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Figure 5: Schematic of oxygen species O* diffusing into the pores. In the pore of small radius (left pore), the concentration of O* inside the pore [O*]pore is dependent on due to collision with pore walls based on Knudsen model, while for pore size of sufficiently large (right pore), [O*]pore is almost equal to the bulk O* concentration in the chamber [O*]bulk.