Oxygen Diffusion Control Research Articles

Electrochemical corrosion behavior of high strength steel in simulated deep-sea environment under different hydrostatic pressure

The corrosion behavior of Ni-Cr-Mo-V high strength steel in the simulated deep-sea environment under different hydrostatic pressure and immersion time is investigated using electrochemical techniques, microscopic morphology observation and Raman spectrometer. During the first 10 days immersion, the corrosion rate presents wave-like changes. The corrosion rate under different hydrostatic pressure tends to be stable after 10 days immersion. The area with uneven composition will preferentially dissolve and form corrosion pits. The local corrosion takes the corrosion pit as the center, expands and fuses around, and finally forms uniform corrosion. High hydrostatic pressure promotes β-FeOOH transforming into other corrosion products. The anode of the steel tends to active dissolution and the cathode show oxygen diffusion control characteristics at the initial stage of corrosion. Under 20 MPa, step-shape passivation appears in the anode region. Due to the rapid reaction, the corrosion product film has poor protection performance and dissolves, which resulting in not obvious passivation phenomenon.

Effect of chloride concentration on the properties of passive film formed on Q235 steel in simulated concrete pore solutions

PurposeThis paper aims to study the effect of chloride concentration on the properties of passive film formed on Q235 steel in simulated concrete pore solutions.Design/methodology/approachMott–Schottky analysis and electrochemical impedance spectroscopy were used to study the passive film of Q235 steel in simulated concrete pore solution. X-ray photoelectron spectroscopy was used to analyze the composition of passive film on Q235 steel.FindingsWhen the chloride concentration is below the chloride threshold value, open circuit potential (OCP) and Rct gradually increases and donor concentration (ND) remains unchanged with the increasing immersion time. When the chloride concentration exceeds chloride threshold value, OCP and Rct decreases after a temporary increase and ND increases. The linear region of the Mott–Schottky curve lost its linearity. The electrochemical process control step is changed from charge transfer control to oxygen diffusion control. As the chloride concentration increases, the FeO content in the passive film increases and the Fe2O3 content decreases. Chloride can destroy the outer layer of passive film and introduce impurities.Originality/valueThe effects of chloride and immersion time on the change process of passive films on Q235 steel in simulated concrete pore solution were studied using electrochemical methods. The mechanism of chloride destroying passive film was analyzed.

Multiscale modeling of steel corrosion in concrete based on micropore connectivity

This paper presents coupled multiscale models of steel corrosion in concrete, focusing on micropore connectivity. The ohmic control is represented by the effective surface area of steel in contact with interconnected pore solution. The oxygen diffusion control is simulated based on oxygen transport through the Nernst's diffusion layer assumed in the connected pore solution. The model validation with experimental data of multiple previous studies indicates that both the exponential change of corrosion current under the ohmic control and the oxygen diffusion control for higher relative humidity (RH) levels can be reasonably simulated. Also, a parametric study on water-to-cement ratios implies that moisture in nm-scale micropores is not involved in corrosion reactions. Moreover, 10-year-long simulations indicate that the long-term weight loss of steel is significantly affected by external RH. Therefore, for accurately predicting the long-term corrosion in real reinforced concrete structures, collecting actual RH data in the surrounding environment is important.

Kinetic Control of the Li0.9Mn1.6Ni0.4O4 Spinel Structure with Enhanced Electrochemical Performance.

The development of more sustainable societies has become an urgent goal worldwide. Electrical batteries are currently seen as one of the most important energy storage technologies for the development of decarbonized societies. However, many lithium-ion battery manufacturers currently utilize cobalt, a toxic and hazardous mineral, in their batteries. Lithium-deficient manganese nickel oxide spinels are considered promising candidates owing to their high potential and environmental friendliness. Their electrochemical performance highly depends on their average and local structures, such as phase purities, lattice parameters, and cation sites. Thus, a synthesis protocol should be designed to control these structural parameters to improve their electrochemical performance. In this study, we controlled the average and local structures of Li0.9Mn1.6Ni0.4O4 spinels obtained by co-precipitation by optimizing their cooling rates. High-resolution techniques, including transmission electron microscopy, synchrotron X-ray diffraction, and Auger-composition analysis combined with density functional theory calculations, X-ray absorption spectroscopy, and electrochemical analysis, were used to understand the average and local structural variations and their effects on the electrochemical properties. As a result, the control of oxygen diffusion at different cooling rates can promote the rearrangement of the structure, resulting in a cation-disordered spinel with minimal variations in lattice parameters and composition. Excellent electrochemical properties were noted in the cation-disordered spinel with high crystallinity and a slightly oxygen-rich surface produced via optimized cooling rates.

