Molybdenum Disulfide Modified by Laser Irradiation for Catalyzing

Mar 1, 2019 - As a low-cost and promising electrocatalyst for hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) possesses both an inert ...
0 downloads 0 Views 358KB Size
Download PDF
Research Article Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

pubs.acs.org/journal/ascecg

Molybdenum Disulfide Modified by Laser Irradiation for Catalyzing Hydrogen Evolution Chao Meng,† Meng-Chang Lin,† Xi-Wen Du,*,‡ and Yue Zhou*,† †

Downloaded via ALBRIGHT COLG on March 17, 2019 at 16:16:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

College of Electrical Engineering and Automation, Shandong University of Science and Technology, No.579 Qianwangang Road, Huangdao District, Qingdao 266590, P.R. China ‡ Institute of New-Energy Materials, School of Materials Science and Engineering, Peiyang Park Campus, Tianjin University, No.135 Yaguan Road, Haihe Education Park, Tianjin 300350, P.R. China S Supporting Information *

ABSTRACT: As a low-cost and promising electrocatalyst for hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) possesses both an inert basal plane and catalytically active edges. As a result, considerable efforts have been made to activate the MoS2 basal plane for improving the HER activity. Herein, we first employed laser ablation in liquid to create plentiful sulfur (S)-vacancies in the basal plane of 2H-MoS2 nanosheets under ambient conditions. The experimental measurements and theoretical calculations prove that S vacancies in the basal plane can serve as the additional active sites and optimize the free energy change for hydrogen adsorption (ΔGH*) at the same time. As a result, in comparison with pristine MoS2 (PMoS2), laser treated MoS2 (L-MoS2) realizes a significant improvement in the HER activity. Our work represents a facile method to enhance the catalytic performance of 2H-MoS2 nanosheets and may help to guide the synthesis of other efficient two-dimensional metal chalcogenide catalysts. KEYWORDS: Molybdenum disulfide, Nanosheet, Hydrogen evolution reaction, Laser ablation, Sulfur vacancies

■

INTRODUCTION MoS2 has been recognized as one of the highest potential alternatives to platinum-based catalysts for electrochemical hydrogen evolution reaction (HER) due to its elemental abundance, electrochemical stability, and potential to be a highly active catalyst.1−6 Recently, experimental and theoretical results demonstrated that both exposed edge sites and S vacancies in the basal plane are major active sites of MoS2 to catalyze HER.7−11 Therefore, it is essential to create S vacancies in the basal plane for enhancing the HER activity of MoS2.12,13 Generally, S vacancies in the basal plane of MoS2 can be introduced by hydrogen annealing or plasma treatments.14−17 However, these methods usually require high-temperature/ pressure synthesis conditions and therefore are not energysaving.18 Very recently, a moderate synthetic approach, electrochemical desulfurization, was adopted to produce S vacancies in the MoS2 basal plane.19 Although high turnover frequencies (TOFs) have been achieved, the total number of active sites is very limited, resulting in low current densities. Thus, more effort should be made on developing effective strategies to create abundant active sites in MoS2 materials. Laser ablation in liquid (LAL), a simple, green, and fast technique, has been widely used to synthesize nanostructures under nominally ambient conditions.20,21 Interestingly, this technique can create very high pressure and temperature at the © XXXX American Chemical Society

