Synergistic Hybrid MoS2/Fe2O3 Composites for Efficient Hydrogen Evolution in Alkaline Media

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It is highly desirable to generate H2 by splitting water (2H2O → O2 + 2H2), because the storage of a large amount of energy (4.92 eV) can be realized in the molecular transformation with no emission of greenhouse gases and other pollutants.(1) The hydrogen evolution reaction (HER) is the cathodic half reaction of water splitting, which is the actual process that produces H2 needed to fuel the purported "hydrogen-based economy".(2) HER on earth-abundant molybdenum disulfide (MoS2) in acidic media is a robust process, but it is kinetically retarded in alkaline media. Thus, improving the sluggish kinetics for HER in alkaline media is crucial for advancing the performance of water-alkali electrolyzers. Here, we demonstrate a dramatic enhancement of HER kinetics in base by judiciously hybridizing vertical MoS2 sheets with another earth-abundant material, iron oxide (Fe2O3). The field-emission scanning electron microscopy (FESEM) images in Figure 1a show that the MoS2/Fe2O3 composite is composed of a particle-like structure of Fe2O3 grown closely on the edge surfaces of the vertically aligned MoS2 sheets. The highly ordered lattice planes in the high-resolution TEM (HRTEM) image of MoS2/Fe2O3 composite are clearly visible in Figure 1b. The d-spacing of 0.63 nm and 0.37 nm, which are corresponds to the (002) and (012) facets of MoS2 and Fe2O3 crystals, respectively, suggests the formation of an interface between the (002) facet of MoS2 and the neighboring (012) facet of Fe2O3 in the composite. Benefiting from the desirable structural characteristics, the MoS2/Fe2O3 interfaces synergistically favor the chemisorption of H (on MoS2) and OH (on Fe2O3), and thus can effectively accelerate the water dissociation step and thus the overall HER catalysis. The resultant MoS2/Fe2O3 heterostructures exhibit much better HER performance than bare MoS2 and outstanding stability in base (Figure 1c and d). Our synergistic hybridization of MoS2 with metal oxide materials enlightens the design and fabrication of promising heterostructures for hydrogen evolution in alkaline media. Figure Caption Figure 1. (a) High- and (inset) low-magnification FESEM images of MoS2/Fe2O3 composite. (b) P High-magnification TEM image of the MoS2/Fe2O3 composite, showing their interfaces. (c) Polarization curves of the MoS2, Fe2O3 and MoS2/Fe2O3 composite catalysts in 1M KOH solution at a scan rate of 5 mV/s. (d) Chronopotentiometry responses (η ~ t) recorded from MoS2/NiCo-LDH composite at high current densities of -10 mA/cm2. References J. L. Dempsey, B. S. Brunschwig, J. R. Winkler, H. B. Gray, Hydrogen evolution catalyzed by cobaloximes. Acc. Chem. Res. 42, 1995-2004 (2009).J. Hu et al., Hydrogen evolution electrocatalysis with binary-nonmetal transition metal compounds. J. Mater. Chem. A 5, 5995-6012 (2017). Figure 1