The mechanism of the oxygen reduction reaction (ORR) in a naturally aerated stagnant 0.5 M H2SO4 was studied using electrochemical methods. The cathodic polarization curve showed three different regions; electrochemical impedance spectroscopy (EIS) measurement was used accordingly. The EIS data were analyzed, and the mechanism for the ORR was proposed consequently. The three regions include a limiting current density region with the main transfer of 4e− controlled by diffusion (−0.50 V < E < −0.40 V), a combined kinetic-diffusion region (−0.40 V < E < −0.20 V) with an additional 2e− transfer due to the adsorption of the anions, and a hump phenomenon region (−0.20 V < E < −0.05 V), in which the chemical redox between the anodic intermediate and the cathodic intermediate , together with the electrochemical reaction, synergistically results in the acceleration of the ORR. Therefore, a coupled electrochemical/chemical process (the EC mechanism) in the hump phenomenon region was proposed, and a good agreement was found between the experimental and fitted results. The EC mechanism was confirmed by the deaerated experiments. 相似文献
The variation of electrode nature and surface structure (the use of stepped single crystal faces with controlled width of (1 1 1) terraces and monoatomic steps of (1 0 0) or (1 1 0) orientation) allows to determine peculiarities of co-adsorption of acetonitrile molecules, hydrogen adatoms and (bi)sulfate anions. It has been shown that first of all acetonitrile blocks adsorption sites at the steps. Anion adsorption at terraces of stepped platinum surfaces in 0.5 M H2SO4 solution with additions of acetonitrile depends on terrace width and the step orientation. This demonstrates the important role of structural factors in competitive adsorption processes. The decrease in adsorption of hydrogen and anions on narrow terraces is substantially due to the influence of acetonitrile molecules placed at the steps or nearby sites. At E < 1.0 V, electrochemical conversion of acetonitrile has not been detected at single crystal Pt surfaces. However, acetonitrile oxidation might proceed on polycrystalline platinum followed by product desorption. On Au(1 1 1) surface acetonitrile adsorption is considerably weaker than that on platinum electrodes. 相似文献
Three new Schiff bases, viz., N,N′-ethylen-bis (salicylidenimine) [S1], N,N′-isopropylien-bis (salicylidenimine) [S2], and N-acetylacetone imine, N′-(2-hydroxybenzophenone imine) ortho-phenylen [S3] have been investigated as corrosion inhibitors for mild steel in 0.5 M H2SO4 using Tafel polarization and electrochemical impedance spectroscopy (EIS). The three Schiff bases function as good inhibitors reaching inhibition efficiencies of ∼97-98% at 300 ppm concentration. The fraction <theta> of the metal surface covered by the inhibitor is found to increase with inhibitor concentration. Of the three Schiff bases, the S2 shows better efficiency than the other two Schiff bases. The adsorption of the inhibitor follows Langmuir isortherm. Thermodynamic calculations indicate the adsorption to be physical in nature. 相似文献
Halide ions are found to enhance the inhibition performance of amines due to enhanced adsorption of amines by the adsorbed halide ions on the metal surface. In this work, the synergistic action of halide ions on the corrosion inhibition of iron in 0.5 M H2SO4 by diphenylamine has been found out by electrochemical impedance and polarization methods. Analysis of impedance data has been made with equivalent circuit with constant phase angle element for calculation of double layer capacitance values. Experiments have been carried out in the concentration range of 100-1000 ppm of diphenylamine in the presence of 0.5-1.0 × 10−3 M of halide ions. Diphenylamine is found to be a cathodic inhibitor and the inhibition efficiency of about 65% is obtained at 1000 ppm. The anodic and cathodic Tafel slopes in the presence of diphenylamine alone and with halide ions are 65 ± 5 and 105 ± 5 mV, respectively. Diphenylamine inhibits corrosion by adsorption and the surface coverage values are increased considerably in the presence of halide ions. In the presence of iodide ions, the inhibition efficiency of diphenylamine at 100 ppm is increased to more than 90%. In the case of other halide ions, the inhibition efficiency of diphenylamine in increased to 80% at 1000 ppm. The order of synergism of halide ions is I− ? Br− > Cl−. The highest synergistic effect of iodide ions is due to chemisorption with metal surface due to its larger size and ease of polarizability. 相似文献
