Regulating the Oxygen Vacancy and Electronic Structure of NiCo Layered Double Hydroxides by Molybdenum Doping for High-Power Hybrid Supercapacitors.

Amelioration of nickel-cobalt layered double hydroxides (NiCo-LDH) with a high specific theoretical capacitance is of great desire for high-power supercapacitors. Herein, a molybdenum (Mo) doping strategy is proposed to improve the charge-storage performance of NiCo-LDH nanosheets growing on carbon cloth (CC) via a rapid microwave process. The regulation of the electronic structure and oxygen vacancy of the LDH is consolidated by the density functional theory (DFT) calculation, which demonstrates that Mo doping narrows the band gap, reduces the formation energy of hydroxyl vacancies, and promotes ionic and charge transfer as well as electrolyte adsorption on the electrode surface. The optimal Mo-doped NiCo-LDH electrode (MoNiCo-LDH-0.05/CC) has an amazing specific capacity of 471.1 mA h g-1 at 1 A g-1 , and excellent capacity retention of 84.8% at 32 A g-1 , far superior to NiCo-LDH/CC (258.3 mA h g-1 and 76.4%). The constructed hybrid supercapacitor delivers an energy density of 103.3 W h kg-1 at a power density of 750 W kg-1 and retains the cycle retention of 85.2% after 5000 cycles. Two assembled devices in series can drive thirty LED lamps, revealing a potential application prospect of the rationally synthesized MoNiCo-LDH/CC as an energy-storage electrode material.

Hierarchical core-shell nickel hydroxide@nitrogen-doped hollow carbon spheres composite for high-performance hybrid supercapacitor.

Designing electrode materials with high performance and maximum utilization is of great desire for supercapacitors, which highly depend on the intrinsic electrochemical properties and the optimal frameworks of the electrode materials. The hierarchical core-shell structure with various types of pores can make the most of the electrode material due to the easy access of electrolyte into the interior electrode and large exposure of electrode into the electrolyte. In this work, nickel hydroxide@nitrogen-doped hollow carbon spheres (Ni(OH)2@NHCSs) electrode material with a hierarchical core-shell structure was obtained using a hard template and the following chemical-precipitation method. Ni(OH)2@NHCSs electrode displays an excellent specific capacity of 214.8 mA h g-1 (that is 1546.6 F g-1), higher than the Ni(OH)2 counterpart (108.9 mA h g-1, that is 784.1 F g-1) at 1 A g-1 in 2 M KOH electrolyte. The assembled Ni(OH)2@NHCSs||NHCSs hybrid supercapacitor (HSC) delivers an energy density of 37.5 W h kg-1 at 800.0 W kg-1 and an outstanding stability with 79.2% of retention rate for 10,000 cycles at a current density of 8 A g-1. The Ni(OH)2@NHCSs electrode exhibits excellent electrochemical performance primarily contributed by its unique hierarchical core-shell structure, high specific surface area and enhanced electrical conductivity.

Photocatalytic Removal of Antibiotics on g-C3N4 Using Amorphous CuO as Cocatalysts.

Amorphous CuO is considered as an excellent cocatalyst, owing to its large surface area and superior conductivity compared with its crystalline counterpart. The current work demonstrates a facile method to prepare amorphous CuO, which is grown on the surface of graphitic carbon nitride (g-C3N4) and is then applied for the photocatalytic degradation of tetracycline hydrochloride. The prepared CuO/g-C3N4 composite shows higher photocatalytic activities compared with bare g-C3N4. Efficient charge transfer between g-C3N4 and CuO is confirmed by the photocurrent response spectra and photoluminescence spectra. This work provides a facile approach to prepare low-cost composites for the photocatalytic degradation of antibiotics to safeguard the environment.

Accelerating Hydrogen Evolution by Anodic Electrosynthesis of Value-Added Chemicals in Water over Non-Precious Metal Electrocatalysts.

