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Pulse Electrolysis

Pulse electrolysis is an alternate electrolysis method that utilises a pulsed direct current to initiate non-spontaneous chemical reactions. Also known as pulsed direct current (PDC) electrolysis, the increased number of variables that it introduces to the electrolysis method can change the application of the current to the electrodes and the resulting outcome. This varies from direct current (DC) electrolysis, which only allows the variation of one value, the voltage applied. By utilising conventional pulse width modulation (PMW), multiple dependent variables can be altered, including the type of waveform, typically a rectangular pulse wave, and the duty cycle, which determines the waveform frequency.^[1]

Currently, there has been a focus on theoretical and experimental research into PDC electrolysis in terms of the electrolysis of water to produce hydrogen. Past research has demonstrated that there is a possibility it can result in a higher electrical efficiency in comparison to DC electrolysis. ^[2] This would allow electrolysis procedures to produce greater volumes of hydrogen with a reduced electrical energy consumption.^[1] Although theoretical research has made large promise for the efficiencies and benefits of utilising pulse electrolysis, it has many contradictions including a common issue that it is difficult to replicate the successes of patents experimentally and produces its own negative effects on the electrolyser. ^[2]^[3]

PDC electrolysis is not only confined to the electrolysis of water. Uses in industry such as electroplating and electrocrystallisation are also undergoing research due to the wider range of properties that can be achieved. ^[4]

The various and alterable effects of using intermittent pulses in PDC electrolysis has resulted in an area of interest that could benefit industry. However, as it is still being researched and has produced conflicting results, a consistent and reliable answer to how dependent electrolysis efficiency is on the properties of an electrical pulse has not been determined^[1], hence, other forms of electrolysis such as polymer electrolyte membrane and alkaline water electrolysis are being used in industry.

History of Research

PDC electrolysis was first considered theoretically in 1952,^[5] and experimental research began as early as 1960 however it was originally focused on it's technical applications to industry and the possibilities of improving the quality and rate of metal deposition.^[6] It partially succeeded, providing promising results it's ability to create smoother, denser deposits, and reducing the amount of metal required in electroplating.^[4]

The first instance it was considered to initialise the electrolysis of water was from the perspective of magnetolysis in 1985, where high strength magnets, or in this case electromagnets, are used in conjunction with homopolar propellers.^[7] Ghoroghichian and Bockris conducted this experimental research to determine how a pulsed current can impact the rate of hydrogen production and provide economic advantages. A current density ratio of 2.07 was observed, demonstrating, for the first time, that a pulsed current can double the production of hydrogen, in comparison to a steady state current. ^[8]

Since hydrogen gas cannot be collected in it's free form, and it can be used to provide a source of renewable and clean energy through fuel cells, discovering an electrolysis method with the greatest efficiency is valued. With early experimental and theoretical success, many patents began to be developed until as recent as 2002,^[3] but since 1985, it has only been researched intermittently with varying levels of success. ^[9]

Experimental Research

With the perspective that the current use of non-renewable fuel sources is a main cause of global environmental problems, hydrogen is being viewed as a possible renewable fuel source replacement.^[10] For this to be feasible, the production of hydrogen, through methods such as electrolysis, must be efficient in terms of the energy, cost and time required.^[9] Whilst multiple methods of pulse electrolysis have been studied, and experimental results are mixed, the underlying theory behind this experimental approach remains consistent.

Theoretical Concept

When a voltage is applied to an electrolysis cell, immediately following this an Electric Double Layer (EDL), or a diffusion layer, is theoretically formed. This can can create a capacitance, or can cause the electrolyser to act as a capacitor. ^[9] When this is present, excess voltage must be supplied by the direct current to compensate for the loss in the 'capacitor', which rises the required voltage supplied to what is called the thermo-neutral voltage. One of the aims of PDC electrolysis is to overcome this, and theoretically, when the PMW switches the current on, a capacitance will be stored, and when the duty cycle is over, it will be released, continuing the flow of current whilst reducing the EDL that is formed. ^[1]

Manipulating the dependent variables, such as the duty cycle, can increase or decrease the effectiveness of pulse electrolysis at reducing this layer. A theoretical equation, the Sand equation, is used to calculate the amount of time required to allow the EDL to fall to zero, and allow PDC electrolysis to achieve its highest efficiencies. ^[11]

Use in Magnetolisis

Electrolysers require high currents produced by very low voltages. ^[8] A homopolar generator has the ability to do this, so in Bockris and Ghoroghchian’s original experiment in 1985, they followed Faraday’s idea. Using a magnetic field of 0.86T produced by permanent magnets, they placed a stainless-steel disc in between. The disc needed a rotation speed of 2000 rpm to reach the correct electrical potential for electrolysis. The difference between Faraday’s original model and Bockris and Ghorogchian’s is that their disc will only rotate when it is in contact with an electrolyte. ^[8]

They encountered one large problem, a viscous force created by the electrolyte, that slowed down the motion of the disc. The two ways they could fix this is to rotate the disc and solution together or increase the magnetic field used. The latter being most practicable, the required magnetic field was calculated according to the power consumption rate or producing a cubic meter of hydrogen. It was discovered a magnetic field of 11T was needed for effective electrolysis^[8], more than 16 times greater than what was originally used. Since superconducting magnets would be required, and they can become too expensive to justify their use, ruling this out as a possible method.

