Abundant Vanadium Diboride with Graphene-like Boron layers for

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Abundant vanadium diboride with graphenelike boron layers for hydrogen evolution Palani Raja Jothi, Yuemei Zhang, Kunio Yubuta, Damian Culver, Matthew P. Conley, and Boniface P. T. Fokwa ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b01615 • Publication Date (Web): 13 Dec 2018 Downloaded from http://pubs.acs.org on December 17, 2018

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ACS Applied Energy Materials

Abundant Vanadium Diboride with Graphene-like Boron layers for Hydrogen Evolution Palani R. Jothi, #a Y. Zhang,#a K. Yubuta,b D. B. Culver,a M. Conley,a B. P. T. Fokwa a* a Departments b

of Chemistry and Center for Catalysis, University of California, Riverside, CA 92521, USA

Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan

#: contributed equally *: E-mail: [email protected], WWW: fokwalab.ucr.edu

Abstract: We report on the design of abundant and highly active VB2 for hydrogen production. Density functional theory (DFT) calculations have predicted very high HER activity of the graphene-like B-layer, the V-terminated {100} layer and the mixed V/B-terminated {101} layer of VB2. Bulk samples and nanoparticles of VB2 were synthesized and tested for their HER performance. The results indicate that both bulk and nano-VB2 are active for HER, consistent with theoretical predictions. In addition, the HER activity of VB2 is significantly increased at the nanoscale if compared to the bulk, reaching an overpotential of 192 mV at 10 mA/cm2 current density. Increased surface area and higher density of active sites are responsible for the higher nanoscale activity, making nano-VB2 the best HER boride to date in terms of abundance, stability and activity in acidic solution. Keywords: Metal borides; Hydrogen evolution; Gibbs free-energy calculations; nanoparticles; Graphene-like boron layers

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Hydrogen is considered as one of the cleanest sources of energy, and electrochemical water splitting is recognized as a promising approach to produce hydrogen.1-2 At present, platinum-group metals are the most efficient electrocatalyst for the hydrogen evolution reaction (HER), but high cost and scarcity hinders their applications in large-scale hydrogen production technologies.2 In recent years, several non-noble metal electrocatalysts for HER have been explored as possible alternatives for Pt, including transition metal dichalcogenides, carbides, nitrides, phosphides, MXenes and recently metal borides.3-9 Among them, nanostructured 2H-MoS2 holds high potential for catalyzing HER because of its excellent chemical stability and high activity, but the fact that it was found to be active only on the edges of its 2D structure has limited its performance.10 Interestingly, the 1T-MoS2 metallic phase shows better HER activity than 2H-MoS2, due to the presence of active sites both on the edges and on the basal plane.11 However, MoS2 is metastable in the 1T-phase. Therefore, most attention has been devoted to improving the HER activity of 2H-MoS2, by increasing the number of defect sites in the basal plane or by hybridization with graphene, just to name a few examples.1214

Likewise, metallic 1T-VS2 nanostructures have recently emerged as excellent catalysts

for HER. Interestingly, they exhibit better HER activity than the other transition metal dichalcogenides, including MoS2.15-17 Transition metal borides (TMBs) are also considered promising HER catalysts for hydrogen evolution, as they can have both metallic character and high stability in acidic and basic solutions.18-19 We recently reported an increase in HER activity with increasing boron content in the phases Mo2B, -MoB, -MoB and -MoB2, thereby suggesting a boron-dependency of bulk molybdenum borides.5 Furthermore, we later found that the activity of -MoB2 could be further enhanced by nanoparticles formation.6 Also, density functional theory (DFT) calculations showed that the catalytic activity of -MoB2 strongly depends on the exhibition of B-terminated MoB2 {001} surface (graphene-like boron layer), which acts like the Pt {111} surface.6 A similar finding was simultaneously reported for FeB2 by Geyer et al.8 However, contrasting results were reported by Zou et al. who found better activity for the Mo-terminated layer in -MoB2.9 To further check the activity of the graphene-like boron layers, we studied -MoB2 (or Mo2B4) which contains both 2 ACS Paragon Plus Environment

