Superamphiphobic Magnesium Alloys with Extraordinary Environmental Adaptability.

The application of magnesium alloys is seriously limited by their poor environmental adaptability. In this work, we report a robust superamphiphobic coating, which endows magnesium alloys with extraordinary environmental adaptability. The coating was fabricated on magnesium alloys by a facile, cost-effective, and scalable method, one-step particle-free spraying. The as-treated magnesium alloys show excellent superamphiphobicity with the static contact angles (CAs) of water, ethylene glycol, benzyl alcohol, and cyclohexanol droplets of 157.5°, 155.1°, 151.7°, and 151.3°, respectively. These samples also display small dynamic CAs (0° for water and 10° for ethylene glycol) and water super-repellency, which endow magnesium surfaces with droplet impact resistance, self-cleaning, and oil-resistance functions. The simulating environmental-adaptability tests demonstrate that the as-treated magnesium alloys can remain superamphiphobic under various mechanical, chemical, and physical damages including sand impact (⩾10 cycles), water impact (v = 4.5 m·s-1, 2 impacts·s-1, 20 h), abrasion (1.0 kPa, 50 cycles), strong acid/alkaline solution (pH = 1-14), organic solvents immersion (ethylene glycol, n-hexane, ≥48 h), high temperature (200 °C, 72 h), and ultraviolet irradiation (λ = 254 nm, 672 h). The natural environmental-adaptability tests in the acidic industrial atmosphere for 40 days further confirm the robustness of the as-treated magnesium alloys under harsh environments. This work not only provides a promising method for industrially fabricating environmental-adaptable coatings on metallic materials but also paves the way for the much wider applications of magnesium alloys.

Conductive Polymer Binder for High-Tap-Density Nanosilicon Material for Lithium-Ion Battery Negative Electrode Application.

High-tap-density silicon nanomaterials are highly desirable as anodes for lithium ion batteries, due to their small surface area and minimum first-cycle loss. However, this material poses formidable challenges to polymeric binder design. Binders adhere on to the small surface area to sustain the drastic volume changes during cycling; also the low porosities and small pore size resulting from this material are detrimental to lithium ion transport. This study introduces a new binder, poly(1-pyrenemethyl methacrylate-co-methacrylic acid) (PPyMAA), for a high-tap-density nanosilicon electrode cycled in a stable manner with a first cycle efficiency of 82%-a value that is further improved to 87% when combined with graphite material. Incorporating the MAA acid functionalities does not change the lowest unoccupied molecular orbital (LUMO) features or lower the adhesion performance of the PPy homopolymer. Our single-molecule force microscopy measurement of PPyMAA reveals similar adhesion strength between polymer binder and anode surface when compared with conventional polymer such as homopolyacrylic acid (PAA), while being electronically conductive. The combined conductivity and adhesion afforded by the MAA and pyrene copolymer results in good cycling performance for the high-tap-density Si electrode.

Facile and Economic Synthesis of Robust Non-Nucleophilic Electrolyte for High-Performance Rechargeable Magnesium Batteries.

A cost-effective and highly efficient electrolyte with a wide electrochemical window, high reversibility of Mg plating/stripping, non-/low-corrosivity, good compatibility with cathode materials, and tolerance of trace water and impurity is crucial for the commercialization of rechargeable magnesium batteries. In this work, a novel boron-centered non-nucleophilic electrolyte that meets all the above requirements is prepared via a facile and economic approach from the raw materials B(TFE)3/MgCl2/CrCl3/Mg (BMCM). The as-prepared BMCM electrolyte is mainly composed of tetracoordinated anions [B(TFE)4]- and solvated cations [Mg2(µ-Cl)2(DME)4]2+. The BMCM electrolyte demonstrates attractive electrochemical performance, with a low overpotential (∼139 mV), a high Coulombic efficiency (∼97%), a high anodic stability (∼3.5 V vs Mg/Mg2+), and a long-term (more than 500 h) cycling stability. Moreover, BMCM shows good compatibility with the CuS cathode material. The CuS|BMCM|Mg full cell delivers a discharge specific capacity of 231 mAh g-1 (at 56 mA g-1), which can retain ∼88% even after 100 cycles. Importantly, the BMCM electrolyte is cost-effective and tolerant of trace impurity and water, which has great potential to be commercialized. This work is expected to promote the development of practical rechargeable magnesium batteries.

Constructing Colorful Surfaces with Mechanical Robustness for Magnesium Alloys via a Reagent-Free Method.

The colorful and mechanically robust surfaces of metallic materials are important for their applications in electronics, automobile, aerospace, and so on, but it is challenging to prepare them at a reasonable cost. Herein, we propose a simple, environment-friendly, and cost-effective method, reagent-free hydrothermal treatment, to prepare colorful surfaces of magnesium alloys with mechanical robustness. The as-treated surface mainly composes of magnesium (hydr)oxides with a biomimetic microstructure, whose thickness and roughness increase linearly with the hydrothermal time. By adjusting the hydrothermal time, a series of surface colors of magnesium alloys are obtained because of light interference. The as-treated surface with film thickness more than 1.1 µm exhibits high Vickers hardness (∼500 HV), low friction coefficient (∼0.26), and low wear rate (1.06 × 10-5 mm3·N-1·m-1), which is superior to most magnesium alloys after surface treatments. The microstructure of the as-treated surface can be retained after harsh tribological tests, demonstrating attractive mechanical robustness. Furthermore, the method proposed here was extended to the surface treatments of other series of magnesium alloys, which verifies the great potential of this method for large-scale industrial application of colorful metallic materials with mechanical robustness.

