Increasing the electrochemical activity of basal plane sites in porous 3D edge rich MoS2 thin films for the hydrogen evolution reaction

Molybdenum disulfide (MoS2) has been extensively utilized as an electrocatalyst for the hydrogen evolution reaction (HER) with edges as the primary active catalytic sites. Previous work on edge-rich MoS2 nanoplatelet 3D porous films (3D-ER-MoS2) shows they are promising catalysts, yet have basal planes that are inactive. Here we demonstrate how hydrogen annealing and oxygen plasma etching of 3D-ER-MoS2 generates defects and increases active site density within the basal plane, leading to dramatic improvements in HER catalytic activity. We also explore the critical processing parameters for electrocatalytic enhancement. Significantly enriched edge density was revealed for both routes. O-2 plasma treatment was more effective in increasing the number of edges by creating micro-cracks and local surface damage on the basal planes as well as structuring saw-toothed edges; H-2 etching mainly introduced irregular shaped basal surface nanopores and strips. By controlling processing parameters, optimum surface area/active sites density enhancement can be achieved, together with the robust 3D porous architecture and superaerophobic surface. The defect-rich MoS2 catalysts exhibit excellent HER activity: 700 degrees C - H-2 - MoS2 shows Tafel slope of 94 mV/dec and low onset overpotential of 193 mV; 15 min - O-2 - MoS2 performs amongst the best with excellent exchange current density of 57 mu A/cm(geo)(-2). Our defect engineered 3D-ER MoS2 exhibits j(geo) (eta = 0.5 mV) of 6-fold and 38-fold compared to monolayer MoS2 subject to similar process, for O-2 plasma and H-2 etching approaches respectively. Our study demonstrates an effective way to realize high performance Pt-free electrocatalysts for hydrogen generation by dual enhancement via edge enrichment and basal surface activation. (C) 2019 Elsevier Ltd. All rights reserved.