The Ramam mapping (20 × 40 µm 2 ) of ID/IG from the oxidized sample shows that oxidation was uniformly implemented at this length scale (Figure ). A systematic study of the mass transfer led to uniform oxidation in the entire oxidation zone (see section on mass transfer). Overall, the novel reactor allowed the realization of oxidation of large graphene coupons (500 cm 2 ) to form large-area PG. This establishes that large-area PG can be prepared uniformly by carefully designing a scale-up oxidation reactor.