Poly(3-octyl thiophene) (P3OT) and poly(3-hexylthiophene) (P3HT) dissolved in toluene were deposited onto 1018 carbon steel and corroded in 0.5 M H2SO4. P3OT and P3HT films were chemically deposited by drop casting onto 1018-type carbon steel with two surface finishing, i.e. abraded with 600-emery paper and with alumina (Al2O3) particles of 1.0 μm in diameter (mirror finish). Their corrosion resistance was estimated by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy, EIS, techniques. In all cases, polymeric films protected the substrate against corrosion, but the protection was improved if the surface was polished with Al2O3 particles of 1.0 μm in diameter. The polymer which gave the best protection was P3HT because the amount of defects was much lower than that for the P3OT films. The polymers did not act only as a barrier layer against aggressive environment, but they improved the passive film properties by decreasing the critical current necessary to passivate the substrate, increasing the pitting potential and broadening the passive interval. 相似文献
Degradation mechanism of Ti/IrO2(0.7) + MnO2(0.3) anode for oxygen evolution was studied in 0.5 M H2SO4 solution by field emission scanning electron microscopes (FESEM), Tafel slope, X-ray diffraction (XRD) and electrochemical impedance spectroscopic (EIS). The whole surface of the non-electrolyzed Ti/IrO2(0.7) + MnO2(0.3) anode consisted of nano-IrO2 poles array. The anode surface had hardly discovered cracks and had compact morphology that can prevent the electrolyte from entering the Ti/oxide interface and an insulating TiO2 film from growing on the Ti-based surface. An insulating TiO2 phase had not been generated on the Ti/oxide interface during the process of O2 evolution and the inactive anode surface still remained mass of the IrO2 and MnO2 oxides. The chemical dissolution of Ti/IrO2(0.7) + MnO2(0.3) anode coating was not the main reason for electrode degradation in 0.5 M H2SO4 solution. The degradation mechanism of Ti/IrO2(0.7) + MnO2(0.3) anode differed from other conventional oxide electrodes for O2 evolution in acid medium. The platforms of Tafel slope and anode potential (900–1050 h) indicated that the change of the oxygen evolution reaction (OER) mechanism was the main reason for degradation of Ti/IrO2(0.7) + MnO2(0.3) anode due to the change of adsorption intermediate. 相似文献
The effect of addition of diamine derivatives on the corrosion of steel in 0.5 M H2SO4 solution is studied using weight loss measurements, electrochemical polarisation and impedance spectroscopy (EIS) methods. This study permits to follow the evolution of the inhibitive effect of diamine derivatives on steel in 0.5 M H2SO4. Polarisation measurements show that the diamines act as mixed inhibitors. The cathodic curves indicate that the reduction of proton at the steel surface happens within a pure activating mechanism. The inhibitors are adsorbed on the steel surface according to the Frumkin adsorption isotherm model. We note a good agreement between gravimetric, electrochemical polarisation and impedance spectroscopy methods. 相似文献
Hydrogen evolution from 0.5 M H2SO4 on Ti electrodes coated with a RuxTi1−xO2 (x=0.04-0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 °C caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe2+ ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from −105 mV/decade for pure titanium to about −40 mV/decade for the (RuTi)O2 coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data, to be about 10−4 A cm−2 after activation. 相似文献
Open circuit dependence of potential on oxygen partial pressure as well as potentiostatic behavior in O2- and He-saturated solution were determined. Stable hydrogen-oxygen species were formed, but potential-determining reversbility was found only in the potential range from 0·64–0·70 V (nhe). This equilibrium could be reasonably explained by an O2/H2O2 exchange. Oxygen, H2O2, or other hydrogen-oxygen species may affect open circuit potentials and potentiostatic behavior, but analysis of data assuming reversibility or quasi-equilibrium kinetic theory may be justified only between 0·64 and 0·70 V. 相似文献
