Review—Strategic Design of Layered Double Hydroxides and Graphitic Carbon Nitride Heterostructures for Photoelectrocatalytic Water Splitting Applications

The layered double hydroxides/graphitic carbon nitride (LDH/g-C 3 N 4 ) heterostructures stand as promising photo- and electro-catalysts for water oxidation and reduction. These materials containing metal ions M p + a n d M ′ q + , represented as M p + M ′ q + − LDH / g ‐ C 3 N 4 , have unique advantages over single component catalysts. This review provides the necessary insights on the material selection and mechanisms involved in electrocatalytic, photocatalytic, and photoelectrocatalytic water splitting processes. The importance of heterojunctions and interfacial chemistry in the water splitting mechanism is explained in detail by taking CuTi-LDH@g-C 3 N 4 and Bi 2 O 2 CO 3 /NiFe-LDH@g-C 3 N 4 as examples. There is a synergistic effect between g-C 3 N 4 and LDH layers that improves the performance of the hybrid materials over individual catalysts. This effect is due to the formation of Type II heterojunction in CuTi-LDH@g-C 3 N 4 for oxygen evolution reaction, and of S-scheme mechanism in Bi 2 O 2 CO 3 /NiFe-LDH@g-C 3 N 4 for both hydrogen and oxygen evolution reactions. Comparison of these two photoelectrocatalysts reveals new insights related to the role of synthesis method (hydrothermal vs coprecipitation), surface active sites (binary vs ternary heterostructures) and type of heterojunctions (Type II vs S-scheme), specifically, in the photoelectrocatalytic oxygen evolution reaction. These insights pave the way for further research in such multi-component hybrid materials to augment the progress in designing highly efficient heterogeneous photo/electro-catalysts for generating renewable fuels.