Faradic efficiency calculation of oxygen evolution reaction and hydrogen evolution reaction

 

Faradaic efficiency is a measure of the fraction of electrons participating in the desired electrochemical reaction compared to the total number of electrons passed through the electrochemical cell. It is commonly used to evaluate the efficiency of oxygen evolution electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution electrocatalysts for the hydrogen evolution reaction (HER).

To calculate the faradaic efficiency, you need to determine the number of electrons involved in the desired reaction and the total number of electrons passed through the cell. Here's how you can perform the calculation for both OER and HER:

1. Oxygen Evolution Reaction (OER):

The OER involves the oxidation of water to produce oxygen gas. The balanced chemical equation for OER is:

4OH⁻ → 2H₂O + O₂ + 4e⁻

To calculate the faradaic efficiency for OER, you need to measure the current (I_OER) passing through the cell during the experiment and the total charge passed (Q_total). The faradaic efficiency (FE_OER) is given by:

FE_OER = (4 * n_OER) / (Q_total * F)

where n_OER is the number of moles of oxygen evolved, F is the Faraday constant (96,485 C/mol), and the factor of 4 in the numerator accounts for the four electrons involved in the reaction.

2. Hydrogen Evolution Reaction (HER):

The HER involves the reduction of protons from water to produce hydrogen gas. The balanced chemical equation for HER is:

2H⁺ + 2e⁻ → H₂

To calculate the faradaic efficiency for HER, you need to measure the current (I_HER) passing through the cell during the experiment and the total charge passed (Q_total). The faradaic efficiency (FE_HER) is given by:

FE_HER = (2 * n_HER) / (Q_total * F)

where n_HER is the number of moles of hydrogen evolved, and the factor of 2 in the numerator accounts for the two electrons involved in the reaction.

In both cases, the number of moles of the evolved species can be determined from the measured volume of gas produced and the ideal gas law.

It's important to note that the faradaic efficiency calculation assumes that the only competing side reactions are negligible. In practical experiments, it's crucial to ensure proper control and minimize any unwanted side reactions that may affect the accuracy of the faradaic efficiency measurement.