Integrating electrolytic hydrogen production from water with thermodynamically more favorable aqueous organic oxidation reactions is highly desired, because it can enhance the energy conversion efficiency in relation to traditional water electrolysis, and produce value-added chemicals instead of oxygen at the anode. In this Minireview, we introduce some key considerations for anodic auxiliary electrosynthesis and outline three types of electrocatalytic organic reactions including biomass derivative, alcohol and amine oxidation reactions, which can boost cathodic hydrogen generation. Furthermore, frequently used noble-metal-free electrocatalysts are classified into nickel-based, cobalt-based, other transition-metal-based and bimetallic electrocatalysts. The preparation methods of these catalysts and their performance towards electrochemical oxidation reactions are also discussed in detail. We specifically highlight the importance of redox active sites on the surface of the electrocatalysts, which act as electron mediators to promote oxidation reactions. Finally, the current challenges and future developments in this emerging field are also discussed.

Accelerating H2 Evolution by Anodic Semi-dehydrogenation of Tetrahydroisoquinolines in Water over Co3 O4 Nanoribbon Arrays Decorated Nickel Foam.

Coupling the H2 evolution reaction in water with thermodynamically favorable organic oxidation reactions is highly desirable, because it can enhance the energy conversion efficiency compared with electrocatalytic water splitting, and produce value-added chemicals instead of O2 in the anodic reaction. Herein, Co3 O4 nanoribbon arrays in situ grown on nickel foam (Co3 O4 @NF) was employed as an effective electrocatalyst for the selective oxidation of tetrahydroisoquinolines (THIQs). Various value-added semi-dehydrogenation products including dihydroisoquinolines with electro-deficient or -rich groups could be obtained with moderate yields and faradaic efficiencies. Benefitting from the rich surface active sites of Co3 O4 @NF, a two-electrode (Co3 O4 @NF||Pt) electrolytic system drove a benchmark current density of 10 mA cm-2 at a cell voltage as low as 1.446 V in 1.0 M KOH aqueous solution containing 0.02 M THIQ, which was reduced by 174 mV in comparison with that of overall water splitting.

Bimetallic nickel molybdate supported Pt catalyst for efficient removal of formaldehyde at low temperature.

Efficient removal of formaldehyde from indoor environments is of significance for human health. In this work, a typical binary transition metal oxide that could provide various oxidation states, ß-NiMoO4, was employed as a support to immobilize the active Pt component (Pt/NiMoO4) for catalytic formaldehyde elimination at low ambient temperature (15°C). The results showed that the hydrothermal preparation temperature and time had a noticeable impact on the morphology and catalytic activity of the samples. The catalyst prepared with hydrothermal temperature of 150°C for 4 hr (Pt-150-4) exhibited superior catalytic activity and stability mainly due to its distinctly porous structure, relative abundance of adsorbed surface hydroxyls/water, and high oxidation ability, which resulted from the interaction of Pt with Ni and Mo of the bimetallic NiMoO4 support. Our results might shed light on the rational design of multifunctional catalysts for removal of indoor air pollutants at low ambient temperature.

Hydroxyapatite-Supported Low-Content Pt Catalysts for Efficient Removal of Formaldehyde at Room Temperature.

Indoor environmental quality directly affects the life quality and health of human beings, and therefore, it is highly vital to eliminate the volatile organic compounds especially formaldehyde (HCHO), which is regarded as one of the most common harmful pollutants in indoor air. Hydroxyapatite (HAP)-supported Pt (Pt/HAP) catalysts with a low content of Pt (0.2 wt %) obtained via hydrothermal and chemical reduction processes could effectively remove gaseous HCHO from the indoor environment at room temperature. The influence of modifier in the preparation on the catalyst activity was investigated. The HAP and HAP modified by sodium citrate and hexamethylenetetramine-supported 0.2 wt % Pt could completely decompose HCHO into CO2 and water, while HAP modified by sodium dodecyl-sulfate-supported Pt removed HCHO primarily via adsorption. The HAP modified by the sodium citrate catalyst exhibited superior catalytic performance of HCHO compared to the HAP and HAP modified by hexamethylenetetramine and sodium dodecyl-sulfate-supported Pt catalysts, which was mainly because of its higher surface Ca/P ratio providing more Lewis acidic sites (Ca2+) for co-operational capture of HCHO molecules and a larger amount of active oxygen species. Our results indicate that an optimized combination of functional supports and low-content noble metal nanoparticles could be a route to fabricate effective room-temperature catalysts for potential application in indoor air purification.

