Preferential Horizontal Growth of WS2 Nanoplate on Porous Carbon: A Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Abstract

Two-dimensional layered transition metal dichalcogenides (2D TMDs) have been of tremendous recent interests. Understanding their growth behavior on specific substrate or support can provide critical insights for designing the TMDs with desirable structure and functionality for targeted applications. Particularly for the electrocatalytic hydrogen evolution reaction (HER), where porous carbons are predominantly used as conductive supports, revealing the growth behavior of TMDs on porous carbon materials can suggest rational design concept for the TMD-based HER catalysts. With an aim to investigate the growth orientation on porous carbon support, we synthesized MS2 (M = W or Mo) nanoplates embedded on porous carbon nanorod arrays by limiting their growth space at the nanoscale. We found that the horizontal growth is preferred in WS2 giving rise to monolayer nanoplates, which is contrast to the growth of MoS2 that favors vertical stacking to generate multilayer structure. Density functional theory calculations of adhesion energy of TMDs on porous carbons and their stacking energies revealed that WS2 favor the basal plane bonding with carbon support and horizontal growth, wheareas the edge bonding and vertical growth is favored for MoS2, supporting experimental results. The orientation-controlled WS2 monolayer NPs embedded in mesoporous carbon exhibited highly efficient electrocatalytic activity for the HER with a low overpotential of 179 mV (vs RHE) at ‒10 mA cm-2 and low Tafel slope of 63 mV sec-1.