Effect of Co-Generated MoO3 on the Electrocatalytic Hydrogen Evolution Performance of O2 Plasma Modified MoS2

Abstract

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.