Novel etched iron oxide mediated synthesis of 3D tremella-like mesoporous Fe/N co-doped graphene composite was investigated. Through a synergistic mediation of acid etched Fe2O3 particles and released Fe3+, the nanoflakes of graphene oxide were transformed to Fe-doped 3D tremella-like mesoporous structure in hydrothermal condition. With high temperature treatment using melamine as the nitrogen source, the novel 3D tremella-like mesoporous Fe/N co-doped graphene composite for platinum-free counter electrode of the sensitized solar cell was synthesized. The samples had good pore size distribution and large specific surface area, which could be considered as an advantage for the permeation of electrolyte and beneficial to reduce the mass transfer resistance and promote the charge transfer. Significantly, the formed Fe-Nx species bonding on the surface of graphene had sturdy covalent structure with high catalytic activity, which contributed to the excellent electrochemical properties and counterelectrode performance of dye-sensitized solar cell. Consequently, the photoelectric conversion efficiency reached 6.52%, which exceeded 5.87% of Pt and 3.49% of reduced graphene oxide electrodes. (C) 2018 Published by Elsevier Ltd.