Spinel oxide CoFe2O4 grown on Ni foam as an efficient electrocatalyst for oxygen evolution reaction.

The effect of the oxygen evolution reaction (OER) is important in water splitting. In this work, we develop sphere-like morphology spinel oxide CoFe2O4/NF by hydrothermal reaction and calcination, and the diameter of the spheres is about 111.1 nm. The CoFe2O4/NF catalyst exhibits excellent electrocatalytic performance with an overpotential of 273 mV at a current density of 10 mA cm-2 and a Tafel slope of 78 mV dec-1. The cycling stability of CoFe2O4/NF is remarkable, and it only increased by 5 mV at a current density of 100 mA cm-2 after 3000 cycles. Therefore, this simple method to prepare CoFe2O4/NF can enhance the OER properties of electrocatalysts, which makes CoFe2O4/NF a promising material to replace noble metal-based catalysts for the oxygen evolution reaction.

Electrodeposition of amorphous molybdenum sulfide thin film for electrochemical hydrogen evolution reaction.

Amorphous molybdenum sulfide (MoSx) is a highly active noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). The MoSx was prepared by electrochemical deposition at room temperature. Low-cost precursors of Mo and S were adopted to synthesize thiomolybdates solution as the electrolyte. It replaces the expensive (NH)2MoS4 and avoid the poison gas (H2S) to generate or employ. The (MoO2S2)2-, (MoOS3)2- and (MoS4)2- ions were determined by UV-VIS spectroscopy. The electrodeposition of MoSx was confirmed with XRD, XPS and SEM. The electrocatalyst activity was measured by polarization curve. The electrolyte contained (MoO2S2)2- ion and (MoOS3)2- ion electrodeposit the MoSx thin film displays a relatively high activity for HER with low overpotential of 211 mV at a current density of 10 mA cm-2, a relatively high current density of 21.03 mA cm-2 at η = 250 mV, a small Tafel slope of 55 mV dec-1. The added sodium dodecyl sulfate (SDS) can efficient improve the stability of the MoSx film catalyst.

In situ raman microscopy of individual LiNi0.8Co0.15Al0.05O2 particles in a Li-ion battery composite cathode.

Kinetic characteristics of Li+ intercalation/deintercalation into/from individual LiNi0.8Co0.15Al0.05O2 particles in a composite cathode were studied in situ using Raman microscopy during galvanostatic charge-discharge in 1.2 M LiPF6, ethylene carbonate (EC): ethyl methyl carbonate (EMC), 3:7 by volume. Ex situ spectroscopic analysis of a cathode that was removed from a tested high-power Li-ion cell, which suffered substantial power and capacity loss, showed that the state of charge (SOC) of oxide particles on the cathode surface was highly nonuniform despite deep discharge of the Li-ion cell at the end of the test. In situ monitoring of the SOC of selected oxide particles in the composite cathode in a sealed spectro-electrochemical cell revealed that the rate at which particles charge and discharge varied with time and location. The inconsistent kinetic behavior of individual oxide particles was attributed to degradation of the electronically conducting carbon matrix in the composite cathode upon testing. These local microphenomena are most likely responsible for the overall impedance rise of the cathode and contribute to the mechanism of lithium-ion cell failure.

Robust biomimetic-structural superhydrophobic surface on aluminum alloy.

The following facile approach has been developed to prepare a biomimetic-structural superhydrophobic surface with high stabilities and strong resistances on 2024 Al alloy that are robust to harsh environments. First, a simple hydrothermal treatment in a La(NO3)3 aqueous solution was used to fabricate ginkgo-leaf like nanostructures, resulting in a superhydrophilic surface on 2024 Al. Then a low-surface-energy compound, dodecafluoroheptyl-propyl-trimethoxylsilane (Actyflon-G502), was used to modify the superhydrophilic 2024 Al, changing the surface character from superhydrophilicity to superhydrophobicity. The water contact angle (WCA) of such a superhydrophobic surface reaches up to 160°, demonstrating excellent superhydrophobicity. Moreover, the as-prepared superhydrophobic surface shows high stabilities in air-storage, chemical and thermal environments, and has strong resistances to UV irradiation, corrosion, and abrasion. The WCAs of such a surface almost remain unchanged (160°) after storage in air for 80 days, exposure in 250 °C atmosphere for 24 h, and being exposed under UV irradiation for 24 h, are more than 144° whether in acidic or alkali medium, and are more than 150° after 48 h corrosion and after abrasion under 0.98 kPa for 1000 mm length. The remarkable durability of the as-prepared superhydrophobic surface can be attributed to its stable structure and composition, which are due to the existence of lanthanum (hydr)oxides in surface layer. The robustness of the as-prepared superhydrophobic surface to harsh environments will open their much wider applications. The fabricating approach for such robust superhydrophobic surface can be easily extended to other metals and alloys.

Water-only hydrothermal method: a generalized route for environmentally-benign and cost-effective construction of superhydrophilic surfaces with biomimetic micronanostructures on metals and alloys.

The present work demonstrates a generalized strategy using water-only hydrothermal oxidation to construct complex biomimetic micronanostructures on a series of metals and alloys, resulting in superhydrophilic surfaces. This general approach is environmentally-benign and cost-effective, which offers a unique clue for the rational fabrication of micronanoscale architectures and superhydrophilic surfaces.