Xuli Ma

Facile preparation of electroactive amorphous α-ZrP/PANI hybrid film for potential-triggered adsorption of Pb2+ ions

An electroactive hybrid film composed of amorphous α-zirconium phosphate and polyaniline (α-ZrP/PANI) is controllably synthesized on carbon nanotubes (CNTs) modified Au electrodes in aqueous solution by cyclic voltammetry method. Electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM) and X-ray power diffraction (XRD) analysis are applied for the evaluation of the synthesis process. It is found that the exfoliated amorphous α-ZrP nanosheets are well dispersed in PANI and the hydrolysis of α-ZrP is successfully suppressed by controlling the exfoliation temperature and adding appropriate supporting electrolyte. The insertion/release of heavy metals into/from the film is reversibly controlled by a potential-triggered mechanism. Herein, α-ZrP, a weak solid acid, can provide an acidic micro-environment for PANI to promote the electroactivity in neutral aqueous solutions. Especially, the hybrid film shows excellent potential-triggered adsorption of Pb(2+) ion due to the selective complexation of Pb(2+) ion with oxygen derived from P-O-H of α-ZrP. Also, it shows long-term cycle stability and rapid potential-responsive adsorption/desorption rate. This kind of novel hybrid film is expected to be a promising potential-triggered ESIX material for separation and recovery of heavy metal ions from wastewater.

Homogeneous nanosheet Co3O4 film prepared by novel unipolar pulse electro-deposition method for electrochemical water splitting

A unipolar pulse electro-deposition (UPED) method is used to prepare nanosheet Co3O4 film on a carbon rod substrate in aqueous solution and compared with other conventional methods, i.e., the cyclic voltammetry (CV) method, potentiostatic method (PM) and pulse potentiostatic method (PPM). Co3O4 films prepared by the UPED method show a more uniform structure on carbon rod and higher catalytic activity than those by other methods, and oxygen evolution reaction over it with an overpotential of 275 ± 2.3 mV results in a current density of 10 mA cm−2 in 1.0 mol L−1 KOH. Such an excellent performance should be attributed to its highly porous nanosheet structure with honeycomb-like morphology.

A novel electroactive λ-MnO2/PPy/PSS core–shell nanorod coated electrode for selective recovery of lithium ions at low concentration

A novel electroactive Li+ ion-imprinted hybrid film consisting of λ-MnO2/PPy/PSS core–shell nanorods is successfully fabricated on an electrode by using the unipolar pulse electrodeposition (UPED) technique. When the electrode is applied for selective electrochemical extraction of low concentrations of Li+ ions from aqueous solutions via an electrochemically switched ion exchange (ESIX) process, the Li+ ion adsorption capacity reaches 35.2 mg g−1 with an adsorption equilibrium time of less than 2 h. The excellent ion separation performance of this hybrid film should be attributed to its low ion transfer resistance due to its porous structure and the high electric driving force during the ESIX process. In particular, owing to the unique Li+ ion imprinted vacant sites in the crystal structure of spinel λ-MnO2 nanorods, the selectivity factor for Li+/Na+ reaches 46.0 with a molar ratio of 1 : 1. It is expected that this λ-MnO2/PPy/PSS hybrid film can be applied as a promising electroactive material for effective separation of Li+ ions from seawater.

Silver-doped molybdenum carbide catalyst with high activity for electrochemical water splitting

A hybrid catalyst composed of silver (Ag) doped wire-like molybdenum carbide (MoxCy) with pure β-phase and carbon nanotubes (CNTs) was coated well on a carbon rod electrode for the hydrogen evolution reaction (HER). The effects of Ag loading amount and carbonization temperature on the crystal form of MoxCy were investigated in detail. It is found that the MoxCy crystal form can be tuned by adjusting the preparation conditions, and nanostructured wire-like Mo2C with pure β-phase was obtained at a temperature over 750 °C. Ag/MoxCy composite nanomaterials were investigated by X-ray diffraction, UV/vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy and Brunauer-Emmett-Teller surface area analysis. The hybrid catalyst was further deposited on the carbon nanotube (CNT) modified carbon rod substrate. Due to the high surface area and 3D porous network-like microstructure, the Ag/Mo2C/CNTs hybrid electrode showed enhanced catalytic performance when comparing with the corresponding pure one. Particularly, for the Ag-doped Mo2C/CNTs hybrid electrode with an optimum 1 Ag : 5 Mo molar ratio of the precursors, a current density of 10 mA cm-2 was obtained by applying an overpotential of 142 mV in 0.5 mol L-1 H2SO4 solution. It is expected that such a hybrid electrode can be widely applied for effective electrolysis of water to produce hydrogen.

