Sonoelectrolytic Hydrogen Production from Dilute Sulfuric Acid
Electrolysis of dilute sulfuric acid produces hydrogen gas and oxygen gas. Ultrasonication reduces the diffusion layer thickness at the electrode surface and improves mass transfer during electrolysis. Ultrasonication can increase hydrogen gas production rates in the electrolytic cell, significantly.
Two experimental setups with a carbon anode and a titanium cathode are described below. To demonstrate the positive effects of ultrasonication on the electrolysis, the titanium cathode is a sonoelectrode. This adds ultrasonic vibrations and cavitation to the electrolytic production of hydrogen and oxygen from dilute sulfuric acid. The combination of ultrasonics with electricity is used in sonoelectrochemistry, sonoelectrolysis and sonoelectrosynthesis.
The Hielscher ultrasonic homogenizer UP100H (100 watts, 30kHz) is equipped with a sonoelectrochemical upgrade. This allows to use the sonotrode as a cathode or anode in an electrolytic process. For industrial sonoelectrolytic setups, please click here!
Sonoelectrolysis Setup 1 – H-type Undivided Cell
The setup uses dilute sulfuric acid (H2SO4, 1.0M). An H-type undivided cell is filled with the electrolyte. This cell is known as a Hofmann Voltameter. It has three joined upright glass cylinders. The inner cylinder is open at the top to allow filling with electrolyte. Opening the valves at the top of the outer tubes allows any gas to escape during filling. In the electrolytic cell, the electrodes are sealed by rubber rings and immersed upside-down into the solution of acidified water. The positive anode electrode is made of carbon (8mm). The negative cathode is a titanium ultrasonic sonoelectrode (10mm, special high surface area sonotrode, Hielscher UP100H, 100 watts, 30kHz). The titanium sonoelectrode and the carbon electrode are inert. Electrolysis will only take place when electricity is passed through the dilute sulfuric acid solution. Therefore, the carbon anode and a titanium cathode are connected to a constant voltage power supply (direct current).
The hydrogen gas and the oxygen gas produced in the electrolysis of the dilute sulfuric acid is collected in the graduated outer tubes above each electrode. The gas volume displaces the electrolyte in the outer tubes, and the volume of the additional gas can be measured. The theoretical ratio of the gas volume is 2:1. During the electrolysis, only water is removed from the electrolyte as hydrogen gas and oxygen gas. Hence, the concentration of the dilute sulfuric acid rises slightly during the electrolysis.
The video below shows the sonoelectrolysis of dilute sulfuric acid using pulsed ultrasonication (100% amplitude, cycle mode, 0.2 seconds on, 0.8 seconds off). Both tests were run at 2.1V (DC, constant voltage).
Sonoelectrolysis Setup 2 – Simple Batch
A glass vessel is filled with an electrolyte of dilute sulfuric acid (H2SO4, 1.0M). In this simple electrolytic cell, the electrodes are immersed into a solution of the acidified water. The positive anode electrode is made of carbon (8mm). The negative cathode is a titanium ultrasonic sonoelectrode (10mm, MS10, Hielscher UP100H, 100 watts, 30kHz). Electrolysis will only take place when electricity is passed through the dilute sulfuric acid solution. Therefore, the carbon anode and a titanium cathode are connected to a constant voltage power supply (direct current). The titanium electrode and the carbon electrode are inert. The hydrogen gas and the oxygen gas produced in the electrolysis of the dilute sulfuric acid is not collected in this setup. The video below shows this very simple setup in operation.
What Happens During Electrolysis?
The hydrogen ions are attracted to the negative cathode. There, the hydrogen ion or water molecules are reduced to hydrogen gas molecules by an electron gain. As a result hydrogen gas molecules are discharged as hydrogen gas. The electrolysis of many reactive metal salts or acid solutions produce hydrogen at the negative cathode electrode.
The negative sulphate ions or the traces of hydroxide ions are attracted to the positive anode. The sulfate ion itself is too stable, so that nothing happens. Hydroxide ions or water molecules are discharged and oxidized at the anode to form oxygen. This positive anode reaction is an oxidation electrode reaction by an electron loss.
Why Do We Use Dilute Sulfuric Acid?
Water contains minute concentrations of hydrogen ions and hydroxide ions, only. This limits electrical conductivity. High concentrations of hydrogen ions and sulfate ions from the dilute sulfuric acid improve the electrical conductivity of the electrolyte. Alternatively, you can use alkaline electrolyte solution such as potassium hydroxide (KOH) or sodium hydroxide (NAOH), and water. The electrolysis of many solutions of salts or sulfuric acid produces hydrogen at the negative cathode and oxygen at the positive anode. The electrolysis of hydrochloric acid or chloride salts produces chlorine at the anode.
What is an Electrolyzer?
An electrolyzer is a device to separate water into hydrogen and oxygen in a process known as electrolysis. The electrolyzer uses electricity to produce hydrogen gas and oxygen gas. The hydrogen gas can be stored as compressed or liquefied gas. Hydrogen is an energy carrier for use in hydrogen fuel cell in cars, trains, buses, or trucks.
A basic electrolyzer contains a cathode (negative charge) and an anode (positive charge) and peripheral components, such as pumps, vents, storage tanks, a power supply, a separator, and other components. Water electrolysis is an electrochemical reaction that occurs within the electrolyzer. The anode and cathode are powered by a direct current and the water (H20) is split into its components hydrogen (H2) and oxygen (O2).
Literature / References
- Bruno G. Pollet; Faranak Foroughi; Alaa Y. Faid; David R. Emberson; Md.H. Islam (2020): Does power ultrasound (26 kHz) affect the hydrogen evolution reaction (HER) on Pt polycrystalline electrode in a mild acidic electrolyte? Ultrasonics Sonochemistry Vol. 69, December 2020.
- Md H. Islam; Odne S. Burheim; Bruno G.Pollet (2019): Sonochemical and sonoelectrochemical production of hydrogen. Ultrasonics Sonochemistry Vol. 51, March 2019. 533-555.
- Jayaraman Theerthagiri; Jagannathan Madhavan; Seung Jun Lee; Myong Yong Choi; Muthupandian Ashokkumar; Bruno G. Pollet (2020): Sonoelectrochemistry for energy and environmental applications. Ultrasonics Sonochemistry Vol. 63, 2020.
- Bruno G. Pollet (2019): Does power ultrasound affect heterogeneous electron transfer kinetics? Ultrasonics Sonochemistry Vol. 52, 2019. 6-12.
- Md Hujjatul Islam; Michael T.Y. Paul; Odne S. Burheim; Bruno G. Pollet (2019): Recent developments in the sonoelectrochemical synthesis of nanomaterials. Ultrasonics Sonochemistry Vol. 59, 2019.
- Sherif S. Rashwan, Ibrahim Dincer, Atef Mohany, Bruno G. Pollet (2019): The Sono-Hydro-Gen process (Ultrasound induced hydrogen production): Challenges and opportunities. International Journal of Hydrogen Energy, Volume 44, Issue 29, 2019, 14500-14526.
- M.D. Esclapez, V. Sáez, D. Milán-Yáñez, I. Tudela, O. Louisnard, J. González-García (2010): Sonoelectrochemical treatment of water polluted with trichloroacetic acid: From sonovoltammetry to pre-pilot plant scale. Ultrasonics Sonochemistry Volume 17, Issue 6, 2010. 1010-1020.
- L. Cabrera, S. Gutiérrez, P. Herrasti, D. Reyman (2010): Sonoelectrochemical synthesis of magnetite. Physics Procedia Volume 3, Issue 1, 2010. 89-94.