Electrochemical oxygen reduction to hydrogen peroxide is now being studied as a promising renewable and localized alternative for the traditional complex anthraquinone process. Catalysts for this two-electron reduction pathway with high selectivity are required to achieve industrialization. Here, we disclose an inexpensive metal-free catalyst that is synthesized from commercial carbon black (CB) with a one-step plasma method for the affordable electrochemical generation of hydrogen peroxide in 100% Faradaic efficiency. This catalyst shows a high onset potential (0.1 mA cm–2 at 0.80 V vs reversible hydrogen electrode (RHE)) and the highest mass activity (300 A g–1 at 0.60 V vs reversible hydrogen electrode) among state-of-the-art catalysts. The performance could be maintained after the removal of oxygen-containing groups. Microscopic and spectroscopic characterizations as well as density functional theory (DFT) calculations indicate that the performance comes from the defective structure after plasma treatment.