Electrochemical Characterization of Ion Selectivity in Electrodeposited Nickel Hexacyanoferrate Thin Films

The ion selectivity of electrodeposited nickel hexacyanoferrate (NiHCF) thin films was investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). NiHCF thin films were prepared by cathodic deposition on Pt and Al substrates. EJS and CV curves were determined in 1 mol/L (KNO3+CsNO3) and 1 mol/L (NaNO3+CsNO3) mixture solutions, which were sensitive to the concentration of Cs(superscript +) in the electrolytes. Experimental results show that all Nyquist impedance plots show depressed semicircies in the high-frequency range changing over into straight lines at lower frequencies. With increasing amounts of Cs(superscript +), the redox potentials in CV curves shift toward more positive values and the redox peaks broaden; the semicircle radius in corresponding EIS curves and the charge transfer resistance also increase. EIS combining CV is able to provide valuable insights into the ion selectivity of NiHCF thin films.

Potential-induced reversible uptake/release of perchlorate from wastewater by polypyrrole@CoNi-layered double hydroxide modified electrode with proton-ligand effect

In this study, CoNi-layered double hydroxide (CoNi-LDH) nanosheets coated conducting polypyrrole (PPy) nanowire was controllably fabricated on Pt plate or carbon cloth by using unipolar pulse electrodeposition (UPED) method and served as a novel electrochemically switched ion exchange (ESIX) hybrid film with proton-ligand effect for the removal of perchlorate anions (ClO4-). It is expected that the space among CoNi-LDH nanosheets of the shell could act as the reservoir for the anions while the PPy core serve as the potential-induced element for proton-ligand. The effects of pulse potential during film deposition and initial pH of the wastewater on the ClO4- removal performance of this core-shell hybrid film were investigated. It is found that ClO4- adsorption onto PPy@CoNi-LDH followed pseudo-second-order model, and the film fabricated with -1.5 V pulse potential showed an excellent performance for the rapid removal of ClO4- with a high selectivity, and the ClO4- adsorption quantity reached as high as 302 mg g-1. In a wide pH range (3-10), the hybrid film removed ClO4- efficiently. The proton-ligand effect in PPy@CoNi-LDH was proved by using XPS analysis and density functional theory. Such a PPy@CoNi-LDH hybrid core-shell film should be a potential electroactive material for the separation of ClO4- and other anions from wastewater.

Acid-free synthesis of oxygen-enriched electroactive carbon with unique square pores from salted seaweed for robust supercapacitor with attractive energy density

Oxygen-enriched porous electroactive carbon (OPEC) is prepared by simply carbonizing salted seaweed and only washing with water. The recrystallized NaCl cube is chemically stable and mainly acts as a pore filler in the pristine seaweed. It helps to maintain the innate pore system and simultaneously templates the formation of square pores. Its shielding effect not only enhances the onset decomposition temperature but also helps to achieve high yield. It can also be completely removed by washing with the green solvent water. The obtained OPEC-800 material not only shows a specific surface area of 329.3 m2 g−1 but also a microporous structure (0.8–2.0 nm) matching with the electrolyte 1.0 M H2SO4. It exhibits a specific capacitance of 324.3 F g−1 (specific surface-area capacitance is 98.5 μF cm−2) at a current density of 0.50 A g−1 in a three-electrode system. Its high oxygen content of 19.1% can lead to a wide operating voltage window of 0.0–1.40 V and an attractive energy density of 15.9 W h kg−1 at a power density of 175.0 W kg−1 in a two-electrode system. Furthermore, it also displays an excellent cyclic stability (98%, 10 000 cycles) and good rate performance. The whole process is a green, oxidant-free, acid-free, and low-cost method for converting green biomass into self-functionalized carbon with naturally connected pores aiming to fabricate green energy devices. All the attractive features make the environmentally friendly route a competitive candidate for preparing other porous electroactive materials.

Preparation and Application of Multirow Graphite Cores NiHCF Film Electrodes for Electrochemically Controlled Cesium Separation

The electractive nickel hexacyanoferrate (NiHCF) thin films were synthesized on the multirow graphite substrates which were composed of 27 graphite cores by a cathodical deposition. The multirow graphite core electrodes were investigated as Electrochemically Controlled Ion Separation (ECIS) materials for the selective separation of cesium (Cs+). In the simulation solution containing Cs+, Cs+ are reversibly intercalated and deintercalated from the matrix by electrochemical modulation of the reduced and oxidized states of the film. This paper presents results of experiments on the development of a flow system for the Cs+ separation. Ion Chromatography (IC) was used to determine the effect of experimental conditions on the Cs+ selective separation for the NiHCF thin film, such as the initial [Cs+] concentration, surface state, regenerability, and flow velocity on the Cs+ selective separation for the NiHCF thin film .The experiment results show that the Cs+ entering into the NiHCF film in oxidized state increase with time. With increasing amounts of Cs+ in solution, the [Cs+] entering into NiHCF film are larger while in the corresponding solution the removing rate of Cs+ is also larger. It is demonstrated that the NiHCF film on the substrate of multiple sequential graphite cores have good ECIS performance and regenerability.