Their final decision was to use a homopolar generator as an external source of power. This follows Faraday’s method more closely.

In this method, a pulse potential was created to take advantage of previous studies that give an effectiveness factor of 2 when either a nickel electrode^[8] or a Teflon-bonded platinum electrode was used. ^[11]

The generator was constructed with a magnetic flux density of 0.6T, a propeller radius of 30cm and a loop coated with copper strips. ^[8] To increase the output potential, and reducing the rotation speed required, these were connected in series. Pulses of 2-3V that were sustained for 1ms were achieved. ^[8]

This was the first instance of a successful application of pulse electrolysis for the production of hydrogen. However, it still presents its own limitations in the possibility for it to be used in industry.

Advantages

In theoretical electrolysis of water, a voltage of only 1.23 V is required to split water into hydrogen and oxygen, The formation of an EDL increases this to its thermo-neutral voltage of 1.45 V. Minimising the EDL formed during pulse electrolysis is advantageous, as it can reduce the thermo-neutral voltage and the energy input required, increasing energy efficiency. ^[1]

Disadvantages

Whilst the method of PDC electrolysis has been proven by Ghoroghichian and Bockris in 1952 and 1985 to work extremely well in theory, it is difficult to replicate with consistently positive results in practical experimentation. Hence, the many mechanisms that have been patented are unable to be repeated and used in industry. ^[3]

During the pulse-off period, if the electrolytic cell is not constructed properly, the current polarity can reverse. This can cause the cathode to deteriorate. ^[2] In electrolysis, the cathode is where the reduction of hydrogen occurs, forming the desired hydrogen gas. Any loss in mass can reduce the speed and effectiveness of the electrolytic reaction, reducing the overall efficiency of the pulse electrolysis method.

Comparison with Alternate Methods

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When measuring the electrical consumption of electrolysis using PDC compared to DC currents, there was a substantially greater electrical efficiency of PDC.^[1]

Theoretical analysis of the benefits of PDC electrolysis in comparison to DC electrolysis has been studied from as early as 1956, with many patents being developed up till 2002. ^[3]

Targeting the resonant frequency of a water electrolysis cell, it has been observed that there is a higher efficiency in this process than in DC electrolysis.^[12]

Whilst there have been many theoretical praises and some experimental proofs that PDC is a greater electrolysis method than DC electrolysis, experiments with a greater focus on crude and high volume methods have proven it to be more Pulse electrolysis is an alternate electrolysis method that utilises a pulsed direct current to initiate non-spontaneous chemical reactions.corrosive. ^[2]

Pulse electrolysis is not only used for the electrolysis of water, but has many uses in industry such as electrocrystallisation.^[4]

