Peeling off the surface: Pt‐decoration of WSe2 nanoflakes results in exceptional photoelectrochemical HER activity

• Published in: SusMat (Online) Vol. 2; no. 6; pp. 749 - 760
• Main Authors: Tóth, Péter S., Szabó, Gábor, Bencsik, Gábor, Samu, Gergely F., Rajeshwar, Krishnan, Janáky, Csaba
• Format: Journal Article
• Language: English
• Published: Chengdu John Wiley & Sons, Inc 01.12.2022; Wiley
• Subjects: Atomic force microscopy; atomic layer deposition; Atomic layer epitaxy; Atomic properties; Bulk density; Carbon; Charge transfer; Decoration; defect migration; Defects; density of states; Efficiency; Electrodes; Electrons; Energy; Graphene; High temperature; Hydrogen; hydrogen evolution; Hydrogen evolution reactions; Irradiation; layered semiconductor; Microscopy; Nanoparticles; Photocatalysis; Photocathodes; Photoelectric effect; Photoelectric emission; photoelectrochemical kinetics; Photoelectrons; Selenides; Silicon nitride; Single crystals; Spectroscopy; Thickness measurement; Tungsten; Tungsten compounds; Valence band
• ISSN: 2692-4552; 2766-8479; 2692-4552
• DOI: 10.1002/sus2.86

Photoelectrochemical (PEC) hydrogen evolution reaction (HER) was studied on exfoliated, pristine and Pt‐decorated tungsten diselenide (p‐WSe2) nanoflake samples, using a previously developed microdroplet PEC microscopy approach. The WSe2 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 WSe2 (WSe2‐Pt) photocathodes. The Pt NP loading and thickness of WSe2 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 WSe2‐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 WSe2. 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 WSe2 nanoflakes, resulting in their vastly improved PEC performance. Atomic layer deposited Pt nanoparticles on p‐WSe2 nanoflakes resulted in a very high photoelectrochemical (PEC) hydrogen evolution activity and internal‐photon‐to‐electron‐conversion efficiency. We found that bulk defects and their migration to the surface play an important role in the PEC activity. The proper defect state passivation (both in the bulk and the surface), together with the atomic layer deposition‐based immobilization of Pt co‐catalyst, allowed us for a resource‐efficient electrode preparation.