TiO2 nanoarrays modification by a novel Cobalt-heteroatom doped graphene complex for photoelectrochemical water splitting: An experimental and theoretical study

Different graphene structures have received much attention due to their unique chemical and electron properties. In this report, we use heteroatom-doped graphene to coordinate Co2+ for use in photoelectrochemical cells. Flower-like TiO2 photoelectrode morphology was used as a semiconductor. Its surface was covalently modified with Co2+ coordinated nitrogen and sulfur-doped graphene quantum dot (S, N-GQD). S, N-GQD was used to improve visible light absorption and electron transport properties. Also, cobalt ions were coordinated with pyridinic nitrogen in the GQD structure and, like the cobalt-bipyridine complexes, acted as a catalyst for the water oxidation reaction. The modified photoelectrode significantly improved cell performance and resulted in a photocurrent density of 1.141 mA/cm2. To study the electronic structure of the compounds in more detail, we also used density functional theory (DFT) calculations. The obtained results confirmed the effective interactions of cobalt and S, N-GQD, and showed the energy levels and band gaps in agreement with the experimental results. This study led to the presentation of a new and robust strategy to improve the optical and catalytic performance of TiO2 nanoarrays in photoelectrochemical cells.