instant of laser action and rapid quenching during the laser pulse interval, which effectively facilitates the defect formation (such as O vacancy,22,23 S vacancy,24,25 N vacancy,26 dislocation,27 and grain boundary28). At present, many researchers have adopted LAL to modify electrocatalysts by introducing anion vacancies, including NiCo2O4,29 Co3O4,23 SmMn2O5,22 and so on.30 The newly introduced anion vacancies can optimize the adsorption of intermediates, increase the number of active sites, and improve the electrical conductivity, thus enhancing the catalytic performance of pristine catalysts. But so far, the LAL technique usually causes excessive damage to the nanostructure or phase of pristine catalysts, which inhibits the obvious improvement of catalytic performance. Herein, we first employ LAL to create plentiful S vacancies in the basal plane of 2H-MoS2 nanosheets under ambient conditions. The experimental results and theoretical calculations prove that S vacancies in the basal plane can not only act as the additional active sites but optimize the ΔGH*, thus resulting in a significant enhancement in the HER performance. Eventually, the laser treated MoS2 presents a small overpotential (178 mV) to reach 10 mA cm−2, a low Tafel slope (41.4 mV dec−1), and excellent catalytic durability. Received: December 21, 2018 Revised: February 26, 2019 Published: March 1, 2019 A

DOI: 10.1021/acssuschemeng.8b06717 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. Synthetic route and structure characterization of L-MoS2. (a) Synthetic procedure of L-MoS2. Color code: cyan represents Mo, yellow represents S, white represents H, and transparent color represents vacancy. (b) XRD patterns of P-MoS2 and L-MoS2. (c) Low-magnification TEM image of L-MoS2 and its corresponding SAED pattern (inset). (d) HRTEM image of L-MoS2.

uration (Figure S3). For comparison, the same measurements for bulk MoS2 (B-MoS2), P-MoS2, and commercial Pt/C were also carried out. It must be stated that all electrode potentials were iR-corrected and converted to the reversible hydrogen electrode (RHE) (Figure S4). As shown in Figure 2a, the catalytic activity of B-MoS2 is negligible, while Pt/C, P-MoS2, and L-MoS2 all exhibit certain HER activities. In comparison with P-MoS2, L-MoS2 realizes significant activity enhance-

Our work provides a very promising technology for significantly improving the catalytic performance of other two-dimensional metal chalcogenide catalysts.

■

RESULTS AND DISCUSSION The synthetic strategy of L-MoS2 was illustrated in detail in Figure 1a. First, P-MoS2 synthesized via hydrothermal method was dispersed in ethanol under ultrasonication and then ablated by pulsed laser to obtain L-MoS2, which was finally used for HER catalysis (see details in the Experimental Section). Figure 1b presents the X-ray diffraction (XRD) patterns of L-MoS2 and P-MoS2, both of which are wellindexed to 2H-MoS2 (JCPDS 37-1492), indicating no crystal structure or chemical element change after LAL. This result was confirmed by energy dispersive spectrometery (EDS), as shown in Figure S1. Moreover, the selected-area electron diffraction (SAED) patterns of L-MoS2 and P-MoS2 (inset of Figure 1c and Figure S2b) show the same diffraction ring patterns, which consist of (100), (103), (110), and (200) planes of 2H-MoS2, revealing that L-MoS2 maintains the polycrystalline structure of P-MoS2. Transmission electron microscopy (TEM) was utilized to survey the microstructures of MoS2 catalysts before and after LAL. As observed in Figures 1c and S2a, the laser products preserve the nanosheet morphology of P-MoS2, and their size is similar to that of P-MoS2 nanosheets. The HRTEM image of an individual L-MoS2 nanosheet is shown in Figure 1d, revealing only a few-layer stacked structure with the interlayer spacing of 0.63 nm, which is in agreement with the result of broadened diffraction peaks in the XRD pattern. However, it is worth noting that, compared with the perfect surface of PMoS2 in Figure S2c, some slight distortions can be observed in the basal plane of L-MoS2 (Figure 1d). Such a defect-rich structure could notably increase active sites; therefore, better HER performance can be expected for L-MoS2.8,31 The HER performance of L-MoS2 in 0.5 M H2SO4 solution (N2 saturated) was initially evaluated by linear sweep voltammetry (LSV) using a typical three-electrode config-

