English

• Hydrogen energy has aroused tremendous attention in face of the depletion of fossil fuels because of its cleanness and high energy density [1-4]. High purity hydrogen can be produced by electrochemical water splitting, which is constitutive of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The HER process is highly dependent on the electrocatalyst to overcome the inherent thermodynamic overpotential and increase the energy conversion efficiency. Up to now, Platinum (Pt)-based materials have been universally regarded as the most active catalysts for HER. However, the exceeding insufficiency of Pt resources has rapidly elevated its price, which limits its large-scale application. An alternative way to lower the cost of catalysts is to reduce the use of Pt in the catalysts. For example, loading Pt on the support can improve the dispersion and the utilization of particles by exposing more active sites. Nowadays, the most commonly used support of Pt-based catalyst are carbon-based materials, which possess excellent electrical conductivity as well as large specific surface area. Nevertheless, the weak interaction between carbon and Pt easily lead to the agglomeration or shedding of catalyst particles in operating conditions, resulting in reduced catalytic service life [5]. A desirable catalyst support not only need excellent conductivity, superior physicochemical stability and low cost, but also requires strong interaction between catalyst and support. Therefore, it is necessary to explore new supports with stronger interaction with catalyst to achieve better stability [6-8].

  Metal oxide is a promising substitute for the carbon-based support owing to its low cost, nontoxicity, excellent mechanical strength and chemical stability. To date, several transition metal oxides (including TiO₂ [9], CeO₂ [10], WO_x [11], SnO₂ [12]) have been developed as alternative supports in electrochemical reactions, especially for TiO₂, which have attracted enormous attentions. It has been reported that TiO₂ can generate strong metal to support interaction (SMSI) with the supported metal catalyst [13, 14]. The SMSI induced charge transfer effect enhances the interaction between the metal and support [15, 16]. However, there are several obstacles hindering the application of TiO₂ support in electrocatalytic system. Most importantly, TiO₂ is a typical semiconductor material with a high band gap [17, 18], however, its inherent low conductivity severely limits its application as an electrocatalyst support. To address these issues, there are some traditional methods including metal atom doping, partial reduction of Ti into Magnéli phase [19, 20] or composite with conductive materials [21-24]. Heteroatom doping is a facile and effective method to improve the conductivity. Researchers have reported such materials including doped elements such as Nb [25, 26], Mo [27], W [28], Ru [29], Ta [30], etc. Recently, Tsai [31] and co-workers reported Mo-doped titanium dioxide as the support for Pt nanoparticles which exhibited enhanced mass activity and stability for the oxygen reduction reaction. The electron transfer from the Mo-doped titanium dioxide to Pt induced by SMSI could be explained for the improved catalytic performance.

  The hydrogen spillover effect has also been reported to enhance the HER performance [11, 32-34], and it is very common in supported metal nanoparticles where the absorbed H atom migrate from the surface of strong binding sites (metal) to that of weak binding sites (support). A study on single atom Pt supported on WO_3-x (Pt SA/WO_3-x) showed that the hydrogen spillover effect between the tungsten oxide and Pt enhanced the HER catalytic activity [11]. In this case, hydrogen insertion/extraction behavior would be expedited due to the rapid re-exposure of the Pt surface. Under the circumstance, we intend to explore the possibility of applying TiO₂-based materials as HER catalyst support. Besides, there are rare reports about TiO₂-based supports applied in HER [35].

  Herein, molybdenum-doped titanium oxide (Ti_0.9Mo_0.1O₂) has been prepared as support to anchor Pt nanoparticles with low metal loading of 5 wt%. Spectroscopy characterization confirms the SMSI effect between the catalyst and support. Combining with hydrogen spillover effect, the Pt/Ti_0.9Mo_0.1O₂ catalyst exhibits 4.4 times higher mass activity and more excellent durability over 10, 000 cycles than 20% Pt/C catalyst. The SMSI between the Pt and the Ti_0.9Mo_0.1O₂ enhance the dispersion of the catalyst particles, the hydrogen spillover effect make it faster for the re-exposure of the active surface of Pt, thus improving the utilization of the Pt and achieving excellent stability.

