C.D. Gu

Three-dimensional astrocyte-network Ni–P–O compound with superior electrocatalytic activity and stability for methanol oxidation in alkaline environments

Three Ni–P–O compound catalysts with tunable architectures and compositions have been fabricated using a facile one-pot solvothermal method, which are named astrocyte-network Ni–P (Ni–Pan), silkworm cocoon-like Ni–P (Ni–Psc), and microsphere Ni–P (Ni–Pm), respectively. The final architecture of the Ni–P–O catalysts is strongly dependent on the Ni2+/H2PO2− molar ratio in the reaction system, which leads to a delicate balance between kinetic and thermodynamic growth regimes. Three-dimensional ensemble of Ni–Pan with a higher P content is composed of many amorphous Ni–P nanowires with a diameter of about 4 nm, which delivers a significantly larger BET surface area of 500.5 m2 g−1. Moreover, nickel phosphides and nickel phosphates are formed in the three Ni–P–O samples. Ni–Pan exhibits a higher peak current density of ∼1490 A g−1, better electrode accessibility, faster charge-transfer process, and long-term chronoamperometry stability (≥20 000 s) toward methanol oxidation in alkaline solution, which are superior to most state-of-art Ni–P catalysts and the Ni–Psc and Ni–Pm in this case. The superior catalytic performance of the Ni–Pan catalyst is attributed to its unique microstructure and compositions. According to X-ray photoelectron spectroscopy, a strong electronic interaction between nickel phosphides and nickel phosphates might also contribute to the improved catalytic activity of the Ni–Pan catalyst.

Bi-functional Mo-doped WO3 nanowire array electrochromism-plus electrochemical energy storage

Metal-doping is considered to be an effective way for construction of advanced semiconducting metal oxides with tailored physicochemical properties. Herein, Mo-doped WO3 nanowire arrays are rationally fabricated by a sulfate-assisted hydrothermal method. Compared to the pure WO3, the optimized Mo-doped WO3 nanowire arrays exhibit improved electrochromic properties with fast switching speed (3.2s and 2.6s for coloration and bleaching, respectively), significant optical modulation (56.7% at 750nm, 83.0% at 1600nm and 48.5% at 10μm), high coloration efficiency (123.5cm(2)C(-1)) and excellent cycling stability. In addition, as a proof of concept, the Mo-doped WO3 nanowire arrays are demonstrated with electrochemical energy storage monitored by the electrochromism. This electrode design protocol can provide an alternative way for developing high-performance active materials for bi-functional electrochromic batteries.

Cation–anion double hydrolysis derived layered single metal hydroxide superstructures for boosted supercapacitive energy storage

As promising battery-type electrode materials, layered single metal hydroxides (LSHs) including α-Ni(OH)2 and α-Co(OH)2 based hybrid supercapacitors exhibit larger operating voltages compared with those that are based on activated carbons and double-layer capacitance mechanisms. This study proposes a novel and facile room-temperature method to fabricate α-Ni(OH)2 and α-Co(OH)2 superstructures by using the double hydrolysis of Ni2+ or Co2+ and NCO− without the presence of any structure directing agent. Two dimensional sheet-like building blocks of the alpha-type metal hydroxide are assembled into various elegant morphologies including a 3D interconnected hierarchical assembly (3D-ICHA), sheet-on-sheet, sheet-on-rod and other nanostructures, which depends on the cation–anion mixing mode. Significantly, the 3D-ICHA α-Ni(OH)2 possesses an ultrahigh specific surface area (320.2 m2 g−1) and robust porous structure. An outstanding initial specific capacity (653.1 C g−1 at 1 A g−1 and 406 C g−1 at 20 A g−1) and an excellent cycling retention (86.2% in 20 000 cycles) were obtained for the 3D-ICHA α-Ni(OH)2, which stands out from most of the state-of-the-art α-Ni(OH)2 powder-based materials. A high-loading asymmetric capacitor with excessive activated carbon (∼10 mg 3D-ICHA α-Ni(OH)2vs. ∼60 mg activated carbon) is demonstrated and it works very steadily even after 20 000 charge/discharge cycles.