Figure 2. Electrochemical HER performance of MoS2 catalysts. (a) LSV curves of commercial Pt/C, L-MoS2, P-MoS2, and B-MoS2 recorded in 0.5 M H2SO4 with iR-correction. (b) Comparison of onset overpotentials, η10, and current density values at high overpotentials for L-MoS2 and P-MoS2. (c) Corresponding Tafel plots of MoS2 catalysts and Pt/C. (d) LSV curves of L-MoS2 before and after chronoamperometry test for 10 h. Inset: chronoamperometry response (J−t) of L-MoS2 at the potential of −0.178 VRHE. B

DOI: 10.1021/acssuschemeng.8b06717 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering ments (Figure 2b), among which the onset overpotential (the overpotential at 0.5 mA cm−2) and the overpotential to reach 10 mA cm−2 (η10) decrease by 34 and 78 mV, respectively; meanwhile, the current densities at high overpotentials of 200 and 250 mV both increase more than an order of magnitude (Figure S5a). Tafel slope is an intrinsic parameter to evaluate the kinetic information for HER catalysis (Figure 2c). On the basis of the Tafel equation (η = b log j + a, where b represents the Tafel slope),32 the Tafel slope for L-MoS2 is calculated as 41.4 mV dec−1, which is much smaller than those for P-MoS2 (72.6 mV dec−1) and B-MoS2 (110.6 mV dec−1), and even close to that for Pt/C (31.3 mV dec−1), suggesting a favorable HER kinetics. This is further supported by the electrochemical impedance spectroscopy (Figure S5b), in which the semicircle diameter of L-MoS2 is smaller than that of P-MoS2, indicating a lower charge transfer resistance in L-MoS2 during HER catalysis.33 Such an HER activity of L-MoS2 is comparable to or better than those of recently reported 2H-MoS2 based catalysts, as summarized in Table S1. Furthermore, the long-term durability is of great importance for an electrocatalyst applied in energy storage and conversion. Figure 2d shows that L-MoS2 maintains 96% of its initial current density after 10 h test, and the corresponding LSV curve almost coincides with the pristine one, suggesting the outstanding durability of L-MoS2. In addition, the composition and morphology of L-MoS2 after electrochemical HER are nearly unchanged (Figure S6), which further demonstrates its structural stability. The gas chromatography (GC) was adopted to quantitatively measure the produced hydrogen. As shown in Figure S7, the practical hydrogen production rate (0.0642 mmol h−1) agrees well with the theoretical value (0.0654 mmol h−1), leading to a high Faradaic efficiency (FE) of 98.2%. To find out the reason for the outstanding performance of LMoS2, its electrochemical surface area (ECSA) and density of active sites were first compared with those of P-MoS2. The ECSA of two MoS2 catalysts were obtained by measuring the double-layer capacitance (Cdl), as the Cdl value is proportional to the ECSA (Figure 3a; Figure S8 and Table S2, Supporting Information),34 and the density of active sites was calculated according to eq S2. The calculated ECSA value and density of active sites for L-MoS2 are 475 cm2ECSA and 5.529 × 1017 sites cm−2, respectively, which are both 1.53 times larger than those 2 and 3.6 × 1017 sites cm−2). for P-MoS2 (310 cmECSA Combining density of active sites and LSV data from Figure 2a, the TOFs at different overpotentials of two MoS2 catalysts were calculated using eq S3.35 The calculation result (Figure 3b) shows that the TOFs for L-MoS2 are higher than those for P-MoS2 at entire range of overpotentials. Particularly at the overpotential of 250 mV, the TOF for L-MoS2 is 7.674 s−1, which is 18.3 times higher than that for P-MoS2 (0.419 s−1), exhibiting an obvious improvement of intrinsic activity for LMoS2. Recently, numerous experimental and theoretical studies have confirmed that both edges and S vacancies in the basal plane can increase active sites, thus improving the intrinsic activity of 2H-MoS2 nanosheets.8 Because L-MoS2 maintains the nanosheet morphology and size of P-MoS2 (see Figure 1c and S2a), the increased active sites should arise from S vacancies in the basal plane rather than the exposed edges. To confirm the selective removal of S atoms in the basal plane of 2H-MoS2 nanosheets by LAL, we adopted X-ray photoelectron spectroscopy (XPS) to analyze element valence

