S-edge-riched MoxSy Arrays Vertically Grown on Carbon Aerogels As Superior Bifunctional HER/OER Electrocatalysts
Molybdenum disulfide (MoS2) is a potential earth-abundant electrocatalyst for hydrogen evolution reaction (HER), but the lack of in-depth understanding for its intrinsic activity still impedes further optimization and design of MoS2-based electrocatalysts. Herein, we report a facile in-situ hydrothermal synthesis to prepare a vertical MoxSy arrays grown on guar gum-derived carbon aerogels (GCA), termed as MoxSy@GCA. The obtained well-assembled MoxSy@GCA architectures consist of uniform, few-layered and S-edge riched MoxSy nanoﬂakes with a length of approximately 100 nm, which effectively prevent the inherent stacking among MoxSy layers and connect the charge transfer path between interlayers, thus endow the MoxSy@GCA with a huge number of active sites and high conductivity. Thanks to all these advantages, the optimal Mo4S16@GCA exhibits extraordinary HER/OER performances, including low onset potential for both HER (24.28 mV) and OER (1.53 V), as well as low overpotential at 10 mA cm-2 for HER (54.13 mV) and OER (370 mV), both are extremely approaching to that of noble Pt/C. Most of all, a series of operando Raman spectroscopy measurements of Mo4S16@GCA were conducted to identify the intrinsic HER/OER-active sites during the HER and OER process. And the results show that S-H bond is generated at the same time as HER/OER excitation, indicating the rich S-edge may be the intrinsic active site, which will accelerate the HER/OER kinetic process. Combining density functional theory (DFT) calculations revealed that the observed superb HER/OER activity could be attributed to a synergistic effect of rich S-edge of MoxSy and confinement effect of GCA, which collaboratively promotes the proton adsorption and electrocatalytic kinetics. Reasonably, this work would have profound guiding value for the rational tailoring in microstructure and size of transition metal electrocatalysts via the hierarchical porous carbon aerogel.