Spinel type CoFe oxide porous nanosheets as magnetic adsorbents with fast removal ability and facile separation

Adsorption is often time consuming due to slow diffusion kinetic. Sizing he adsorbent down might help to accelerate adsorption. For CoFe spinel oxide, a magnetically separable adsorbent, the preparation of nanosheets faces many challenges including phase separation, grain growth and difficulty in preparing two-dimensional materials. In this work, we prepared porous CoFe oxide nanosheet with chemical formula of Co2.698Fe0.302O4 through topochemical transformation of a CoFe precursor, which has a layered double hydroxide (LDH) analogue structure and a large interlayer spacing. The LDH precursor was synthesized from a cheap deep eutectic solvent (DES) system. The calcined Co2.698Fe0.302O4 has small grain size (10-20nm), nanosheet morphology, and porous structure, which contribute to a large specific surface area of 79.5m(2)g(-1). The Co2.698Fe0.302O4 nanosheets show fast removal ability and good adsorption capacity for both organic waste (305mgg(-1) in 5min for Congo red) and toxic heavy metal ion (5.27mgg(-1) in 30min for Cr (VI)). Furthermore, the Co2.698Fe0.302O4 can be separated magnetically. Considering the precursor can be prepared through a fast, simple, surfactant-free and high-yield synthetic strategy, this work should have practical significance in fabricating adsorbents.

Crystalline/amorphous tungsten oxide core/shell hierarchical structures and their synergistic effect for optical modulation

High-performance electrochromic films with large color contrast and fast switching speed are of great importance for developing advanced smart windows. In this work, crystalline/amorphous WO3 core/shell (c-WO3@a-WO3) nanowire arrays rationally are synthesized by combining hydrothermal and electrodeposition methods. The 1D c-WO3@a-WO3 core/shell hierarchical structures show a synergistic effect for the enhancement of optical modulation, especially in the infrared (IR) region. By optimizing the electrodeposition time of 400s, the core/shell array exhibits a significant optical modulation (70.3% at 750nm, 42.0% at 2000nm and 51.4% at 10μm), fast switching speed (3.5s and 4.8s), high coloration efficiency (43.2cm(2)C(-1) at 750nm) and excellent cycling performance (68.5% after 3000 cycles). The crystalline/amorphous nanostructured film can provide an alternative way for developing high-performance electrochromic materials.

Electrodeposition, Morphology, Composition, and Corrosion Performance of Zn-Mn Coatings from a Deep Eutectic Solvent

Different Zn-Mn coatings were successfully electrodeposited on copper substrates from deep eutectic solvent-based electrolytes containing boric acid as an additive. The main objective of this work was to optimize the Zn/Mn ratios and morphologies of the as-electrodeposited Zn-Mn films in order to obtain better corrosion protection performance coatings. The electrodeposition behaviors of Zn-Mn alloys as studied by cyclic voltammetry showed that with increase in electrolyte Mn(II) concentration, Zn(II) ion reduction occurs at higher overpotentials while Mn reduction occurs at lower overpotentials, and this in turn enhances Mn incorporation into the deposit. Characterization results showed that the electrodeposition potential and electrolyte Mn(II) concentration significantly affects the Mn content, crystal structure, surface morphology, and corrosion performance of the deposits. With increase in electrodeposition potential and electrolyte Mn(II) concentration, the alloy Mn increased and the grain morphology was refined. The crystal structure of Zn-Mn deposits consists of Zn and hexagonal close packed ε-phase Zn-Mn at low electrodeposition potentials and low electrolyte Mn(II) content. However, at high electrodeposition potentials and electrolyte Mn(II) contents, the crystal structure was only composed of hexagonal close packed ε-phase Zn-Mn. Corrosion measurements show that all the Zn-Mn samples have a passivating behavior and exhibits higher corrosion resistances when compared to those from aqueous solutions. Thus, optimum electrodeposition potential and electrolyte Mn(II) concentration were determined producing compact Zn-Mn films with the best corrosion resistance.

Niobium doped tungsten oxide mesoporous film with enhanced electrochromic and electrochemical energy storage properties

Exploring high performance cathode materials is of great means for the development of bi-functional electrochromic energy storage devices. Herein, Nb-doped WO3 mesoporous films as integrated high-quality cathode are successfully constructed via a facile sol-gel method. Chemical state and crystallinity of the WO3 based films are significantly influenced by doping concentration. Compared with the pure WO3, the optimal Nb-doped film shows improved optical-electrochemical properties with high specific capacity (74.4 mAh g-1 at 2 A g-1), excellent high-rate capability, large optical contrast (61.7% at 633 nm), and ultra-fast switching speed (3.6 s and 2.1 s for coloring and bleaching process, respectively). These positive features suggest the potential application of Nb-doped WO3 mesoporous cathode. Our research paves the way for the development of multifunctional photoelectrochemical energy devices.