Figure 3. (a) Linear fitting of the capacitive currents versus scan rates. The calculated Cdl are 28.5 and 18.6 mF cm−2 for L-MoS2 and PMoS2, respectively. (b) Calculated TOFs at the overpotentials smaller than 250 mV for L-MoS2 and P-MoS2. (c) XPS Mo 3d, (d) XPS S 2p, and (e) Raman spectra of L-MoS2 and P-MoS2.

states of MoS2 catalysts. The Mo 3d spectra (Figure 3c) consisting of peaks at about 229.4 and 232.6 eV are almost same for both L-MoS2 and P-MoS2, which suggests that surface Mo atoms are unaffected.16 However, the S 2p peaks at about 162.3 and 163.5 eV for L-MoS2 are slightly lower than those for P-MoS2 (Figure 3d), demonstrating the removal of surface S atoms via LAL.19,36 After quantitative analysis, the peak area ratio of S/Mo for L-MoS2 (∼1.84) is smaller than that for PMoS2 (∼2), indicating that an ∼8% concentration of S vacancies exists in L-MoS2.10 The Raman spectra were also used to verify that S vacancies exist in the basal plane of L-MoS2. As exhibited in Figure 3e, PMoS2 shows two main characteristic peaks, which correspond to the out-of-plane (A1g, 405.4 cm−1) and in-plane (E12g, 382.3 cm −1 ) Mo−S phonon modes of typical MoS 2 layer structure.1,17,36 But for L-MoS2, the peak position of A1g mode blue-shifts to 406.5 cm−1, while the E12g peak red-shifts to 381.4 cm−1, proving the existence of S vacancies in LMoS2.15 Moreover, the peak intensities for both phonon modes of L-MoS2 are reduced, which suggests that the symmetry of its crystal structure is broken owing to the S vacancies introduced through LAL.37 But, it should be noted that the intensity ratio of A1g/E12g for L-MoS2 (2.05) is close to that for P-MoS2 (1.98) (Figure S9), clearly indicating that the number of edge sites of L-MoS2 is seldom increased by laser treatment, which agrees with TEM observation.38,39 Therefore, the above Raman results confirm the presence of S vacancies in the basal plane of L-MoS2. We speculate that the formation of S vacancies originates from the high temperature caused by laser heating and the existence of ethanol, which have been demonstrated very crucial on the synthesis of MoS2 nanosheets with S vacancies.40 Density functional theory (DFT) calculations were used to study the HER activity difference between L-MoS2 and PMoS2. In principle, the HER pathway involves an initial state (H+ + e−), an intermediate state (adsorbed H, H*), and a final C

DOI: 10.1021/acssuschemeng.8b06717 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

ACS Sustainable Chemistry & Engineering

■

state (1/2 H2).41 Previous studies illuminated that the ΔGH* is an excellent indicator for HER catalysts, and the optimum catalytic activity is associated with a ΔGH* = 0.42 Based on the characterizations of two MoS2 catalysts, we built the surfaces of perfect 4 × 4 unit for P-MoS2 and that with S vacancies (Vs) for L-MoS2 to compute the corresponding ΔGH* (see Figure S10 and Supporting Information for calculation details). The final adsorption states of H atom on P-MoS2 and L-MoS2 are presented in Figures 4a and 4b, respectively, and the calculated

Research Article

AUTHOR INFORMATION

Corresponding Authors

*E-mail for Y. Z.: [email protected]. *E-mail for X.W.D.: [email protected]. ORCID

Xi-Wen Du: 0000-0002-2811-147X Yue Zhou: 0000-0002-1193-6467 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (Grant 2017RCJJ057) and the National Natural Science Foundation of China (Grants 51671141, 51571149, 51471115, and 21573117).

