Hierarchically Structured Nanoporous Palladium with Ordered/Disordered Channels for Ultrahigh and Fast Strain.

Metallic actuators have increasingly shown the potential to replace conventional piezoelectric ceramics and conducting polymers. However, it is still a great challenge to achieve strain amplitudes over 4% while maintaining fast strain responses. Herein, we fabricated bulk nanoporous palladium (NP-Pd) with microsheet-array-like hierarchically nanoporous (MAHNP) structure by dealloying a eutectic Al-Pd precursor. The hierarchical structure consists of array-like microsized channels/sheets and disordered nanosized networks. The locally ordered channels play a critical role in fast mass transport while nanoligaments accumulate a large surface area for hydrogen adsorption/absorption and desorption. Therefore, the MAHNP-Pd not only obtains a fast strain rate with the maximum value close to 1 × 10-4 s-1 but also exhibits an ultrahigh strain amplitude of 4.68%, exceeding all reported values for bulk electrochemical metallic actuators to date. Additionally, the superiority of the MAHNP structure is demonstrated in transport kinetics as benchmarked with the scenario of unimodal NP-Pd.

Formation, lithium storage properties, and mechanism of nanoporous germanium fabricated by dealloying.

Germanium (Ge) has become a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and decent electron/ion conductivity, but it exhibits inferior lifespan caused by dramatic volume variations during the (de)lithiation process. Herein, hierarchically, nanoporous Ge (np-Ge) was fabricated by the combination of selective phase corrosion with chemical dealloying. As an anode for LIBs, the np-Ge electrode exhibits marvelous cycling stability with capacity retentions of 1060.0 mA h g-1 at 0.2 A g-1 and 767.1 mA h g-1 at 1 A g-1 after 100 cycles. Moreover, the electrode shows excellent rate capability with a capacity retention of 844.2 mA h g-1 at 5 A g-1. Noticeably, the (de)lithiation mechanisms of np-Ge and porous Si-Ge (p-Si6Ge4) were unveiled by operando X-ray diffraction.

Design of Metal@Titanium Oxide Nano-heterodimers by Laser-Driven Photodeposition: Growth Mechanism and Modeling.

In order to circumvent the usual nucleation of randomly distributed tiny metallic dots photodeposited on TiO2 nanoparticles (NPs) induced by conventional UV lamps, we propose to synthesize well-controlled nanoheterodimers (NHDs) using lasers focused inside microfluidic reactors to strongly photoactivate redox reactions of active ions flowing along with nanoparticles in water solution. Since the flux of photons issued from a focused laser may be orders of magnitude higher than that reachable with classical lamps, the production of electron-hole pairs is tremendously increased, ensuring a large availability of carriers for the deposition and favoring the growth of a single metallic dot as compared to secondary nucleation events. We show that the growth of single silver or gold nanodots can be controlled by varying the beam intensity, the concentration of the metallic salt, and the flow velocity inside the microreactor. The confrontation to a build-in model of the metallic nanodot light-induced growth onto the surface of TiO2 NPs shows the emergence of a predictable "master behavior" on which individual growths obtained from various tested conditions do collapse. We also characterized the associated quantum yield. Eventually, we successfully confronted our model to growth data from the literature in the case of silver on TiO2 and gold on II-VI semiconducting NPs triggered by UV lamps. It shows that for the photosynthesis of NHDs the efficiency of the electron-hole pair production rate matters much more than the number of pairs produced and that the use of laser light can provide a photodeposition-based synthesis at the nanoscale.

Hydrothermal Transformation of Titanate Scrolled Nanosheets to Anatase over a Wide pH Range and Contribution of Triethanolamine and Oleic Acid to Control the Morphology.

