Jing Zhang 1,† , Jingjie Wu 2,† , Xiaolong Zou 3 , Ken Hackenberg 1 , Wu Zhou 4 , Weibing Chen 1 , Jiangtan Yuan 1 , Kunttal Keyshar 1 , Gautam Gupta 5 , Aditya Mohite 6 , Pulickel M. Ajayan 1 , Jun Lou ⇑ ,1 1 Department of Materials Science and Nanoengineering, Rice University, Houston, TX 77005, United States 2 Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, OH, 45221, United States 3 Shenzhen Geim Graphene Center and Low-Dimensional Materials and Devices Laboratory, Tsinghua-Berkeley Shenzhen Institute (TBSI), Tsinghua University, Shenzhen 518055, PR China 4 School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 200049, China 5 Department of Chemical Engineering, University of Louisville, Louisville, KY 40292 6 Department of Chemical and Biomolecular Engineering Rice University, Houston, Texas 77005 The emerging non-noble metal two-dimensional (2D) catalyst, such as MoS 2 , for the hydrogen evolution reaction (HER) is known to have an inert basal plane unless being converted to a metastable metallic phase or defect engineered. In order to take advantage of the majority of the material in such layered catalysts, fast screening of 2D catalysts with superior basal plane activity is imperative. A local electrochemical measurement method assisted by the e-beam lithography patterning was developed and applied to quantify the activity of basal planes of different layered transition metal dichalco- genides (TMDs) toward HER. This local measurement offers a robust platform to discover active TMDs fast and precisely. The construction of HER volcano plot leads to the discovery of superior basal plane active group VB metal disulfides, especially 3R-NbS 2 . Interestingly, the trends found in the volcano plot imply distinctive differences in the mechanism of TMD catalysts compared to their metal counterparts. The intensive hydrogen evolution reaction in-between the basal planes drives self-nanostructuring in morphology of 3R-NbS 2 . The increase in the effective surface area, and decrease in the electron-transfer resistance across the substrate and basal plane interface induced by the self-nanostructuring in turn enhances the HER performance of 3R-NbS 2 . The 3R-NbS 2 clearly stands out among non-noble metal catalysts for HER. Introduction Direct identification of active site in the heterogeneous catalyst is a grand challenge, especially in the situation involving a variety of different active sites that are capable of catalyzing the same reaction. Simple hydrogen evolution reaction (HER), H + +e  ? 1/2 H 2 , catalyzed by the 2D TMDs like 2H-MoS 2 , is an excellent example of that. Density functional theory (DFT) has predicted that the most active site in 2H-MoS 2 located at edges [1], while basal plane could be activated via conversion to a metastable metallic phase or defect engineering [2,3]. Later the scanning tunneling microscopy combined with the electrochemical char- acterization were used to quantitatively show a much stronger dependence of the overall HER current on the edge length over the basal plane area of MoS 2 nanocrystals [4], providing first experimental evidence to support the computational result. Discovering superior basal plane active two-dimensional catalysts for hydrogen evolution ⇑ Corresponding author. E-mail address: Lou, J. (jlou@rice.edu) † The authors contribute equally to the work. Materials Today d Volume xxx, Number xx d xxxx 2019 RESEARCH RESEARCH: Original Research 1369-7021/Ó 2019 Elsevier Ltd. All rights reserved. https://doi.org/10.1016/j.mattod.2019.02.014 1 Please cite this article in press as: J. Zhang et al., Materials Today (2019), https://doi.org/10.1016/j.mattod.2019.02.014