■

Figure 4. Atomic models for H atom bonded on (a) P-MoS2 and (b) L-MoS2. (c) Calculated free energy diagram of the HER on P-MoS2 and L-MoS2.

ΔGH* on two MoS2 catalysts are summarized in Figure 4c and Table S3. Compared with ΔGH* of P-MoS2 (1.66 eV), L-MoS2 shows a more preferable value (−0.17 eV), which ensures fast proton/electron adsorption and hydrogen release. Thus, LMoS2 exhibits superior HER activity to P-MoS2 due to the existence of S vacancies in the basal plane. In view of above, we attribute the excellent HER performance of L-MoS2 to two reasons. On the one hand, LMoS2 contains a large amount of S vacancies in the basal plane, which act as the additional active sites to catalyze HER. On the other hand, S vacancies in the basal plane optimize the ΔGH* efficiently, thus accelerating the whole HER process.

■

CONCLUSION In summary, we successfully employed the LAL technique to introduce S vacancies into the basal plane of 2H-MoS2 nanosheets under ambient conditions and identified their role in HER electrocatalysis from experimental and theoretical views. S vacancies in the basal plane can not only serve as additional active sites but also optimize the ΔGH* efficiently; as a result, L-MoS2 displays excellent catalytic properties (η10 of 178 mV, Tafel slope of 41.4 mV dec−1). Our work provides a simple and powerful approach to improve the catalytic performance of 2H-MoS2 nanosheets and may be a guide to synthesize other efficient two-dimensional metal chalcogenide catalysts.

■

REFERENCES

(1) Hu, J.; Huang, B.; Zhang, C.; Wang, Z.; An, Y.; Zhou, D.; Lin, H.; Leung, M. K. H.; Yang, S. Engineering stepped edge surface structures of MoS2 sheet stacks to accelerate the hydrogen evolution reaction. Energy Environ. Sci. 2017, 10 (2), 593−603. (2) Kim, Y.; Jackson, D. H. K.; Lee, D.; Choi, M.; Kim, T. W.; Jeong, S. Y.; Chae, H. J.; Kim, H. W.; Park, N.; Chang, H.; Kuech, T. F.; Kim, H. J. In Situ Electrochemical Activation of Atomic Layer Deposition Coated MoS2 Basal Planes for Efficient Hydrogen Evolution Reaction. Adv. Funct. Mater. 2017, 27 (34), 1701825. (3) Zhang, X.; Lai, Z.; Tan, C.; Zhang, H. Solution-Processed TwoDimensional MoS2 Nanosheets: Preparation, Hybridization, and Applications. Angew. Chem., Int. Ed. 2016, 55 (31), 8816−8838. (4) Wu, C.; Li, J. Unique Hierarchical Mo2C/C Nanosheet Hybrids as Active Electrocatalyst for Hydrogen Evolution Reaction. ACS Appl. Mater. Interfaces 2017, 9 (47), 41314−41322. (5) Du, H.; Kong, R. M.; Guo, X.; Qu, F.; Li, J. Recent progress in transition metal phosphides with enhanced electrocatalysis for hydrogen evolution. Nanoscale 2018, 10 (46), 21617−21624. (6) Xu, G.; Wang, X.; Sun, Y.; Chen, X.; Zheng, J.; Sun, L.; Jiao, L.; Li, J. Metallic and ferromagnetic MoS2 nanobelts with vertically aligned edges. Nano Res. 2015, 8 (9), 2946−2953. (7) Voiry, D.; Fullon, R.; Yang, J.; de Carvalho Castro e Silva, C.; Kappera, R.; Bozkurt, I.; Kaplan, D.; Lagos, M. J.; Batson, P. E.; Gupta, G.; Mohite, A. D.; Dong, L.; Er, D.; Shenoy, V. B.; Asefa, T.; Chhowalla, M. The role of electronic coupling between substrate and 2D MoS2 nanosheets in electrocatalytic production of hydrogen. Nat. Mater. 2016, 15 (9), 1003−1009. (8) Li, G.; Zhang, D.; Qiao, Q.; Yu, Y.; Peterson, D.; Zafar, A.; Kumar, R.; Curtarolo, S.; Hunte, F.; Shannon, S.; Zhu, Y.; Yang, W.; Cao, L. All The Catalytic Active Sites of MoS2 for Hydrogen Evolution. J. Am. Chem. Soc. 2016, 138 (51), 16632−16638. (9) Yin, Y.; Han, J.; Zhang, Y.; Zhang, X.; Xu, P.; Yuan, Q.; Samad, L.; Wang, X.; Wang, Y.; Zhang, Z.; Zhang, P.; Cao, X.; Song, B.; Jin, S. Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets. J. Am. Chem. Soc. 2016, 138 (25), 7965−7972. (10) Li, H.; Tsai, C.; Koh, A. L.; Cai, L.; Contryman, A. W.; Fragapane, A. H.; Zhao, J.; Han, H. S.; Manoharan, H. C.; AbildPedersen, F.; Norskov, J. K.; Zheng, X. Corrigendum: Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies. Nat. Mater. 2016, 15 (3), 364. (11) Zhang, G.; Liu, H.; Qu, J.; Li, J. Two-dimensional layered MoS2: rational design, properties and electrochemical applications. Energy Environ. Sci. 2016, 9 (4), 1190−1209. (12) Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS2 nanosheets

