-Co which may exhibit unique properties and potential applications. [ABSTRACT FROM AUTHOR]

Realizing highly efficient and selective electrochemical CO2 reduction by using cost-effective catalysts is a key to the large-scale commercialization of this technology. In this work, a nanoporous amalgam catalyst with a tuneable amount of Ag–Hg bonding sites has been developed for selective CO2 electroreduction to formate or CO via a one-step wet-chemistry method. This catalyst is composed of a Ag(Hg) solid solution phase and a Ag–Hg intermetallic compound, exhibiting a loosened nanorod-channel network morphology. The Ag70Hg30 alloy drives efficient formate generation with a high faradaic efficiency of 85% at a moderate overpotential of 790 mV while the Ag91Hg9 alloy promotes CO2 reduction to CO with a faradaic efficiency of 58% at a low overpotential of 590 mV. The switchable product selectivity has been correlated with preferable formation of HCOO* or *COOH intermediates at Ag–Hg and Ag–Ag bonding sites. This work highlights amalgams as novel electrocatalysts for CO2 reduction to valuable products on demand. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction (ECR) depends significantly on the nanostructures of electrocatalysts. Here we show a nanoporous Ag network catalyst (np-Ag) for efficient electrochemical reduction of CO2. The np-Ag samples with an average ligament size of 21 nm (denoted by np-Ag (21 nm)) and 87 nm (denoted by np-Ag (87 nm)) were fabricated by dealloying the rapidly solidified Mg80Ag20 (wt%) alloy ribbons in 1 wt% citric acid and 5 wt% phosphoric acid, respectively. The ligament size effect on the electrocatalytic activity and selectivity of CO2 conversion into CO is investigated. When catalysing CO2 reduction in 0.1 M KHCO3, the np-Ag (21 nm) catalyst exhibits a significantly enhanced selectivity with a faradaic efficiency for CO formation of 85.0% at −0.8 V versus RHE, about two times that (41.2%) over the np-Ag (87 nm). Additionally, a superior catalytic activity is also achieved over the np-Ag (21 nm), with a ＞2.5-fold increase in the CO partial current density relative to the np-Ag (87 nm). The improved selectivity and activity of np-Ag (21 nm) are attributed to the enhanced electrochemical surface area, higher local pH derived from ligament size effect, as well as more defect sites (i.e., grain boundaries) in ligaments. [ABSTRACT FROM AUTHOR]

Rechargeable lithium ion batteries (LIBs) have transformed portable electronics and will play a crucial role in transportation, such as electric vehicles. For higher energy storage in LIBs, two issues should be addressed, that is, the fundamental understanding of the chemistry taking place in LIBs and the discovery of new materials. Here we design and fabricate two-dimensional (2D) WS2 nanosheets with preferential [001] orientation and perfect single crystalline structures. Being used as an anode for LIBs, the WS2-nanosheet electrode exhibits a high specific capacity, good cycling performance and excellent rate capability. Considering the controversy in the lithium storage mechanism of WS2, ex-situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses clearly verify that the recharge product (3.0 V vs. Li+/Li) of the WS2 electrode after fully discharging to 0.01 V (vs. Li+/Li) tends to reverse to WS2. More remarkably, the [001] preferentially-oriented 2D WS2 nanosheets are also promising candidates for applications in photocatalysis, water splitting, and so forth. [ABSTRACT FROM AUTHOR]

As promising electrode materials for electrochemical supercapacitors, pseudocapacitive transition metal oxides such as NiO possess high theoretical specific capacitance, environmental benignity and good abundance. However their areal capacitance and cycling stability are greatly restricted by their poor electronic conductivity (NiO, 10−2 to 10−3 S cm−1). Here we propose an in situ growth strategy in combination with nanoscale design to construct ultrathin mesoporous NiO nanosheets on a 3D network of nickel foam. The hybrid structures show well enhanced conductivity and ion transfer, giving rise to an ultrahigh specific capacitance of 2504.3 F g−1 which is close to the theoretical value of NiO. The electrodes also exhibit remarkable cycling stability (no degradation of the overall capacitance after 45 000 cycles). The amazing electrochemical performance of such hybrid structures makes them potential electrodes in supercapacitors. The present strategy could be popularized in other transition metal oxides like Co3O4, MnO2, etc. to create electrodes with desirable nanostructures. [ABSTRACT FROM AUTHOR]

Here we report the preparation of 3D binder-free NiO nanorod-anchored Ni foam electrodes, and their application as anode materials for rechargeable lithium-ion batteries. By anodization followed by thermal annealing, blooming flower-like NiO arrays were anchored to Ni foam, and were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption experiments. Electrochemical properties were evaluated by cyclic voltammetry (CV) and galvanostatic cycling. Cycling performance shows that after 70 cycles the NiO nanorod-anchored Ni foam electrode can still deliver a stable reversible capacity up to 705.5 mA h g−1 and 548.1 mA h g−1 with a high coulombic efficiency (≥98%) at a constant current density of 1 A g−1 and 2 A g−1, respectively. The superior performance of the NiO electrode can be attributed to its favorable morphology and the excellent electrical contact between NiO and the current collector of Ni foam. The present strategy can be extended to fabricate other self-supported transition metal oxide nanostructures for high-performance lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Nanostructured Cu oxides/hydroxides are promising materials for supercapacitors because of their high theoretical capacitance, low cost and friendliness to environment. However, the development of commercially viable Cu oxides/hydroxides with superior capacitive performance is still challenging. Here, 3D binder-free Cu2O@Cu nanoneedle arrays electrode was developed via facile electrochemistry. The electrode exhibits a high capacitance of 862.4 F g−1 and excellent cycling stability (20 000 cycles). Furthermore, we have successfully constructed a Cu2O@Cu//AC asymmetric supercapacitor, which can achieve an energy density of 35.6 W h kg−1 at 0.9 kW kg−1 and excellent stability with a capacitance retention of 92% after 10 000 cycles. After being charged for dozens of seconds, the in-series Cu2O@Cu//AC supercapacitors can light up LED arrays and even charge a mobile phone. These fascinating performances reasonably indicate their potential in commercial applications for energy storage. [ABSTRACT FROM AUTHOR]

Here we report a facile efficient anodization approach to fabricate nickel oxalate nanostructures on nickel foam (NON@NF). The NON@NF electrode exhibits high specific capacitance and excellent cycling performance. Moreover, an assembled asymmetric super-capacitor based upon NON@NF and activated carbon shows excellent performance with high energy/power density and long cycling stability. [ABSTRACT FROM AUTHOR]