An interconnected catalyst architecture has been in situ fabricated on Ni foam through facile electrochemical corrosion in sodium phytate containing Co and Fe metal ions. The introduction of Co and Fe in the N-phy system enables the phytate ions to link more active metal ions and then creates abundant catalytic sites to enhance the water oxidation performance and simultaneously to improve the overall water splitting activity. As a result, this self-supported C6FN-phy electrode delivers a high current density of 200 mA cm−2 at an overpotential of 285 mV for oxygen production and at 327 mV for hydrogen evolution in 1 M KOH, surpassing most catalysts recently reported. Besides, the electrocatalytic activity can be maintained for at least 45 h with a subtle potential increase, illustrating the versatile and practical application in industry. What's more, we achieve a current density of 100 mA cm−2 at 1.91 V by using C6FN-phy as the cathode and anode for overall water splitting, which is well comparable to the integrated performance of Pt/C and RuO2. Most importantly, multiple alternating chronopotentiometric tests of C6FN-phy as both the OER and the HER catalyst also verify the high availability and robust durability of the electrode as a true bifunctional electrocatalyst.

Zn-air battery, as an ideal energy conversion and storage device, is always limited by the expensive and less-than-ideal air electrode materials. The coupling of outstanding oxygen evolution reaction (OER) active sites (oxides derived from Co-Fe nitrides) and superior oxygen reduction reaction (ORR) active centers (metal-N-C and graphitic N) to acquire high-performance and low-cost catalysts is an ideal solution. Herein, we have successfully combined cobalt-iron bimetallic nitrides with N-doped multi-walled carbon nanotubes (Co-Fe-N@MWCNT) as a robust bifunctional material. Benefiting from the synergistic effect between Co, Fe and MWCNTs, Co-Fe-N@MWCNT not only possesses large electrochemically active surface area and effective transport path, but also realizes the integration of superior OER and ORR active sites. Only a low overpotential (290 mV) is needed to achieve a current density of 10 mA cm-2 for OER and the ORR catalytic activity is close to that of the commercial Pt/C. Additionally, Co-Fe-N@MWCNT as an ideal air electrode material can also be applied in Zn-air battery, which exhibits low voltage drop and favorable stability. The voltage gap has a slight change (about 0.03 V) even after 100 cycles of galvanostatic charge-discharge. More importantly, the synthetic strategy in our work may facilitate the design of more high-efficient bifunctional catalysts in various domains.

In the present work, we described the facile hydrothermal fabrication of Mn2O3 nanoparticle-assembled hierarchical hollow spheres and their application for the electrochemical determination of hydrogen peroxide (H2O2). The composition and morphology of the as-prepared samples were well characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Because of the electrochemical responses toward H2O2, a novel nonenzymatic electrochemical sensor for the H2O2 determination based on Mn2O3 hollow spheres modified glassy carbon electrode was proposed. The electrochemical properties of the modified electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The modified electrode displayed distinct amperometric response to H2O2 in a wide concentration range 0.10–1276.5 μM, with a linear range of 0.10–126.5 μM and a detection limit of 0.07 μM (S/N = 3). It exhibited excellent analytical performance in terms of long-time stability, good reproducibility and acceptable anti-interference ability. In addition, it was applied for the H2O2 determination in real samples directly with acceptable accuracy and recovery, demonstrating its potential application in routine H2O2 analysis.Keywords: fabrication; H2O2; hollow spheres; Mn2O3; modified electrode;

•Microwave-assisted synthesis method was used to prepare NiCo2O4 nanostructure.•3D mesoporous NiCo2O4 nanospheres are constructed by intertwined 2D ultrathin nanosheets.•Nanosphere-like NiCo2O4 nanostructures have a large specific surface area.•NiCo2O4 nanospheres exhibit high electro-catalytic activity and good long-term stability of methanol oxidation.A fast microwave-assisted synthesis method followed by a post-calcining process is used to prepare three-dimensional (3D) nanosphere-like NiCo2O4 nanostructure. The 3D NiCo2O4 nanospheres are constructed by intertwined two-dimensional (2D) ultrathin mesoporous nanosheets. The nanosphere-like NiCo2O4 has a large specific surface area (SSA, 146.5 m2 g−1) and is successfully applied to electro-catalytic oxidation of methanol. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (CA) measurements are used to investigate electro-catalytic performance of the as-prepared NiCo2O4. The current density of NiCo2O4/Ni foam (NiCo2O4/NF) electrode in 1 M KOH with 0.5 M methanol is up to 40.9 A g−1. And the current density can be returned to 97% of the original value by replacing new 1 M KOH electrolyte with 0.5 M methanol after a long-term CV cycle (500 cycles). These results show that our prepared NiCo2O4 possesses high electro-catalytic activity and good long-term stability for methanol oxidation. This may be benefit from the unique porous nanosphere-like structure and large SSA.