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.8b06717. Experimental section, structural and electrochemical characterizations of MoS2 catalysts, details on TOF and DFT calculations (PDF) D

DOI: 10.1021/acssuschemeng.8b06717 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering as catalysts for hydrogen evolution reaction. Nano Lett. 2013, 13 (12), 6222−6227. (13) Lukowski, M. A.; Daniel, A. S.; Meng, F.; Forticaux, A.; Li, L.; Jin, S. Enhanced hydrogen evolution catalysis from chemically exfoliated metallic MoS2 nanosheets. J. Am. Chem. Soc. 2013, 135 (28), 10274−10277. (14) Ye, G.; Gong, Y.; Lin, J.; Li, B.; He, Y.; Pantelides, S. T.; Zhou, W.; Vajtai, R.; Ajayan, P. M. Defects Engineered Monolayer MoS2 for Improved Hydrogen Evolution Reaction. Nano Lett. 2016, 16 (2), 1097−1103. (15) Cheng, C. C.; Lu, A. Y.; Tseng, C. C.; Yang, X.; Hedhili, M. N.; Chen, M. C.; Wei, K. H.; Li, L. J. Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma. Nano Energy 2016, 30, 846−852. (16) Lu, A. Y.; Yang, X.; Tseng, C. C.; Min, S.; Lin, S. H.; Hsu, C. L.; Li, H.; Idriss, H.; Kuo, J. L.; Huang, K. W.; Li, L. J. High-SulfurVacancy Amorphous Molybdenum Sulfide as a High Current Electrocatalyst in Hydrogen Evolution. Small 2016, 12 (40), 5530− 5537. (17) Zhu, J.; Wang, Z.; Yu, H.; Li, N.; Zhang, J.; Meng, J.; Liao, M.; Zhao, J.; Lu, X.; Du, L.; Yang, R.; Shi, D.; Jiang, Y.; Zhang, G. Argon Plasma Induced Phase Transition in Monolayer MoS2. J. Am. Chem. Soc. 2017, 139 (30), 10216−10219. (18) Xie, J.; Zhang, H.; Li, S.; Wang, R.; Sun, X.; Zhou, M.; Zhou, J.; Lou, X. W.; Xie, Y. Defect-rich MoS2 ultrathin nanosheets with additional active edge sites for enhanced electrocatalytic hydrogen evolution. Adv. Mater. 2013, 25 (40), 5807−5813. (19) Tsai, C.; Li, H.; Park, S.; Park, J.; Han, H. S.; Norskov, J. K.; Zheng, X.; Abild-Pedersen, F. Electrochemical generation of sulfur vacancies in the basal plane of MoS2 for hydrogen evolution. Nat. Commun. 2017, 8, 15113. (20) Zeng, H. B.; Du, X. W.; Singh, S. C.; Kulinich, S. A.; Yang, S. K.; He, J. P.; Cai, W. P. Nanomaterials via Laser Ablation/Irradiation in Liquid: A Review. Adv. Funct. Mater. 