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Elucidating the mechanistic origins of photocatalytic hydrogen evolution mediated by MoS2/CdS quantum-dot heterostructures

DOI: 10.1021/acsami.0c12583 DOI Help

Authors: Junsang Cho (Texas A&M University; Duksung Womenís University) , Nuwanthi Suwandaratne (University at Buffalo, The State University of New York) , Sara Razek (Binghamton University) , Yun-Hyuk Choi (Texas A&M University; University at Buffalo, The State University of New York) , Louis F. J. Piper (Binghamton University) , David F. Watson (University at Buffalo, The State University of New York) , Sarbajit Banerjee (Texas A&M University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Applied Materials & Interfaces

State: Published (Approved)
Published: August 2020
Diamond Proposal Number(s): 22148

Abstract: Solar fuel generation mediated by semiconductor heterostructures represents a promising strategy for sustainable energy conversion and storage. The design of semiconductor heterostructures for photocatalytic energy conversion requires the separation of photogenerated charge carriers in real space and their delivery to active catalytic sites at the appropriate overpotentials to initiate redox reactions. Operation of the desired sequence of light harvesting, charge separation, and charge transport events within heterostructures is governed by the thermodynamic energy offsets of the two components and their photoexcited charge-transfer reactivity, which determine the extent to which desirable processes can outcompete unproductive recombination channels. Here, we map energetic offsets and track the dynamics of electron transfer in MoS2/CdS architectures, prepared by interfacing two-dimensional MoS2 nanosheets with CdS quantum dots (QDs), and correlate the observed charge separation to photocatalytic activity in the hydrogen evolution reaction. The energetic offsets between MoS2 and CdS have been determined using hard and soft X-ray photoemission spectroscopy (XPS) in conjunction with density functional theory. A staggered type-II interface is observed, which facilitates electron and hole separation across the interface. Transient absorption spectroscopy measurements demonstrate ultrafast electron injection occurring within sub-5 ps from CdS QDs to MoS2, allowing for creation of a long-lived charge-separated state. The increase of electron concentration in MoS2 is evidenced with the aid of spectroelectrochemical measurements and by identifying the distinctive signatures of electron—phonon scattering in picosecond-resolution transient absorption spectra. Ultrafast charge separation across the type-II interface of MoS2/CdS heterostructures enables a high Faradaic efficiency of ca. 99.4 ± 1.2% to be achieved in the hydrogen evolution reaction (HER) and provides a 40-fold increase in the photocatalytic activity of dispersed photocatalysts for H2 generation. The accurate mapping of thermodynamic driving forces and dynamics of charge transfer in these heterostructures suggests a means of engineering ultrafast electron transfer and effective charge separation in order to design viable photocatalytic architectures.

Journal Keywords: Hydrogen evolution; Quantum dots; 2D nanosheets; 2D/0D heterostructures; Photocatalytic water splitting; Hard X-ray Photoemission Spectroscopy; Transient Absorption Spectroscopy

Diamond Keywords: Photocatalysis; Semiconductors; Solar fuel

Subject Areas: Materials, Chemistry, Energy

Instruments: I09-Surface and Interface Structural Analysis

Other Facilities: Advanced Photon Source

Added On: 07/09/2020 10:28

Discipline Tags:

Surfaces Energy Storage Quantum Materials Earth Sciences & Environment Sustainable Energy Systems Energy Physics Climate Change Physical Chemistry Catalysis Energy Materials Chemistry Materials Science interfaces and thin films

Technical Tags:

Spectroscopy X-ray Photoelectron Spectroscopy (XPS) Hard X-ray Photoelectron Spectroscopy (HAXPES)