Modification of Conductive Electrodes with Two-Dimensional Materials

A full understanding of how the electrochemical properties of two-dimensional (2D) materials depend on their structure and surrounding environment is critical for their successful implementation in electrochemistry-related technologies. Although this understanding is currently limited, the complex and tunable electronic structure of 2D materials suggests that a large landscape of possibilities exists in optoelectronics, energy storage/conversion, and photocatalysis. 1 Here we show that modification of conductive electrodes with sub-nanometer thick 2D materials leads to a reciprocal interaction between the electrode and the 2D material. This interaction can be viewed as a chemical passivation of the electrode surface by the 2D material, alongside the endowment of the 2D material with the electronic properties of the conductive substrate. We will present two examples of this approach in the context of electrochemistry. First, we will discuss hexagonal boron nitride (hBN) on graphite, which represents a wide-gap tunneling barrier on a semimetallic substrate (Figure). We will examine the dependence of the electrochemical tunneling current and the electron transfer kinetics on the number of hBN layers. Second, we will discuss molybdenum disulfide (MoS 2 ) on gold, which represents a semiconducting (1.9 eV bandgap) barrier on a metallic substrate. We will show that a single layer of MoS 2 effectively passivates the surface chemistry of the underlying Au substrate, and that in turn, the Au increases the density of the electronic state of the MoS 2 , rendering it metallic. 2 These findings show that a tunable electrochemical response can be achieved by modification of conductive substrates with 2D materials, either through the nature or thickness of the 2D material. Our results can be exploited in future research and applications in areas such as electrode modification, electrochemical switching or surface passivation. Velický M. and Toth P. S., Appl. Mater. Today 8, 2017 ,68-103. Velický M. et al. , ACS Nano 12, 2018 , 10463-10472. Figure 1