  Fig. 1a shows the X-ray diffraction (XRD) patterns of Pt/Ti_0.9Mo_0.1O₂, Ti_0.9Mo_0.1O₂ and TiO₂. The Ti_0.9Mo_0.1O₂ support exhibits amorphous structure while the TiO₂ prepared with similar methods exhibits the crystal structure of anatase titanium dioxide (PDF card 01-071-1167). No signal corresponding to the phase of Mo metal/oxides were observed due to the low content of Mo. As shown in Fig. S1 (Supporting information), the Pt/Ti_xMo_1-xO₂ with different Mo content and Pt/MoO₂ exhibits similar crystal structure with amorphous support, demonstrating that the structure transformation of TiO₂ is possibly due to the Mo doping. After the deposition of Pt, the Pt/Ti_0.9Mo_0.1O₂ exhibits typical diffraction peaks centered at 39.6°, 46.1°, 67.2° and 80.9°, which are assigned to the (111), (200), (220), (311) plane for face-center cubic Pt (PDF card 01-087-0640), indicating the successful loading of Pt onto the amorphous Ti_0.9Mo_0.1O₂.

  Figure 1

  

  Figure 1.  (a) XRD patterns of Pt/Ti_0.9Mo_0.1O₂, Ti_0.9Mo_0.1O₂ and TiO₂. (b) Raman spectra of Pt/Ti_0.9Mo_0.1O₂, Ti_0.9Mo_0.1O₂ and Pt/TiO₂ composite. Inset: the magnification of the selected area.

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  Raman spectroscopy was conducted to reveal the structure of catalysts as shown in Fig. 1b. All the catalysts exhibit the same peaks located at 150 cm⁻¹ (E_g), 396 cm⁻¹ (B_1g), 636 cm⁻¹ (E_g), suggesting the existence of TiO₂. An additional peak located at 993 cm⁻¹ was observed in both the Pt/Ti_0.9Mo_0.1O₂ and Ti_0.9Mo_0.1O₂, which is attributed to the stretching vibration of Mo=O for molybdenum oxide [31]. This result further demonstrate the successful doping of Mo into TiO₂. From the inset in Fig. 1b, the peaks at 150 cm⁻¹ for Pt/Ti_0.9Mo_0.1O₂ are obviously shifted to higher Raman shift after anchoring Pt onto the Ti_0.9Mo_0.1O₂ support, which verifies the interaction between Ti_0.9Mo_0.1O₂ support and Pt. And two obvious peaks at around 1350 cm⁻¹ and 1580 cm⁻¹ are characteristic for the D-band and G-band of carbon materials, respectively. The existence of carbon in Ti_0.9Mo_0.1O₂ is due to the carbonization of glycerate formed in solvothermal process. As a matter of fact, the residual carbon in Ti_0.9Mo_0.1O₂ support is beneficial for the conductivity of the catalyst.

  The morphology of the synthesized Ti_0.9Mo_0.1O₂ and Pt/Ti_0.9Mo_0.1O₂ was examined by scanning electron microscopy (SEM) in Fig. S2 (Supporting information). The Ti_0.9Mo_0.1O₂ shows a spherical structure with a diameter of 800 nm approximately, and the structure of Pt/Ti_0.9Mo_0.1O₂ was nearly identical to the Ti_0.9Mo_0.1O₂ after 5% Pt was loaded on the support (Fig. 2a). To get a better view of the dispersion of the Pt particles, the transmission electron microscopy (TEM) in association with energy-dispersive X-ray spectroscopy (EDS) was employed. Fig. 2b presents a high resolution TEM (HRTEM) image of Pt/Ti_0.9Mo_0.1O₂, in which Pt nanoparticles about 2−3 nm were well dispersed on the support. The obvious lattice fringe with a spacing of 0.23 nm was measured as shown in the inset of Fig. 2b, which was corresponding to the (111) plane of the Pt. The homogeneous distribution of Pt, Ti, Mo and O species further proved the well dispersion of the Pt catalyst as shown by EDS mapping in Figs. 2c-h.