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graphene-like and puckered phosphorene-like boron layers and discovered that puckering the boron layers renders them less active as they then bind hydrogen very strongly.7 Vanadium diboride (VB2) has the same AlB2-type crystal structure as -MoB2 and contains the flat graphene-like boron layer. Also, recent research findings of better HER activity of VS2 if compared to MoS2

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and the higher abundance of vanadium

compared to molybdenum (two orders of magnitudes) hinted at intensifying research on the VB2 materials for HER. In this work, we have investigated the HER activity of VB2 using DFT calculations and validated the theoretical findings experimentally. The Gibbs free energy (ΔGH) for atomic hydrogen (H) adsorption on a catalyst surface has been successfully used as a descriptor for correlating theoretical predictions with experimental measurements of the HER activity for various systems.6,20-22 Optimal HER activity can be achieved at a ΔGH value close to zero, where the overall reaction of both H adsorption and H2 desorption has the maximum rate.21 DFT calculations were applied to explore the active sites and the distinct HER activities of different VB2 surfaces. TEM identified several surfaces of nano-VB2: {001}, {100} and {101} (see experimental section and supporting information). In addition, our results on isostructural MoB2 compound indicated that the B-terminated {001}, mixed Mo/B {110} and {101} surfaces are very active surfaces.6 Therefore, the V- and B- terminated {001} and {100}, the mixed V/B {110} and {101} surfaces in VB2 were investigated (more details in supporting information (SI)). The H-surface binding energy (ΔEH) and ΔGH on each VB2 surface were calculated and compared with the same surfaces in MoB2. The results are listed in the SI Tables S1 and S2 and plotted in Figures 1a and S1. Like in MoB2, the bridge (Bg) sites of the Bterminated {001} and V-terminated {100} surfaces, the hollow (Ho) site of V-terminated {001}, the V/B mixed {110} and {101} surfaces, the top (T) site of B-terminated {100} surface in VB2 are the most active sites because of their relatively high H-surface binding energy at 25% hydrogen coverage (H-coverage) (Table S1). Just as in MoB2, the Vterminated {001} and B-terminated {100} surfaces in VB2 has poor HER activity because of the strong H-surface binding energies (ΔEH = −0.88 eV and −1.40 eV, respectively) and low ΔGH (−0.68 eV and −1.20 eV, respectively). ΔGH for {110}, B-terminated {001} and V-terminated {100} surfaces are −0.42 eV, −0.38 eV and −0.31 eV, respectively, 3 ACS Paragon Plus Environment


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indicating better HER activity than the V-terminated {001} and B-terminated {100} surfaces. However, the {101} surface has an even higher activity because its ΔGH is the closest to zero (−0.10 eV, Figure 1a). VB2 {101}, MoB2 {110}, B-terminated VB2 and MoB2 {001}, metal-terminated VB2 and MoB2 {100} surfaces have comparable free energies to the noble metal Pt. Therefore, VB2 should be highly HER active. However, to fully understand the HER activity it is important to examine the behavior of ΔGH as function of H-coverage, the results of which is plotted in Figure 1b for different surfaces.

Figure 1. (a) Calculated free-energy (at 25% hydrogen coverage) diagram for HER over different surfaces of MoB26 (colored dashed lines) and VB2 (colored solid lines). The freeenergy of Pt {111} Ho is provided for comparison (dashed line in purple, value from ref. 6). Blue, green, red, orange, navy and magenta colors represent mixed {101}, {110}, Bterminated {001}, metal-terminated {001}, B-terminated {100} and metal-terminated {100} surfaces in VB2 (MoB2), respectively. Ho, T and Bg represent hollow, top and bridge sites, respectively. (b) The Gibbs free energy (ΔGH) for H adsorption on the Bg site of Bterminated {001} (red), metal-terminated {100} (magenta), Ho site of mixed metal/B {110} (green) and {101} (blue) surfaces for MoB26 and VB2 plotted as function of hydrogen coverage. Solid and dashed lines represent VB2 and MoB2, respectively. At low H-coverage (25%), hydrogen binds stronger on the B-terminated {001} surface of VB2 than on that of MoB2. At 50% and 75% H-coverage, ΔGH for the B-terminated VB2 {001} surface is comparable to that of MoB2, indicating comparable HER activity for both 4 ACS Paragon Plus Environment

