Article Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
www.acsaem.org
Large-Area CVD MoS2/WS2 Heterojunctions as a Photoelectrocatalyst for Salt-Water Oxidation Peter C. Sherrell,† Pawel Palczynski,† Maria S. Sokolikova, Francesco Reale, Federico M. Pesci, Mauro Och, and Cecilia Mattevi* Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom
Downloaded via 5.62.154.178 on July 23, 2019 at 07:11:21 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: Splitting salt water via sunlight into molecular oxygen and hydrogen for use as fuel or as an energy carrier is a clear pathway toward renewable energy. Monolayer MoS2 and WS2 are promising materials for the energetically demanding water oxidation reaction, absorbing ∼10% of incident light in the visible spectrum and possessing chemical stability and band edges more positive than the oxidation potential of water. A heterostructure of MoS2/WS2 forms a type-II heterojunction, supporting fast separation of the photogenerated charge carriers across the junction. Here, we show the role played by defects in determining the efficiency of the photon-driven oxidation process. By reducing the defects in this material system, it is possible to obtain an incident photon-to-current conversion efficiency (IPCE) of ∼1.6% and a visible-light-driven photocurrent density of 1.7 mA/cm2 for water oxidation. The efficiency is one order of magnitude higher than that of photoelectrocatalytic hydrogen reduction and water oxidation supported by liquid-phase exfoliated transition-metal dichalcogenides (TMDs). This result has been achieved with chemically vapor deposited (CVD) MoS2/WS2 heterojunctions, in the form of 100 μm large flakes assembled to form thin films. The large flakes sizes, compared to liquid-phase exfoliated materials (normally 1.18 V vs RHE (Figure 3 a, b and Figure S8). An early onset of measurable photocurrent at +0.48 V vs RHE was observed with the maximum on/off ratio at +1.01 V vs RHE (Figure S8a). A bare gold foil, which had been subjected to the CVD process C
DOI: 10.1021/acsaem.9b01008 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Energy Materials
Figure 3. Photoelectrochemical characterization of MoS2/WS2 heterostructure on gold in 3.5% w/v NaCl in DI water. (a) Photograph of the active electrode at +0.75 V vs Ag/AgCl (left: no-illumination; right: illuminated) showing gas bubble formation. (b) Linear sweep voltammetry at 2.5 mV/s from +0.8 to −0.8 V vs Ag/AgCl, demonstrating the complete protection of the Au surface as minimal noble-metal hydrogen evolution is observed and a negligible contribution of the substrate to either dark or photocurrent in the water oxidation region occurred. (c) Chronoamperometry at +0.75 V vs Ag/AgCl with chopped illumination at 0.2 Hz. (d) Photocurrent dependence on monochromatic light at +0.75 V vs Ag/AgCl and corresponding absorbance spectra of the heterostructures dispersed via sonication in ethanol.
the scalability of the synthesis process. This approach renders scalable CVD a compelling approach for the synthesis of TMDs, which can overcome the widely used solution-based exfoliation methods. This approach can be extended to different TMD heterojunctions, promoting photoreduction and photo-oxidation reactions including H2 evolution, CO2 conversion, and more.
