Out of the two types of electrodes, active electrodes get involved in the redox reaction by accumulating or consuming materials of electrodes. Steel and iron are the most commonly used for electrolysis of water.
These electrodes are used as anode and it is sacrificed in electrolysis, as the anode rusts get oxidized and the cathode de-rusts get reduced. Many works have been carried out in stainless steel, brass and aluminum as anodes, due to the familiar corrosion-resistant properties of these materials.
Unfortunately, stainless steel releases toxic materials when it decays, brass deposits copper onto the cathode which accelerates rusting of steel , and aluminum quickly deteriorates.
In this connection, the carbon based electrodes such as carbon and graphite are much more interested due to low cost, good electrical and thermal conductivity, the relatively inert property in alkaline solution compared to metals and also for its porous structure with high purity.
The porous structure helps graphite to adsorb hydrogen molecules However, the hydrogen production is not systematically studied over the graphite electrode to improve hydrogen production by simple electrolytic process. In the present paper, the effects of electrolyte concentration, temperature, applied voltage and reaction time on the amount of hydrogen gas produced and consequently on the overall electrolysis efficiency is experimentally investigated.
The experiment is carried out as in the setup shown in Figure 1. It consists of two compartments ID and height of each compartment were 6 cm and 20 cm, respectively in the electrolyzer of total capacity of 1. The distance between the two electrodes is kept constant at a value of 2 cm. The electrodes are then connected with bridge rectifier AC to DC converter. The range of DC output is varied from 0 to 12 V. A variac is used to vary the applied voltage.
Ammeter 0 - 20 A DC and voltmeter 0 - 50 V DC are connected respectively in series and parallel to the electrolyzer to measure current and voltage applied to the system.
The gases obtained from the anode and the cathode limbs are collected separately. The volume of hydrogen produced is twice the amount of oxygen produced and it can be measured by down displacement method. Bases and acids are known to change the nonconductive nature of pure water. These compounds have a great reducing effect on the overvoltage value of an electrolyzer They improve the ionic conductivity aqueous electrolyte compounds.
However, the concentration level of acidic and alkali solutions are limited in practice due to the highly corrosive behavior of electrodes. In this regard, the concentration of electrolyte was systematically varied from 0.
The study revealed that the hydrogen production gradually increases with increase in electrolytic concentration. This may be due to the amount of current that passes depends on the conductance of the electrodes and electrolyte concentration.
In another perspective, the increase in hydrogen evolution in increased electrolytic concentration is due to a greater number of effective ionic collisions per unit time. The effect of various electrolytic concentrations on graphite electrodes is studied and represented in Figure 3. The results are shown that when there is an increase in electrolytic concentration from 0. The decomposition behavior of graphite rod is calculated by weight loss after the electrolytic process.
The weight loss may be due to high electrolytic concentration in the presence of applied voltage. The KOH acts up to the surface carbon of graphite material and it leads to the electrolytic solution turning into black slurry. From the results, we concluded that the high electrolytic concentration above 0. Temperature is known to be one of the most effective variables on the electric power demand of an electrolytic cell. Electrolysis process is much more efficient at increased temperatures 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 Asked 7 years, 1 month ago. Active 6 years, 11 months ago. Viewed 15k times. Improve this question. Add a comment. Active Oldest Votes. Improve this answer. I remember that even electrodes from batteries slowly decayed and left black stuff all over the solution.
I've only ever used graphite electrodes at relatively low potentials and I've never had that problem. I can't attest to the quality of graphite that's used in batteries. Since they're disposable anyways, they really don't have to be that durable. If you're running at high potential, it's possible to actually oxidize the graphite, a known problem with strong oxyacid solutions, though the binder seems to be more strongly attacked than the actual graphite, so it depends on how the electrode is made.
Eric Lee Eric Lee 1 1 silver badge 4 4 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Usually, it is made out of an allot rope of carbon compound called graphite.
They are made from joining many carbon atoms in a hexagonal shape and linked with more number of hexagonal to make a layer and it will be one atom thick. Email: info orientcarbongraphite. Why carbon electrodes are used in the electrolysis? Most of the scientists have suggested that carbon electrode has several freely moving electrons within their structure so it acts as the highly conductive material.
They are more stable at high temperatures, durable and consider being tough material.
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