Efficient and steady electrogeneration of H2O2 is a significant step in the Electro-Fenton water treatment process. This study fabricates a polytetrafluoroethylene (PTFE) coated graphite felt cathode with a polydimethylsiloxane (PDMS) damp-proof coating to generate H2O2 in a flow-through system without an external oxygen supply. We evaluated the effect of PDMS content, current, flow rate, and pH on H2O2 production. PDMS coating inhibits electrowetting to extend the longevity of the modified graphite felt for electrogeneration of H2O2. However, increasing PDMS content can decrease H2O2 production due to reduction of active sites on the graphite felt. Graphite felt electrodes (surface area = 14.5 cm2) coated with 500 mg of PDMS can generate 10 mg/L of H2O2 under a flow rate of 3 mL/min with only 2% production reduction after 24-hour use. This modified graphite felt has better performance in a neutral or alkaline environment than in an acidic condition. Up to 38.5 mg/L of H2O2 will be generated at optimum current (120 mA) at the flow rate of 3 mL/min. Increasing the flow rate decreases the concentration of H2O2 in the electrolyte but enhances total production after 145 mins.