structure and lead to the large grains overlapping with grain boundaries offset from one another. This offset allows for photogenerated charges to move laterally as well as vertically through the heterojunction with minimal recombination sites. These factors are proposed to minimize loss during charge transfer between MoS2 and WS2 layers. Finally, the relatively high volatility of utilized H2WO4 (and oxyhalide intermediates) ensures enriched WS2 at the surface of the heterostructure (Figure S2) in contact with the electrolyte, providing the ability for photogenerated holes, transferred in the WS2, to directly interact with water molecules. Additionally, the observed kinetics of charge carrier recombination has similar time-scales to those reported by Yu et al. using WSe2 (and WSe2/Pt heterostructures) as photocathodes for the hydrogen evolution reaction.14,15,31
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.9b01008. Experimental details; supporting materials characterization, including SEM, Raman, STEM, EDS, and reflectance spectra; and supporting electrochemical characterization, including stability testing, CA at 1 sun, LSV, CA, and O2 measurements and IPCE, VRHE, and FE calculations (PDF)
■
CONCLUSION In conclusion, we have demonstrated promising photocatalytic performance for water oxidation in salt-water conditions based on large area 2D MoS2/WS2 heterojunctions. Minimization of recombination sites enables fast charge carrier kinetics, with a photocurrent density of up to 1.7 mA/cm2 (at 1.19 V vs RHE) for 80 nm thick materials. The epitaxial interface of heterostructures fabricated by CVD enable minimization of atomic defects and nanosheets edge density while preserving
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Peter C. Sherrell: 0000-0003-4644-6238 D
DOI: 10.1021/acsaem.9b01008 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Energy Materials
(14) Yu, X.; Prévot, M. S.; Guijarro, N.; Sivula, K. Self-Assembled 2D WSe2 Thin Films for Photoelectrochemical Hydrogen Production. Nat. Commun. 2015, 6, 7596. (15) Yu, X.; Sivula, K. Photogenerated Charge Harvesting and Recombination in Photocathodes of Solvent-Exfoliated WSe2. Chem. Mater. 2017, 29 (16), 6863−6875. (16) Pesci, F. M.; Sokolikova, M. S.; Grotta, C.; Sherrell, P. C.; Reale, F.; Sharda, K.; Ni, N.; Palczynski, P.; Mattevi, C. MoS2/WS2 Heterojunction for Photoelectrochemical Water Oxidation. ACS Catal. 2017, 7, 4990−4998. (17) Jariwala, D.; Sangwan, V. K.; Lauhon, L. J.; Marks, T. J.; Hersam, M. C. Emerging Device Applications for Semiconducting Two-Dimensional Transition Metal Dichalcogenides. ACS Nano 2014, 8 (2), 1102−1120. (18) Bi, W.; Wu, C.; Xie, Y. Atomically Thin Two-Dimensional Solids: An Emerging Platform for CO2 Electroreduction. ACS Energy Lett. 2018, 3 (3), 624−633. (19) Fan, X.; Zhou, Y.; Zhang, G.; Liu, T.; Dong, W. In Situ Photoelectrochemical Activation of Sulfite by MoS2 Photoanode for Enhanced Removal of Ammonium Nitrogen from Wastewater. Appl. Catal., B 2019, 244, 396−406. (20) Liu, C.; Kong, D.; Hsu, P.-C.; Yuan, H.; Lee, H.-W.; Liu, Y.; Wang, H.; Wang, S.; Yan, K.; Lin, D.; Maraccini, P. A.; Parker, K. M.; Boehm, A. B.; Cui, Y. Rapid Water Disinfection Using Vertically Aligned MoS2 Nanofilms and Visible Light. Nat. Nanotechnol. 