Hierarchical Hybrids\nMade of Mixed Metal-Based Sillen-Structured\nCd<sub><i>x</i></sub>BiO<sub>2</sub>Br @ Graphene Oxide\nfor Efficient Photocatalytic H<sub>2</sub>O<sub>2</sub> Production

In this article, multilayered Sillén-structured\nmixed metallic\nCd<sub><i>x</i></sub>BiO<sub>2</sub>Br has been synthesized\nthrough hydrothermal methods. Detailed structure–property correlations\nsuggest that replacement of Bi<sup>3+</sup> cations by Cd<sup>2+</sup> transforms the conduction band position suitable for the desired\noxygen reduction reaction. It is further correlated by density functional\ntheory calculations. Finally, unique flower-like hierarchical hybrid\nheterostructures have been fabricated by growing this multilayered\nCd<sub><i>x</i></sub>BiO<sub>2</sub>Br on graphene oxide\n(GO) nanosheets. Here, GO nanosheets play dual roles, i.e., (i) GO\nacts as the template to grow these typical hybrid heterostructures\nwith improved surface-active sites and oxygen vacancies and (ii) second,\nthe GO sheet further improves the photoinduced charge separation processes\nwith respect to bare Cd<sub><i>x</i></sub>BiO<sub>2</sub>Br and BiOBr. All the as-synthesized materials have been utilized\nfor photocatalytic H<sub>2</sub>O<sub>2</sub> productions, and maximum\nproduction efficiency has been observed (∼13 mM g<sub>catalyst</sub><sup>–1</sup>) for the optimized hierarchical hybrids of Cd<sub><i>x</i></sub>BiO<sub>2</sub>Br and GO nanosheets. The\noverall trends in H<sub>2</sub>O<sub>2</sub> production efficiencies\nhave been further supported by detailed transient photocurrent response\nstudies and electrochemical impedance spectroscopy. Finally, molecular\ninsights into the overall photocatalytic mechanism have been unveiled\nby scavenging the free radicals and the respective reaction intermediates.