IrO2–CeO2-graphene/Ti porous electrode with high charge-transfer speed and enhanced capacitance

Exploring composite materials with ideal structures is an effective way to achieve synergy among different functional components. In this paper, a thermal decomposition method was adopted to prepared IrO2–CeO2-graphene/Ti composite electrodes. The influence of adding graphene on the composite material's electronic structure was analyzed by first-principles calculations, and its microstructure and electrochemical performance were also observed though various tests. The results indicated that coatings containing graphene exhibited a hierarchical porous structure, which could enlarge the specific surface area effectively. The band gaps of the IrO2–CeO2 composite oxides were filled by the energy level of C, which reduced the electron-transfer resistance. With amorphous CeO2 and the graphene acting as highly efficient ion-diffusion and electron-transfer channels respectively, the electrodes' charge storage performances were improved. The electrodes' specific capacitance values rose at first, then decreased as the graphene contents increased, reaching a maximum of 368 F g−1 when the content was 2 mg mL−1. However, adding graphene could harm the electrodes' cycling stability; excessive graphene could also encapsulate IrO2 nanoparticle and hinder contact with the electrolyte, thus reducing the electrodes' specific capacitances.