  Figure 2

  

  Figure 2.  (a) TEM images of Ti_0.9Mo_0.1O₂ and (b) HRTEM images of Pt/Ti_0.9Mo_0.1O₂, inset: the magnification of the selected area in yellow circle. (c–h) Elemental mapping of Pt/Ti_0.9Mo_0.1O₂.

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  X-ray photoelectron spectroscopy (XPS) was further carried out to evaluate the electronic interaction between Pt and Ti_0.9Mo_0.1O₂. The survey spectrum of Pt/Ti_0.9Mo_0.1O₂ was shown in Fig. S3a (Supporting information), which proved the existence of Pt, Ti, Mo, O, and C elements, and this result was consistent with the EDS analysis. The high-resolution Mo 3d spectrum (Fig. S3b in Supporting information) can be deconvoluted into four peaks, which are attributed to Mo⁴⁺ and Mo⁶⁺, respectively. As shown in Fig. 3a, the Ti 2p spectrum shows doublet peaks at 458.8 and 464.6 eV, demonstrating the existence state of Ti⁴⁺ in the catalyst. An obvious positive shift of Ti⁴⁺ 2p_3/2 orbitals was observed towards higher binding energy relative to that of Ti_0.9Mo_0.1O₂, which is possibly due to the electronic interaction between Pt and Ti_0.9Mo_0.1O₂. Fig. 3b presents the Pt 4f core level spectra of Pt/Ti_0.9Mo_0.1O₂ and Pt/C. The two main peaks located at binding energy of 71.1 eV and 74.4 eV can be attributed to the 4f_7/2 and 4f_5/2 orbitals of Pt⁰, respectively. Indeed, the existence of Pt²⁺ and Pt⁴⁺ species in both Pt/Ti_0.9Mo_0.1O₂ and Pt/C is due to the inevitable oxidation of Pt when exposed to air. The binding energy for Pt⁰ 4f_7/2 exhibits 0.25 eV lower relative to that of Pt/C, indicating electron donation from the Ti_0.9Mo_0.1O₂ to Pt. It is suggested that the interaction between the Ti_0.9Mo_0.1O₂ support and Pt obviously changed the electronic structure of Pt, which is possibly beneficial to the catalytic performance [35, 36].

  Figure 3

  

  Figure 3.  (a) Ti 2p and (b) Pt 4f high-resolution XPS spectra of the Pt/Ti_0.9Mo_0.1O₂ catalyst.

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  To investigate the electrocatalytic performance of these catalysts towards HER, the electrochemical characterizations were performed in 0.5 mol/L H₂SO₄. Pt/TiO₂, homemade 5% and 20% Pt/C were also performed for comparison. It can be observed in Fig. S4 (Supporting information) that the Pt/TiO₂ exhibits much lower current density because of its low electric conductivity. However, the Pt/Ti_0.9Mo_0.1O₂ shows a greater current density as a result of improved conductivity by Mo doping. The current improvement phenomenon can also be observed when compared with Pt/MoO₂ in Fig. S5a (Supporting information), which is assigned to weaker interaction between Pt and MoO₂. Furthermore, both 5% Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C show small overpotentials (26 mV and 29 mV, respectively) in the polarization curves as shown in Fig. 4a, indicating all these catalysts are highly efficient for HER. Normalized to the Pt loading, the calculated mass specific activity was compared at different over-potentials in Fig. 4b. The mass activity of 1.72 A/mg_Pt for 5% Pt/Ti_0.9Mo_0.1O₂ at an overpotential of 50 mV is 4.4-fold higher than that of 20% Pt/C (0.39 A/mg_Pt). It could be inferred that Pt/Ti_0.9Mo_0.1O₂ exhibits a better Pt utilization than Pt/C, which could effectively decrease the catalyst cost. The Tafel slope for the Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C were calculated in Fig. 4c with close values (36 mV/dec and 30 mV/dec, respectively), illustrating a similar reaction mechanism.

