The effect of the thiourea on the electrochemical impedance during copper electrodeposition was investigated using a rotating ring disk electrode. The rest potential of the copper electrode measured in the solution containing thiourea was shifted to less noble due to the adsorption of thiourea. The cathode polarization curve of the copper electrode demonstrated that the current density of the copper electrode decreased remarkably because of an increase in the concentration of thiourea. The Nyquist plot of impedance spectrum in the presence of the thiourea described the capacitive loop, which was related to the time constant of the charge transfer resistance and the electric double layer capacitance, in the high frequency range and a part of the large locus crossing the imaginary axis in the low frequency range. This low frequency locus is related to negative resistance which contributes to “leveler” effect. In order to clarify the negative resistance, the theoretical equations of the Faraday impedance were derived. We proposed the four steps of the copper electrodepostion reactions in the presence of thiourea.
To improve the performances of fuel cells at low humidity, we have prepared composite electrolyte membranes by incorporating SiO2 nanoparticles into poly(arylene ether sulfone ketone) (SPESK) membrane. SiO2 particles were able to be dispersed in SPESK highly uniformly on the nanometer scale by the use of a commercial SiO2–dimethylacetamide sol. The SiO2/SPESK cell exhibited improved I–E performance at 53% relative humidity (RH) and 80°C. It was found that such an improvement was due to the reduction of the ohmic resistance and the oxygen-transport overpotential at high current densities, probably because the SiO2 nanoparticles promoted the back-diffusion of water generated at the cathode catalyst layer toward the anode. Both the ohmic resistance and the oxygen-transport overpotential were reduced further by using a thin (ca. 12 µm) SiO2/SPESK membrane, resulting in remarkably high performances at 53% RH and 30% RH.
In order to establish a simple, sensitive and rapid method for the determination of azithromycin, the gold electrode modified with Silica sol/Nano-Au/PVP/Ru(bpy)32+ was prepared, and the electrochemiluminescence (ECL) method was developed for the determination of azithromycin based on the sensitizing effect of azithromycin on Ru(bpy)32+. Moreover, the electrochemical behaviors and the electrochemical luminescence behaviors of the Ru(bpy)32+ system and the Ru(bpy)32+- azithromycin system were investigated by ECL respectively. The results show that the proposed electrode showed very good electrochemical activity and electrochemiluminescence response to the Ru(bpy)32+- azithromycin system, under the optimum experimental condition, the linearity of azithromycin concentration to ECL intensity was achieved in the concentration of azithromycin from 1.0 × 10−7 to 1.0 × 10−4 mol L−1 and the detection limit (S/N = 3) was 1.33 × 10−9 mol L−1. Through the parallel determination of 1.0 × 10−5 mol L−1 azithromycin for 8 times, the RSD of results was 1.82%, and the recovery ranging from 97.9% to 101.6% was obtained in the detection of azithromycin tabelets and the RSD was 1.36% (n = 5). The proposed method showed high selectivity and sensitivity and simplicity, and it could be applied to the analysis of azithromycin with satisfactory results.
Esterification of carboxylic acids with alkyl halides using electroreduction has been investigated. The reaction of carboxylic acids, such as benzoic acid, 3-phenylpropanoic acid, nonanoic acid, cinnamic acid, and 1-naphthoic acid, under electrochemical reduction conditions followed by the addition of alkyl halides afforded the corresponding esters in moderate to good yields. The reactions proceeded via the SN2 mechanism of the alkyl halide, with the carboxylate ion bearing the ammonium ion as the counter cation, which was generated and accumulated from the carboxylic acid. The generation of the carboxylate ion intermediate is essential, and it appears to have high reactivity because the counter cation of the carboxylate ion intermediate is an ammonium ion.
Based on the method of in-situ polymerization synthesis, combining with two-step sintering process and two-step carbon coating, LiFePO4/C composite cathode material had been prepared. The structure, microstructure and morphology were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) micrograph and scanning electron microscope (SEM) respectively. The electrochemical performances were researched by cyclic voltammetry (CV) and charge/discharge capacity. The results indicated that two-step carbon coating for LiFePO4 was of more remarkable advantages compared with one-step carbon coating sample, such as more complete carbon coating and better electrochemical performance.