Question

In a standard electrode potential, oxidation or reduction of hydrogen takes place?

Answer 1

The standard electrode potential of the system is defined as the emf of an electrochemical cell in which at 298K , the hydrogen gas (1 atm)/ aq. H⁺ (1M) half cell electrode is coupled with the other half-cell electrode system. The electrode potential of SHE is zero.
SHE act as anode when the another half cell with which it is combining has positive value of reduction potential so that E_cell will be positive. (E_cell = E_cathode - E_anode)
SHE will act as cathode when another half cell has negative reduction potential so that E_cell will be positive.
So If SHE (Standard hydrogen electrode) acts as anode then oxidation takes place as in case of Cu (E⁰ = 0.34 V) when coupled with Hydrogen.
H_{2 $\to$} 2H⁺ + 2e^-.
The anode half cell will be represented as:
Pt, H₂(g)1atm | H⁺(1M)
And if SHE acts as cathode then reduction takes place. Reaction is:
2H⁺ + 2e^- $\to$ H₂(g)
The cathode half cell will be represented as:
H⁺(1M) | H₂(g) 1 atm , Pt

The electrode potential of Standard Hydrogen electrode (SHE) is taken as zero