Study on TMD/Graphene Based Film Fabrication and Its Applications

Abstract

The production of hydrogen by photocatalytic water splitting has attracted much, recently. Photocatalytic material requires two characteristics, capability of exciton generation and catalytic surface for hydrogen evolution reaction (HER). Since transition metal dichalcogenides (TMDs) satisfy these requirements, it has been investigated for their application as photocatalyst over the past few decades. The most popular TMD material, MoS2, has a two different crystal phase, 1T- and 2H- MoS2, and they have metallic- and semiconducting-properties, respectively. 1T-MoS2 shows outstanding catalytic effect for HER, and exfoliated 2H-MoS2 has a direct band-gap for light absorption. However, the photocatalytic efficiency of such TMDs nanosheets for hydrogen evolution reaction (HER) is still not enough for the practical use as catalyst, which is supposed to be caused by the inevitable restacking TMDs nanosheets during electrode preparation process. Moreover, the low conductivity of TMDs impedes the electrons transport upon HER. MoS2 based heterostructure with high conducting material has been regarded as a candidate to overcome these limitations. Therefore, the development of for scalable fabrication methods for MoS2 based heterostructure remains as an important challenge in TMD-based research field. Here, we present a facile synthetic method to fabricate TMD electrode on transparent electrode indium tin oxide (ITO) for PEC and characterization of TMD-based hybrid thin film. Monolayer of graphene oxide (GO) and MoS2 sheets were prepared by modified hummers method and n-butyllithium intercalation method, respectively. Then, TMD-based films were deposited on ITO substrate by several methods; including Langmuir Blodgett, spin coating, spray coating and simple filtration method on Anodisc After annealing as-prepared GO film or using hydrazine reduction method to reduce as reduced graphene oxide (rGO), thin TMDs film was placed on rGO film by using spin coating or spray coating. In addition, membrane method we developed enables to fabricate thin film by simple filtration. The filtration is implemented with a target material to make a film on Anodisc. Then, the produced films were floated on the surface of KOH to remove Anodisc. Finally, it was able to be transferred to any substrate needed. The films were characterized by SEM, AFM, Raman and UV-Vis, which reveals that the TMD film was uniformly distributed on any substrate which is including another film fabricated by the same membrane method. We also demonstrated that the coverage of TMD on the substrate or film can be controlled by mass of the material in filtration step. We believe that further work with optimization of the photoelectrode structure will significantly enhance photocurrent efficiencies. Therefore, the future possibility to have hydrogen energy at a low cost, with clean material to the environment, seems to be closer, since most of the demands for an appropriate hydrogen evolution material are achieved by TMDs.