Metal-free nitrogen-doped graphenic materials as cathode catalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells

Exhibiting a very high surface area, a good electrical conductivity and a high density of active sites, nitrogen-doped graphenic materials are considered as promising catalysts for the oxygen reduction reaction (ORR). Seldom studied in acidic media, N-doped graphenic foams were tested here as the cathode catalysts of a polymer electrolyte membrane fuel cell (PEMFC). The materials were prepared via a solvothermal-based process, by reacting either cyclohexanol and ethanolamine or 1-(2-hydroxyethylethyl) piperidine with metallic sodium, under high pressure and temperature. Membrane electrode assemblies were prepared with a Pt/C anode, 212 Nafion membrane, and an 8 mm disk cathode based on the graphenic materials. The performance exhibited by the PEMFC was evaluated using chronopotentiometry and impedance spectroscopy, depending on the synthesis conditions. The kinetic parameters of the ORR were estimated by interpretation of the experimental data: the high Tafel slope found might express the partial control of oxygen diffusion through the graphenic microporous structure. Relationships between the electrochemical behavior of the materials and their structural properties are discussed. Moderately crystallized materials with a low oxygen content showed the highest catalytic properties, with a current density larger than 30 mA cm−2 and a maximum power density at 2.3 mW cm−2.

The Evolution of Cholesterol-Rich Membrane in Oxygen Adaption: The Respiratory System as a Model.

The increase in atmospheric oxygen levels imposed significant environmental pressure on primitive organisms concerning intracellular oxygen concentration management. Evidence suggests the rise of cholesterol, a key molecule for cellular membrane organization, as a cellular strategy to restrain free oxygen diffusion under the new environmental conditions. During evolution and the increase in organismal complexity, cholesterol played a pivotal role in the establishment of novel and more complex functions associated with lipid membranes. Of these, caveolae, cholesterol-rich membrane domains, are signaling hubs that regulate important in situ functions. Evolution resulted in complex respiratory systems and molecular response mechanisms that ensure responses to critical events such as hypoxia facilitated oxygen diffusion and transport in complex organisms. Caveolae have been structurally and functionally associated with respiratory systems and oxygen diffusion control through their relationship with molecular response systems like hypoxia-inducible factors (HIF), and particularly as a membrane-localized oxygen sensor, controlling oxygen diffusion balanced with cellular physiological requirements. This review will focus on membrane adaptations that contribute to regulating oxygen in living systems.

Patching of Lattice Defects in Two-Dimensional Diffusion Barriers

Two-dimensional crystals offer promise as diffusion barriers that can also facilitate electronic conduction through the barrier plane via tunneling. We present barriers in which crystal imperfections are patched, leaving the pristine regions of the crystal exposed and able to both prevent diffusion and allow electronic conduction. This is accomplished by atomic layer deposition, where nucleation of patch material is inhibited on the pristine crystal and promoted elsewhere. Demonstrations of the effectiveness of this technique are performed in the contexts of sulfur diffusion control in photovoltaic kesterite devices and oxygen diffusion control in oxide-based resistive switching devices.

Graded functionalization of biomaterial surfaces using mussel-inspired adhesive coating of polydopamine

Biomaterials with graded functionality have various applications in cell and tissue engineering. In this study, by controlling oxidative polymerization of dopamine, we demonstrated universal techniques for generating chemical gradients on various materials with adaptability for secondary molecule immobilization. Diffusion-controlled oxygen supply was successfully exploited for coating of polydopamine (PD) in a gradient manner on different materials, regardless of their surface chemistry, which resulted in gradient in hydrophilicity and surface roughness. The PD gradient controlled graded adhesion and spreading of human mesenchymal stem cells (hMSCs) and endothelial cells. Furthermore, the PD gradient on these surfaces served as a template to allow for graded immobilization of different secondary biomolecules such as cell adhesive arginine-glycine-aspartate (RGD) peptides and siRNA lipidoid nanoparticles (sLNP) complex, for site-specific adhesion of human mesenchymal stem cells, and silencing of green fluorescent protein (GFP) expression on GFP-HeLa cells, respectively. In addition, the same approach was adapted for generation of nanofibers with surface in graded biomineralization under simulated body fluid (SBF). Collectively, oxygen-dependent generation of PD gradient on biomaterial substrates can serve as a simple and versatile platform that can be used for various applications realizing in vivo tissue regeneration and in vitro high-throughput screening of biomaterials.

