H2-Directing Strategy on In Situ Synthesis of Co-MoS2 with Highly Expanded Interlayer for Elegant HER Activity and its Mechanism

MoS2 has drawn great attention as a promising Pt-substituting catalyst for the hydrogen evolution reaction (HER). This work utilizes H-2 as the structure directing agent (SDA) to in situ synthesize a range of Co-MoS2-n (n = 0, 0.5, 1.0, 1.4, 2.0) with expanded interlayer spacings (d = 9.2 - 11.1 angstrom), which significantly boost their HER activities. The Co-MoS2-1.4 with an interlayer spacing of 10.3 angstrom presents an extremely low overpotential of 56 mV (at 10 mA cm(-2)) and a Tafel slope of 32 mV dec(-1), which is superior than most reported MoS2-based catalysts. Density function theory calculations are used to gain insights that i) the H-2 can be dissociatively adsorbed on MoS2 and greatly affect the related surface free energy by regulating the interlayer spacing; ii) the expanded interlayer spacing can significantly decrease the absolute value of Delta G(H), thereby leading to greatly promoted HER activity. Additionally, the large amounts of 1T phase (73.9-79.2%) and Co-Mo-S active sites (40.9-91.3%) also contribute to the enhanced HER activity of the synthesized samples. Overall, a simple new strategy for in situ synthesis of Co-MoS2 with an expanded interlayer spacing is proposed, which sheds light on other 2D energy material designs.