A double input capacitively coupled contactless conductivity detector (DIC4D) device which gets higher sensitivity has been described in this paper. The detector consists of two input electrodes and one output electrode. When two alternating current (AC) voltages with the same amplitude and different phases are imposed on each input electrode, the equivalent resistance of the output electrode is reduced because of the interference of the two signals with different phase angles. For a capacitively coupled contactless conductivity detector (C4D), the ratio of the response of KCl solution to that of distilled water is 1.6. However, for DIC4D, the ratio is 1.55 at a phase difference of 0° and increases to 1.8 at the phase difference of 170°, respectively. For C4D, the response of KCl solution is a linear function of the logarithm of concentrations from 10–5 M to 10–2 M, and the slope is 5.58. However, the slope of the response increases to 7.13 in DIC4D, and the limit of detection (LOD) of DIC4D is estimated to be 5 × 10–8 M. The slope of the three-way DIC4D is increased to 69.78. A flow injection device is employed for the evaluation of the applicability of DIC4D with the same range, and good reproducibility is confirmed through flow injection of the same solution 10 times. The relative standard deviation (RSD) is 0.7%, which demonstrates a promising application to capillary electrophoresis (CE).

A self-assembled net structure to immobilize tris(2,2′-bipyridyl)ruthenium(II) ditetrakis(4-chlorophenyl)borate (RuDB) onto a gold surface is presented here for the first time. The formation of the net structure involved alternately depositing 1,10-decanedithiol (DDT) and gold nanoparticles (AuNPs) on the gold surface. The RuDB molecules became distributed in the spaces between the long chains of DDT and were successfully immobilized in the formed net structure. Repeating the modification process fabricated a much larger net structure incorporating more RuDB. The fabrication process is very simple, effective and low cost. An electrogenerated chemiluminescence (ECL) study confirmed that RuDB immobilized in the net structure was considerably stable and exhibited excellent ECL behavior. Moreover, the ECL signal of the proposed sensor was sensitively inhibited by phenol and exhibited a low detection limit of 0.6 nM with a signal-to-noise ratio of 3. Consequently, the design of the net structure for immobilizing probe molecules may be promising for other sensing applications.

In this paper, the anodic electrogenerated chemiluminescence (ECL) behavior of graphite-like carbon nitride (g-C3N4) is studied using cyclic voltammetry with triethanolamine (TEA) as a coreactant. The possible anodic ECL response mechanism of the g-C3N4/TEA system is proposed. Furthermore, it is observed that the anodic ECL signal can be quenched efficiently in the presence of rutin, on the basis of which a facile anodic ECL senor for the determination of rutin is developed. This ECL sensor is found to have a linear response in the range of 0.20–45.0 μM and a low detection limit of 0.14 μM (at signal-to-noise of 3). These results suggest that semiconductor g-C3N4 has great potential in extending the application in the ECL field as an efficient luminophore.

A nitrite (NO2−) sensor has been fabricated by immobilizing cytochrome c (Cyt c) on a graphene/gold nanoparticle-chitosan (Gra/Au NPs–Chit) modified glass carbon electrode (GCE). Graphene/gold nanoparticles (Gra/Au NPs) nanocomposite was prepared by dispersing graphene in an aqueous solution of β-cyclodextrin (β-CD) and hydrogen tetrachloroaurate and followed by NaBH4 reduction. An aliquot of Gra/Au NPs in a 0.50 wt% chitosan solution was drop-coated on the surface of a GCE to form a Gra/Au NPs–Chit/GCE which was subsequently adsorbed with Cyt c. The Cyt c–Gra/Au NPs–Chit/GCE shows a quasi-reversible cyclic voltammetric redox couple at a formal potential of −0.037 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution, suggesting that Gra/Au NPs–Chit film offers a biocompatible microenvironment for the Cyt c. It was found that the Cyt c–Gra/Au NPs–Chit sensor displays good electrocatalytic activity for NO2− oxidation at a relatively low working potential. The sensor possesses a linear response range of 10.0–420.0 μM NO2− with a correlation coefficient of 0.9989 and a sensitivity of 110.0 μA mM−1. The limit of detection is determined as 2.46 μM NO2− based on a signal-to-noise ratio of 3. The proposed sensor has been applied successfully to the determination of NO2− in spiked and real water samples.