2016, 11, 1098. (21) Kozawa, D.; Kumar, R.; Carvalho, A.; Kumar Amara, K.; Zhao, W.; Wang, S.; Toh, M.; Ribeiro, R. M.; Castro Neto, A. H.; Matsuda, K.; Eda, G. Photocarrier Relaxation Pathway in Two-Dimensional Semiconducting Transition Metal Dichalcogenides. Nat. Commun. 2014, 5, 4543. (22) Tributsch, H.; Bennett, J. C. Electrochemistry and Photochemistry of MoS2 Layer Crystals. I. J. Electroanal. Chem. Interfacial Electrochem. 1977, 81, 97. (23) Baglio, J. A.; Calabrese, G. S.; Kamieniecki, E.; Kershaw, R.; Kubiak, C. P.; Ricco, A. J.; Wold, A.; Wrighton, M. S.; Zoski, G. D. Characterization of N-Type Semiconducting Tungsten Disulfide Photoanodes in Aqueous and Nonaqueous Electrolyte Solutions: Photo-oxidation of Halides with High Efficiency. J. Electrochem. Soc. 1982, 129 (7), 1461−1472. (24) Schneemeyer, L. F.; Wrighton, M. S. Flat-Band Potential of nType Semiconducting Molybdenum Disulfide by Cyclic Voltammetry of Two-Electron Reductants: Interface Energetics and the Sustained Photooxidation of Chloride. J. Am. Chem. Soc. 1979, 101 (22), 6496− 6500. (25) Chen, H.; Wen, X.; Zhang, J.; Wu, T.; Gong, Y.; Zhang, X.; Yuan, J.; Yi, C.; Lou, J.; Ajayan, P. M.; Zhuang, W.; Zhang, G.; Zheng, J. Ultrafast Formation of Interlayer Hot Excitons in Atomically Thin MoS2/WS2 Heterostructures. Nat. Commun. 2016, 7, 12512. (26) Wang, Q.; Wu, P.; Cao, G.; Huang, M. First-Principles Study of the Structural and Electronic Properties of MoS 2 -WS 2 and MoS 2 -MoTe 2 Monolayer Heterostructures. J. Phys. D: Appl. Phys. 2013, 46 (50), 505308. (27) Voiry, D.; Yang, J.; Chhowalla, M. Recent Strategies for Improving the Catalytic Activity of 2D TMD Nanosheets Toward the Hydrogen Evolution Reaction. Adv. Mater. 2016, 28 (29), 6197− 6206. (28) Parzinger, E.; Miller, B.; Blaschke, B.; Garrido, J. A.; Ager, J. W.; Holleitner, A.; Wurstbauer, U. Photocatalytic Stability of Single- and Few-Layer MoS2. ACS Nano 2015, 9 (11), 11302−11309. (29) Yu, X.; Guijarro, N.; Johnson, M.; Sivula, K. Defect Mitigation of Solution-Processed 2D WSe2 Nanoflakes for Solar-to-Hydrogen Conversion. Nano Lett. 2018, 18 (1), 215−222. (30) Raza, F.; Park, J. H.; Lee, H.-R.; Kim, H.-I.; Jeon, S.-J.; Kim, J.H. Visible-Light-Driven Oxidative Coupling Reactions of Amines by Photoactive WS2 Nanosheets. ACS Catal. 2016, 6 (5), 2754−2759. (31) Yu, X.; Sivula, K. Toward Large-Area Solar Energy Conversion with Semiconducting 2D Transition Metal Dichalcogenides. ACS Energy Lett. 2016, 1 (1), 315−322.
Federico M. Pesci: 0000-0003-2558-2222 Cecilia Mattevi: 0000-0003-0005-0633 Author Contributions †
These authors contributed equally to the work.
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors would like to thank Dr. Ecaterina Ware for the preparation of the TEM lamella via FIB. The authors acknowledge the use of the characterization facilities within the Harvey Flower Electron Microscopy Suite and the X-Ray Diffraction Suite of the Department of Materials, Imperial College London. M.S.S. would like to acknowledge the President’s Ph.D. Scholarship programme at the Imperial College London for financial support. C.M. would like to acknowledge the EPSRC awards, EP/K01658X/1, EP/ K016792/1, EP/M022250/1, the EPSRC-Royal Society Fellowship Engagement Grant EP/L003481/1, the Research Fellows Enhancement Award 2017 RGF\EA\180090, and the award of a Royal Society University Research Fellowship by the U.K. Royal Society.
■
REFERENCES