Mild hydrothermal conditions used for the treatment of titanate scrolled nanosheets (SNSs) suspensions (140 °C, 72 h) resulted in a large variety of anatase TiO2 anisotropic nano-objects depending on the studied parameters: influence of the medium pH and the presence or not of structuring agents (SAs). The present work shows that such a hydrothermal treatment of the SNSs, whatever the pH, resulted in the formation of single-crystalline anatase nanoneedles (NNs) with a specific crystal-elongation direction and a pH-dependent morphological anisotropy with aspect ratios (ARs) from 1 to 8. The SNSs suspensions were prepared by the conventional ultrabasic treatment of TiO2 with NaOH, followed by washing with HNO3 to different pH values. The crystal size of the anatase TiO2 obtained from this hydrothermal treatment increased with the pH of the suspensions, from 15 nm nanoparticles (NPs; AR = 1) at pH 2.2 to 500 nm NNs (AR = 8) at a pH 10.8 with a long axis systematically along the anatase [001] direction. Triethanol amine and oleic acid were used as SAs. Their respective influence, when acting on their own, had little influence on the control of the size, shape, or polydispersity of the NNs. However, their concomitant use provided a much better control of not only the size and polydispersity, which was strongly reduced, but also on (i) the shape and morphology giving rise to a controlled access to well-defined nanorods as opposed to nanoneedles and (ii) the crystal phase purity eliminating the few percent brookite still visible in the X-ray diffraction patterns of samples prepared in SA-free conditions. This approach offers an on-demand control over the production of anatase morphologies with defined aspect ratios.

A systems approach to extraordinarily major coal mine accidents in China from 1997 to 2011: an application of the HFACS approach.

This study aimed to provide a greater understanding of the systemic factors involved in coal mine accidents and to examine the relationships between the contributing factors across all levels of the system. Ninety-four extraordinarily major coal mine accidents that occurred in China from 1997 to 2011 were analyzed using the human factors analysis and classification system (HFACS). The empirical results showed that the frequencies of unsafe behaviors, inadequate regulation and failure to correct hidden dangers were the highest among five levels, 14 categories and 48 indicators, respectively. The odds ratio technique was applied to quantitatively examine the relationships between contributing factors. Various statistically significant associations were discovered and should receive greater attention in future attempts to develop accident measures. In addition, several strategies concerning the main contributing factors and routes to failure are proposed to prevent accidents from reoccurring in an organization.

Decision-Making and Environmental Implications under Cap-and-Trade and Take-Back Regulations.

To reduce carbon emissions during production and realize the recycling of resources, the government has promulgated carbon cap-and-trade regulation and take-back regulation separately. This paper firstly analyses the manufacturing, remanufacturing and collection decisions of a monopoly manufacturer under cap-and-trade regulation and take-back regulation conditions, and then explores the environmental impact (i.e., carbon emissions) of both carbon regulation and more stringent take-back regulation. Finally, numerical examples are provided to illustrate the theoretical results. The results indicate that it will do good for the environment once the cap-and-trade regulation is carried out. We also conclude that government’s supervision of carbon trading price plays an important role in reducing the environmental impact. Furthermore, unexpectedly, we prove that if emissions intensity of a remanufactured (vis-á-vis new) product is sufficiently high, the improvement of collection and remanufacturing targets might lead to the deterioration of environment.

Sign inversion of surface stress-charge response of bulk nanoporous nickel actuators with different surface states.

The surface stress-charge coefficient, ζ, is a fundamental material parameter and reflects the response of surface stress to the change of superficial charge. The sign and the quantity of ζ play a crucial role in electrochemically induced actuation of nanostructured metals. Here, for the first time, we address the electrochemical actuation and the associated stress-charge coefficients of bulk nanoporous nickel (np-Ni) in both strongly (NaOH) and weakly (NaF) adsorbed electrolytes. The results reveal a normal negative value of ζ for the np-Ni with the clean surface, and unusual positive values of ζ for the oxide-covered surface. Interestingly, the oxidized np-Ni cannot recover the conventional negative value of ζ even in the cathodic potential window. Moreover, the reversible strain amplitude and the involved charge are quite different in distinct potential windows (the same electrolyte) or in different electrolytes (strongly or weakly adsorbed). In addition, density functional theory (DFT) calculations have been performed to understand the electrochemical actuation behaviors of the np-Ni with different surface states. In some aspects, the scenario of the np-Ni indeed differs from that of nanoporous noble metals like Au or Pt. Our findings provide useful information on understanding the electrochemical actuation of nanostructured metals, and novel actuators or sensors could be developed based upon earth-abundant metals like Ni, Co, and so forth.

Dealloying-driven nanoporous palladium with superior electrochemical actuation performance.

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.