From Hexagonal to Monoclinic: Engineering Crystalline Phase to Boost the Intrinsic Catalytic Activity of Tungsten Oxides for the Hydrogen Evolution Reaction

The intrinsic activity of catalysts is crucial for the electrocatalytic hydrogen evolution reaction, which is essentially dependent on their crystal structure and surface electronic state. The variable crystalline phase in tungsten oxide (WO3) can provide a favorable opportunity for modulating surface electronic state. In this work, the structure-activity relationship of the representative hexagonal and monoclinic phase WO3 (h-WO3 and m-WO3) for the hydrogen evolution reaction was discussed in detail by experimental techniques combined with density functional theory (DFT) calculations. DFT calculations reveal that m-WO3 exhibits the modest H-adsorption/desorption energy, which is beneficial to the fast desorption of active H∗ intermediate compared to h-WO3, displaying superior catalytic activity in the hydrogen evolution reaction. To accelerate the charge transfer, introduction of reduced graphene oxide (rGO) further amplifies the intrinsic catalytic activity endowed with this crystalline phase. In acid media, the m-WO3/rGO catalyst shows a low Tafel slope of 32 mV dec-1, requires an overpotential of only 35 mV to drive a current density of 10 mA cm-2, and keeps excellent stability during accelerated durability test. This work presents significance of crystalline phase for optimizing the intrinsic activity of catalyst and provides a novel idea to design a high-efficient catalyst for the hydrogen evolution reaction.