Qingguo Bai

Ultrafine nanoporous PdFe/Fe3O4 catalysts with doubly enhanced activities towards electro-oxidation of methanol and ethanol in alkaline media

Here, we report the fabrication of ultrafine nanoporous PdFe/Fe3O4 electrocatalysts by a facile dealloying strategy. The results show that the phase formation of the as-dealloyed samples is dependent upon the Pd : Fe atomic ratio in the Al–Pd–Fe ternary precursors. The size of ligaments is as small as ∼2 nm in the nanoporous structure of the as-dealloyed samples, which is the smallest among the literature data reported for nanoporous metals/alloys. The present nanoporous PdFe/Fe3O4 nanocomposites show excellent electrocatalytic activities towards the oxidation of methanol and ethanol in alkaline media due to the double enhancement from Fe3O4 and Fe in PdFe. In addition, the nanoporous PdFe/Fe3O4 sample dealloyed from the Al75Pd12.5Fe12.5 precursor exhibits the highest electrocatalytic activity. These materials are potential anode electrocatalysts for applications in direct alcohol fuel cells.

NiO nanorod array anchored Ni foam as a binder-free anode for high-rate lithium ion batteries

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.

Ultrathin mesoporous NiO nanosheet-anchored 3D nickel foam as an advanced electrode for supercapacitors

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.

Nickel oxide nanopetal-decorated 3D nickel network with enhanced pseudocapacitive properties

Metal oxides possess high theoretical specific capacitance, but their pseudocapacitive properties are restricted by the poor electronic conductivity. Here we present a strategy to synthesize a three-dimensional binder/conducting agent-free nickel oxide (NiO) electrode through the combination of anodization with calcination. The NiO electrode is composed of a 3D conductive nickel network decorated with nanopetal-like NiO arrays. The influence of calcination temperature has been investigated, with respect to the microstructure and pseudocapacitive properties of the NiO electrodes. The NiO electrode demonstrates great electrochemical properties, especially remarkable rate capability (82% retention of the highest value for the 25-fold enhanced current density) and cycling stability (good capacitance retention after 30000 cycles). Moreover, an asymmetric supercapacitor has been assembled using NiO as the positive electrode and activated carbon (AC) as the negative electrode. The NiO//AC supercapacitor presents excellent cycling stability (91.3% retention after 10000 cycles), and could power a mini fan as well as a commercial red LED for more than 270 min.

Atomic layer-by-layer construction of Pd on nanoporous gold via underpotential deposition and displacement reaction

Atomic layer-by-layer construction of Pd on nanoporous gold (NPG) has been investigated through the combination of underpotential deposition (UPD) with displacement reaction. It has been found that the UPD of Cu on NPG is sensitive to the applied potential and the deposition time. The optimum deposition potential and time were determined through potential- and time-sensitive stripping experiments. The NPG-Pd electrode shows a different voltammetric behavior in comparison to the bare NPG electrode, and the deposition potential was determined through the integrated charge control for the monolayer UPD of Cu on the NPG-Pd electrode. Five layers of Pd were constructed on NPG through the layer-by-layer deposition. In addition, the microstructure of the NPG-Pdx (x = 1, 2, 3, 4 and 5) films was probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The microstructural observation demonstrates that the atomic layers of Pd form on the ligament surface of NPG through epitaxial growth, and have no effect on the nanoporous structure of NPG. In addition, the hydrogen storage properties of the NPG-Pdx electrodes have also been addressed.

Flexible and ultralong-life cuprous oxide microsphere-nanosheets with superior pseudocapacitive properties

Nanostructured transition metal oxides have been investigated extensively for supercapacitor electrodes due to their high theoretical specific capacitance, low-cost, environment benignity and abundance. However, pristine transition metal oxides suffer from difficulty of synthesis, poor electronic conductivity and mechanical flexibility. In this work, we report a facile, low-cost and high-throughput synthesis of hierarchical structure which consists of cuprous oxide (Cu2O) microsphere-nanosheets on the surface of flexible Cu foil (namely Cu2O@Cu) via a two-step electrochemical method (anodization and electro-oxidation). The influence of the anodization parameters on surface roughness of Cu foil has been investigated, and the optimum anodization procedure was determined to be 50 V for 4 cycles. This Cu2O@Cu electrode exhibits excellent capacitance properties, such as up to 390.9 mF cm−2 at 2 mA cm−2 in areal capacitance, and high flexibility, as observed by cyclic voltammetry measurement under various deformation (bending and folding) situations. Furthermore, the Cu2O@Cu electrode presents superior long-term cycling stability over 100 000 cycles, with the capacitance retention of over 80%. The present binder-free Cu2O@Cu microsphere-nanosheets electrode is highly promising for future applications in flexible supercapacitors.

Hierarchically nanoporous nickel-based actuators with giant reversible strain and ultrahigh work density

Metallic actuators (metallic muscles) have attracted a great deal of interest because of their potential advantages over piezoelectric ceramics and conducting polymers. However, to develop high performance actuators using earths abundant and inexpensive metallic elements is a formidable challenge so far. Here, we report the design and fabrication of nickel-based actuators with low material cost (<1/2000 of gold), which demonstrate an unprecedented performance including giant reversible strain (up to 2%), ultrahigh work density (11.76 MJ m−3, the highest among the known actuator materials), and long cycle life (70% strain retention after 10 000 cycles). This outstanding performance of the nickel-based actuators originates from their unique hierarchically nanoporous structure and the oxide-covered nature of the Ni surface.

Large-scale synthesis and catalytic activity of nanoporous Cu–O system towards CO oxidation

Nanoporous Cu–O system catalysts with different oxidation states of Cu have been fabricated through a combination of dealloying as-milled Al66.7Cu33.3 alloy powders and subsequent thermal annealing. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the microstructure and surface chemical states of Cu–O catalysts. The peculiar nanoporous structure can be retained in Cu–O catalysts after thermal treatment. Catalytic experiments reveal that all the Cu–O samples exhibit complete CO conversion below 170 °C. The optimal catalytic performance could be achieved through the combination of annealing in air with hydrogen treatment for the Cu–O catalyst, which shows a near complete conversion temperature (T90%) of 132 °C and an activation energy of 91.3 KJ mol−1. In addition, the present strategy (ball milling, dealloying and subsequent thermal treatment) could be scaled up to fabricate high-performance Cu–O catalysts towards CO oxidation.