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materials at these H-coverages. However, at 100% H-coverage, ΔGH drops slightly (−0.10 eV) for B-terminated VB2, while it increases in the case of MoB2. As Figure 1b (red lines) shows, ΔGH reaches 0 eV at about 85% H-coverage for MoB2 while it never reaches zero up to 100% H-coverage for VB2, even though it remains very close to zero. For the {101} surface, ΔGH remains nearly constant and close to zero (~ −0.1 eV) for all hydrogen coverages indicating good activity, in contrast to the MoB2 {101} surface which has high and positive ΔGH values (Figure 1b, blue lines). For the V-terminated VB2 {100} surface, ΔGH increases from −0.31 eV up to −0.09 eV, also indicating good HER activity, unlike the Mo-terminated MoB2 {100} surface which shows a decrease of ΔGH with increasing H-coverage (Figure 1b, magenta lines). For the {110} VB2 surface, as H-coverage increases from 25% to 100% ΔGH increases from −0.42 eV to −0.29 eV, thus it remains far away from zero indicating less catalytic activity than the corresponding surface in MoB2 (Figure 1b, blue lines). Consequently, the three surfaces (B-terminated {001}, Vterminated {100} and mixed {101}) are active in VB2, compared to only 2 in MoB2 (Bterminated {001}, and mixed {101}). However, the ΔGH values of VB2 active surfaces never reach 0 in contrast to those of MoB2, indicating slightly better activity for MoB2 than VB2 (see discussion below). In addition, the Ho sites are the active sites on the mixed VB2 {101} surface, where the hydrogen atom binds to one boron at a B-H distance of 1.28 Å and to two vanadium atoms at a relatively long V-H distance (2.12 Å). However, on the B-terminated {001} surface the Bg sites are more active, and hydrogen binds to two boron atoms at a B-H distance of 1.36 Å (Figure S1). Therefore, boron is crucial to the HER activity of both surfaces. To confirm the predictions from DFT, we have synthesized bulk - and nano-VB2 and tested their HER activity. The detailed synthesis procedures of VB2 nanoparticles and bulk-VB2 are discussed in the supporting information. For nano-VB2, the synthesis was carried out using a recently discovered synthetic method toward various transition metal boride nanomaterials, 23 while the bulk sample was synthesized by arc-melting. Figure 2a shows the powder X-Ray diffraction (PXRD) data of synthesized VB2 nanoparticles, which is indexed to the single crystalline phase of VB2 (space group 5 ACS Paragon Plus Environment


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P6/mmm, ICSD No. – 1510849). The broad diffraction peaks of the sample indicate the formation of small crystalline particles. The refined lattice parameters of VB2, a = 3.006 (4) and c = 3.057 (4) Å, matched with the reported values (a = 2.997 Å, c = 3.045 Å) as well as those of our bulk sample [a = 2.998 (2) Å, c = 3.056 (2) Å] as shown in Figure S2.24 The chemical composition of VB2 was analyzed by energy dispersive X-ray spectroscopy (EDS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The EDS results confirmed the presence of vanadium and boron, and the ICP results revealed a 1:2.05 molar ratio for V:B, which is consistent with the starting composition and the single-phase nature of the product (Figure S3). The surface composition of the VB2 nanoparticles was analyzed by X-Ray photoelectron (XPS) spectroscopy. The V 2p, B 1s and O 1s core-level spectra are shown in Figure 2b-d. The deconvolution of the V 2p spectrum (Figure 2b) was fit to three peaks at 513.7 eV, 517.4 eV and 524.9 eV. The small peak at 513.7 corresponds to V0 in VB2 whereas the peaks at 517.4 and 524.9 eV are due to splitting of V 2p3/2 and V 2p1/2 in vanadium pentoxide.25 The surface species of boron (B) were analyzed by deconvoluting the B 1s spectrum (Figure 2c) to B0 (188.9 eV), boron suboxide B2O2 (191.2 eV) and B3+ (193.0 eV).24,26 The existence of vanadium and boron surface oxidized species reveals that the VB2 nanoparticles surface is significantly contaminated by oxygen. To further examine the surface oxidation in the sample, the O 1s spectrum was also deconvoluted (Figure 2d), and it shows two peaks at 531.2 eV and 533.1 eV, which closely match the oxygen peak positions of V2O5 and B2O3, respectively.24, 27 However, the observed peaks at 513.7 eV in vanadium 2p and 188.9 eV in B 1s evidence the presence of unoxidized VB2.27 Also, the high crystallinity (see PXRD and electron microscopy studies) of the nanoparticles suggests that only the surface is oxidized. It was shown for MoB bulk materials5 that the oxide surface is usually leached out during HER in acidic conditions, thus we expect the same to happen for the VB2 surface, as evidenced by the activity studies below. More details about the fitting of peak positions, relative concentrations, and assignments of species are given in Table S3.