Enhanced room-temperature catalytic decomposition of formaldehyde on magnesium-aluminum hydrotalcite/boehmite supported platinum nanoparticles catalyst.

Magnesium-aluminum hydrotalcite (Mg-Al HT)/boehmite (AlOOH) composite supported Pt catalysts were obtained via one-pot microemulsion synthesis of Mg-Al HT/AlOOH composite and NaBH4-reduction of Pt precursor processes. The catalytic performances of the catalysts were evaluated for formaldehyde (HCHO) removal at room temperature. The performance tests showed that the catalyst obtained by immobilizing Pt nanoparticles (NPs) on Mg-Al HT/AlOOH support with Al/Mg molar ratio equivalent to 9:1 (Pt/Al9Mg1) displayed a superior catalytic activity and stability for HCHO removal. In order to find out the causes of its higher activity, X-ray diffraction, transmission electron microscopy, N2 adsorption/desorption, X-ray photoelectron spectroscopy, temperature programmed desorption of CO2 and reduction of H2 were used to analyze the physicochemical properties of Pt/Al9Mg1 and Pt/AlOOH. The remarkable catalytic performance of Pt/Al9Mg1 is mainly attributed to the relatively larger amount of surface oxygen species, and more reactive oxygen species led by the interaction of Mg-Al HT and AlOOH/Pt, and relatively larger number of weak base sites caused by Mg-Al HT. The formate species are the main reaction intermediate over Pt/Al9Mg1 during HCHO oxidation at room temperature, which could be further oxidized into CO2 and H2O in the presence of O2. This study might shed some light on further improving the catalytic performance of the catalyst for indoor air purification at room temperature.

Effect of microstructure and surface hydroxyls on the catalytic activity of Au/AlOOH for formaldehyde removal at room temperature.

A series of Au/AlOOH catalysts was prepared by impregnating different AlOOH supports with Au precursor followed by NaBH4-assisted reduction, and examined their activity toward oxidation of indoor formaldehyde (HCHO) pollutant at room temperature. The AlOOH supports used were synthesized by microemulsion, microwave and hydrothermal methods. Among these supports the catalyst obtained by deposition of Au nanoparticles (NPs) on AlOOH prepared by microemulsion method (Au/AlOOH-m) exhibited the highest catalytic activity. Based on the detailed characterization of the catalysts, the microstructure of AlOOH support, dispersion and size of Au NPs, surface hydroxyls, and interactions between Au and the support are important factors controlling the efficient removal of HCHO at room temperature. The superior catalytic performance of Au/AlOOH-m is attributed to its larger specific surface area, small size of Au NP, large amount of reactive surface hydroxyls, and better adsorption properties of this support. This study shows not only the importance of the microstructure and surface hydroxyls on the oxidative degradation of HCHO on Au/AlOOH at room temperature, but also provides a new insight into rational synthesis of high-efficiency catalysts for removal of indoor air pollutants.

Highly active mesoporous ferrihydrite supported pt catalyst for formaldehyde removal at room temperature.

Ferrihydrite (Fh) supported Pt (Pt/Fh) catalyst was first prepared by combining microemulsion and NaBH4 reduction methods and investigated for room-temperature removal of formaldehyde (HCHO). It was found that the order of addition of Pt precursor and ferrihydrite in the preparation process has an important effect on the microstructure and performance of the catalyst. Pt/Fh was shown to be an efficient catalyst for complete oxidation of HCHO at room temperature, featuring higher activity than magnetite supported Pt (Pt/Fe3O4). Pt/Fh and Pt/Fe3O4 exhibited much higher catalytic activity than Pt supported over calcined Fh and TiO2. The abundance of surface hydroxyls, high Pt dispersion and excellent adsorption performance of Fh are responsible for superior catalytic activity and stability of the Pt/Fh catalyst. This work provides some indications into the design and fabrication of the cost-effective and environmentally benign catalysts with excellent adsorption and catalytic oxidation performances for HCHO removal at room temperature.