(1) Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37. (2) Boddy, P. J. Oxygen Evolution on Semiconducting TiO2. J. Electrochem. Soc. 1968, 115 (2), 199−203. (3) Biswas, S. K.; Baeg, J.-O. A Facile One-Step Synthesis of Single Crystalline Hierarchical WO3 with Enhanced Activity for Photoelectrochemical Solar Water Oxidation. Int. J. Hydrogen Energy 2013, 38 (8), 3177−3188. (4) Yang, Y.; Niu, S.; Han, D.; Liu, T.; Wang, G.; Li, Y. Progress in Developing Metal Oxide Nanomaterials for Photoelectrochemical Water Splitting. Adv. Energy Mater. 2017, 7 (19), 1700555. (5) Cheng, K.-W.; Tsai, W.-T.; Wu, Y.-H. Photo-Enhanced SaltWater Splitting Using Orthorhombic Ag8SnS6 Photoelectrodes in Photoelectrochemical Cells. J. Power Sources 2016, 317, 81−92. (6) Kang, J.; Tongay, S.; Zhou, J.; Li, J.; Wu, J. Band Offsets and Heterostructures of Two-Dimensional Semiconductors. Appl. Phys. Lett. 2013, 102 (1), 012111. (7) Jiang, C.; Moniz, S. J. A.; Wang, A.; Zhang, T.; Tang, J. Photoelectrochemical Devices for Solar Water Splitting - Materials and Challenges. Chem. Soc. Rev. 2017, 46 (15), 4645−4660. (8) Zhang, H. Ultrathin Two-Dimensional Nanomaterials. ACS Nano 2015, 9 (10), 9451−9469. (9) Kamat, P. V. Photophysical, Photochemical and Photocatalytic Aspects of Metal Nanoparticles. J. Phys. Chem. B 2002, 106 (32), 7729−7744. (10) Voiry, D.; Yamaguchi, H.; Li, J.; Silva, R.; Alves, D. C. B.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Enhanced Catalytic Activity in Strained Chemically Exfoliated WSNanosheets for Hydrogen Evolution. Nat. Mater. 2013, 12, 850−855. (11) Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS- Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 2013, 13, 6222−6227. (12) Xue, Y.; Zhang, Q.; Wang, W.; Cao, H.; Yang, Q.; Fu, L. Opening Two-Dimensional Materials for Energy Conversion and Storage: A Concept. Adv. Energy Mater. 2017, 7 (19), 1602684. (13) Xu, J.; Zhang, J.; Zhang, W.; Lee, C.-S. Interlayer Nanoarchitectonics of Two-Dimensional Transition-Metal Dichalcogenides Nanosheets for Energy Storage and Conversion Applications. Adv. Energy Mater. 2017, 7 (23), 1700571. E
DOI: 10.1021/acsaem.9b01008 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Article
ACS Applied Energy Materials (32) Sivula, K.; van de Krol, R. Semiconducting Materials for Photoelectrochemical Energy Conversion. Nat. Rev. Mater. 2016, 1, 15010. (33) Reale, F.; Palczynski, P.; Amit, I.; Jones, G. F.; Mehew, J. D.; Bacon, A.; Ni, N.; Sherrell, P. C.; Agnoli, S.; Craciun, M. F.; Russo, S.; Mattevi, C. High-Mobility and High-Optical Quality Atomically Thin WS 2. Sci. Rep. 2017, 7 (1), 14911. (34) Chen, K.; Wan, X.; Wen, J.; Xie, W.; Kang, Z.; Zeng, X.; Chen, H.; Xu, J.-B. Electronic Properties of MoS2-WS2 Heterostructures Synthesized with Two-Step Lateral Epitaxial Strategy. ACS Nano 2015, 9 (10), 9868−9876. (35) Tan, C.; Chen, J.; Wu, X.-J.; Zhang, H. Epitaxial Growth of Hybrid Nanostructures. Nat. Rev. Mater. 2018, 3, 17089. (36) Li, X.; Dai, Y.; Li, M.; Wei, W.; Huang, B. Stable Si-Based Pentagonal Monolayers: High Carrier Mobilities and Applications in Photocatalytic Water Splitting. J. Mater. Chem. A 2015, 3 (47), 24055−24063. (37) Shi, J.; Ma, D.; Han, G.-F.; Zhang, Y.; Ji, Q.; Gao, T.; Sun, J.; Song, X.; Li, C.; Zhang, Y.; Liu, Z.; Lang, X.-Y.; Zhang, Y. Controllable Growth and Transfer of Monolayer MoS2 on Au Foils and Its Potential Application in Hydrogen Evolution Reaction. ACS Nano 2014, 8 (10), 10196−10204. (38) Gao, Y.; Liu, Z.; Sun, D.-M.; Huang, L.; Ma, L.