| 초록 |
The edge sites of MoS2 have been shown to be efficient electrocatalysts for the hydrogen evolution reaction (HER) replacing expensive noble metals, e.g., Pt. Here, we first describe that when atomic layer deposition (ALD) is applied to layered materials such as MoS2. MoS2 exhibits the non-ideal mode of ALD growth on planar surfaces. The non-ideality does not allow for the conventional linear relationship between the growth thickness and the number of cycles. Instead, it provides the ability to control the relative ratios of the edge-sites and basal planes of MoS2 to the exposed surfaces. The number of edge sites produced was carefully characterized in terms of the geometric surface area and effective work function. It was correlated to the HER performance, including Tafel slopes and exchange current densities. When MoS2 as a representative 2-D material is deposited on self-supported Cu substrates in a controlled manner, the sulfidation reactions also occur with the metal. We observed the spontaneous formation of a composite chalcogenide materials that consist of two-dimensional (2-D) materials dispersed in bulk, i.e., bulk layered heterojunctions (BLHJs) of Cu-Mo-S that contain MoS2 flakes inside, which are uniformly dispersed in the Cu2S matrix, and their unusual charge transport properties for application in hydrogen evolution reactions (HERs). The resulting structures were expected to induce asymmetric charge transfer via layered frameworks and tested as electrocatalysts for HERs. Upon suitable thermal treatments, the BLHJ surfaces exhibited the efficient HER performance of approximately 10 mA/cm2 at a potential of as low as -0.1 V versus a reversible hydrogen electrode (RHE). The Tafel slope was approximately 30 to 40 mV/dec. The present strategy was further generalized by demonstrating the formation of BLHJs on other transition metals such as Ni. |
