Electrochemical H2O2 sensor based on a Au nanoflower-graphene composite for anticancer drug evaluation.

Reliable H2O2 sensors for in situ cellular monitoring under drug stimulation can be developed as a powerful and versatile tool for drug evaluation. Herein, a novel electrochemical biosensor capable of detecting and quantifying H2O2 was fabricated by graphene and shape-controlled gold nanostructures. With the help of polyelectrolytes, gold exhibited hierarchical flower-like nanostructures. This kind of nanozyme material exhibited a prominent electrochemical response for H2O2. Electrocatalytic activity for H2O2 reduction with high sensitivity (5.07◊10-4 mA µmol L-1 cm-2) and good detection capability (the lowest detection limit is 4.5 µmol L-1 (S/N = 3)) were achieved. This electrochemical biosensor was successfully used to measure the concentration of H2O2 released from HepG2 hepatoma cells. Ascorbic acid (AA) and Camellia nitidissima Chi saponins (CNCS) were selected as model drugs, and their anticancer activities were compared by in situ monitoring of H2O2. Interestingly, the electrochemical sensor showed remarkable sensitivity, accuracy, and rapidity compared with the traditional enzymatic detection kit. In brief, the as-synthesized nanostructured H2O2 sensors can be applied to assess the antitumor properties of candidate drugs and inspire developments for personalized health care monitoring and cancer treatment.

Electrochemical CaC2 -Mediated Conversion of Biochar to C2 H2 : High Carbon Efficiency and Low Contamination.

The carbon to CaC2 route is promising to provide a sustainable elementary unit, C2 H2 , for the organic synthesis industry, but the traditional thermal reaction process suffers from low carbon efficiency, harmful gas contamination, high temperature operation, and risky CO management. We herein report a high carbon efficiency (ca. 100 %) conversion of biochar to C2 H2 through an electrolytic synthesis of solid CaC2 in molten CaCl2 /KCl/CaO at 973 K. The main reactions are carbon reduction to CaC2 at the solid carbon cathode and oxygen evolution at an inert anode. Meanwhile, the electrolysis removes S and P from the solid cathode, avoiding the formation of CaS and Ca3 P2 in CaC2 and consequently eliminating H2 S and PH3 contamination in the finally produced C2 H2 .

Electrochemical behaviors of Li-B alloys in a LiCl-LiBr-KBr molten salt system.

Li-B alloys present higher voltages and better power performances than those of conventional Li-Al and Li-Si anodes for thermal batteries. Herein, the electrochemical characteristics of the Li-B alloy in the LiCl-LiBr-KBr electrolyte, including the discharge mechanism, charge transfer coefficient and exchange current density, were investigated in the temperature range of 623-823 K by open circuit potential (OCP), cyclic voltammetry (CV), chronopotentiometry (CP), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. Consequently, the OCP of the Li-B alloy in the LiCl-LiBr-KBr electrolyte is close to that of pure lithium at the investigated temperatures. The discharge of the Li-B alloy electrode includes electrochemical dissolution of free lithium (Li → Li+) and compounded lithium (LiB → Li+ + B). The charge transfer coefficient in the anodic direction (Li → Li+) is about 0.63 at 623 K, which slightly increases as the temperature increases. The exchange current density of the Li (Li-B)/Li+ couple determined by the EIS method increases from 3.84 A cm-2 to 8.40 A cm-2 when the temperature increases from 623 to 823 K, corresponding to an activation energy of 16.4 kJ mol-1. These results suggest that the Li-B anode allows ultrahigh-rate discharge in thermal batteries.

Nanoporous bismuth for the electrocatalytic reduction of CO2 to formate.

Bi is an attractive catalyst towards the electrochemical reduction of CO2 to formate. In this work, nanoporous bismuth was prepared by dealloying Mg3Bi2 with tartaric acid (TA) solution, and the size of the primary Bi nanoparticles was adjusted according to the concentration of TA. When the concentration of TA increased from 2 wt% to 20 wt%, the particle size of Bi increased from about 70 nm to 400 nm. The synthesized nanoporous Bi samples were investigated as electrocatalysts for the reduction of CO2 in KHCO3 electrolyte, and it was found that the smaller the particle size, the higher the catalytic activity. However, nanoporous Bi comprising 70 nm particles suffered from mass transfer difficulty and sintering during the reaction, whereas the 100 nm nanoporous Bi delivered both a high formate formation current and faradaic efficiency (FE) (16 mA cm-2, FE > 90% at -0.88 V vs. RHE) and showed excellent durability.