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Figure 2. (a) X-Ray diffractogram (XRD) of VB2 nanoparticles and (b-d) Deconvoluted XPS spectra of VB2: (b) core-level V 2p, (c) core-level B 1s and (d) core-level O1s. The morphology of the VB2 nanoparticles was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM image of VB2 shows aggregated nanoparticles that are composed of small nanograins (Figure 3a). Arc melted bulk VB2 sample were also analyzed by SEM, which shows much larger particles as expected (Figure S4). The TEM image in Figure 3b reveals that the nanograins are less than ten nanometers in size. The high-resolution TEM (HRTEM) images in Figures 3c and S3 show the crystallinity of the VB2 nanoparticles with different orientations of lattice fringes with d-spacings of 0.19 nm, 0.26 nm and 0.31 nm corresponding to the {101}, {100} and {001} sets of crystal planes of hexagonal VB2 (ICSD no. 1510849). The selected area electron diffraction (SAED) pattern (Figure 3d) on an ensemble of 7 ACS Paragon Plus Environment


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nanoparticles reveals intense diffraction peaks building rings which could be indexed to {001}, {100} and {101} sets of crystal planes of hexagonal VB2, thus further confirming the crystalline nature of the VB2 nanoparticles. The N2-sorption studies on VB2 led to a Brunauer−Emmett−Teller (BET) surface area of only 16.7 m2 /g, in accordance with the absence of pores in the sample and the high degree of agglomeration of the nanoparticles. The BET isotherm curve is shown in Figure S5.

Figure 3. (a) Low magnification SEM image (b) TEM image, (c) HRTEM image and (d) SAED pattern of the VB2 nanoparticles.


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The electrocatalytic HER activity was performed in 0.5 M H2SO4 electrolyte using a mass loading of ~0.5 mg/cm2. Bulk-VB2, commercial 5% Pt/C, vanadium, elemental boron and carbon sheet were also tested for comparison (Figure 4a). The obtained polarization curves indicate that the carbon sheet shows negligible HER activity, whereas commercial Pt/C shows the highest activity as expected. Vanadium and boron have poor HER activities, the former being significantly more active than the latter due to its higher metallic conductivity. Interestingly, combining these two elements to make the VB2 phase results in significantly higher activity for both the bulk and nanomaterials, even though the far less active boron is the major component. This behavior is reminiscent of that found in the Mo-B system, where an increase in HER activity was found as boron content increased in the order Mo2B, MoB and MoB2.5 Theoretical calculations revealed that only boron-containing layers in MoB2 were highly active, findings which were confirmed by the above theoretical results on VB2 as well. As in MoB2,6 nano-VB2 is more active than bulkVB2 with a polarization curve showing an overpotential of 192 mV at 10 mA/cm2 current density, which is much lower than for the bulk (348 mV) and it is comparable to nanoMoB26 (154 mV, Figure S7). Also, nano-VB2 can reach higher current density than bulkVB2 (Figure S8). This finding suggests that the density of active sites in nano-VB2 is much higher than in bulk-VB2. Indeed, the electrochemical surface area (ECSA) which was evaluated using electrochemical double layer capacitance (Cdl), indicates that nano-VB2 has a 2.6-times higher Cdl value (Figure 4b) than bulk-VB2 (3.1 mF/cm2) (Figure S9). Using the ECSA to normalize the current density of both nano-VB2 and bulk-VB2 leads to the same conclusion of higher activity for nano-VB2, as shown in Figure S9. Figure 4c shows the Tafel plots of nano-VB2 and bulk-VB2, which provide further insights into the HER reaction mechanism on the catalyst surfaces. Pt has a lower Tafel slope value of ~31 mV/dec suggesting the Tafel reaction (Tafel slope ~30 mV/dec) as the rate determining step (RDS), which is in good agreement with values obtained in a previous work. The nano-VB2 catalyst yields a Tafel slope of ~68 mV/dec which is smaller than that of bulk-VB2 (~126 mV/dec), thus indicating a faster increase of HER rate with increasing overpotential.28 However, the obtained Tafel slope values of nano-VB2 do not match any of the known ideal Tafel slopes, the closest being that of the Heyrovsky 9 ACS Paragon Plus Environment