A new strategy for the fabrication of a sulfide sensor based on room-temperature phosphorescence (RTP) of PbO/SiO2 nanocomposite is proposed. The PbO/SiO2 phosphor is prepared by a sol−gel method, and it produces highly emissive broad-band RTP under the irradiation of UV light. The phosphorescence intensity of PbO/SiO2 nanocomposite could be quenched by sulfide, and the response behavior of the sensor is dependent on the value of pH of the solution. At pH 11.0, the sensor exhibits a linear response toward sulfide at the concentration range from 2.67 to 596 μM. The detection limit for the sensor is estimated to be 0.138 μM (3 σ), and the precision for five replication detections of 6 μM sulfide is 1.82% (relative standard deviation). The color of the sensor and its phosphorescence intensity change obviously and could be observed with the naked eye when there was continuous addition of sulfide from the concentration of 50 μM. The phosphorescence intensity of quenched PbO/SiO2 phosphor can be recovered when dipping it into H2O2 solution, which demonstrates a good sulfide response characteristic of reusability. Furthermore, the sensor is easy to apply for trace hydrogen sulfide determination in the gas phase.

An environmentally friendly sulfide sensor based on the room-temperature phosphorescence (RTP) of the ZnO/SiO2 nanocomposite has been developed. The ZnO/SiO2 nanocomposite prepared by the sol–gel route produces highly emissive broadband RTP which can be clearly observed by the naked eye. The phosphorescence intensity monitored at 460 nm (excitation at 320 nm) decreases with increasing sulfide ions concentrations. The response behavior of the sensor is dependent on the pH value of the solution. At pH 10, the sensor shows a good, linear response to sulfide from 4.88 × 10−5 to 1.02 × 10−2 M with a detection limit of 1.64 × 10−6 M (3σ). It has been successfully applied to the determination of sulfide in spiked water and wastewater. Furthermore, this sensor can be regenerated by dipping it into an H2O2 solution. The mechanisms for the RTP detection of sulfide based on the ZnO/SiO2 nanocomposite and the sensor regeneration by H2O2 are proposed.

•The Ni-phytate electrode is prepared without the use of binder or conducting agent.•More active sites and good charge transfer efficiency due to the film and bubble-like structure•The Ni-phytate catalyst presents a low overpotential, small Tafel slope and good stability.•The introduction of phytate units significantly improves the performance of the electrocatalyst.•This method could be used to develop other catalysts based on transition metals.Electrochemical water splitting in an alkaline electrolyte for large-scale hydrogen production is currently a hot research topic. However, developing high-performance and durable oxygen-evolving electrocatalysts is an ongoing challenge. In this work we prepared Ni-phytate thin films with a bubble-like structure on Ni-foam through an in situ growth process. The resulting material can be used as an oxygen-evolving electrode in basic media without requiring the use of a conductive binder. The Ni-phytate electrode has high catalytic activity (ηj = 10 mA cm− 2 = 280 mV) and good stability (the current activity remained 95% after 5 h) towards OER. This is an effective approach to simplifying the large-scale preparation of catalysts for water-splitting applications.

A nitrite (NO2−) sensor has been fabricated by immobilizing cytochrome c (Cyt c) on a graphene/gold nanoparticle-chitosan (Gra/Au NPs–Chit) modified glass carbon electrode (GCE). Graphene/gold nanoparticles (Gra/Au NPs) nanocomposite was prepared by dispersing graphene in an aqueous solution of β-cyclodextrin (β-CD) and hydrogen tetrachloroaurate and followed by NaBH4 reduction. An aliquot of Gra/Au NPs in a 0.50 wt% chitosan solution was drop-coated on the surface of a GCE to form a Gra/Au NPs–Chit/GCE which was subsequently adsorbed with Cyt c. The Cyt c–Gra/Au NPs–Chit/GCE shows a quasi-reversible cyclic voltammetric redox couple at a formal potential of −0.037 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution, suggesting that Gra/Au NPs–Chit film offers a biocompatible microenvironment for the Cyt c. It was found that the Cyt c–Gra/Au NPs–Chit sensor displays good electrocatalytic activity for NO2− oxidation at a relatively low working potential. The sensor possesses a linear response range of 10.0–420.0 μM NO2− with a correlation coefficient of 0.9989 and a sensitivity of 110.0 μA mM−1. The limit of detection is determined as 2.46 μM NO2− based on a signal-to-noise ratio of 3. The proposed sensor has been applied successfully to the determination of NO2− in spiked and real water samples.