Investigations of Thallium(Ⅰ) Underpotential Deposition on the Silver Rotating Disk Electrode and Its Analytical Application

The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.

Investigation on the Electrochemical Polymerization of Catechol by Means of Rotating Ring-disk Electrode

The electrolysis of catechol was studied in the pH values of 1 to 10. The results from the rotating ring disk electrode (RRDE) experiments show that at low pH values, the electrochemical polymerization of catechol was performed by one step, and at higher pH values, the electrochemical polymerization of catechol was carried out by two steps, i.e . oxidation of catechol and followed by polymerization. The intermediates generated at the disk were detected at the ring electrode in the ring potential region of -0.2 to 0 V (vs. Ag/AgCl). One of reasons for the decrease in the ratio of i r to i d with increasing the ring potential is caused by formation of positively charged intermediates at the disk electrode. This ratio increases with increasing the rotation rate of the RRDE, which indicates that the intermediates are not stable. A shielding effect during polymerization of catechol was observed when the ring potential was set at 0.1 V (vs. Ag/AgCl). The electron spin resonance (ESR) of polycatechol shows that polycatechol possesses unpaired electrons. The images of polycatechol films synthesized at different conditions are described.

Correlation between impedance spectroscopy and bubble-induced mass transport in the electrochemical reduction of carbon dioxide

In the electrochemical conversion of carbon dioxide, high currents need to be employed to obtain large production rates, thus implying that mass transport of reactants and products is of crucial importance.This aspect can be investigated by employing a model that depicts the local environment for the reduction reactions. Simultaneously, electrochemical impedance spectroscopy, despite being a versatile technique, has rarely been adopted for studying the mass transport features during the carbon dioxide(CO_(2))electroreduction. In this work, this aspect is deeply analyzed by correlating the results of impedance spectroscopy characterization with those obtained by a bubble-induced mass transport modeling under controlled diffusion conditions on a gold rotating disk electrode. The effects of potential and rotation rate on the local environment are also clarified. In particular, it has been found that CO_(2) depletion occurs at high kinetics when the rotation is absent, giving rise to an increment of the competing hydrogen evolution reaction. This feature reflects in an enlargement of the diffusion resistance, which overcomes the charge transport one.

Influence of Mg^(2+) on Initial Stages of CaCO_3 Scale Formed on Metal Surface

Magnesium ions, which exist in formation water and injection water under downhole conditions in the oil and gas production industry, are a key determinant in the CaCO_3 scale formation. Many studies have focused their attention on the effect of magnesium on the kinetics, the morphology and the content of Mg in the CaCO_3 scale. Little attention has been paid to the effect of Mg 2+ on the initial stages of CaCO_3 formation on a metal surface. In this study, an electrochemical technique was used to study the influence of Mg 2+ on the initial stages of CaCO_3 scale formed on a metal surface. With this electrochemical technique, the reduction of the dissolved oxygen in an analysis solution is considered on the surface of a rotating disk electrode(RDE) under potentiostatic control.The rate of oxygen reduction on the surface of the RDE enables the extent of surface coverage of scale to be assessed. With this electrochemical technique, a new insight into the effect of Mg 2+ on CaCO_3 scale formed on a metal surface is given.

Enhanced ethanol oxidation over Pd nanoparticles supported porous graphene-doped MXene using polystyrene particles as sacrificial templates

Fabrication of superior catalytic performance palladium-based catalysts with affordable cost is the key to develop direct ethanol fuel cell.Herein,Pd-decorated three-dimensional(3D)porous constructed from graphene oxide(GO)and MXene combining with polystyrene(PS)particles as sacrificial templates(Pd/GO-MXene-PS)to elevate the catalytic performance for ethanol oxidation was proposed.The 3D porous interconnected structure of Pd/GO-MXene-PS was characterized by scanning electron microscope(SEM),transmission electron microscope(TEM)and Brunner−Emmet−Teller(BET).By optimizing the doping ratio of MXene to GO,the mass activity of Pd/GO_(5)-MXene_(5)-PS(2944.0 mA·mg^(−1))was 3.0 times higher than that of commercial Pd/C(950.4 mA·mg^(−1))toward ethanol oxidation in base solution.Meanwhile,the rotating disk electrode(RDE)results demonstrated that Pd/GO5-MXene5-PS had a faster kinetics of ethanol oxidation.The enhanced ethanol oxidation over Pd/GO5-MXene5-PS could attribute to the excellent 3D interconnected porous structure,large surface area,good conductivity and homogeneous Pd distribution.This work provided a new idea for creating 3D porous MXene composite materials in electrocatalysis.