Vol 53, No 5 (2017)

Through the gel-casting process, the tubular cathode for direct ethanol fuel cell (DEFC) is prepared using the mesocarbon microbeads (MCMB) and graphite as the main raw materials. According to the tubular cathode’s physical performance and electrical property tests, the performance of cathode tube is studied at different graphite proportions. As shown by the results of strength test, the strength of cathode tube is better with a graphite ratio from 0 to 40%. It can be found that the linear and volumetric shrinkage of tubular cathode support will decrease with the increment of the graphite content. As displayed by the electrical property tests, the charge transmission ability is extremely close when the graphite surpasses 30%. With 40% of graphite doping ratio, the electrode electrochemical reaction will be reinforced when the temperature gets higher. In the meanwhile, the electricity capacity will be higher when the air flow rate is 100 mL min^–1.

A simple and practical sensor of hydrogen peroxide (H₂O₂) was designed successfully. The mixture of horseradish peroxidase (HRP) and chitosan (Chit) are effectively immobilized on the surface of poly-L-leucine/polydopamine modified glassy carbon electrode (PL-LEU/PDA/GCE). Under the optimum conditions, the biosensor based on HRP exhibits a fast amperometric response (within 3 s) to H₂O₂. The linear response range of the sensor is 0.5–952.0 μmol L^–1, with the detection limit of 0.1 μmol L^–1 (S/N = 3) and the sensitivity of 0.23 A L moL^–1 cm^–2. The apparent Michaelis–Menten constant (k_M^app) of the biosensor is evaluated to be 0.12 mmol L^–1, which suggests that the HRP-Chit/PL-LEU/PDA/GCE shows a higher affinity for H₂O₂. The sensor exhibits good sensitivity, selectivity, stability and reproducibility. The proposed method has been successfully applied to the determination of H₂O₂ in practical samples.

Cobalt microparticles (Co MPs) modified Pt electrode is simply and conveniently fabricated. The electrochemical properties of paracetamol (PCT) at the prepared modified electrode are investigated using cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements. Based on these techniques, a sensitive and rapid electrochemical method is developed for the determination of PCT. The result indicates that the oxidation of PCT is strongly improved at the Co MPs/Pt electrode as compared with the bare Pt electrode, with relatively high sensitivity, stability and life time. The determination of PCT on the Co MPs/Pt with square wave voltammetry displays a high sensitivity of 101 μA/mM and a low detection limit of 0.42 μM (S/N = 3) in the range (0.5–100 μM). The sensitivity of the modified electrode for the detection of PCT is almost 17 times greater than on the bare Pt electrode. The proposed method is successfully applied to the PCT determination in tablets.

A multiwalled carbon nanotube-modified carbon paste electrode (MWCNT-PE) was used for determination of 1,4-diazabicyclo[2,2,2]octane (DABCO or TEDA) in 0.1 M phosphate buffer solutions (pH 10.25). Cyclic voltammetry(CV) and differential pulse voltammetry (DPV) techniques were used to investigate the electrocatalytic oxidation of DABCO at the surface of modified electrode. The results shown that the oxidation peak current of DABCO at the surface of MWCNT-PE was 2.40 times larger than that at the bare electrode. The experimental formal redox potential (E°') of DABCO was obtained 986 mV versus SHE (Standard Hydrogen Electrode). Density functional theory (DFT) method at B3LYP/6-311++G** level of theory and a conductor-like Polarizable Continuum Model (CPCM) was used to calculate the E°' values. The highest occupied molecular orbital (E_HOMO), lowest unoccupied molecular orbital (E_LUMO) and some thermodynamic parameters such as Gibbs free energy of DABCO and its oxidation forms were calculated. Both direct and indirect methods were used to calculate the theoretical standard electrode potential for DABCO and the results were found to be in good agreement with the experimental values.

For supercapacitors with sulfuric acid electrolyte, a promising carbon material was suggested, namely, activated carbon from waste wood. It was shown how the synthesis conditions of activated carbon affect its porous structure and electrochemical characteristics of supercapacitors on its basis. The changes in the porous material under different synthesis conditions were controlled using the highly informative limited evaporation method, which allows us to obtain complete information about the porous structure of the micro- and mesopores of the material within a relatively short period of time. The negative effect of the excess volume of macropores in the electrode on the capacity and energy based on the dry mass of electrodes was shown experimentally and analyzed. The properties of the synthesized material were compared with those of other carbon materials. The best samples of the developed material possess a specific electric capacity of over 390 F/g.

The characteristics of porous Pt/YSZ (ZrO₂ + 10 mol % Y₂O₃) electrodes activated with small amounts of either oxides of rare-earth elements (REE) of the cerium subgroup (CeO₂, PrO_x, TbO_x) or a mixed oxide with the Сe₂Tb₄O₁₁ composition by the procedure of impregnating the electrodes with ethanol solutions of REE nitrates and subsequent heating at 850°С are studied by the impedance method. The studies are carried out for those cases where the REE oxides after thermal treatment form a film on the electrolyte and also where no activator film is formed. The characteristics of films and activated electrodes are compared. Film-activated Pt/YSZ electrodes are discussed within the framework of the model of compact oxide electrodes.

In this study, cellulose-manganese dioxide nano-composites were synthesized and their electrochemical behavior studied as electrode in an electrochemical supercapacitor (ECS). The morphology of composites were investigated by scanning electron microscopy (SEM). Thermal gravimetric analysis (TGA) was used to determine the thermal stability and water content of the composites. The electrochemical capacitance of the composites is studied by cyclic voltammetry (CV) in Na₂SO₄ electrolyte (0.5 M) at room temperature. The results show that the capacitance of the composites are strongly affected by the nano-structure, structural continuity, thermal stability and surface/structural water of manganese dioxide. A high specific capacitance of 171 F/g was obtained for cellulose-manganese dioxide nano-composite which has higher structural continuity, lower water content and better thermal stability.

The Ag–Ge–Se system was studied in the range of compositions Ag₂Se–GeSe₂–Se by measuring the EMF of the concentration (relative to the silver electrode) circuits with a solid electrolyte Ag₄RbI₅ in the temperature range 290–430 K. The polymorphic transition temperature of Ag₈GeSe₆ (320 K) was determined and the partial molar functions of silver were calculated for both crystal modifications of this compound based on the EMF measurements. The thermodynamic functions of formation and entropy of both modifications of Ag₈GeSe₆ and the thermodynamic functions of its polymorphic transition were calculated.