Striving Toward Noble-Metal-Free Photocatalytic Water Splitting: The Hydrogenated-Graphene–TiO₂ Prototype

Abstract

Graphane, graphone, and hydrogenated graphene (HG) have been extensively studied in recent years due to their interesting properties and potential use in commercial and industrial applications. The present study reports investigation of hydrogenated graphene/TiO2–x (HGT) nanocomposites as photocatalysts for H2 and O2 production from water without the assistance of a noble metal cocatalyst. By combination of several techniques, the morphologies, bulk/atomic structure, and electronic properties of all the powders were exhaustively interrogated. Hydrogenation treatment efficiently reduces TiO2 nanoparticles, while the graphene oxide sheets undergo the topotactic transformation from a graphene-like structure to a mixture of graphitic and turbostratic carbon (amorphous/disordered) upon altering the calcination atmosphere from a mildly reducing to a H2-abundant environment. Remarkably, the hydrogenated graphene–TiO2–x composite that results upon H2-rich reduction exhibits the highest photocatalytic H2 evolution performance equivalent to low loading of Pt (∼0.12 wt %), whereas the addition of HG suppresses the O2 production. We propose that such an enhancement can be attributed to a combination of factors including the introduction of oxygen vacancies and Ti3+ states, retarding the recombination of charge carriers, and thus, facilitating the charge transfer from TiO2–x to the carbonaceous sheet.