Extensive efforts have been devoted to developing MoS₂ nanostructures to maximize the number of active edge sites [1], but little attention has been paid to simultaneously tailoring of both the edge and planar structure itself for enhancing the HER kinetics. In this work, we used the one-step O₂ plasma modification to simultaneously engineer the edge and planar structure of MoS₂ to fabricate the high-performance MoS₂ electrocatalyst with defect-rich edge and oxygen-doped planar structure. We further notice that the influence of the inevitably generated MoO₃ species on the HER activity and stability of MoS₂ and its structure changes after long-term electrocatalytic reaction, which are significant to understand the HER electrocatalysis on the O-incorporated MoS₂ catalysts, however, are still unknown [2]. Herein, controlled plasma exposure time has been designed to explore the influence of MoO₃ species on the HER performance of O₂ plasma modified MoS₂ catalysts. We find that the MoO₃ species in MoS₂ are not conductive to the HER electrocatalysis. More importantly, these co-generated MoO₃ species are reduced and resolved from the MoS₂ lattice during the electrocatalytic hydrogen evolution, leading to a holey structure in the MoS₂ nanosheets and thus a significant improvement of its hydrogen evolution stability (Figure 1a). This work is the first to explore the Janus effect of O₂ plasma modification on MoS₂ for acceleration the hydrogen evolution reaction, and opens a new way to developing layered materials for electrochemical energy applications. Aside from the fundamental insight attained from the rational materials design, the MoS₂ O₂-plasma 60s catalyst exhibits a boosted HER activity with the overpotential as low as 131 mV at the current density of 10 mA/cm² and striking long-term durability, better than most reported MoS₂-based catalysts (Figure 1b).

Figure captions

Figure 1. (a) Polarization curves recorded from the MoS₂ O₂-plasma 60s catalyst at a scan rate of 5 mV/s before and after the chronopotentiometry test. Inset: chronopotentiometry responses (η ~ t) recorded at a constant current density of -10 mA/cm². (b) TEM image of the MoS₂ O₂-plasma 60s sample after the chronopotentiometry test at -10 mA/cm² for 20 hours.

References

[1] Hu J, Huang B, Zhang C, Wang Z, An Y, Zhou D, et al. Engineering stepped edge surface structures of MoS₂ sheet stacks to accelerate the hydrogen evolution reaction. Energy Environ Sci. 2017;10:593-603.

[2] Tao L, Duan X, Wang C, Duan X, Wang S. Plasma-engineered MoS₂ thin-film as an efficient electrocatalyst for hydrogen evolution reaction. Chem Commun. 2015;51:7470-3.