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reaction mechanism (Tafel slope 40 mV/dec). In the case of bulk-VB2 the reaction mechanism seems to be controlled by the Volmer mechanism (Tafel slope ~120 mV/dec). A similarly high Tafel slope value was found for bulk-MoS2 with less active edge sites.10, 29-30

The main reason for high Tafel slopes is the limited accessibility to the active sites

on these bulk samples by protons in solution. The electrocatalytic stability of nano-VB2 nanoparticles was measured through CV experiments up to 2000 cycles, as presented in Figure 4d. The overpotential required to reach the current density of 10 mA/cm2 for nanoVB2 at 2000th cycle is about 210 mV, which is ~91% retention from its initial value indicating good stability of the nano-VB2 catalyst in acidic conditions. The long-term durability of nano-VB2 was also studied by chronoamperometry (CA) measurement over 12h and found that the current density decreases only ~6.5% from its initial value, which might be due to the physical separation of electrode material from the substrate. (Figure S10).


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Figure 4. (a) Polarization curves of nano-VB2 in 0.5 M H2SO4 electrolyte at a scan rate of 1 mV/s compared with curves for bulk-VB2, commercial 5%Pt/C, vanadium, elemental boron and carbon sheet; (b) CV curves of nano-VB2 at different scan rates from 40 to 120 mV/s. Inset: The capacitive current at 0.15 V as a function of the scan rate for nano-VB2; (c) Tafel plots of nano-VB2 and bulk-VB2; and (d) Electrochemical stability curves of nanoVB2 of the first and the 2000th cycle. Turnover frequency (TOF), which is defined as the number of hydrogen molecules evolved per second per active site, was used to determine the inherent HER activity of nano-VB2 and bulk-VB2 to better compare them and other reported catalysts. The number of active sites for calculation inferred from ECSA and details are provided in the supporting information. The calculated TOF of nano-VB2 at an overpotential 100 mV is 11 ACS Paragon Plus Environment


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0.02 H2 s-1, which is 4 times higher than that of bulk-VB2 (0.005 H2 s-1) further indicating that nanoscale VB2 provides more active sites to HER. Even though the TOF value of nano-VB2 is much lower than that of the best HER nanoboride catalyst to date, FeB2 (0.165 H2 s-1), it is in the same order of magnitude as nano-Fe2B (0.034 H2 s-1) and many recently reported binary non‐noble phosphides electrocatalysts.8 In conclusion, DFT calculations were used to predict that the B-terminated (graphene like boron layer) {001} and the mixed V/B {101} surfaces of AlB2-type VB2 are highly active for HER and their performances are comparable to similar surfaces in MoB2. Our experimental results on bulk- and nano-VB2 confirm and extend this theoretical prediction, as the HER activity of VB2 also significantly increases at the nanoscale. Nano-VB2 demonstrates comparable HER performance like nano-MoB2. Because of the abundance of vanadium compared to molybdenum (two order magnitude), nano-VB2 is considered as one of the best non-noble metal HER catalyst candidates. ASSOCIATED CONTENT Supporting Information Available: Full experimental and computational details, synthetic and electrochemical procedures, physio- and electro-chemical characterization of bulk-VB2 and applied DFT calculations on different VB2 surfaces. Acknowledgments We thank UC Riverside (startup fund to BPTF) for financial support. We acknowledge the San Diego Supercomputer Center (SDSC) and the High-Performance Computing Center (HPCC) at UC Riverside for providing computing resources. The XPS data were collected with an instrument acquired through the NSF MRI program (DMR-0958796).


