Research on renewable energy must be hastened to solve the energy crisis we are now facing. Among all sustainable energy sources, solar energy and hydrogen gas fuel are two of the most clean and powerful. Photo-electrochemical (PEC) reactions use solar energy to electrochemically split water to produce hydrogen gas. Photoelectrocatalyst materials play an important role in increasing the e ciency of PEC reactions by absorbing solar energy and directing the energy towards the desired electrochemical reactions. Two-dimensional (2D) layered materials including MoS2, WS2, and SnS2 have drawn considerable attention as electrocatalysts and photo-electrocatalysts because of the catalytically-active nature of their edges and high charge mobility and transport e ciency within their layers. This work focuses on the synthesis, measurement, and simulation of PEC properties and behavior of WS2 nanotubes and SnS2 nano akes. The rst part of this work focuses on experimental synthesis and PEC measurement of edge-on oriented WS2 nanotubes and theoretical simulation of the atomic con guration and electronic structure of the edges by density functional theory (DFT) . WS2 nanotubes were synthesized by chemical vapor deposition (CVD) and sulfurization, but showed very poor photresponse. The DFT simulation shows the edges of the WS2 nanotubes are metallic, like those of 2H-MoS2. The metallic edges likely act as recombination sites for photogenerated charges, which explains the poor photoresponse of WS2. The second part of this work focuses on experimental synthesis and PEC measurement of edge-on oriented SnS2 nano akes and theoretical simulation by DFT. The edge-on oriented SnS2 nano akes exhibited high photoresponse and excellent PEC performance. The DFT simulation determined the atomic con gurations of SnS2 edges, and the stability of both bulk-like and monolayer SnS2 edges at various S potentials. In contrast to WS2 and MoS2, the DFT simulation also determined that the edges of SnS2 are semiconducting, not metallic. Therefore, the edges of SnS2 would not cause recombination of photoexcited charges, and would enable SnS2 to achieve a high photoresponse, as was experimentally observed. The DFT results also showed that the band gap energy of the SnS2 edges becomes smaller with increasing sulfur coverage, and allowed the in uence of chemical synthesis conditions on the electronic structure of the edges to be determined.
|17 May 2020
|Pratap M. Rao, Advisor, Richard D. Sisson, Jr., Committee Member, Jianyu Liang, Committee Member, Lyubov Titova, Committee Member
|Worcester Polytechnic Institute
|Doctoral Dissertations (All Dissertations, All Years)
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