3D binder-free NiO nanorod-anchored Ni foam electrodes synthesized by in situ anodization and annealing exhibit superior cyclability and high rate performance.

Here, we report the fabrication of ultrafine nanoporous PdFe/Fe 3 O 4 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/Fe 3 O 4 nanocomposites show excellent electrocatalytic activities towards the oxidation of methanol and ethanol in alkaline media due to the double enhancement from Fe 3 O 4 and Fe in PdFe. In addition, the nanoporous PdFe/Fe 3 O 4 sample dealloyed from the Al 75 Pd 12.5 Fe 12.5 precursor exhibits the highest electrocatalytic activity. These materials are potential anode electrocatalysts for applications in direct alcohol fuel cells.

As promising electrode materials for electrochemical supercapacitors, pseudocapacitive transition metal oxides such as NiO possess high theoretical specific capacitance, environmental benignity and well abundance. However their areal capacitance and cycling stability are greatly restricted by poor electronic conductivity (NiO, 10 −2~1 0 -3 S cm -1 ). Here we propose an in-situ growth strategy in combination with nanoscale design to construct ultrathin mesoporous NiO nanosheets on 3D network of nickel foam. The hybrid structures show well enhanced conductivity and ion transfer, giving rise to ultrahigh specific capacitance of 2504.3 F g -1 which is close to the theoretical value of NiO. The electrodes also exhibit remarkable cycling 2 stability (no degradation of the overall capacitance after 45000 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 Co 3 O 4 , MnO 2 , etc, to create electrodes with desirable nanostructures. IntroductionDue to the development of portable systems and hybrid electric vehicles (HEVs), the demand for high power in short-term pulses is increasing greatly. Among energy storage devices, supercapacitors have attracted considerable interests recently owing to their high power density, long lifespan and good pulse charge-discharge characteristics. 1-3 Since practical applications of supercapacitors highly depend on the performance of electrodes, how to design and obtain high-capacity, low-cost and safe electrode materials turns to be a great challenge. As is well known, conventional carbon-based materials suffer from really low specific capacitance (100-120 F g -1 ) and energy density (~4-5 Wh kg -1 ). 4 Transition metal oxides are considered as promising alternative electrode materials for high pseudocapacitance owing to their multiple accessible valence states for efficient reversible redox reactions. 5,6 Pseudocapacitive transition metal oxides, hydroxides and oxalates (such as RuO 2 , MnO 2 , NiO, Co 3 O 4 , Ni(OH) 2 , Co(OH) 2 , NiC 2 O 4 etc.) and their composites could produce a much higher 3 capacitance than carbonaceous electrode materials. For example, RuO 2 demonstrates high specific capacitance (more than 600 F g -1 ) and excellent reversibility. 4, 7 Yang et al.have reported that Co 3 O 4 demonstrated superior capacitance (~1782 F g -1 ) and long-term stability (>90% of capacitance after 2000 cycles). 8 NiC 2 O 4 electrodes have been developed to show high specific capacitance of 813.5 F g -1 and excellent cycling performance with 92.5 % retention after 10000 cycles and excellent capability as asymmetric supercpacitors. 9 Nevertheless, the semiconductor or insulator nature of transition metal oxides largely restricts their performances in supercapacitors. Among the pseudocapacitive materials, NiO is considered to be particularly potential for applications in supercapacitors, owing to its low cost, environmental friendliness an...

Bulk hierarchically nanoporous nickel has been fabricated by dealloying and it shows state-of-the-art electrochemical actuation properties in alkaline electrolytes.

Metal-hydrogen (in particular, Pd-H) interactions have been receiving considerable attention over the past 150 years within the scope of hydrogen storage, catalytic hydrogenation, hydrogen embrittlement and hydrogen-induced interfacial failure. Here, for the first time, we show that the coupling of hydrogen adsorption and absorption could trigger giant reversible strain in bulk nanoporous Pd (np-Pd) in a weakly adsorbed NaF electrolyte. The bulk np-Pd with a hierarchically porous structure and a ligament/channel size of ∼10 nm was fabricated using a dealloying strategy with compositional/structural design of the precursor. The np-Pd actuator exhibits a giant reversible strain of up to 3.28% (stroke of 137.8 μm), which is a 252% enhancement in comparison to the state-of-the-art value of 1.3% in np-AuPt. The strain rate (∼10(-5) s(-1)) of np-Pd is two orders of magnitude higher than that of current metallic actuators. Moreover, the volume-/mass-specific strain energy density (10.71 MJ m(-3)/3811 J kg(-1)) of np-Pd reaches the highest level compared with that of previously reported actuator materials. The outstanding actuation performance of np-Pd could be attributed to the coupling of hydrogen adsorption/absorption and its unique hierarchically nanoporous structure. Our findings provide valuable information for the design of novel high-performance metallic actuators.