Efficient Nanostructuring of Silicon by Electrochemical Alloying/Dealloying in Molten Salts for Improved Lithium Storage.

Application of nanostructured silicon (nSi) is significantly retarded by challenges in the production of affordable nSi. We herein report a high-yield (ca. 100 %) and low-energy (2 kWh Kg-nSi-1 ) nanostructuring of industrial microsized silicon (mSi) through a closed-loop electrochemical Mg alloying/dealloying in molten MgCl2 /NaCl/KCl at 773 K. The resulting nSi unexpectedly shows a salt-unwetted character, allowing an automatic separation from the melts. Thus water washing and accompanying oxidation of the nSi can be avoided. The final product has a nanoporous structure and comprises Si nanorods (ca. 30 nm in diameter) with an ultrathin oxide coating. It can be used for Li storage giving a combination of high initial coulombic efficiency, high specific capacity, and long cycling stability. This nanostructuring process consumes very few chemicals except for the mSi and produces almost zero waste.

Amorphous Carbon-Derived Nanosheet-Bricked Porous Graphite as High-Performance Cathode for Aluminum-Ion Batteries.

Graphite is an attractive cathode material for energy storage because it allows reversible intercalation/deintercalation of many compound anions at high potentials. However, because the sizes of the compound anions are greatly larger than the lamellar spacing of graphite, common graphite used as cathode may suffer from slow kinetics and large volume expansion. Here, it is demonstrated that graphite with high crystallinity and nanosheet-bricked porous structure can be an excellent cathode for aluminum-ion batteries. This porous graphite is derived from carbon black via a simple electrochemical graphitization in molten CaCl2, and the high crystallinity and thin layer characters facilitate the high capacity and high rate storage of aluminum tetrachloride ions. Moreover, the bricked porous structure endows the fabricated cathode with a providential porosity to perfectly match the huge volume expansion of graphite (650% against a charging capacity of 100 mA h g-1), thus this electrochemical graphite exhibits integrated high gravimetric and volumetric capacities as well as high structural stability during cycling.

Imidazolium Ions with an Alcohol Substituent for Enhanced Electrocatalytic Reduction of CO2.

Electrochemical reduction of CO2 to CO is an attractive process for carbon capture and energy regeneration. Imidazolium ionic liquids (IMILs) are promising electrolyte catalytically active additives for this important reaction. Herein, we report functionalizing the imidazolium ion with a propanol substituent at the N site can significantly enhance the catalytic activity of IMILs, causing a positive shift of the onset potential for the CO2 reduction by about 90 mV in an acetonitrile electrolyte. Theoretical calculations indicated that the propanol hydroxyl could bridge a local hydrogen-bonding chain as shortcut for proton transfer, leading to a dramatic decrease of the activation barrier for the catalytic reduction of CO2 in IMIL.

Correction: Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl.

Correction for 'Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl' by Haiping Gao et al., Phys. Chem. Chem. Phys., 2014, 16, 19514-19521.

Electrochemical Graphitization: An Efficient Conversion of Amorphous Carbons to Nanostructured Graphites.

This concept paper describes a new electrochemical method for the graphitization of amorphous carbons. The graphitization is achieved by a simple cathodic polarization of the carbons at merely ≈1100 K in molten CaCl2 . This electrochemical process is applicable to both graphitizable and non-graphitizable carbons, generating porous graphitic structures of high-crystallinity nanosheets. The transformation of carbon blacks, microspheres, and fibers to porous graphites, hollow graphite spheres, and pipes with porous shells have been demonstrated and the potential graphitization mechanism discussed.

Electrochemically Driven Transformation of Amorphous Carbons to Crystalline Graphite Nanoflakes: A Facile and Mild Graphitization Method.

Although, in the carbon family, graphite is the most thermodynamically stable allotrope, conversion of other carbon allotropes, even amorphous carbons, into graphite is extremely hard. We report a simple electrochemical route for the graphitization of amorphous carbons through cathodic polarization in molten CaCl2 at temperatures of about 1100 K, which generates porous graphite comprising petaloid nanoflakes. This nanostructured graphite allows fast and reversible intercalation/deintercalation of anions, promising a superior cathode material for batteries. In a Pyr14 TFSI ionic liquid, it exhibits a specific discharge capacity of 65 and 116 mAh g-1 at a rate of 1800 mA g-1 when charged to 5.0 and 5.25 V vs. Li/Li+ , respectively. The capacity remains fairly stable during cycling and decreases by only about 8 % when the charge/discharge rate is increased to 10000 mA g-1 during cycling between 2.25 and 5.0 V.

