The charge-transfer characteristics of nanostructured carbon/TiO2 electrodes are studied by cyclic voltammetry under photoelectrochemical conditions exploiting the electrooxidation and electroreduction of H2O2 in an alkaline medium. Films of composites were prepared by physically mixing TiO2 with 5 wt% of either single-walled carbon nanotubes (SWCNTs) or reduced graphene oxide (rG0). In addition, a layer-by-layer rGO/TiO2 electrode was prepared. Under dark conditions, both mixed SWCNTs and rGO facilitate H2O2 reduction. Under light irradiation, the blank TiO2 electrode shows a cathodic photopotential, the SWCNT/TiO2 an anodic photopotential, and the mixed rGO/TiO2 an increased cathodic photopotential. This scenario unambiguously reveals a photoelectron acceptor behavior for SWCNTs and a photohole acceptor performance for rGO. The latter one also agrees with the photoactivity observed in the layer-by-layer electrode. Overall, the value of H2O2 redox reactions for unraveling the electron-donor or electron-acceptor character of carbon nanostructures in C/metal oxide electrodes is demonstrated.