The compressive strength of carbon electrode under normal temperature is greater than that of graphitized electrode. The carbon electrode is suitable for the smelting of some common electric steel and ferro-alloy in medium and small electric furnaces and ferro-alloy furnaces. Because of the high ash content of carbon electrode, it is not suitable for smelting high-grade alloy steel. The raw material of carbon electrode is easy to be solved. It does not need to be graphitized in production.
In this part of the experiment, the electrolyte temperature has gradually increased from to K Figure 4. The study clearly reveals that when there is an increase in temperature the hydrogen production increases linearly.
The reasons for this behavior can be drawn from the thermodynamic characteristics of a water molecule since its splitting reaction potential is known to reduce as the temperature increases. Moreover, ionic conductivity and surface reaction of an electrolyte rise directly with temperature High temperature water electrolysis requires less energy to reach any given current density in analogy with a low temperature process 18, The main outcome of the study is that a substantial part of the energy needed for the electrolysis process is added as heat, which is much cheaper than electric energy.
In addition, the high temperature accelerates the reaction kinetics, reducing the energy loss due to electrode polarization, thus increasing the overall system efficiency. The ohmic losses are due to the resistance of the imperfect electrodes and the nature electrolytes. The resistivity of the given electrolytic solution can be calculated by varying the current density with respect to applied voltage as shown in Figure 5. It is clearly shows that, the ohmic loss of the alkaline KOH is perfectly linear In most cases, the ohmic loss is considered to have the relationship of I Current and R, where R is constant.
From the linear graph, the resistivity of aqueous KOH is calculated as The influence of an applied voltage on the hydrogen evolution reaction HER can be studied over cylindrical graphite electrode at the temperature of K with a 0. The applied voltage is varied from 4. It shows that, the rate of production of hydrogen gas gradually increases with increase in applied voltage. The plausible reason is the uniform charge density increases on the surface of cylindrical electrode.
In order to study the sustainability and stability of the cylindrical graphite electrode, the effect of time on the hydrogen evolution reaction is studied under the optimized reaction conditions.
The obtained results were illustrated in Figure 7. The unchanged profile of hydrogen production for the period of 90 minutes demonstrates that the graphite electrode remains stable state without any destruction on the surface of the electrode throughout the testing time. The rate of production of hydrogen is much more similar to that of initial run. This means the graphite electrode regain its original activity of its regeneration.
The overall performance of the graphite electrode has shown an acceptable level of stability under the present experimental conditions. The efficiency of graphite electrode is compared with commercially available various electrodes like L stainless steel, EN8 and carbon rods and the results are shown in Figure 8. From the experimental results, it was observed that even though, the carbon and graphite electrodes are allotropy of carbon materials, the efficiency of hydrogen production is much higher on graphite electrode.
The plausible reasons it may be due to the either layer of structure graphite electrode or the porous nature of material which significantly enhances the diffusion of water molecule without any blockage. On the other hand, the contact time of water molecule per unit time is much higher on graphite electrode than the carbon electrode.
Therefore, from the above results it might be concluded that hydrogen evolution reaction is preferentially taking place in the internal porous structure. Further, the significant corrosion behavior can be seen on both stainless steel and EN8 electrodes by using alkaline KOH as the electrolyte and it leads to decrease in the rate of hydrogen production.
The observed trend is more pronounced on EN8 electrode compared to the stainless steel electrode. Among all the cylindrical electrodes, graphite is found to be the best choice for hydrogen evolution reaction under the present experimental conditions. The rate data for the alkaline water electrolysis is studied on cylindrical graphite electrode and it could be fitted well to first order rate law.
The following relationship derived between relative conversion 'X' and contact time has been used for evaluating the rate parameters. Where, 'X' is the fractional conversion of hydrogen gas, 'k' is the apparent first order rate constant.
From the slope of linear plot, the first order rate constant value 'k' can be calculated by using equation 1, which is used to determine the activity of electrodes through the evaluation of activation energy. The apparent activation energy is calculated as 7.
The Electrolytic production of hydrogen is systematically studied by using commercially available graphite electrode at room temperature. On increasing the electrolytic concentration the hydrogen production is greatly increases. However, the gradual decomposition of anodic graphite rods is observed.
From the study we concluded that the high electrolytic concentration above 0. The efficiency of graphite electrode is compared with commercially available various electrodes like L stainless steel, EN8 and carbon rods. Further research is necessary to develop this laboratory scale study into a practical reality.
Abrir menu Brasil. Materials Research. Abrir menu. Under these conditions, diffusion from the bulk of solution where concentration is constant to the electrode surface is nearly all linear in nature, in a direction perpendicular to the electrode surface.
In cyclic voltammetry see Section II A, part 2-b these conditions typically give rise to the traditional peak-shaped voltammogram. A CV recorded for ferrocene at a 3 mm diameter glassy carbon disk electrode is shown at the left side of Figure Ferrocene was present at a concentration of 0. The scan rate was 0. Next consider a planar microelectrode with micrometer or smaller dimensions. At the right side of Figure 36 , a voltammogram for 0. With all of the other experimental conditions remaining the same, a sigmoidal rather than a peak-shaped voltammogram was observed.
This was the result of a steady-state condition between diffusion and electron transfer, where the rate of diffusion matches the rate of electron transfer.
Why the difference? Because of the small size of the electrode, the contribution to the current by diffusion from the edges of the electrode becomes important in the total mass transport of electroactive species. This edge effect, or radial diffusion is generally very small at large electrodes relative to the linear diffusion mentioned above. For microelectrodes, the flux per unit time and area is greater than for large electrodes because the region from which electroactive species diffuses to the surface is in essence hemispherical in shape.
It is important to understand that the voltammograms in Figure 36 are for one set of conditions. There are conditions in which a CV recorded at a large planar electrode will demonstrate steady-state behavior, and conditions for which peak-shaped voltammograms are seen at microelectrodes. The normalizing factor for all conditions is the experimental time. The approximate distance in cm a diffusing molecule can travel during a time period t in seconds is given by.
When d is small relative to the radius of the electrode, linear diffusion will predominate, and the observed voltammogram will be peak shaped. For small electrode dimensions, d will frequently be large relative to the electrode radius, and a steady-state voltammogram will result.
While this has been only a cursory look at the differences between macro- and micro-sized electrodes, there are many excellent review articles available for readers desiring more in-depth information on this topic. Ideally, a working electrode should behave reproducibly each time that it is used. Factors that affect the electrochemical behavior of a surface are its cleanliness, the kind and extent of chemical functionalities including oxides that are present, and the microstructure of the electrode material itself.
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