and ω is the rotating speed of the RDE (unit: rad/s). where 𝑐 𝑖 is the concentration of species 𝑖 (with i = K + , H + and OTf -), 𝐷 𝑖 is the diffusion coefficient of species 𝑖 , 𝑛 𝑖 is the charge of species 𝑖 , 𝑅 is the ideal gas constant, 𝑇 is the temperature, 𝐹 is the Faradaic constant, 𝜑 is the potential and 𝑣 𝑥 is the velocity of solution in x-direction. For a rotating disk electrode, the velocity in axial direction at different x-locations can be estimated as: 8