Molten salt electrolysis synthesis of NbS2@MoS2 and its performance for water splitting into hydrogen
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摘要: 电解水制氢(HER)相比于传统的制氢方式具有更广阔的研究前景,但由于其动力学过程缓慢,因此价格低廉且高效的电催化剂在HER中尤为重要。通过一步熔盐电解法制备了具有纳米花和纳米片形貌的NbS2@MoS2。采用XRD、SEM、HRTEM、XPS、SAED等手段表征催化剂的物理化学特性。结果表明,NbS2@MoS2纳米花催化剂表现出薄膜花状结构的多晶态,Nb元素均匀分布在MoS2表面。通过电化学测试来验证其HER性能,测试结果表明纳米花结构在HER中表现出优异的电催化性能,在1 mol/L KOH溶液中,电流密度10.0 mA·cm−2下其过电位为292.9 mV,塔菲尔斜率为107.0 mV·dec−1,电荷传递阻抗为31.0 Ω,电化学活性表面积为13.7 mF·cm−2。并且经过20 h催化后仍能保持较好的电催化活性。Nb沉积在MoS2表面形成缺陷,同时在表面形成NbS2,提供了更多的活性位点,从而进一步增强了水分解性能。高温熔盐电结晶为催化材料的合成提供了一种新方法。Abstract: The hydrogen evolution reaction (HER) has broader research prospects than traditional hydrogen production methods, but because of its slow kinetics, low-cost and high-efficiency electrocatalysts have become parti-cularly important in HER. NbS2@MoS2 with the morphology of nanoflowers and nanosheets was prepared by one-step molten salt electrolysis. Using XRD, SEM, TEM, XPS, SAED and other methods to characterize the physical and chemical properties of the electrocatalysts. The results show that the NbS2@MoS2 nanoflower catalyst exhibits a polycrystalline state with a thin and film flower-like structure, and the Nb elements are uniformly distributed on the surface of MoS2. The HER performance is verified by electrochemical tests. The test results show that the nanoflower structure shows excellent electrocatalytic performance in HER. In a 1 mol/L KOH solution, the overpotential is 292.9 mV at a current density of 10.0 mA·cm−2, and the Tafel slope is 107.0 mV·dec−1, the charge transfer impe-dance is 31.0 Ω, and the electrochemically active surface area is 13.7 mF·cm−2. And after 20 h of catalysis, it can still maintain good electrocatalytic activity. Nb deposition forms defects on the surface of MoS2, and at the same time forms NbS2 on the surface, which provides more active sites and improves water splitting performance. High-temperature molten salt electrocrystallization provides a new method for the synthesis of catalytic materials.
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图 2 873.0 K时LiCl-KCl-Nb3Cl8体系下Mo电极上循环伏安(CV)曲线 (a) 和方波伏安(SWV)曲线 (b)
Figure 2. Cyclic voltammetry (CV) curves (a) and square wave voltammetry (SWV) curve (b) on Mo electrode at 873.0 K in the LiCl-KCl-Nb3Cl8 system
D′—Li oxidation peak; D—Li reduction peak; A′, B′, C′—Nb oxidation peak; A, B, C—Nb reduction peak
图 4 NbS2@MoS2纳米花 (a)、NbS2@MoS2纳米片 (b) 的SEM图像;NbS2@MoS2纳米花 (c)、NbS2@MoS2纳米片 (d) 的EDS图像;NbS2@MoS2纳米花 (e)、NbS2@MoS2纳米片 (f) 的元素分布图像
Figure 4. SEM images of NbS2@MoS2 nanoflowers (a) and NbS2@MoS2 nanosheets (b); EDS images of NbS2@MoS2 nanoflowers (c) and NbS2@MoS2 nanosheets (d); Elemental mapping images of NbS2@MoS2 nanoflowers (e) and NbS2@MoS2 nanosheets (f)
图 5 NbS2@MoS2纳米花TEM图像 (a)、选区电子衍射图像(SAED) (b)、HRTEM图像 (c) 和矩形区域A中的快速傅里叶变换(FFTs)和逆傅里叶变换图像(IFFTs) (d)
Figure 5. TEM images (a), selected area electron diffraction (SAED) pattern (b), HRTEM images (c), fast fourier transform (FFTs) and inverse fast fourier transform (IFFTs) of rectangle “A” (d) of NbS2@MoS2 nanoflowers
图 10 MoS2纳米花、MoS2纳米片、NbS2@MoS2纳米花、NbS2@MoS2纳米片和铂电解水制氢(HER)性能:(a)极化曲线;(b) 极化曲线对应的塔菲尔斜率;(c) 在200 mV过电位下交流阻抗图;(d) 不同电流密度与扫描速率下的双电层电容(Cdl);(e) NbS2@MoS2纳米花初始极化曲线和循环1000圈后的极化曲线;(f) NbS2@MoS2纳米花在−20.0 mA·cm−2和−100.0 mA·cm−2恒电流密度下分别持续10 h的恒电位曲线
Figure 10. Hydrogen evolution reaction (HER) performance of MoS2 nanoflowers, MoS2 nanosheets, NbS2@MoS2 nanoflowers, NbS2@MoS2 nanosheets and Pt: (a) LSV curves; (b) Polarization curves derived Tafel slopes for corresponding electrocatalysts; (c) Nyquist plots of corresponding electrocatalysts at the overpotential of 200 mV; (d) Difference in current density plotted against the scan rate for the determination of the double-layer capacitance (Cdl); (e) LSV curves of the NbS2@MoS2 nanoflowers for the initial and 1000 cycles; (f) Chronopotentiostatic curves of NbS2@MoS2 nanosheets at a constant current density of −20.0 mA·cm−2 for 10 h and −100.0 mA·cm−2 for another 10 h
Rs—Solution resistance; Rct—Contact resistance; Cdl—Double-layer capacitance; RHE—Reversible hydrogen electrode
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