  Figure 4

  

  Figure 4.  (a) HER polarization curves for Pt/Ti_0.9Mo_0.1O₂, 20% Pt/C and Pt/TiO₂ in 0.5 mol/L H₂SO₄. Scan rate: 5 mV/s and rotating rate: 1600 rpm. (b) Comparison of the mass specific activities of Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C at various overpotentials. (c) Corresponding Tafel plots of polarization curves. (d) The polarization curves for Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C before and after the stability test. Inset: The mass specific activities of Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C before and after the stability test at an overpotential of 50 mV.

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  Cyclic voltammetry (CV) tests were performed in 0.5 mol/L H₂SO₄ solution. Obvious redox peaks between 0.44 V and 0.62 V can be shown in the CV profiles of Pt/Ti_xMo_1-xO₂ in Fig. S6a (Supporting information). These peaks are attributed to the formation of hydrogen molybdenum bronzes [37, 38]. It is known to all that MoO_y could absorb the hydrogen and forms H_xMoO_y [19] in the presence of noble metals. The CV of Pt/Ti_0.9Mo_0.1O₂ in Fig. S4 (Supporting information) did not show these peaks because the Mo content is too low in the catalyst to show this characteristic. This revealed that the Ti_0.9Mo_0.1O₂ support is electrochemical inert under the operating condition. This results can be further proved by the comparison in Fig. S6b (Supporting information), the Pt/Ti_0.9Mo_0.1O₂ exhibited the best HER performance among the catalyst with different Mo content.

  The durability of the Pt/Ti_0.9Mo_0.1O₂ catalyst was evaluated via the accelerated degradation tests (ADT) by applying 10, 000 continuous cyclic voltammetry cycles between −0.15 V and 0.4 V (vs. RHE) at a scan rate of 100 mV/s. It can be observed in Fig. 4d that the polarization curve of Pt/Ti_0.9Mo_0.1O₂ after the ADT was almost the same with the fresh catalyst, only 7.8% current density loss was seen compared with the initial value at an overpotential of 50 mV vs. RHE (inset in Fig. 4d). However, the Pt/C suffered from 33.8% current density loss, which demonstrated excellent durability of the Pt/Ti_0.9Mo_0.1O₂ catalyst. The SMSI between the Ti_0.9Mo_0.1O₂ support and Pt attributed to the enhanced stability as the particle migration and agglomeration were inhibited during the cycling test.

  To better understand the performance of the catalysts, the turn over frequency (TOF) were also calculated, which is particular illustrated in Supporting information. Fig. 5a shows the TOF values of 5% Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C along with other recently reported HER catalysts. The TOF values of Pt/Ti_0.9Mo_0.1O₂ at 50 mV and 100 mV were 1.70 H₂/s and 3.98 H₂/s. It is obvious that Pt/Ti_0.9Mo_0.1O₂ exhibited greater TOF values than Pt/C and most of other catalyst at various overpotential. Moreover, the overpotential at 10 mA/cm² of 5% Pt/Ti_0.9Mo_0.1O₂, 20% Pt/C, 5% Pt/C and other recently reported noble metal HER catalyst were summarized in Table S1 (Supporting information). To achieve 10 mA/cm² current density, the 5% Pt/Ti_0.9Mo_0.1O₂ requires only 26 mV overpotential as shown in Fig. 5b. These results imply the excellent performance of Pt/Ti_0.9Mo_0.1O₂ with smaller overpotential compared with majority of the reported noble metal based HER catalyst.

