Peeling off the surface: Pt-decoration of WSe 2 nanoflakes results in exceptional photoelectrochemical HER activity

[摘要] Photoelectrochemical (PEC) hydrogen evolution reaction (HER) was studied on exfoliated, pristine and Pt-decorated tungsten diselenide ( p -WSe 2 ) nanoflake samples, using a previously developed microdroplet PEC microscopy approach. The WSe 2 nanoflakes had well-defined thicknesses as measured by atomic force microscopy, and the Pt nanoparticles (NPs) were deposited by a variable number of atomic layer deposition (ALD) cycles. An exceptionally high photocurrent density of 49.6 mA cm −2 (under 220 mW cm −2 irradiation) and internal-photon-to-electron-conversion efficiency (∼90% at 550 nm) were demonstrated on these Pt-decorated WSe 2 (WSe 2 -Pt) photocathodes. The Pt NP loading and thickness of WSe 2 nanoflakes (in the 24–235 nm range) were used to fine-tune their PEC activity for HER. We found similar charge transfer and surface recombination kinetics of pristine and WSe 2 -Pt specimens (as assessed by intensity-modulated photocurrent spectroscopy), which indicated significant differences in their bulk properties. X-ray and ultraviolet photoelectron spectroscopies were performed to identify defect states and quantify the density of states around the valence band of WSe 2 . The elevated temperature of the ALD process and the evolving Pt NP phase conspired to passivate the sub-surface (i.e., bulk) defects in the WSe 2 nanoflakes, resulting in their vastly improved PEC performance.

[学科分类] 电力

[关键词] atomic layer deposition;defect migration;density of states;hydrogen evolution;layered semiconductor;photoelectrochemical kinetics