2012, 22 (7), 1333−1353. (21) Blakemore, J. D.; Gray, H. B.; Winkler, J. R.; Müller, A. M. Co3O4 Nanoparticle Water-Oxidation Catalysts Made by PulsedLaser Ablation in Liquids. ACS Catal. 2013, 3 (11), 2497−2500. (22) Dong, C.; Liu, Z. W.; Liu, J. Y.; Wang, W. C.; Cui, L.; Luo, R. C.; Guo; Zheng, X. L.; Qiao, S. Z.; Du, X. W.; Yang, J. Modest Oxygen-Defective Amorphous Manganese-Based Nanoparticle Mullite with Superior Overall Electrocatalytic Performance for Oxygen Reduction Reaction. Small 2017, 13 (16), 1603903. (23) Zhou, Y.; Dong, C. K.; Han, L. L.; Yang, J.; Du, X. W. TopDown Preparation of Active Cobalt Oxide Catalyst. ACS Catal. 2016, 6 (10), 6699−6703. (24) Zhu, Y.; Yuan, C. L.; Ong, P. P. Room temperature visible photoluminescence from undoped ZnS nanoparticles embedded in SiO2 matrices. J. Appl. Phys. 2002, 92 (11), 6828−6832. (25) Hu, J. J.; Zabinski, J. S.; Bultman, J. E.; Sanders, J. H.; Voevodin, A. A. Structure characterization of pulsed laser deposited MoSx − WSey composite films of tribological interests. Tribol. Lett. 2006, 24 (2), 127−135. (26) Kushvaha, S. S.; Kumar, M. S.; Shukla, A. K.; Yadav, B. S.; Singh, D. K.; Jewariya, M.; Ragam, S. R.; Maurya, K. K. Structural, optical and electronic properties of homoepitaxial GaN nanowalls grown on GaN template by laser molecular beam epitaxy. RSC Adv. 2015, 5 (107), 87818−87830. (27) Hu, J. Q.; Li, Q.; Meng, X. M.; Lee, C. S.; Lee, S. T. Synthesis of β-Ga2O3Nanowires by Laser Ablation. J. Phys. Chem. B 2002, 106 (37), 9536−9539. (28) Murugesan, S.; Kuppusami, P.; Parvathavarthini, N.; Mohandas, E. Pulsed laser deposition of anatase and rutile TiO2 thin films. Surf. Coat. Technol. 2007, 201 (18), 7713−7719. (29) Liu, Y.; Liu, P.; Qin, W.; Wu, X.; Yang, G. Laser modificationinduced NiCo2O4‑δ with high exterior Ni3+/Ni2+ ratio and substantial oxygen vacancies for electrocatalysis. Electrochim. Acta 2019, 297, 623−632. (30) Ou, G.; Fan, P.; Ke, X.; Xu, Y.; Huang, K.; Wei, H.; Yu, W.; Zhang, H.; Zhong, M.; Wu, H.; Li, Y. Defective molybdenum sulfide