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References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

13. 14. 15. 16. 17.

Li, X. M.; Hao, X. G.; Abudula, A.; Guan, G. Q. Nanostructured catalysts for electrochemical water splitting: current state and prospects. J. Mater. Chem. A 2016, 4, 11973-12000. Roger, I.; Shipman, M. A.; Symes, M. D. Earth-abundant catalysts for electrochemical and photoelectrochemical water splitting. Nature Reviews Chemistry 2017, 1, 0003. Zou, X.; Zhang, Y. Noble metal-free hydrogen evolution catalysts for water splitting. Chem. Soc. Rev. 2015, 44, 5148-5180. Gao, G.; O’Mullane, A. P.; Du, A. 2D MXenes: A New Family of Promising Catalysts for the Hydrogen Evolution Reaction. ACS Catal. 2017, 7, 494-500. Park, H.; Encinas, A.; Scheifers, J. P.; Zhang, Y.; Fokwa, B. P. T. Boron-Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction. Angew.Chem. 2017, 129, 5667-5578. Jothi, P. R.; Zhang, Y.; Scheifers, J. P.; Park, H.; Fokwa, B. P. T. Molybdenum diboride nanoparticles as a highly efficient electrocatalyst for the hydrogen evolution reaction. Sustainable Energy Fuels 2017, 1, 1928-1934. Park, H.; Zhang, Y.; Scheifers, J. P.; Jothi, P. R.; Encinas, A.; Fokwa, B. P. T. Graphene- and Phosphorene-like Boron Layers with Contrasting Activities in Highly Active Mo2B4 for Hydrogen Evolution. J. Am. Chem. Soc. 2017, 139, 12915-12918. Li, H.; Wen, P.; Li, Q.; Dun, C.; Xing, J.; Lu, C.; Adhikari, S.; Jiang, L.; Carroll, D. L.; Geyer, S. M. Earth_Abundant Iron Diboride (FeB2) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Energy Mater. 2017, 7, 1700513. Chen, Y.; Yu, G.; Chen, W.; Liu, Y.; Li, G. D.; Zhu, P.; Tao, Q.; Li, Q.; Liu, J.; Shen, X.; Li, H.; Huang, X.; Wang, D.; Asefa, T.; Zou, X. Highly Active, Nonprecious Electrocatalyst Comprising Borophene Subunits for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2017, 139, 12370. Jaramillo, T. F.; Jørgensen, K. P.; Bonde, J.; Nielsen, J. H.; Horch, S.; Chorkendorff, I. Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts. Science 2007, 317, 100-102. Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 2013, 13, 6222-6227. Li, H.; Tsai, C.; Koh, A. L.; Cai, L.; Contryman, A. W.; Fragapane, A. H.; Zhao, J.; Han, H. S.; Manoharan, H. C.; Abild-Pedersen, F.; Nørskov, J. K.; Zheng, X. Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies. Nature Materials 2015, 15, 48-53. Biroju, R. K.; Das, D.; Sharma, R.; Pal, S.; Mawlong, L. P. L.; Bhorkar, K.; Giri, P. K.; Singh, A. K.; Narayanan, T. N. Hydrogen Evolution Reaction Activity of Graphene–MoS2 van der Waals Heterostructures. ACS Energy Lett. 2017, 2, 1355-1361. Ouyang, Y.; Ling, C.; Chen, Q.; Wang, Z.; Shi, L.; Wang, J. Activating Inert Basal Planes of MoS2 for Hydrogen Evolution Reaction through the Formation of Different Intrinsic Defects. Chem. Mater. 2016, 28, 4390-4396. Qu, Y.; Shao, M.; Shao, Y.; Yang, M.; Xu, J.; Kwok, C. T.; Shi, X.; Lu, Z.; Pan, H. Ultra-high electrocatalytic activity of VS2 nanoflowers for efficient hydrogen evolution reaction. J. Mater. Chem. A, 2017, 5, 15080-15086. An, Y.-R.; Fan, X.-L.; Luo, Z.-F.; Lau, W.-M. Nanopolygons of Monolayer MS2: Best Morphology and Size for HER Catalysis. Nano Lett. 2017, 17, 368-376. Zhang, J.; Zhang, C.; Wang, Z.; Zhu, J.; Wen, Z.; Zhao, X.; Zhang, X.; Xu, J.; Lu, Z. Synergistic Interlayer and Defect Engineering in VS2 Nanosheets toward Efficient Electrocatalytic Hydrogen Evolution Reaction. Small 2018, 14, 1703098, 1-10.



