Hydrogen peroxide (H2O2) is a powerful oxidant with a wide range of applications, for example, organic synthesis and wastewater treatment. The present work describes the phosphorus-doped multiwall carbon nanotubes (P-CNTs) catalyst for electrogeneration of H2O2 in acidic and neutral medium using gas diffusion electrode. These P-CNTs are synthesized by a simple and efficient hydrothermal method. The structure and morphology are characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) respectively. The kinetics of the oxygen reduction reaction (ORR) is evaluated by the rotating disk electrode technique. The accumulation of H2O2 reaches to 1291.3 mg/L after 60 min for P-CNTs gas diffusion electrode, while the CNTs gas diffusion electrode produces 415.9 mg/L of H2O2. The current efficiency for the formation of H2O2 is 88.5% when using P-CNTs gas diffusion electrode, which is higher than 64.7% of CNT gas diffusion electrode in 60 min. The operational parameters for P-CNTs gas diffusion electrode such as cathodic potential, pH and O-2 flow rate are optimized systematically. Finally the P-CNTs gas diffusion electrode is experimentally confirmed to be efficient in the degradation of 200 mg/L metronidazole (MNZ) by electro-Fenton (EF) process at both acidic and neutral pH, indicating its potential for the treatment of refractory organic pollutants wastewaters.