Electrolysis of metal oxides in MgCl2 based molten salts with an inert graphite anode.

Electrolysis of solid metal oxides has been demonstrated in MgCl2-NaCl-KCl melt at 700 °C taking the electrolysis of Ta2O5 as an example. Both the cathodic and anodic processes have been investigated using cyclic voltammetry, and potentiostatic and constant voltage electrolysis, with the cathodic products analysed by XRD and SEM and the anodic products by GC. Fast electrolysis of Ta2O5 against a graphite anode has been realized at a cell voltage of 2 V, or a total overpotential of about 400 mV. The energy consumption was about 1 kW h kgTa(-1) with a nearly 100% Ta recovery. The cathodic product was nanometer Ta powder with sizes of about 50 nm. The main anodic product was Cl2 gas, together with about 1 mol% O2 gas and trace amounts of CO. The graphite anode was found to be an excellent inert anode. These results promise an environmentally-friendly and energy efficient method for metal extraction by electrolysis of metal oxides in MgCl2 based molten salts.

Thickness- and Particle-Size-Dependent Electrochemical Reduction of Carbon Dioxide on Thin-Layer Porous Silver Electrodes.

The electrochemical reduction of CO2 can not only convert it back into fuels, but is also an efficient manner to store forms of renewable energy. Catalysis with silver is a possible technology for CO2 reduction. We report that in the case of monolithic porous silver, the film thickness and primary particle size of the silver particles, which can be controlled by electrochemical growth/reduction of AgCl film on silver substrate, have a strong influence on the electrocatalytic activity towards CO2 reduction. A 6 µm thick silver film with particle sizes of 30-50 nm delivers a CO formation current of 10.5 mA cm(-2) and a mass activity of 4.38 A gAg (-1) at an overpotential of 0.39 V, comparable to levels achieved with state-of-the-art gold catalysts.

Hierarchically superstructured prussian blue analogues: spontaneous assembly synthesis and applications as pseudocapacitive materials.

Hierarchically superstructured Prussian blue analogues (hexacyanoferrate, M=Ni(II) , Co(II) and Cu(II) ) are synthesized through a spontaneous assembly technique. In sharp contrast to macroporous-only Prussian blue analogues, the hierarchically superstructured porous Prussian blue materials are demonstrated to possess a high capacitance, which is similar to those of the conventional hybrid graphene/MnO2 nanostructured textiles. Because sodium or potassium ions are involved in energy storage processes, more environmentally neutral electrolytes can be utilized, making the superstructured porous Prussian blue analogues a great contender for applications as high-performance pseudocapacitors.

Preparation of Mo nanopowders through electroreduction of solid MoS2 in molten KCl-NaCl.

Electrolysis of MoS2 to produce Mo nanopowders and elemental sulfur has been studied in an equimolar mixture of NaCl and KCl at 700 °C. The reduction mechanism was investigated by cyclic voltammetry (CV), potentiostatic and constant voltage electrolysis together with spectroscopic and scanning electron microscopic analyses. The reduction pathway was identified to be MoS2 → LxMoS2 (x ≤ 1, L = Na or K) → L3Mo6S8 and LMo3S3 → Mo, and the last step to format metallic Mo was found to be relatively slow in kinetics. Electrolysis at a cell voltage of 2.7 V has led to a rapid reduction of MoS2 to nodular Mo nanoparticles (50-100 nm), with the current efficiency and energy consumption being about 92% and 2.07 kW h kg(-1)-Mo, respectively.

Sulfuric acid intercalated graphite oxide for graphene preparation.

Graphene has shown enormous potential for innovation in various research fields. The current chemical approaches based on exfoliation of graphite via graphite oxide (GO) are potential for large-scale synthesis of graphene but suffer from high cost, great operation difficulties, and serious waste discharge. We report a facile preparation of graphene by rapid reduction and expansion exfoliation of sulfuric acid intercalated graphite oxide (SIGO) at temperature just above 100°C in ambient atmosphere, noting that SIGO is easily available as the immediate oxidation descendent of graphite in sulfuric acid. The oxygenic and hydric groups in SIGO are mainly removed through dehydration as catalyzed by the intercalated sulfuric acid (ISA). The resultant consists of mostly single layer graphene sheets with a mean diameter of 1.07 µm after dispersion in DMF. This SIGO process is reductant free, easy operation, low-energy, environmental friendly and generates graphene with low oxygen content, less defect and high conductivity. The provided synthesis route from graphite to graphene via SIGO is compact and readily scalable.