References

^ ^a ^b ^c ^d Poláčik, Ján; Pospíšil, Jiří (2016-10-01). "Some Aspects of PDC Electrolysis". Technological Engineering. 13 (1): 33–34. doi:10.2478/teen-2016-0011. ISSN 2451-3156.
^ ^a ^b ^c Shaaban, Aly H. (1993). "Water Electrolysis and Pulsed Direct Current". Journal of The Electrochemical Society. 140 (10): 2863. doi:10.1149/1.2220923.
^ ^a ^b ^c Vanags, Martins; Kleperis, Janis; Bajars, Gunars (2012-10-17), Kleperis, Janis (ed.), "Water Electrolysis with Inductive Voltage Pulses", Electrolysis, InTech, doi:10.5772/52453, ISBN 9789535107934, retrieved 2019-04-11
^ ^a ^b ^c Ibl, N.; Puippe, J.Cl.; Angerer, H. (1978). "Electrocrystallization in pulse electrolysis". Surface Technology. 6 (4): 287–300. doi:10.1016/0376-4583(78)90044-4.
^ Bockris, J. O'M.; Potter, E. C. (1952). "The Mechanism of Hydrogen Evolution at Nickel Cathodes in Aqueous Solutions". The Journal of Chemical Physics. 20 (4): 614–628. doi:10.1063/1.1700503. ISSN 0021-9606.
^ Arouete, S.; Blurton, K. F.; Oswin, H. G. (1969). "Controlled Current Deposition of Zinc from Alkaline Solution". Journal of The Electrochemical Society. 116 (2): 166. doi:10.1149/1.2411787.
^ Ehrenhaft, Felix (1944-05-01). "The Decomposition of Water by the So-Called Permanent Magnet and the Measurement of the Intensity of the Magnetic Current". Physical Review. 65 (9–10): 287–289. doi:10.1103/PhysRev.65.287.2. ISSN 0031-899X.
^ ^a ^b ^c ^d ^e ^f ^g Ghoroghchian, J; Bockris, J (1985). "Use of a homopolar generator in hydrogen production from water". International Journal of Hydrogen Energy. 10 (2): 101–112. doi:10.1016/0360-3199(85)90042-4.
^ ^a ^b Monk, Nigel; Watson, Simon (2016). "Review of pulsed power for efficient hydrogen production". International Journal of Hydrogen Energy. 41 (19): 7782–7791. doi:10.1016/j.ijhydene.2015.12.086.
^ Nicoletti, Giovanni; Arcuri, Natale; Nicoletti, Gerardo; Bruno, Roberto (2015). "A technical and environmental comparison between hydrogen and some fossil fuels". Energy Conversion and Management. 89: 205–213. doi:10.1016/j.enconman.2014.09.057.
^ Tseung, A.C.C.; Vassie, P.R. (1976). "A study of gas evolution in teflon bonded porous electrodes—III. Performance of teflon bonded Pt black electrodes for H2 evolution". Electrochimica Acta. 21 (4): 315–318. doi:10.1016/0013-4686(76)80026-6.
^ "(PDF) An Investigation into the Electrical Impedance of Water Electrolysis Cells – With a View to Saving Energy". ResearchGate. Retrieved 2019-04-11.

[:0-1] Poláčik, Ján; Pospíšil, Jiří (2016-10-01). "Some Aspects of PDC Electrolysis". Technological Engineering. 13 (1): 33–34. doi:10.2478/teen-2016-0011. ISSN 2451-3156.

[:1-2] Shaaban, Aly H. (1993). "Water Electrolysis and Pulsed Direct Current". Journal of The Electrochemical Society. 140 (10): 2863. doi:10.1149/1.2220923.

[:2-3] Vanags, Martins; Kleperis, Janis; Bajars, Gunars (2012-10-17), Kleperis, Janis (ed.), "Water Electrolysis with Inductive Voltage Pulses", Electrolysis, InTech, doi:10.5772/52453, ISBN 9789535107934, retrieved 2019-04-11

[:3-4] Ibl, N.; Puippe, J.Cl.; Angerer, H. (1978). "Electrocrystallization in pulse electrolysis". Surface Technology. 6 (4): 287–300. doi:10.1016/0376-4583(78)90044-4.

[5] Bockris, J. O'M.; Potter, E. C. (1952). "The Mechanism of Hydrogen Evolution at Nickel Cathodes in Aqueous Solutions". The Journal of Chemical Physics. 20 (4): 614–628. doi:10.1063/1.1700503. ISSN 0021-9606.

[6] Arouete, S.; Blurton, K. F.; Oswin, H. G. (1969). "Controlled Current Deposition of Zinc from Alkaline Solution". Journal of The Electrochemical Society. 116 (2): 166. doi:10.1149/1.2411787.

[7] Ehrenhaft, Felix (1944-05-01). "The Decomposition of Water by the So-Called Permanent Magnet and the Measurement of the Intensity of the Magnetic Current". Physical Review. 65 (9–10): 287–289. doi:10.1103/PhysRev.65.287.2. ISSN 0031-899X.

[:5-8] ^ ^a ^b ^c ^d ^e ^f ^g Ghoroghchian, J; Bockris, J (1985). "Use of a homopolar generator in hydrogen production from water". International Journal of Hydrogen Energy. 10 (2): 101–112. doi:10.1016/0360-3199(85)90042-4.

[:4-9] Monk, Nigel; Watson, Simon (2016). "Review of pulsed power for efficient hydrogen production". International Journal of Hydrogen Energy. 41 (19): 7782–7791. doi:10.1016/j.ijhydene.2015.12.086.

[10] Nicoletti, Giovanni; Arcuri, Natale; Nicoletti, Gerardo; Bruno, Roberto (2015). "A technical and environmental comparison between hydrogen and some fossil fuels". Energy Conversion and Management. 89: 205–213. doi:10.1016/j.enconman.2014.09.057.

[11] Tseung, A.C.C.; Vassie, P.R. (1976). "A study of gas evolution in teflon bonded porous electrodes—III. Performance of teflon bonded Pt black electrodes for H2 evolution". Electrochimica Acta. 21 (4): 315–318. doi:10.1016/0013-4686(76)80026-6.

[12] "(PDF) An Investigation into the Electrical Impedance of Water Electrolysis Cells – With a View to Saving Energy". ResearchGate. Retrieved 2019-04-11.

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