For a hydrogen half-cell to function under standard conditions, the following conditions need to be met:
1. Standard Temperature: The temperature should be 25°C (298.15 K) as per the standard conditions.
2. Standard Pressure: The pressure should be 1 bar (1 atm) as per the standard conditions.
3. Standard Concentrations: The concentration of hydrogen ions (H⁺) should be 1 mol/L (1 M) under standard conditions.
4. Platinum Electrode: The electrode used for the hydrogen half-cell is typically made of platinum. Platinum is used because it is inert and does not participate in any side reactions, ensuring that the half-cell potential is solely determined by the hydrogen ion activity.
5. Hydrogen Gas: The half-cell is bubbled with pure hydrogen gas at 1 bar (1 atm) pressure. The hydrogen gas serves as the reducing agent, supplying electrons to the half-cell.
6. Proton-Selective Membrane: A proton-selective membrane (usually made of a solid electrolyte, like Nafion) separates the hydrogen gas from the solution to prevent gas mixing and to allow only the passage of protons (H⁺) into the solution.
These conditions are collectively referred to as "standard hydrogen electrode" conditions and are used as a reference point for measuring the electrode potentials of other half-cells in electrochemical reactions. The standard hydrogen electrode (SHE) has an assigned electrode potential of 0 volts at standard conditions and is crucial for establishing the electrochemical scale
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