-P.; Yin, L.-C.; Ma, T.; Zhang, Z.; Ma, X.-L.; Peng, L.-M.; Cheng, H.-M.; Ren, W. Large-Area Synthesis of High-Quality and Uniform Monolayer WS2 on Reusable Au Foils. Nat. Commun. 2015, 6, 8569. (39) Song, J.-G.; Ryu, G. H.; Lee, S. J.; Sim, S.; Lee, C. W.; Choi, T.; Jung, H.; Kim, Y.; Lee, Z.; Myoung, J.-M.; Dussarrat, C.; LansalotMatras, C.; Park, J.; Choi, H.; Kim, H. Controllable synthesis of Molybdenum Tungsten Disulfide Alloy for Vertically CompositionControlled Multilayer. Nat. Commun. 2015, 6, 7817. (40) Mitioglu, A. A.; Plochocka, P.; Deligeorgis, G.; Anghel, S.; Kulyuk, L.; Maude, D. K. Second-Order Resonant Raman Scattering in Single-Layer Tungsten Disulfide. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89 (24), 245442. (41) Chakraborty, B.; Matte, H. S. S. R.; Sood, A. K.; Rao, C. N. R. Layer-Dependent Resonant Raman Scattering of a Few Layer MoS2. J. Raman Spectrosc. 2013, 44 (1), 92−96. (42) Tongay, S.; Fan, W.; Kang, J.; Park, J.; Koldemir, U.; Suh, J.; Narang, D. S.; Liu, K.; Ji, J.; Li, J.; Sinclair, R.; Wu, J. Tuning Interlayer Coupling in Large-Area Heterostructures with CVD-Grown MoS2 and WS2Monolayers. Nano Lett. 2014, 14 (6), 3185−3190. (43) Sahoo, P. K.; Memaran, S.; Xin, Y.; Balicas, L.; Gutiérrez, H. R. One-Pot Growth of Two-Dimensional Lateral Heterostructures via Sequential Edge-Epitaxy. Nature 2018, 553, 63. (44) Freedman, M. L. The Tungstic Acids. J. Am. Chem. Soc. 1959, 81 (15), 3834−3839. (45) Wang, Z.; Liu, P.; Ito, Y.; Ning, S.; Tan, Y.; Fujita, T.; Hirata, A.; Chen, M. Chemical Vapor Deposition of Monolayer Mo1-xWxS2 Crystals with Tunable Band Gaps. Sci. Rep. 2016, 6, 21536. (46) Zhuang, H. L.; Hennig, R. G. Computational Search for SingleLayer Transition-Metal Dichalcogenide Photocatalysts. J. Phys. Chem. C 2013, 117 (40), 20440−20445. (47) Hong, X.; Kim, J.; Shi, S.-F.; Zhang, Y.; Jin, C.; Sun, Y.; Tongay, S.; Wu, J.; Zhang, Y.; Wang, F. Ultrafast Charge Transfer in Atomically Thin MoS2/WS2 Heterostructures. Nat. Nanotechnol. 2014, 9 (9), 682−686. (48) Ma, X.; Wu, X.; Wang, H.; Wang, Y. A Janus MoSSe Monolayer: A Potential Wide Solar-Spectrum Water-Splitting Photocatalyst with a Low Carrier Recombination Rate. J. Mater. Chem. A 2018, 6, 2295. (49) Rigosi, A. F.; Hill, H. M.; Li, Y.; Chernikov, A.; Heinz, T. F. Probing Interlayer Interactions in Transition Metal Dichalcogenide Heterostructures by Optical Spectroscopy: MoS2/WS2 and MoSe2/ WSe2. Nano Lett. 2015, 15 (8), 5033−5038. (50) Shi, X.; Choi, I. Y.; Zhang, K.; Kwon, J.; Kim, D. Y.; Lee, J. K.; Oh, S. H.; Kim, J. K.; Park, J. H. Efficient Photoelectrochemical Hydrogen Production from Bismuth Vanadate-Decorated Tungsten Trioxide Helix Nanostructures. Nat. Commun. 2014, 5, 4775.
(51) Hong, S. J.; Lee, S.; Jang, J. S.; Lee, J. S. Heterojunction BiVO4/WO3 Electrodes for Enhanced Photoactivity of Water Oxidation. Energy Environ. Sci. 2011, 4 (5), 1781−1787. (52) Pilli, S. K.; Furtak, T. E.; Brown, L. D.; Deutsch, T. G.; Turner, J. A.; Herring, A. M. Cobalt-Phosphate (Co-Pi) Catalyst Modified Mo-Doped BiVO4 Photoelectrodes for Solar Water Oxidation. Energy Environ. Sci. 2011, 4 (12), 5028−5034. (53) McCrory, C. C. L.; Jung, S.; Ferrer, I. M.; Chatman, S. M.; Peters, J. C.; Jaramillo, T. F. Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices. J. Am. Chem. Soc. 2015, 137 (13), 4347.
F
DOI: 10.1021/acsaem.9b01008 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
