The photocatalytic activity of a commercial titanium dioxide (P25) and of an in-house prepared P25/graphene composite is assessed according to standard ISO 22197-1:2007. The photoactivity performances of bare and composite TiO2-based materials were further studied by electrochemical impedance spectroscopy (EIS) technique to better understand the function of the graphene in the composite. EIS experiments were performed using a three-electrode configuration, which allows obtaining more detailed information about the complex charge transfer phenomena at the semiconductor/electrolyte interface. The Bandies equivalent circuit was selected as the most suitable for modelling the present photocatalysts. The use of the graphene composite allows a more effective charge separation with lower charge transfer resistance and less e(-)/h(+) recombination on the composite photocatalyst, reflected in the higher values of NO conversion. (C) 2016 Elsevier B.V. All rights reserved.