The electrochemical behavior of the annealed Cu-5wt.%Ni alloy in 0.5 M H2SO4 was studied by means of open-circuit potential (EOCP) measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and quasi-stationary linear potential sweep. The hydrodynamics of the system was also studied. This material is constituted by a single α1 phase. The anodic behavior of a Cu-Ni alloy in H2SO4 consists fundamentally on the electrodissolution of Cu, its main component, and the formation of a sulfur-containing passive layer. The presence of Ni decreases the rate of Cu oxidation, mostly at high positive potentials. The impedance spectra, obtained for the unrotating electrode, can be interpreted in terms of a simple charge-transfer reaction across a surface layer. When the electrode is rotated, the occurrence of an inductive loop evidenced the existence of an adsorbed layer. All the resistance estimated from the proposed equivalent circuits diminished with the electrode rotation rate, emphasizing the influence of ion transport in the overall electrode process. The system presented two anodic Tafel slopes: 40 mV dec−1 for E<255 mV and 67 mV dec−1 for E>275 mV. A Tafel slope of 40 mV dec−1 evidences that copper dissolution can be interpreted in terms of the mechanism proposed by Mattsson and Bockris. The second Tafel suggests that at potentials more positive than 275 mV, copper dissolves according to a mechanism that considers the disproportionation of adsorbed Cu(I) species. 相似文献
The electrochemical oxidation of glucose on smooth platinum in 1 M H2SO4 has been studied by linear potential sweeps.In the potential range from 1.0–1.5 V vs rhe (a hydrogen electrode in the same solution), where the platinum is oxide covered, the anodic current-potential curves has been explained by the following oxidation mechanism.After adsorption and chemical rearrangement glucose is oxidized in a two electron process to gluconic acid: The model is also shown to work in neutral solutions. A quantitative model has been made and some of the parameters determined in 1 M H2SO4 are 相似文献
In the present study, different types of 75% Cr3C2-25% NiCr coatings were applied on a steel substrate by means of high velocity oxygen fuel spraying (HVOF), and studied using ac and dc electrochemical measurements in an aerated and unstirred 0.5 M H2SO4 solution. Structural characterization was determined before and after electrochemical tests. Differences between all sprayed systems are related to the gun transverse speed and number of deposited layers, which strongly affected the electrochemical characteristics of the coated steels. The coating obtained with a higher torch speed showed better resistance against corrosion. The electrochemical impedance results were analyzed using an equivalent circuit where porosity of the coatings and substrate oxidation were considered. 相似文献
In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H2SO4 solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings. 相似文献
Anodic charging curves have been measured on polycrystalline Bi in H2SO4 solutions (0·01–6·0 N) at 30°C. The effect of various experimental procedures, eg electrode treatment and stirring, has been established. The anodic behaviour of Bi depends markedly on the acid concentration. In the high range, the results indicate dissolution which follows a Tafel relation. However, in dilute solutions, growth of oxide film occurs, and the potential rises rapidly with time, reaching over 100 V at high cds. Sparking and oxide breakdown start at about 150 V. Oxide growth follows the high field ionic conduction. The reciprocal capacitance is linearly related to the logarithm of cd. The constants of the exponential law, the half-barrier width, and the field strength have been calculated The last lies between 1 and 3 × 106 V/cm at 1 mA/cm2. The effect of F− and Cl− ions on oxide growth in H2SO4 has been also investigated. 相似文献
The oxygen reduction reaction (ORR) was studied on carbon dispersed Pt and Pt-Co alloyed nanocatalysts with high contents of Co in H2SO4 and H2SO4/CH3OH solutions. The characterization techniques considered were transmission electron microscopy (TEM), X-ray diffraction (XRD) and in situ X-ray absorption near edge structure (XANES). The electrochemical activity for the ORR was evaluated from steady state polarization measurements, which were carried out in an ultra thin layer rotating disk electrode. The results showed that with the increase of Co content, the nanoparticle size distributions become sharper and the mean particle diameters become smaller. XRD indicated low degree of alloy formation but significant