BACKGROUND: Hydrogen peroxide (H2O2) is an important chemical product, and this study investigated its synthesis at the cathode of a microbial fuel cell (MFC) system using spectrographically pure graphite (SPG) rods as cathode electrode. RESULTS: Electrochemical methods showed that oxygen reduction reaction (ORR) on SPG mainly followed the two-electron pathway yielding H2O2, while, the optimal condition for H2O2 production was in 0.1 mol L-1 Na2SO4 electrolyte. When SPG was used as the cathodic electrode in the MFC system, H2O2 concentration reached 78.85 mg L-1 after 12 h operation with an external resistance of 20 Omega (H2O2 production rate was 6.57 mg L-1 h(-1)). Coulombic efficiency, current efficiency and COD conversion efficiency were 12.26%, 69.47% and 8.51%, respectively. Repeated experiments proved this system had a stable operating performance. CONCLUSIONS: H2O2 was synthesized at the cathode of an MFC, and this study provides a proof-of-concept demonstration to realize the process of synthesizing H2O2 with wastewater. (C) 2010 Society of Chemical Industry