  Figure 5

  

  Figure 5.  Comparison of (a) TOF and (b) overpotentials at 10 mA/cm² of 20% Pt/C and Pt/Ti_0.9Mo_0.1O₂ with several HER electrocatalysts in recent literatures in 0.5 mol/L H₂SO₄.

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  To understand the improvement of catalytic performance, we proposed a reaction mechanism based on the hydrogen spillover effect [33] (Fig. 6), where the adsorbed H atom on the surface of Pt may easily migrate to Ti_0.9Mo_0.1O₂. It consists of three steps: (i) A hydronium ion adsorbs on the Pt surface combines an electron to form an adsorbed H atom; (ii) the neutral adsorbed-H atom migrates to the Ti_0.9Mo_0.1O₂ surface due to the spillover effect; and (iii) such H atom combines another hydronium ion and an electron to release hydrogen gas. The whole HER process may be described as following equation. It was reported that hydrogen insertion/extraction behavior is likely to be accelerated through the hydrogen spillover effect [11], the adsorption of H atom is completed on Pt surface with stronger adsorption capacity while desorption process is achieved on Ti_0.9Mo_0.1O₂ surface with stronger desorption capacity, which is beneficial for the HER process (reactions 1-3).

  (1)

  (2)

  (3)

  Figure 6

  

  Figure 6.  The schematic illustration of the HER mechanism on Pt/Ti_0.9Mo_0.1O₂ catalyst.

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  In summary, we have synthesized Mo-doped titanium oxide (Ti_0.9Mo_0.1O₂) as support for Pt nanoparticles. It is convincing that the Ti_0.9Mo_0.1O₂ support effectively improves the durability of the catalyst owing to the strong interaction between support and Pt. As expected, such catalyst delivers remarkable HER activity with only 26 mV overpotential, moreover, it shows 4.4 times higher mass activity than Pt/C at an overpotential of 50 mV. The excellent performance of Pt/Ti_0.9Mo_0.1O₂ is ascribed to the SMSI effect and the hydrogen spillover effect. The SMSI effect regulates the electronic structure of the Pt and the hydrogen spillover effect accelerates the hydrogen evolution process. This work is anticipated to provide a new idea to apply this support effect to electrocatalytic systems.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  Acknowledgments

  This work was supported by the National Natural Science Foundation of China (No. 91963109) and the Innovation Research Funds of Huazhong University of Science and Technology (No. 2017KFYXJJ164). The authors thank the Analytical and Testing Center of HUST for its help and allowing the use of facilities for XRD, SEM and TEM.

  Appendix A. Supplementary data

  Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.cclet.2020.05.030.

  
  ^* Corresponding author.
  E-mail address: wangdl81125@hust.edu.cn (D. Wang).
  
• 1. [1]

     G.W. Crabtree, M.S. Dresselhaus, M.V. Buchanan, Phys. Today 57 (2004) 39-44. doi: 10.1063/1.1878333

  2. [2]

     M.S. Dresselhaus, I.L. Thomas, Nature 414 (2001) 332-337. doi: 10.1038/35104599

  3. [3]

     J.A. Turner, Science 305 (2004) 972-974. doi: 10.1126/science.1103197

  4. [4]

     T. Huang, T. Shen, M.X. Gong, et al., Chin. J. Catal. 40 (2019) 1867-1873. doi: 10.1016/S1872-2067(19)63331-0

  5. [5]

     X.X. Chen, X.J. Zhen, H.Y. Gong, et al., Chin. Chem. Lett. 30 (2019) 681-685. doi: 10.1016/j.cclet.2018.09.017

  6. [6]

     Q.B. Liu, L. Du, G.T. Fu, et al., Adv. Energy Mater. 9 (2018) 1803040.

