The 2D materials are generally composed of strong covalent bonds leading to in-plane stability and weak van der Waals bonds, which sustain the stacked layer structure. Following the discovery of graphene in 2004, a new horizon has opened up for exploring other 2D layered materials such as transition metal dichalcogenides (TMD), transition metal oxides, graphitic carbon nitride (GCN), and hexagonal boron nitride (h-BN). These 2D materials can be integrated with a three dimensional (3D) SC material as a new building block to fabricate interfacial heterostructures. The electrocatalytic activity of this material strongly depends on its quality and morphology. For instance, defects and oxygen-containing groups may increase graphene electrocatalytic properties, while simultaneously reducing its electrical conductivity if they damage the conjugated Π structure.

In order to store sustainable energy, such as solar energy, and transform it into current power, photocatalytic or photoelectrochemical reactions in water splitting for hydrogen generation are promising candidates. Numerous informative papers on nanostructures for oxygen evolution reactions (OER) have been published. In addition, significant reports on applying 2D materials as counter electrodes in solar cells and/or water splitting devices, providing a thorough comparison concerning various synthesis and characterization methods of this class of new materials as well as their performance as a CE.

However, in many cases, the 2D materials themselves are neither photocatalysts nor photoelectrodes; however, these materials have been successfully applied as sensitizers, electron mediators, co-catalysts, and protective layers in combination with other SC materials. The 2D/SC hybrid materials can induce synergetic effects and ultimately improve the electrical, optical, and PEC properties of 2D/SC electrodes. Here, review of recent trends in this subject is available:

1- Irani et al. A review of 2D-based counter electrodes applied in solar-assisted devices, Coordination Chemistry Review, 2016.

2-  Faraji et al. Two-dimensional materials in semiconductor photoelectrocatalytic systems for water splitting, Energy & Environmental Science, 2018.