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Title: Single-Nanoflake Photo-Electrochemistry Reveals Champion and Spectator Flakes in Exfoliated MoSe2 Films

Abstract

Semiconducting transition-metal dichalcogenide (TMD) nanoflake thin films are promising large-area electrodes for photo-electrochemical solar energy conversion applications. However, their energy conversion efficiencies are typically much lower than those of bulk electrodes. It is unclear to what extent this efficiency gap stems from differences among nanoflakes (e.g., area, thickness, and surface structural features). It is also unclear whether individual exfoliated nanoflakes can achieve energy conversion efficiencies similar to those of bulk crystals. Here, we use a single-nanoflake photo-electrochemical approach to show that there are both highly active and completely inactive nanoflakes within a film. For the exfoliated MoSe2 samples studied herein, 7% of nanoflakes are highly active champions, whose photocurrent efficiency exceeds that of the bulk crystal. However, 66% of nanoflakes are inactive spectators, which are mostly responsible for the overall lower photocurrent efficiency compared to the bulk crystal. The photocurrent collection efficiency increases with nanoflake area and decreases more at perimeter edges than at interior step edges. These observations, which are hidden in ensemble-level measurements, reveal the underlying performance issues of exfoliated TMD electrodes for photo-electrochemical energy conversion applications.

Authors:
 [1];  [1];  [2]; ORCiD logo [2]; ORCiD logo [1]
+ Show Author Affiliations
  1. Colorado State Univ., Fort Collins, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1435696
Report Number(s):
NREL/JA-5900-71132
Journal ID: ISSN 1932-7447; TRN: US1900084
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 12; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; transition-metal dichalcogenide; nanoflake thin films; photovoltiacs; solar energy conversion

Citation Formats

Todt, Michael A., Isenberg, Allan E., Nanayakkara, Sanjini U., Miller, Elisa M., and Sambur, Justin B. Single-Nanoflake Photo-Electrochemistry Reveals Champion and Spectator Flakes in Exfoliated MoSe2 Films. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.7b12715.
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Todt, Michael A., Isenberg, Allan E., Nanayakkara, Sanjini U., Miller, Elisa M., & Sambur, Justin B. Single-Nanoflake Photo-Electrochemistry Reveals Champion and Spectator Flakes in Exfoliated MoSe2 Films. United States. https://doi.org/10.1021/acs.jpcc.7b12715
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Todt, Michael A., Isenberg, Allan E., Nanayakkara, Sanjini U., Miller, Elisa M., and Sambur, Justin B. Tue . "Single-Nanoflake Photo-Electrochemistry Reveals Champion and Spectator Flakes in Exfoliated MoSe2 Films". United States. https://doi.org/10.1021/acs.jpcc.7b12715. https://www.osti.gov/servlets/purl/1435696.
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@article{osti_1435696,
title = {Single-Nanoflake Photo-Electrochemistry Reveals Champion and Spectator Flakes in Exfoliated MoSe2 Films},
author = {Todt, Michael A. and Isenberg, Allan E. and Nanayakkara, Sanjini U. and Miller, Elisa M. and Sambur, Justin B.},
abstractNote = {Semiconducting transition-metal dichalcogenide (TMD) nanoflake thin films are promising large-area electrodes for photo-electrochemical solar energy conversion applications. However, their energy conversion efficiencies are typically much lower than those of bulk electrodes. It is unclear to what extent this efficiency gap stems from differences among nanoflakes (e.g., area, thickness, and surface structural features). It is also unclear whether individual exfoliated nanoflakes can achieve energy conversion efficiencies similar to those of bulk crystals. Here, we use a single-nanoflake photo-electrochemical approach to show that there are both highly active and completely inactive nanoflakes within a film. For the exfoliated MoSe2 samples studied herein, 7% of nanoflakes are highly active champions, whose photocurrent efficiency exceeds that of the bulk crystal. However, 66% of nanoflakes are inactive spectators, which are mostly responsible for the overall lower photocurrent efficiency compared to the bulk crystal. The photocurrent collection efficiency increases with nanoflake area and decreases more at perimeter edges than at interior step edges. These observations, which are hidden in ensemble-level measurements, reveal the underlying performance issues of exfoliated TMD electrodes for photo-electrochemical energy conversion applications.},
doi = {10.1021/acs.jpcc.7b12715},
journal = {Journal of Physical Chemistry. C},
number = 12,
volume = 122,
place = {United States},
year = {2018},
month = {3}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1021/acs.jpcc.7b12715
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Cited by: 9 works
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Figures / Tables:

Figure 1 Figure 1: Photo-electrochemical characterization and microscopy of nanoflake and bulk MoSe2 electrodes. (a) Experimental setup for single-nanoflake photocurrent mapping in a three-electrode electro-chemical flow cell. The same cell was used for bulk crystal mapping. ctr = Pt wire counter electrode and ref = Ag/AgI wire reference electrode. (b) Current−potential curvesmore » of a 1.3 mm2 MoSe2 single crystal in 1 M NaI and 1 mM I2 electrolyte under dark (black line) and chopped 20 mW/cm2 532 nm laser illumination (red line). The light spot was larger than the crystal to illuminate the entire electrode surface. (c) Bright-field optical transmission image of the nanoflake-coated electrode immersed in 1 M NaI and 1 mM I2. (d) EQE map of the nanoflakes in (c) measured at +0.5 V vs Ag/AgI by scanning a 690 nm diameter 532 nm laser spot in 1 μm increments across the electrode surface. The illumination area and power were 0.37 μm2 and 3.0 μW, respectively, corresponding to a power density of 805 W/cm2. The red lines represent the nanoflake contour. (e) Photograph of the parent bulk MoSe2 crystal used for mechanical exfoliation. (f) EQE map of the bulk crystal in (e) measured at +0.5 V with a 4.94 μm diameter 532 nm laser spot in 7 μm increments across the electrode surface. The red line indicates the epoxy contour. The illumination area and power were 19.17 μm2 and 2.4 μW, corresponding to a power density of 12.5 W/cm2. The solution flow rate for both mapping experiments was 50 μL/min.« less
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    Single nanoparticle photoelectrochemistry: What is next?
    journal, November 2019

    • Wang, Li; Schmid, Merranda; Sambur, Justin B.
    • The Journal of Chemical Physics, Vol. 151, Issue 18
    • DOI: 10.1063/1.5124710
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