  7. [7]

     C. Cui, R.F. Cheng, C. Zhang, et al., Chin. Chem. Lett. 31 (2020) 988-991. doi: 10.1016/j.cclet.2019.08.026

  8. [8]

     D. Zhou, B. Jiang, R. Yang, et al., Chin. Chem. Lett. 31 (2020) 1540-1544. doi: 10.1016/j.cclet.2019.11.014

  9. [9]

     S. Nong, W. Dong, J. Yin, et al., J. Am. Chem. Soc. 140 (2018) 5719-5727. doi: 10.1021/jacs.7b13736

  10. [10]

      L. Nie, D.H. Mei, H.F. Xiong, et al., Science 358 (2017) 1419-1423. doi: 10.1126/science.aao2109

  11. [11]

      J. Park, S. Lee, H.E. Kim, et al., Angew. Chem. Int. Ed. 131 (2019) 16184-16188. doi: 10.1002/ange.201908122

  12. [12]

      J.M. Kim, Y.J. Lee, S.H. Kim, et al., Nano Energy 65 (2019) 104008. doi: 10.1016/j.nanoen.2019.104008

  13. [13]

      H. Li, X.F. Weng, Z.Y. Tang, et al., ACS Catal. 8 (2018) 10156-10163. doi: 10.1021/acscatal.8b02883

  14. [14]

      J. Li, H. Zhou, H. Zhuo, et al., J. Mater. Chem. A 6 (2018) 2264-2272. doi: 10.1039/C7TA09831F

  15. [15]

      J.H. Kim, S. Chang, Y.T. Kim, Appl. Catal. B: Environ. 158-159 (2014) 112-118. doi: 10.1016/j.apcatb.2014.04.003

  16. [16]

      Y. Ji, Y.I. Cho, Y. Jeon, et al., Appl. Catal. B: Environ. 204 (2017) 421-429. doi: 10.1016/j.apcatb.2016.11.053

  17. [17]

      U. Caudillo-Flores, M.J. Muñoz-Batista, M. Fernández-García, et al., Appl. Catal. B: Environ. 238 (2018) 533-545. doi: 10.1016/j.apcatb.2018.07.047

  18. [18]

      L.P. Qin, G.J. Wang, Y.W. Tan, Sci. Rep. 8 (2018) 16198. doi: 10.1038/s41598-018-33795-z

  19. [19]

      R.A.M. Esfahani, S.K. Vankova, A.H.A.M. Videla, et al., Appl. Catal. B: Environ. 201 (2017) 419-429. doi: 10.1016/j.apcatb.2016.08.041

  20. [20]

      A.D. Duma, Y.C. Wu, W.N. Su, et al., ChemCatChem 10 (2018) 1155-1165. doi: 10.1002/cctc.201701503

  21. [21]

      Y. Jeon, Y. Ji, Y.I. Cho, et al., ACS Nano 12 (2018) 6819-6829. doi: 10.1021/acsnano.8b02040

  22. [22]

      J.Y. Wang, M. Xu, J.Q. Zhao, et al., Appl. Catal. B: Environ. 237 (2018) 228-236. doi: 10.1016/j.apcatb.2018.05.085

  23. [23]

      B.Y. Xia, S.J. Ding, H.B. Wu, et al., RSC Adv. 2 (2012) 792-796. doi: 10.1039/C1RA00587A

  24. [24]

      B.Y. Xia, B. Wang, H.B. Wu, et al., J. Mater. Chem. 22 (2012) 16499-16505. doi: 10.1039/c2jm32816j

  25. [25]

      K.W. Park, K.S. Seol, Electrochem. Commun. 9 (2007) 2256-2260. doi: 10.1016/j.elecom.2007.06.027

  26. [26]

      R.V. Genova-Koleva, F. Alcaide, G. Álvarez, et al., J. Energy Chem. 34 (2019) 227-239. doi: 10.1016/j.jechem.2019.03.008

  27. [27]

      R.A.M. Esfahani, L.M.R. Gavidia, G. García, et al., Renew. Energy 120 (2018) 209-219. doi: 10.1016/j.renene.2017.12.077

  28. [28]

      D.L. Wang, C.V. Subban, H.S. Wang, et al., J. Am. Chem. Soc. 132 (2010) 10218-10220. doi: 10.1021/ja102931d

