What product (s) forms at the anode in the electrolysis of an aqueous solution of k3po4?

The SRP (standard hydrogen electrode) of 2H⁺ + 2e⁻→H₂ is 0

and SRP of K⁺ + e⁻→K is lower than 0.

It means that if there are potassium ion and hydogen ion, it is easy for H⁺ to be reduced than oxidized. (H⁺ is reduced before K⁺ is reduced.)

By process '4H₂O + 4e⁻ → 2H₂ + 4OH⁻

H₂ is formed

PO₄³⁻ is much bigger than H₂O so the charge density is much lower than the O²⁻ side of H₂O.

PO₄³⁻ can't be formed.

By process '2H₂O→O₂ + 4H⁺ + 4e⁻'

O₂ is formed