Transient Study of Adsorbed Oxygen Species Arising from Exposure to Dissolved Oxygen

The oxygen reduction reaction (ORR) was studied using Pt based microelectrodes under different mass transfer regimes. Current transients at different potentials were recorded by first applying a cleaning waveform and a rest potential 1–3 transformed to sampled current voltammograms and finally normalised using the equation proposed by Mahon and Oldham 4. In the steady state, the normalised current is akin to an apparent number of electrons n app, while for shorter times, the presence of an extra current that is attributed to the reduction of oxygen adsorbed species (adspecies) can be seen 2,3. These adspecies are only observed after exposure of the surface to dissolved oxygen during the rest potential and their reduction was tested with different types of Pt electrodes. First, Pt nanoparticles were deposited on carbon fibre microdisc electrodes (7 μm Ø). The normalisation gave n app = 3 at steady state conditions; this value is large for an electrode of this size 5 and it is believed that this is due to the effectiveness of the nanoparticles to reduce peroxide towards water due to their close proximity with each other. At shorter times, the normalisation showed an extra current attributed to the reduction of oxygen adspecies 2,3 but also to the reduction of carbon functionalities. To solve this, carbon nanoelectrodes were electroplated with Pt until sub-micron spheres were obtained and covered the carbon surface completely. At the steady state, n app = 2. Since no carbon was exposed to the solution, this n appis attributed to the high rate of mass transfer that can be achieved with these electrodes. At short timescales, the extra current due to the reduction of oxygen adspecies was also visible. Different sizes of Pt microdiscs were also used (5, 10, 25 and 50 μm Ø). The value of n app for each electrode agrees with those reported under steady state conditions 5. Using the equation proposed by Mahon and Oldham 4, a subtraction between the experimental and theoretical current densities was obtained and integrated to calculate the charge density associated to the reduction of the oxygen adspecies. The results from the millisecond to the second scale showed a value of 55 μC cm-2 in agreement with previous works 2,3. This value corresponds to 0.1 monolayers and seems to indicate that the coverage does not depend on the electrode size. Further analysis of the current transients assuming a first order process for the rate of reduction of the oxygen adspecies suggests that the maximum coverage that can be obtained corresponds to approximately 0.3 monolayers. This is currently being studied by recording current transients at the microsecond scale. The dependency of the rate of reduction of the oxygen adspecies on the applied potential is also under study. It is expected that this work will help elucidate the lifetime of the processes involved, namely the reduction of oxygen adsorbed species and the reduction of diffusion controlled oxygen that comes from the bulk. Overall these transient experiments shed new light on the interaction between dissolved oxygen and Pt electrodes and provide new insight on the oxygen reduction reaction. (1) Perry, S. C.; Al Shandoudi, L. M.; Denuault, G. Sampled-Current Voltammetry at Microdisk Electrodes: Kinetic Information from Pseudo Steady State Voltammograms. Anal. Chem. 2014, 86(19), 9917–9923. (2) Perry, S. C.; Denuault, G. Transient Study of the Oxygen Reduction Reaction on Reduced Pt and Pt Alloys Microelectrodes: Evidence for the Reduction of Pre-Adsorbed Oxygen Species Linked to Dissolved Oxygen. Phys. Chem. Chem. Phys. 2015, 17(44), 30005–30012. (3) Perry, S. C.; Denuault, G. The Oxygen Reduction Reaction ( ORR ) on Reduced Metals : Evidence for a Unique Relationship between the Coverage of Adsorbed Oxygen Species and Adsorption Energy. Phys. Chem. Chem. Phys. 2016, 18, 10218–10223. (4) Mahon, P. J.; Oldham, K. B. Diffusion-Controlled Chronoamperometry at a Disk Electrode. Anal. Chem. 2005, 77(18), 6100–6101. (5) Sosna, M.; Denuault, G.; Pascal, R. W.; Prien, R. D.; Mowlem, M. Development of a Reliable Microelectrode Dissolved Oxygen Sensor. Sensors Actuators, B Chem. 2007, 123 (1), 344–351.

