Scale-up is a critical step in moving the air cathodes from laboratory research to practical applications. However, the coexistence of a hydrophobic gas diffusion layer and a submerged catalyst layer in an air cathode requires an ultra-high water-proof performance in vertical configurations, severely hampering the scale up of air cathodes. To overcome this obstacle, we proposed a floating air cathode (FAC), fundamentally eliminating the risk of water leakage. This FAC was successfully enlarged to 707 cm(2) by a simple phase inversion method, much larger than the scaled air cathode of 145 cm(2) reported previously. Under a fixed set voltage of 1.8 V, a scaled-up FAC with a 30 cm diameter produced H2O2 at a maximum rate of 196.3 +/- 0.2 mg h(-1) with a low energy consumption of 4.9 +/- 0.06Wh g(-1). Rhodamine B (RhB) was used as a representative refractory contaminant to test the feasibility of the scaled FAC in the electro-Fenton system. Using the 30 cm FAC in a 3000 mL reactor resulted in RhB removal of 87.5% and a mineralization degree of 13.1% after 60 min of electrochemical treatment, lower than those obtained in a lab-scale 40 mL reactor with a 3.5 cm FAC (97.5% RhB removal and 64.3% mineralization). Therefore, this successful scale-up of the FAC makes the practical application of environmental remediation possible in the future. (C) 2019 Elsevier Ltd. All rights reserved.