Photocatalysis provides an attractive strategy for synthesizing H₂O₂ at ambient condition. However, the photocatalytic synthesis of H₂O₂ is still limited due to the inefficiency of photocatalysts and decomposition of H₂O₂ during formation. Here, we report SnO₂-TiO₂ heterojunction photocatalysts for synthesizing H₂O₂ directly in aqueous solution. The SnO₂ passivation suppresses the complexation and decomposition of H₂O₂ on TiO₂. In addition, loading of Au cocatalyst on SnO₂-TiO₂ heterojunction further improves the production of H₂O₂. The in situ electron spin resonance study revealed that the formation of H₂O₂ is a stepwise single electron oxygen reduction reaction (ORR) for Au and SnO₂ modified TiO₂ photocatalysts. We demonstrate that it is feasible to enhance H₂O₂ formation and suppress H₂O₂ decomposition by surface passivation of the H₂O₂-decomposition-sensitive photocatalysts.