No abstract

Nano-structured molybdenum disulfide (MoS2) catalysts have been extensively developed for the hydrogen evolution reaction (HER). Herein, a novel hydrothermal intercalation approach is employed to fabricate nanoflower-like 2H-MoS2 with the incorporation of three polymers, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylenimine (PEI). The as-prepared MoS2 specimens were characterized by techniques of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), together with Raman and Fourier transform infrared spectroscopy (FTIR). The HER properties of these lamellar nanoflower-like composites were evaluated using electrochemical tests of linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The existent polymer enlarges the interlayer spacing of the lamellar MoS2, and reduces its stacked thickness. The lamellar MoS2 samples exhibit a promoting activity in HER at low additions of these three polymers (0.04 g/g MoS2 for PVA and PEI, and 0.08 g/g MoS2 for PVP). This can be attributed to the fact that the expanded interlayer of MoS2 can offer abundant exposed active sites for HER. Conversely, high additions of the polymers exert an obvious interference in the HER activity of the lamellar MoS2. Compared with the samples of MoS2/PVP-0.08 and MoS2/PEI-0.04, the MoS2/PVA-0.04 composite exhibits excellent activity in HER, in terms of higher current density and lower onset potential. OPEN ACCESSMetals 2015, 5 1830

Abstract:The hydrogen evolution reaction (HER) property of molybdenum disulfide (MoS 2 ) is undesirable because of the insufficient active edge sites and the poor conductivity. To enhance HER performance of MoS 2 , nickel phosphide (Ni 2 P) was combined with this catalyst and three MoS 2 /Ni 2 P hybrids (38 wt % Ni 2 P addition for MoS 2 /Ni 2 P-38, 50 wt % Ni 2 P addition for MoS 2 /Ni 2 P-50, and 58 wt % Ni 2 P addition for MoS 2 /Ni 2 P-58) were fabricated via a hydrothermal synthesis process. Morphologies, crystallinities, chemical components, specific surface areas, and HER properties of the fabricated MoS 2 /Ni 2 P samples in an alkaline electrolyte were characterized and tested. In addition, the insight into the HER properties of as-prepared catalysts were revealed by the density functional theory (DFT) calculation. Additionally, the stabilities of pure MoS 2 , Ni 2 P, and MoS 2 /Ni 2 P-50 samples were evaluated. The results show that the addition of Ni 2 P can enhance the HER property of the MoS 2 catalyst. Although HER properties of the above-mentioned three MoS 2 /Ni 2 P hybrids are inferior to that of pure Ni 2 P, they are much higher than that of MoS 2 . Among as-prepared three hybrids, MoS 2 /Ni 2 P-50 exhibits the best HER performance, which may be due to its uniform morphology, large specific surface area, and excellent stability. The MoS 2 /Ni 2 P-50 hybrid shows a high cathodic current density (70 mA/cm 2 at −0.48 V), small Tafel slope (~58 mV/decade), and a low charge transfer resistance (0.83 kΩ·cm 2 ).

Molybdenum disulfide (MoS 2 ) is unfavorable for practical application in the hydrogen evolution reaction (HER) process due to its inert basal surface, inferior conductivity, and limited amount of active edge sites. For the purpose of enhancing the HER performance of this catalyst, the HER activity of its basal surface should be increased. Herein, three types of nickel-phosphorus (Ni-P) coatings-namely, low phosphorus (LP), medium phosphorus (MP) and high phosphorus (HP) -were anchored onto the surfaces of MoS 2 nanoparticles via an electroless plating process; thus, three Ni-P/MoS 2 composites (Ni-LP/MoS 2 , Ni-MP/MoS 2 , and Ni-HP/MoS 2 ) were fabricated. Crystal structures, morphologies, chemical components, and HER performances of each in an alkaline solution were characterized. Both Ni-LP/MoS 2 and Ni-MP/MoS 2 showed a crystal nature, while the amorphous feature for Ni-HP/MoS 2 was validated. The three Ni-P/MoS 2 composites exhibited a higher HER activity than the pure MoS 2 . The HER performance of the Ni-MP/MoS 2 composite was more outstanding than those of other two composites, which could be attributed to the presence of metastable nickel phosphides, and the excellent conductivity of Ni-MP coating anchored on the basal surface of MoS 2 .