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Technologies

NaOH production by Ion Exchange Membrane Electrolyzer

In the ion-exchange membrane methode, sodium chloride solution is divided in the anodic and cathodic sides by an ion-exchange membrane made of special resin. The ion-exchange membrane used in this method has a specific characteristic of allowing only cations (positively-charged ions) to pass through it while not allowing anions (negatively-charged ions) to do so.

As shown in the figure on the right, chlorine, caustic soda and hydrogen are produced by electrolyzing sodium chloride solution with the electricity applied to the solution through the electric terminals while sodium chloride solution and water are supplied to the cathodic and anodic chambers, respectively, in the ion-exchange membrane method.

As the anodic chamber is filled with sodium chloride solution, there are sodium ions (Na+) and chloride ions (Cl-) in the chamber. When electricity is applied to the solution, movement of the ions will occur. Since Na+ ions are cations, they will move from the anodic chamber, through the membrane and into the cathodic chamber, while Cl- ions will remain in the anodic chamber, since they are anions. Then, they will move to the anode, release electrons and become chlorine gas (Cl2) on the anode.

Meanwhile, part of water supplied into the cathodic chamber has been broken down to hydrogen ions (H+) and hydroxide ions (OH-). When electricity is applied to the solution, hydrogen ions will move to the cathode, acquire electrons on the cathode and become hydrogen gas (H2). Meanwhile, the hydroxide ions will move toward the anodic chamber. However, their movement will be blocked by the ion-exchange membrane and they will remain in the cathodic chamber with the sodium ions which have moved from anodic chamber. As a consequence, there will be a solution of caustic soda (NaOH) generated in the cathodic chamber.

KOH production by Ion Exchange Membrane Electrolyzer

In the ion-exchange membrane methode, potassium chloride solution is divided in the anodic and cathodic sides by an ion-exchange membrane made of special resin. The ion-exchange membrane used in this method has a specific characteristic of allowing only cations (positively-charged ions) to pass through it while not allowing anions (negatively-charged ions) to do so.

As shown in the figure on the right, chlorine, potassium hydroxide and hydrogen are produced by electrolyzing potassium chloride solution with the electricity applied to the solution through the electric terminals while potassium chloride solution and water are supplied to the cathodic and anodic chambers, respectively, in the ion-exchange membrane method.

As the anodic chamber is filled with potassium chloride solution, there are potassium ions (K+) and chloride ions (Cl-) in the chamber. When electricity is applied to the solution, movement of the ions will occur. Since K+ ions are cations, they will move from the anodic chamber, through the membrane and into the cathodic chamber, while Cl- ions will remain in the anodic chamber, since they are anions. Then, they will move to the anode, release electrons and become chlorine gas (Cl2) on the anode.

Meanwhile, part of water supplied into the cathodic chamber has been broken down to hydrogen ions (H+) and hydroxide ions (OH-). When electricity is applied to the solution, hydrogen ions will move to the cathode, acquire electrons on the cathode and become hydrogen gas (H2). Meanwhile, the hydroxide ions will move toward the anodic chamber. However, their movement will be blocked by the ion-exchange membrane and they will remain in the cathodic chamber with the potassium ions which have moved from anodic chamber. As a consequence, there will be a solution of potassium hydroxide (KOH) generated in the cathodic chamber.

LiOH production by Ion Exchange Membrane Electrolyzer

In the ion-exchange membrane methode, lithium chloride solution is divided in the anodic and cathodic sides by an ion-exchange membrane made of special resin. The ion-exchange membrane used in this method has a specific characteristic of allowing only cations (positively-charged ions) to pass through it while not allowing anions (negatively-charged ions) to do so.

As shown in the figure on the right, chlorine, lithium hydroxide and hydrogen are produced by electrolyzing lithium chloride solution with the electricity applied to the solution through the electric terminals while lithium chloride solution and water are supplied to the cathodic and anodic chambers, respectively, in the ion-exchange membrane method.

As the anodic chamber is filled with lithium chloride solution, there are lithium ions (Li+) and chloride ions (Cl-) in the chamber. When electricity is applied to the solution, movement of the ions will occur. Since Li+ ions are cations, they will move from the anodic chamber, through the membrane and into the cathodic chamber, while Cl- ions will remain in the anodic chamber, since they are anions. Then, they will move to the anode, release electrons and become chlorine gas (Cl2) on the anode.

Meanwhile, part of water supplied into the cathodic chamber has been broken down to hydrogen ions (H+) and hydroxide ions (OH-). When electricity is applied to the solution, hydrogen ions will move to the cathode, acquire electrons on the cathode and become hydrogen gas (H2). Meanwhile, the hydroxide ions will move toward the anodic chamber. However, their movement will be blocked by the ion-exchange membrane and they will remain in the cathodic chamber with the lithium ions which have moved from anodic chamber. As a consequence, there will be a solution of lithium hydroxide (LiOH) generated in the cathodic chamber.

Alkali liquid Electrolyzer produce Hydrogen and Oxygen

Alkaline water electrolysis has a long history in the chemical industry. Its application for energy conversion in the hydrogen energy system is attracting attention, and advanced electrolyzers have been developed.

The principle of the alkaline water electrolysis is quite simple. Oxygen and hydrogen are separated from the water when the direct current is applied to the water, as shown in the equations.

Two water molecules dissociate and hydrogen arises at the cathode by this reaction. At the anode, oxygen arises and a water molecule is generated at the same time. As a result, when a water molecule dissociates, another water molecule moves to the anode. Alkaline electrolyzers contain caustic water solution and potassium hydroxide (KOH). Sodium hydroxide (NaOH) and sodium chloride (NaCl) are used as the catalyst. The liquid electrolyte allows ions to be transported between the electrodes and is not consumed in the chemical reaction, but is periodically replenished depending on the losses in the system. AEL devices are the most commonly used hydrogen generators in the industry. The hydrogen production becomes pure with 99%. After certain purification processes, it will reach the high purity rates required for hydrogen fuel cells.

Performance and technological developments

In industry, hydrogen and oxygen of electrolytic grade are produced using ‘zero gap’ alkaline cells.

Electrochemical performance of a conventional alkaline ‘membrane cell’ water electrolyser at 90°C, (I) Thermodynamic voltage (1.18 V), (II) ionic ohmic drop across electrolyte, (III) anodic (O2) over-voltage, (IV) cathodic (H2) over-voltage, (V) electronic ohmic drop of electrodes.

Large scale water electrolysis has also been (and still is) considered for the regulation of electric power production from nuclear plants.

Two areas that have a significant impact on cell efficiency are electrocatalysts and cell membranes. Research efforts reported in the literature have been made to increase the efficiency of the water electrolysis cell by preparing and evaluating (a) electrocatalysts based on non-precious metals (nickel, cobalt, molybdenum and others), transition metal macrocycles and (b) alkaline exchange membranes that primarily conduct hydroxyl ions in the cell electrolyte. The ultimate design of such cells is the AEM cell (using an anion exchange membrane as SPE in place of a proton-conducting membrane) in which no liquid electrolyte is used.