18. 19. 20. 21. 22.

23. 24. 25. 26. 27. 28. 29. 30.

Page 14 of 15

Vrubel, H.; Hu, X. Molybdenum Boride and Carbide Catalyze Hydrogen Evolution in both Acidic and Basic Solutions. Angew.Chem. 2012, 124, 12875-12878. Masa, J.; Weide, P.; Peeters, D.; Sinev, I.; Xia, W.; Sun, Z.; Somsen, C.; Muhler, M.; Schuhmann, W. Amorphous Cobalt Boride (Co2B) as a Highly Efficient Nonprecious Catalyst for Electrochemical Water Splitting: Oxygen and Hydrogen Evolution. Adv. Energy Mater. 2016, 6, 1502313. Hammer, B.; Hansen, L. B.; Nørskov, J. K. Improved adsorption energetics within densityfunctional theory using revised Perdew-Burke-Ernzerhof functionals. Phys. Rev. B 1999, 59, 74137421. Xiao, P.; Sk, M. A.; Thia, L.; Ge, X.; Lim, R. J.; Wang, J.-Y.; Lim, K. H.; Wang, X. Molybdenum phosphide as an efficient electrocatalyst for the hydrogen evolution reaction. Energy Environ. Sci. 2014, 7, 2624-2629. Skúlason, E.; Tripkovic, V.; Björketun, M. E.; Gudmundsdóttir, S.; Karlberg, G.; Rossmeisl, J.; Bligaard, T.; Jónsson, H.; Nørskov, J. K. Modeling the Electrochemical Hydrogen Oxidation and Evolution Reactions on the Basis of Density Functional Theory Calculations. J. Phys. Chem. C 2010, 114, 18182-18197. Jothi, P. R.; Yubuta, K.; Fokwa, B. P. T. A Simple, General Synthetic Route toward Nanoscale Transition Metal Borides. Adv. Mater. 2018, 1704181, 1-6. Terlan, B.; Levin, A. A.; Börrnert, F.; Simon, F.; Oschatz, M.; Schmidt, M.; Cardoso-Gil, R.; Lorenz, T.; Baburin, I. A.; Joswig, J.-O.; Eychmüller, A. Effect of Surface Properties on the Microstructure, Thermal, and Colloidal Stability of VB2 Nanoparticles. Chem. Mater. 2015, 27, 5106-5115. Silversmit, G.; Depla, D.; Poelman, H.; Marin, G. B.; De Gryse, R. Determination of the V2p XPS binding energies for different vanadium oxidation states (V5+ to V0+). Journal of Electron Spectroscopy and Related Phenomena 2004, 135, 167-175. Yajun, W.; Michael, T. Surface Chemistry of Boron Oxidation. 2. The Reactions of B2O2 and B2O3 with Boron Films Grown on Ta(110). Chem. Mater. 1993, 5, 199-205. Stuart, J.; Hohenadel, A.; Li, X.; Xiao, H.; Parkey, J.; Rhodes, C. P.; Licht, S. The Net Discharge Mechanism of the VB2/Air Battery. Journal of The Electrochemical Society 2015, 162, A192-A197. Daniel, M.; Xile, H. Recent developments of molybdenum and tungsten sulfides as hydrogen evolution catalysts. Energy Environ. Sci. 2011, 4, 3878-3888. 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, 16632-16638. Benson, J.; Li, M.; Wang, S.; Wang, P.; Papakonstantinou, P. Electrocatalytic Hydrogen Evolution Reaction on Edges of a Few Layer Molybdenum Disulfide Nanodots. ACS Appl. Mater. Interfaces 2015, 7, 14113-14122.


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Abundant Vanadium Diboride with Graphene-like Boron layers for

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