Typical Electrode Reactions and Electrolyte pH.
For organic contaminants in an aqueous electrolyte, the desired anode reaction is the oxidation of the organic
contaminants. Using formate as an example the anode reaction is:
Desired Anode Reaction: HCOO- = CO2 + H+ + 2 e- (R1)
This reaction tends to decrease pH by producing H+ ions.
The typical reaction, which competes with oxidation of organic contaminants, is the evolution of oxygen by
the following reaction:
Competing Anode Reaction: H2O = 2 H+ + ½ O2 + 2 e- (R2)
This reaction tends to decrease the electrolyte pH at an even faster rate than R1 because two H+ ions are
produced per pair of electrons instead of one.
The typical cathode reaction is the production of hydrogen by the following reactions:
Typical Cathode Reaction (Basic Electrolyte): 2 H2O + 2 e- = 2 OH- + H2 (R3)
Typical Cathode Reaction (Acidic Electrolyte): 2H+ + 2 e- = H2 (R4)
These reactions tend to increase the electrolyte pH by removing H+ ions or producing OH- ions.
If the H+ and OH- ions are allowed to mix, they combine and neutralize each other to produce water.
H+ + OH- = H2O (R5)
If no organic contaminants are oxidized, production of H+ ions in R2 is balanced by removal of H+ ions in R3 and R5, or
R4 and the electrolyte pH will remain constant. If organic contaminants are oxidized, less H+ ions are produced per R1,
reaction R3 or R4 predominates, and the electrolyte pH will increase.
While the pH trends indicated have been observed, these trends are not universal. There are other factors that can affect
pH. Carbonates can buffer the pH for example. In applications where pH may have a significant impact it should be
monitored. For example, cyanide-containing solutions will evolve toxic HCN if the pH is reduced below approximately 9 pH
and it is critical that the electrolytic system be monitored and controlled to prevent this. In other cases polymerization of
crystallization may occur because of changes in pH. In separated cells the anolyte pH typically decreases and the
catholyte pH increases.
Below is a diagram showing the electrode reactions and the electrochemical cell.
For organic contaminants in an aqueous electrolyte, the desired anode reaction is the oxidation of the organic
contaminants. Using formate as an example the anode reaction is:
Desired Anode Reaction: HCOO- = CO2 + H+ + 2 e- (R1)
This reaction tends to decrease pH by producing H+ ions.
The typical reaction, which competes with oxidation of organic contaminants, is the evolution of oxygen by
the following reaction:
Competing Anode Reaction: H2O = 2 H+ + ½ O2 + 2 e- (R2)
This reaction tends to decrease the electrolyte pH at an even faster rate than R1 because two H+ ions are
produced per pair of electrons instead of one.
The typical cathode reaction is the production of hydrogen by the following reactions:
Typical Cathode Reaction (Basic Electrolyte): 2 H2O + 2 e- = 2 OH- + H2 (R3)
Typical Cathode Reaction (Acidic Electrolyte): 2H+ + 2 e- = H2 (R4)
These reactions tend to increase the electrolyte pH by removing H+ ions or producing OH- ions.
If the H+ and OH- ions are allowed to mix, they combine and neutralize each other to produce water.
H+ + OH- = H2O (R5)
If no organic contaminants are oxidized, production of H+ ions in R2 is balanced by removal of H+ ions in R3 and R5, or
R4 and the electrolyte pH will remain constant. If organic contaminants are oxidized, less H+ ions are produced per R1,
reaction R3 or R4 predominates, and the electrolyte pH will increase.
While the pH trends indicated have been observed, these trends are not universal. There are other factors that can affect
pH. Carbonates can buffer the pH for example. In applications where pH may have a significant impact it should be
monitored. For example, cyanide-containing solutions will evolve toxic HCN if the pH is reduced below approximately 9 pH
and it is critical that the electrolytic system be monitored and controlled to prevent this. In other cases polymerization of
crystallization may occur because of changes in pH. In separated cells the anolyte pH typically decreases and the
catholyte pH increases.
Below is a diagram showing the electrode reactions and the electrochemical cell.
Spartan Environmental Technologies
Air and Water Treatment
Air and Water Treatment
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Spartan Environmental
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com
Technologies, L.L.C.
7383 Lauren J Dr
Mentor, OH 44060
USA
Phone: 800-492-1252
Fax: 440-368-3569
E-mail: info@
spartanwatertreatment.com