Iron and nitrogen co-modified multi-walled carbon nanotubes for efficient electrocatalytic oxygen reduction.

Multi-walled carbon nanotubes (MWCNTs) with one-dimensional nanostructure are an ideal support for oxygen reduction reaction (ORR) catalysts thanks to their intrinsic outstanding electrical conductivity and high specific surface area. Iron and nitrogen doping could alter the local electronic structure and therefore enhance the ORR activity of MWCNTs, but the preparation process always includes complicated growth conditions and post-treatment. Herein, an iron and nitrogen co-modified multi-walled carbon nanotubes (Fe-N-MWCNTs) with hierarchical nanostructure is engineered and synthesized via a simple two-step pyrolysis approach. Large specific surface area, low resistivity, and intensified charge density near the Fermi level synergistically endow the Fe-N-MWCNTs with outstanding ORR activity. The optimal Fe-N-MWCNTs exhibit a higher onset potential value of 0.92 V (versus RHE) and half-wave potential (E1/2) of 0.85 V (versus RHE) in 0.1 M KOH medium, which exceeds the benchmark Pt/C electrocatalyst (E1/2= 0.84 V). This strategy of modifying MWCNTs support by a simple calcination process provides a feasible method to prepare cost-efficient ORR electrocatalysts.

Highly sensitive detection of Pb2+ and Cu2+ based on ZIF-67/MWCNT/Nafion-modified glassy carbon electrode.

A series of different facile modification layers (MLs) was designed to gradually increase the electrochemical sensing performance of glassy carbon electrode (GCE) for simultaneously detecting Pb2+ and Cu2+. ML designs were mainly a different combination of ZIF-67, MWCNT and Nafion, and their different electrochemical sensing performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave stripping voltammetry (SWSV) and chronocoulometry. The fabricated sensor, which modified with ZIF-67/MWCNT and Nafion layer, exhibited the biggest response peak current to Pb2+ and Cu2+. In addition, it displayed a wide linear detection range of 1.38 nM-5 µM for Pb2+ and 1.26 nM-5 µM for Cu2+, a detection accuracy of about 1 nM for both Pb2+ and Cu2+, and an excellent stability for both Pb2+ and Cu2+. We also analyzed the real water sample taken from Changchun's Sanjia Lake and Yan Lake. We believe this ML design provides instruction for building high-performance electrochemical sensing systems.

Insight into the effect of the continuous testing and aging on the SO2 sensing characteristics of a YSZ (Yttria-stabilized Zirconia)-based sensor utilizing ZnGa2O4 and Pt electrodes.

In this paper, YSZ-based mixed potential SO2 sensor with ZnGa2O4 and Pt electrodes was developed and the effect of the continuous testing and aging process on the sensing characteristics was discussed. The results showed that with this process the response of the sensor to SO2 performed an opposite direction to that in the sensor's initial state. The reason might be that the PtS produced at the Pt electrode increased the electrochemical catalytic activity of the Pt electrode, leading to the mixed potential of the Pt electrode higher than that of the ZnGa2O4 electrode. XPS and EDS results proved that a lot of Pt2+ and S2- were produced at Pt electrode after this process. Moreover, vulcanized sensor also performed similar sensing properties to the above aging sensor, which indicated that the produced PtS should be the reason that the sensor performed reverse deflection on sensing properties. In addition, the sensor after sulfuration can detect 0.05-500 ppm SO2 with the sensitivity being 5 mV/decade to 0.05-1 ppm and 41 mV/decade to 1-500 ppm. The sensor also had a reliable stability during the continuous measurement.

Fabrication of Well-Ordered Three-Phase Boundary with Nanostructure Pore Array for Mixed Potential-Type Zirconia-Based NO2 Sensor.

A well-ordered porous three-phase boundary (TPB) was prepared with a polystyrene sphere as template and examined to improve the sensitivity of yttria-stabilized zirconia (YSZ)-based mixed-potential-type NO2 sensor due to the increase of the electrochemical reaction active sites. The shape of pore array on the YSZ substrate surface can be controlled through changing the concentration of the precursor solution (Zr(4+)/Y(3+) = 23 mol/L/4 mol/L) and treatment conditions. An ordered hemispherical array was obtained when CZr(4+) = 0.2 mol/L. The processed YSZ substrates were used to fabricate the sensors, and different sensitivities caused by different morphologies were tested. The sensor with well-ordered porous TPB exhibited the highest sensitivity to NO2 with a response value of 105 mV to 100 ppm of NO2, which is approximately twice as much as the smooth one. In addition, the sensor also showed good stability and speedy response kinetics. All these enhanced sensing properties might be due to the structure and morphology of the enlarged TPB.