Metallic monoclinic phase in VO2 induced by electrochemical gating: In situ Raman study

We report in situ Raman scattering studies of electrochemically top gated VO2 thin film to address metal-insulator transition (MIT) under gating. The room temperature monoclinic insulating phase goes to metallic state at a gate voltage of 2.6 V. However, the number of Raman modes do not change with electrolyte gating showing that the metallic phase is still monoclinic. The high-frequency Raman mode Ag(7) near 616 cm−1 ascribed to V-O vibration of bond length 2.06 Å in VO6 octahedra hardens with increasing gate voltage and the Bg(3) mode near 654 cm−1 softens. This shows that the distortion of the VO6 octahedra in the monoclinic phase decreases with gating. The time-dependent Raman data at fixed gate voltages of 1 V (for 50 minutes, showing enhancement of conductivity by a factor of 50) and 2 V (for 130 minutes, showing further increase in conductivity by a factor of 5) show similar changes in high-frequency Raman modes Ag(7) and Bg(3) as observed in gating. This slow change in conductance together with Raman frequency changes show that the governing mechanism for metalization is more likely due to the diffusion-controlled oxygen vacancy formation due to the applied electric field.

Compensation for the influence of temperature and humidity on oxygen diffusion in a reactive polymer matrix

Abstract. In a previous work (Marek et al., 2013) a time-monitoring oxygen sensor was proposed. This sensor is based on a diffusion-controlled oxygen reaction of the indicator system methylene blue (MB)/leuco methylene blue (LMB) and riboflavin embedded in a water-loaded poly(vinyl alcohol) (PVA) matrix. It can be used in packaging, sensors, and biotechnology applications. Since the oxygen diffusion coefficient in the PVA matrix strongly depends on temperature and humidity, two different approaches were developed within this work to compensate for these two effects. To compensate for faster oxygen diffusion at higher temperatures, iron particles were added to the PVA matrix, resulting in a novel PVA/iron composite matrix. Adding silicone particles allows compensating the influence of humidity. Both temperature and humidity compensation were modeled using the finite-element method in good accordance with the experimental data. This allows tuning the sensor for application at different conditions of temperature and humidity and therewith in different environments.

Influence of Water Contents on Corrosion Behavior of Continuous Casting Copper-clad Steel in Dagang Soil

The corrosion behavior of continuous casting copper-clad steel in Dagang soil with 20%~30% water contents was studied by polarization curve measurement and EIS. It is shown that during the initial corrosion stage, the corrosion rates of continuous casting copper-clad steel are al- most equal, which imply the water contents have little influence on the corrosion behavior. The con- trol step for corrosion of continuous casting copper-clad steel in the soil is activation polarization process at the initial stage. During the later stage, the corrosion rates of continuous casting copper- clad steel decrease and then tend to be stable with the increase of water contents, which may be due to the synergistic effect of the two opposite factors i.e. the block effect with reducing oxygen and the stimulation effect with environmental water on the electrode process. However the corrosion be- havior is mainly affected by oxygen diffusion control.

Influences of Concrete Resistivity on Corrosion Rate of Steel Bar in Concrete

Corrosion rate of steel bar in concrete plays an important role in load bearing-capacity evaluation, maintenance decision and residual life prediction of existing RC structures. A macro cell corrosion model was developed to investigate the influences of concrete resistivity on corrosion rate of steel bar in concrete based on the electrochemical principle and the Bulter-Volmer equation. Analysis results show that concrete resistivity has significant effect on corrosion rate of steel bar in concrete if the limit current density is relative large and the steel corrosion is under control of ion transportation. With the increase of relative humidity, the limit current density decreases obviously and the steel corrosion is influenced by both oxygen diffusion and concrete resistivity. However, if the concrete resistivity is relative small, steel corrosion will be under control of oxygen diffusion.

Corrosion Fouling of Carbon Steel for Convective Heat Transfer in an Annulus

Heat transport through a corroded carbon steel pipe in a double-pipe heat exchanger, with an aerated 0.1 N NaCl solution flowing in the annular space, has been investigated. Experiments under heat transfer turbulent flow conditions were carried out in a Reynolds number range of 5000–15,000, at three bulk temperatures (30, 40, and 50°C), and a heat flux of 15 kW/m2. Rates of heat transfer were determined by measuring surface temperature, while mass transfer rates (corrosion rates), due to the diffusion-controlled oxygen reduction reaction, were estimated by measuring the limiting current density. Fouling due to corrosion deposits that form on heat transfer surfaces has an asymptotic form. The value of the asymptotic fouling resistance ranged from 2.17 × 10−4 to 2.54 × 10−4 m2 °C/W with 200 h of exposure time.

