PHOTO-CATALYTIC PROPERTY OF 2D MATERIALS

Energy Environ. Sci., 2019, doi: 10.1039/c9ee00513g

The exploitation of heterogeneous semiconductor (photo)electrocatalysis is a significant avenue to study renewable energy for adapting a commodity chemical supply to satisfy the growing global energy demands. The fundamental thermodynamics that guided the understanding of electron transfer processes and predictive power of materials design for bulk-semiconductor heterogeneous (photo)electrocatalysis are generally understood within the framework pioneered by Gerischer and Marcus. However, new materials, such as van der Waals bound 2D transition metal dichalcogenides (TMDCs), display electronic characteristics unlike those found in bulk semiconductors. Therefore, it is necessary to adapt the fundamental electrochemical principles that guide catalyst design for utilization these materials to construct heterogeneous catalysts.

Recently, Carroll group studied the interfacial energetics of 2H-phase MoS₂ by probing the changes to its electronic structure as a function of applied potential using in situ spectroelectrochemical measurements. The results showed that electron injection into the conduction band was coupled with a low energy shift of the exciton resonance, both properties are closely related to the number of MoS₂ layers in the vertical dimensions. In addition, the broadening Raman signals indicated that the applied electric field/electronic doping imparted a structural change. In contrast to conventional semiconductors, the conduction band electron injection was dependent on the change in the excitonic energy and not just the applied potential. This observation indicated that the relevant semiconductor liquid interfacial energetics changed with varied electric fields, a property not observed in typical semiconductors. It also demonstrated that the spectroscopic signatures of band gap reduction and carrier injection occur under electrocatalytic hydrogen evolution conditions. The results reported by the group highlighted the possibility of using 2D TMDCs more effectively to improve energy conversion efficiencies over traditional semiconductors, and provided a new and potentially interesting avenue to explore for heterogeneous (photo)electrocatalysis.

Zhijie Wang (Institute of Semiconductors, CAS, Beijing, China)

doi: 10.1088/1674-4926/40/6/060202