Vertically Oriented Arrays of ReS2 Nanosheets for Electrochemical Energy Storage and Electrocatalysis.

Transition-metal dichalcogenide (TMD) nanolayers show potential as high-performance catalysts in energy conversion and storage devices. Synthetic TMDs produced by chemical-vapor deposition (CVD) methods tend to grow parallel to the growth substrate. Here, we show that with the right precursors and appropriate tuning of the CVD growth conditions, ReS2 nanosheets can be made to orient perpendicular to the growth substrate. This accomplishes two important objectives; first, it drastically increases the wetted or exposed surface area of the ReS2 sheets, and second, it exposes the sharp edges and corners of the ReS2 sheets. We show that these structural features of the vertically grown ReS2 sheets can be exploited to significantly improve their performance as polysulfide immobilizers and electrochemical catalysts in lithium-sulfur (Li-S) batteries and in hydrogen evolution reactions (HER). After 300 cycles, the specific capacity of the Li-S battery with vertical ReS2 catalyst is retained above 750 mA h g(-1), with only ∼0.063% capacity decay per cycle, much better than the baseline battery (without ReS2), which shows ∼0.184% capacity decay per cycle under the same test conditions. As a HER catalyst, the vertical ReS2 provides very small onset overpotential (<100 mV) and an exceptional exchange-current density (∼67.6 μA/cm(2)), which is vastly superior to the baseline electrode without ReS2.