Selective Oxidation of Glucose Over Carbon-supported Pd and Pt Catalysts

Selective oxidation of glucose into gluconic acid by molecular oxygen over carbon-supported Pt and Pd catalysts was studied. Under examination were kinetic regularities of the process in respect of the electronic state of the noble metal surface, dispersion of the active component particles as well as substrate:Pt(Pd) ratio. Catalytic activity of the Pt/C catalysts being normalized to the dispersion of the platinum particles appeared independent of the particles mean diameter in the 1–5 nm range. A negative particle size effect for the Pd/C catalysts, caused by feasibility of oxidation of the surface of noble metal particles with the size less than 3 nm, was observed. Pt/C catalysts exhibited lower specific activity and provided poor selectivity of the glucose oxidation in comparison with Pd/C. Deactivation of Pd/C catalysts arising from the formation of surface Pd(II) oxides was retarded when the reaction was carried out under an oxygen-diffusion control. Selective oxidation of glucose to gluconic acid over carbon supported palladium and platinum catalysts proceeds with the selectivity up to 97 and 77%, respectively. Catalytic activity of the carbon-supported Pt nanoparticles with diameters ranging from 1 to 5 nm towards the selective oxidation of glucose is directly proportional to platinum surface area. Finely dispersed Pd/C catalysts (〈d Pd〉 =3 nm) are prone to deactivation due to oxidation of their surface, while larger metal particles (〈d Pd〉 =6 nm) are more tolerant and stable. The activity of Pd nanoparticles can be maintained when the process is controlled by diffusion of oxygen towards the active component of the catalyst.

The argon-induced decline in nitrogenase activity commences before the beginning of a decline in nodule oxygen uptake

Replacement of N(2) by argon in the air around nodules directs nitrogenase electron flow in its total onto H(+) resulting in increased nodule H(2) evolution (total nitrogenase activity (TNA)). However, argon application induces a so-called argon-induced decline in nitrogenase activity (Ar-ID) connected with decreased nodule oxygen permeability. Consequently, TNA measurements tend to underestimate total nitrogenase activity. It is unclear whether the decline in oxygen diffusion into nodules induces the Ar-ID, or whether a decline in nitrogenase activity is followed by lower nodule O(2) uptake. The objective of the present work was to examine the time sequence of the decline in nodule H(2) evolution and O(2) uptake after argon application. In addition, the reliability of TNA values, taken as quickly as possible after the switch to Ar/O(2), was tested through comparative measurement of (15)N(2) uptake of the same plants. Short-term TNA measurements in an optimized gas exchange measurement system yielded reliable results, verified by parallel determination of (15)N(2) uptake. A five min application of Ar/O(2) was without effect on the subsequent H(2) evolution in ambient air. A parallel experiment on control plants revealed that a decrease in nodule oxygen uptake began several minutes after the onset of the decline in H(2) evolution. We conclude that the primary effect of the replacement of N(2) by argon differs from oxygen diffusion control. A gas exchange system allowing an immediate taking of TNA yields reliable results and does not disturb nodule activity. Gas exchange measurements provide a powerful tool for studying nodule physiology and should be combined with material from molecular studies.

Electrochemical behaviour of Ti–Ni SMA and Co–Cr alloys in dynamic Tyrode’s simulated body fluid

The electrochemical behaviour of Ti-Ni shape memory alloy and Co-Cr alloys were investigated in dynamic Tyrode's simulated body fluid on a Model CP6 Potentiostat/Galvanostat. The results indicated that, for all alloys, the anodic dissolution and the pitting sensitivity increased with the flow rate of the Tyrode's solution increasing while the open-circuit potentials and pitting corrosion potentials decreased with the Tyrode's solution increasing. Pitting corrosion of Ti-Ni alloy was easier than Co-Cr alloys. Since the solution's flow enhanced oxygen transform and made it easy to reach the surface of electrodes, the plateau of oxygen diffusion control was diminished. All these indicated that the cathodic reduction and the corrosion reaction, which was controlled by the electrochemical mass transport process, were all accelerated in dynamic Tyrode's simulated body fluid.