phase segregation of Co was observed only for Pt-Co/C 1:3 and 1:5 (Pt:Co atomic ratios). The electrochemical measurements indicated that the four-electrons mechanism is mainly followed for the ORR on all materials and the electrocatalytic activities per gram of Pt is higher for the catalysts with higher Co contents. This was explained based on the XANES results which evidenced a decrease of the coverage of oxygenated Pt adsorbates due to the presence of Co. In the methanol-containing electrolyte, the Pt-Co/C 1:5 catalyst showed the highest performance. This was attributed to its low activity for the methanol oxidation due to the smaller probability for presenting three Pt neighboring Pt active sites. 相似文献
Physical and electrochemical investigations of vanadium phosphates, Li2xVO(H2−xPO4)2 (0 < x < 2), have been undertaken. H+/Li+ ionic exchange from VO(H2PO4)2 to Li2VO(HPO4)2 leads to grain decrepitation. Further ionic exchange toward formation of Li4VO(PO4)2 lowers the symmetry. As inferred from potentiodynamic cycling correlated to ex situ and in situ X-ray diffraction (XRD), the system Li/Li4VO(PO4)2 shows several phase transformations that are associated with thermodynamical potential hysteresis that span from roughly 15 mV to more than 1.8 V. Small hysteresis are associated with topotactic reactions and with VV/VIV and VIII/VII redox couples. Large potential hysteresis values (>1 V) were observed when oxidation of VIII to VIV is involved. 相似文献
This work summarises available measurements of laminar burning velocities in CH4 + H2 + O2 + N2 flames at atmospheric pressure performed using a heat flux method. Hydrogen content in the fuel was varied from 0% to 40%, amount of oxygen in the oxidiser was varied from 20.9% down to 16%, and initial temperature of the mixtures was varied from 298 to 418 K. These mixtures could be formed when enrichment by hydrogen is combined with flue gas recirculation. An empirical correlation for the laminar burning velocity covering a complete range of these measurements is derived and compared with experiments and other correlations from the literature. 相似文献
The corrosion of titanium in H2SO4 electrolytes (0.001-1.0 M) at temperatures from ambient to 98 °C has been investigated using steady-state polarization measurements. Four distinct regions of behaviour were identified, namely active corrosion, the active-passive transition, passive region and the dielectric breakdown region. The active corrosion and active-passive transition were characterized by anodic peak current (im) and voltage (Em), which in turn were found to vary with the experimental conditions, i.e., d(log?(im))/dpH=−0.8±0.1 and dEm/dpH which was −71 mV at 98 °C, −58 mV at 80 °C and −28 mV at 60 °C. The activation energy for titanium corrosion, determined from temperature studies, was found to be 67.7 kJ mol−1 in 0.1 M H2SO4 and 56.7 kJ mol−1 in 1.0 M H2SO4. The dielectric breakdown voltage (Ed) of the passive TiO2 film was found to vary depending on how much TiO2 was present. The inclusion of Mn2+ into the H2SO4 electrolyte, as is done during the commercial electrodeposition of manganese dioxide, resulted in a decrease in titanium corrosion current, possibly due to Mn2+ adsorption limiting electrolyte access to the substrate. 相似文献
To investigate the role of polyaniline (PANI) in the corrosion protection of stainless steel (SS) in oxygen-deficient acidic solution, a separate doped PANI film electrode on a glass substrate was prepared and the test solution (1 M H2SO4) was purged with high-purity N2 until dissolved oxygen level decreased more than two orders of magnitude. In this deaerated 1 M H2SO4 solution, the galvanic coupling interaction between the separate PANI film electrode and 410 SS was studied. Results reveal that the separate PANI film can passivate the 410 SS steadily for a long period of time. A variety of experimental methods including potentiodynamic measurement, potentiostatic (current-time) examination and X-ray photoelectron spectroscopy (XPS) are used to explore the mechanism by which the separate PANI film passivated the galvanic coupling SS in the deaerated sulfuric solution. These studies show that passivation is achieved because PANI film provides a large critical current at the early stage of coupling and a persistent passive current by its electrochemical dedoping/re-doping equilibrium activity with the acidic environment at the subsequent stage of coupling. 相似文献