| dc.description.abstract | Societal challenges such as global warming and world poverty necessitate the development of alternative energy technologies which are independent of hydrocarbon combustion, utilize earth-abundant materials, and are inexpensive. Thus, in this Ph.D. dissertation, catalytic nanomaterials chemistry was employed to develop molybdenum(IV) sulfide (MoS2) as a device component in a variety of technologies including solar energy conversion, water-splitting, and energy storage. A simple, hydrothermal preparation was developed to grow MoS2 and MoSe2 films directly from Mo foils, resulting in a petaled morphology that exposes a large number of catalytically active crystallite edge sites. Various characterization techniques indicated that the resulting multilayer MoS2 films are frayed and exhibit single-layer MoS2 behavior at the edges. These self-supported electrodes also have an intermediate, MoSxOy layer. A synthetic approach to prepare MoSxOy-negative controls was also developed by growing petaled MoS2 on Au. Petaled MoS2 electrodes are highly active for the electrochemical reduction of aqueous polysulfide, demonstrating superior efficiency in quantum dot sensitized solar cells compared to those employing Pt cathodes. The electrocatalytic hydrogen evolution reaction activity of petaled MoS2 and MoSxOy-negative controls are also compared. In addition to the equivalent chemical environment on the surface, we find that petaled MoS2/Au and petaled MoS2/Mo exhibit comparable HER activity and kinetics. However, the exchange current density of petaled MoS2/Au is 3x smaller than that of petaled MoS2/Mo, being attributed to lower packing density on the Au support. Both petaled MoS2 films have nearly ohmic contacts to their supports, demonstrating that MoSxOy is not resistive. Additionally, petaled MoS2 was evaluated in lithium ion batteries and it was found that the MoSxOy layer contributes greatly to the capacity of the electrode by promoting reversible Mo-MoO3 conversion, while other typical Li-S cycling intercalation reactions are not as prevalent. Ex situ characterization was utilized to elucidate the primary chemical species and reactions involved in the charge/discharge processes. Finally, Cu2S@SnS and SnS@Cu2S core@shell nanocubes prepared using a novel, rapid, cation exchange technique were evaluated as photoabsorbers in quantum dot sensitized solar cells. | |