  29. [29]

      V.T. Thanh Ho, K.C. Pillai, H.L. Chou, et al., Energy Environ. Sci. 4 (2011) 4194-4200. doi: 10.1039/c1ee01522b

  30. [30]

      M.T. Anwar, X.H. Yan, S.Y. Shen, et al., Int. J. Hydrogen Energy 42 (2017) 30750-30759. doi: 10.1016/j.ijhydene.2017.10.152

  31. [31]

      M.C. Tsai, T.T. Nguyen, N.G. Akalework, et al., ACS Catal. 6 (2016) 6551-6559. doi: 10.1021/acscatal.6b00600

  32. [32]

      J.J. Li, Q.Q. Guan, H. Wu, et al., J. Am. Chem. Soc. 141 (2019) 14515-14519. doi: 10.1021/jacs.9b06482

  33. [33]

      Y.F. Cheng, S.K. Lu, F. Liao, et al., Adv. Funct. Mater. 27 (2017) 1700359. doi: 10.1002/adfm.201700359

  34. [34]

      N. Doudin, S.F. Yuk, M.D. Marcinkowski, et al., ACS Catal. 9 (2019) 7876-7887. doi: 10.1021/acscatal.9b01425

  35. [35]

      X. Cheng, Y.H. Li, L.R. Zheng, et al., Energy Environ. Sci. 10 (2017) 2450-2458. doi: 10.1039/C7EE02537H

  36. [36]

      R.A.M. Esfahani, I.I. Ebralidze, S. Specchia, et al., J. Mater. Chem. A 6 (2018) 14805-14815. doi: 10.1039/C8TA02470G

  37. [37]

      P.A. Zosimova, A.V. Smirnov, S.N. Nesterenko, et al., J. Phys. Chem. C 111 (2007) 14790-14798. doi: 10.1021/jp073410j

  38. [38]

      P. Justin, G. Ranga Rao, Int. J. Hydrogen Energy 36 (2011) 5875-5884. doi: 10.1016/j.ijhydene.2011.01.122

• 

  Figure 1  (a) XRD patterns of Pt/Ti_0.9Mo_0.1O₂, Ti_0.9Mo_0.1O₂ and TiO₂. (b) Raman spectra of Pt/Ti_0.9Mo_0.1O₂, Ti_0.9Mo_0.1O₂ and Pt/TiO₂ composite. Inset: the magnification of the selected area.

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  Figure 2  (a) TEM images of Ti_0.9Mo_0.1O₂ and (b) HRTEM images of Pt/Ti_0.9Mo_0.1O₂, inset: the magnification of the selected area in yellow circle. (c–h) Elemental mapping of Pt/Ti_0.9Mo_0.1O₂.

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  Figure 3  (a) Ti 2p and (b) Pt 4f high-resolution XPS spectra of the Pt/Ti_0.9Mo_0.1O₂ catalyst.

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  Figure 4  (a) HER polarization curves for Pt/Ti_0.9Mo_0.1O₂, 20% Pt/C and Pt/TiO₂ in 0.5 mol/L H₂SO₄. Scan rate: 5 mV/s and rotating rate: 1600 rpm. (b) Comparison of the mass specific activities of Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C at various overpotentials. (c) Corresponding Tafel plots of polarization curves. (d) The polarization curves for Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C before and after the stability test. Inset: The mass specific activities of Pt/Ti_0.9Mo_0.1O₂ and 20% Pt/C before and after the stability test at an overpotential of 50 mV.

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  Figure 5  Comparison of (a) TOF and (b) overpotentials at 10 mA/cm² of 20% Pt/C and Pt/Ti_0.9Mo_0.1O₂ with several HER electrocatalysts in recent literatures in 0.5 mol/L H₂SO₄.

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  Figure 6  The schematic illustration of the HER mechanism on Pt/Ti_0.9Mo_0.1O₂ catalyst.

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•