Application of Ce0.33Zr0.63Pr0.04O2-supported noble metal catalysts in the catalytic wet air oxidation of 2-chlorophenol: Influence of the reaction conditions

A series of noble metal (Pt, Pd, Ru) loaded Ce0.33Zr0.63Pr0.04O2 catalysts were used in the Catalytic Wet Air Oxidation (CWAO) of 2-chlorophenol (2-CP) at relatively low temperature (393K). Among the investigated noble metals, Ru exhibited the best activity. To optimize the reaction conditions, the effects of different parameters, such as the nature of the ruthenium precursor, the reaction temperature, the total pressure, the initial 2-CP concentration and the initial pH of the 2-CP solution on the catalytic performances of 3wt.% Ru/Ce0.33Zr0.63Pr0.04O2 were evaluated. It was confirmed that the nature of the ruthenium precursor had nearly no effect on the activity of Ru/Ce0.33Zr0.63Pr0.04O2. The activation energy for the 2-CP CWAO over Ru/Ce0.33Zr0.63Pr0.04O2 was calculated to be 34kJmol−1. Unexpectedly, the 2-CP removal rate was 0.5 order with respect to the initial 2-CP concentration. Furthermore, the CWAO of 2-CP changed from first order (“oxygen diffusion control”) to zero order (“kinetic control”) with respect to the oxygen partial pressure, when the total pressure was higher than 4MPa. The 2-CP conversion increased with the pH of the initial 2-CP solution. The dechlorination reaction is promoted at higher pH. However, too high pH hindered the total mineralization of 2-CP due to the possible poisoning effect of adsorbed carbonate and hydroxycarbonate species. The optimum initial pH was about 6.

Dose rate effects on the radiation induced oxidation of polyethylene

The yields and spatial distribution of the products arising from the in source oxidation of 50 μm LDPE films induced by 60-Co gamma radiations and by 300 kev electrons have been investigated as a function of the dose rate. The dose rate was found to have a strong influence on the reaction, the hydroperoxides and carbonyls yields at the lowest gamma dose rate of 0.04 kGy/h being decreased by a factor of about three with increasing the gamma dose rate up to 0.69 kGy/h and by a factor of about 30 when operating at the e-beam dose rate of 1.5 kGy/s. The carbonyls depth concentration profiles, the EPR measurements on radicals intermediates and the experiments of post-irradiation oxidation are consistent with the conclusion that, as far as the gamma irradiation is concerned, the observed dose rate effects cannot be imputed to oxygen diffusion control and/or to the chain branching via hydroperoxides decomposition coupled to the longer times between the initiation events. The hypothesis of the dose rate acting on the kinetic chain length of the radioxidation which in turn implies a substantially uniform distribution of radicals in the amorphous phase attained through spur expansion is proposed.

Mechanism transition of mixed diffusion and charge transfer-controlled to diffusion-controlled oxygen reduction at Pt-dispersed carbon electrode by Pt loading, Nafion content and temperature

The mechanism transition in the oxygen reduction reaction at the Pt-dispersed carbon (Pt/C) electrode was investigated in an oxygen-saturated 0.5 M H 2SO 4 solution. The reaction was monitored by acquiring data for Pt loading, Nafion content and temperature by analyses of the rotating disk voltammograms and potentiostatic current transients (PCTs). From the shape of the cathodic PCTs and the dependence of the initial current density on the potential drop, it is suggested that oxygen reduction at the Pt/C electrode is controlled by the charge transfer at the electrode surface mixed with the oxygen diffusion in the solution below the value of the potential drop, Δ E tr, needed for the occurrence of the mechanism transition, whereas oxygen reduction is purely governed by the oxygen diffusion in the solution above Δ E tr. In particular, it was noted that the value of Δ E tr remained nearly constant irrespective of the Pt loading and Nafion content. On the other hand, the value of Δ E tr decreased as temperature increased, which is ascribed to the fact that the contribution of the Cottrell current enhanced by temperature rise to the fall in Δ E tr is overwhelmed by that contribution of the Butler–Volmer current increased. Consequently, it is concluded that it strongly depends upon the extrinsic parameters such as Pt loading, Nafion content and temperature as well as the intrinsic parameters such as rate constant for interfacial reaction and oxygen diffusivity in the solution, which mechanism of the overall oxygen reduction reaction is operative.