quantum dots as highly active hydrogen evolution electrocatalysts. Nano Res. 2018, 11 (2), 751−761. (31) Yang, L.; Zhou, W.; Lu, J.; Hou, D.; Ke, Y.; Li, G.; Tang, Z.; Kang, X.; Chen, S. Hierarchical spheres constructed by defect-rich MoS2/carbon nanosheets for efficient electrocatalytic hydrogen evolution. Nano Energy 2016, 22, 490−498. (32) Tang, Y. J.; Wang, Y.; Wang, X. L.; Li, S. L.; Huang, W.; Dong, L. Z.; Liu, C. H.; Li, Y. F.; Lan, Y. Q. Molybdenum Disulfide/ Nitrogen-Doped Reduced Graphene Oxide Nanocomposite with Enlarged Interlayer Spacing for Electrocatalytic Hydrogen Evolution. Adv. Energy Mater. 2016, 6 (12), 1600116. (33) Meng, C.; Ling, T.; Ma, T. Y.; Wang, H.; Hu, Z.; Zhou, Y.; Mao, J.; Du, X. W.; Jaroniec, M.; Qiao, S. Z. Atomically and Electronically Coupled Pt and CoO Hybrid Nanocatalysts for Enhanced Electrocatalytic Performance. Adv. Mater. 2017, 29 (9), 1604607. (34) Tang, C.; Zhong, L.; Zhang, B.; Wang, H. F.; Zhang, Q. 3D Mesoporous van der Waals Heterostructures for Trifunctional Energy Electrocatalysis. Adv. Mater. 2018, 30 (5), 1705110. (35) Behranginia, A.; Asadi, M.; Liu, C.; Yasaei, P.; Kumar, B.; Phillips, P.; Foroozan, T.; Waranius, J. C.; Kim, K.; Abiade, J.; Klie, R. F.; Curtiss, L. A.; Salehi-Khojin, A. Highly Efficient Hydrogen Evolution Reaction Using Crystalline Layered Three-Dimensional Molybdenum Disulfides Grown on Graphene Film. Chem. Mater. 2016, 28 (2), 549−555. (36) Li, J.; Kang, J.; Cai, Q.; Hong, W.; Jian, C.; Liu, W.; Banerjee, K. Boosting Hydrogen Evolution Performance of MoS2 by Band Structure Engineering. Adv. Mater. Interfaces 2017, 4 (16), 1700303. (37) Parkin, W. M.; Balan, A.; Liang, L.; Das, P. M.; Lamparski, M.; Naylor, C. H.; Rodriguez-Manzo, J. A.; Johnson, A. T.; Meunier, V.; Drndic, M. Raman Shifts in Electron-Irradiated Monolayer MoS2. ACS Nano 2016, 10 (4), 4134−4142. (38) Gong, Q.; Cheng, L.; Liu, C.; Zhang, M.; Feng, Q.; Ye, H.; Zeng, M.; Xie, L.; Liu, Z.; Li, Y. Ultrathin MoS2(1−x)Se2x Alloy Nanoflakes For Electrocatalytic Hydrogen Evolution Reaction. ACS Catal. 2015, 5 (4), 2213−2219. (39) Yu, X. Y.; Feng, Y.; Jeon, Y.; Guan, B.; Lou, X. W.; Paik, U. Formation of Ni-Co-MoS2 Nanoboxes with Enhanced Electrocatalytic Activity for Hydrogen Evolution. Adv. Mater. 2016, 28 (40), 9006− 9011. (40) Cai, L.; He, J.; Liu, Q.; Yao, T.; Chen, L.; Yan, W.; Hu, F.; Jiang, Y.; Zhao, Y.; Hu, T.; Sun, Z.; Wei, S. Vacancy-induced ferromagnetism of MoS2 nanosheets. J. Am. Chem. Soc. 2015, 137 (7), 2622−7. (41) Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions. Chem. Soc. Rev. 2015, 44 (8), 2060−2086. (42) Noerskov, J. K.; Bligaard, T.; Logadottir, A.; Kitchin, J. R.; Chen, J. G.; Pandelov, S.; Stimming, U. Trends in the Exchange Current for Hydrogen Evolution. J. Electrochem. Soc. 2005, 152 (3), J23−J26.

E

DOI: 10.1021/acssuschemeng.8b06717 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX