Targeted Assembly of Ultrathin NiO/MoS2 Electrodes for Electrocatalytic Hydrogen Evolution in Alkaline Electrolyte

Abstract

The development of non-noble metal catalysts for hydrogen revolution in alkaline media is highly desirable, but remains a great challenge. Herein, synergetic ultrathin NiO/MoS2 catalysts were prepared to improve the sluggish water dissociation step for HER in alkaline conditions. With traditional electrode assembly methods, MoS2:NiO-3:1 exhibited the best catalytic performance; an overpotential of 158 mV was required to achieve a current density of 10 mA/cm2. Further, a synergetic ultrathin NiO/MoS2/nickel foam (NF) electrode was assembled by electrophoretic deposition (EPD) and post-processing reactions. The electrode displayed higher electrocatalytic ability and stability, and an overpotential of only 121 mV was needed to achieve a current density of 10 mA/cm2. The improvement was ascribed to the better catalytic environment, rather than a larger active surface area, a higher density of exposed active sites or other factors. DFT calculations indicated that the hybrid NiO/MoS2 heterostuctured interface is advantageous for the enhanced water dissociation step and the corresponding lower kinetic energy barrier—from 1.53 to 0.81 eV.

Synthesis of molybdenum disulfide for the hydrogen evolution reaction electrocatalysts activity by electrochemical method

“…Similarly, the lowest point of the overpotential value at 10 mA/cm 2 reached 144 mV at current density i= 2.5 mA/cm 2 . In general, the sample at current density i =2.5 mA/cm 2 displayed the highest HER activity; moreover, the corresponding Tafel slope and overpotential value were smaller than the results of many previous public papers such as MO3-MoS2 hybrid nanospheres (200 mV and 74 mV/dec) [26], amorphous MoSx film (211 mV and 55 mV/dec) [19], N doped MoS2 (232 mV and 127 mV/dec) [30], NiS@MoS2 core-shell microspheres (208 mV and 62.4 mV/dec) [31], MoSx/V2O3 (145 mV and 45 mV/dec) [34] (it can be observed more information on table 3).…”

Co3O4-MoSe2@C nanocomposite as a multi-functional catalyst for electrochemical water splitting and lithium-oxygen battery

“…For the HER, the overpotentials of C, MoSe 2 @C and CMC-3 are 667 mV, 186 mV and 144 mV at the current density of 10 mA cm −2 , respectively (figure 3(a)). Even at higher current densities of 100 and 300 mA cm −2 , the CMC-3 features low overpotentials of only 245 mV and 268 mV, respectively, which are superior to those of Mo-based catalysts reported before [45][46][47][48]. Compared to C and MoSe 2 @C, it also shows a much smaller Tafel slope of 95.5 mV dec −1 , which suggests that the Volmer-Heyrovsky mechanism predominates the process of the HER catalyzed by the CMC (figure 3(b)) [49].…”

Plasmon–Exciton Coupling-Assisted Efficient Overall Water Splitting in Alkaline Medium Using a Plexcitonic NiO/Ni Foam Catalyst

“…31,32 Doping or heterostructure engineering with suitable low-barrier water adsorption/dissociation components can be performed to activate the alkaline HER activity of MoS 2 . 22,30,33,34 Past studies have shown that the kinetic energy barrier for water dissociation is effectively reduced by the incorporation of Ni sites into MoS 2 (ΔG Hd 2 O = 0.66 eV for the Ni−MoS 2 system, 29 0.81 eV for the NiO−MoS 2 system, 35 and 0.05 eV for the Ni(OH) 2 /MoS 2 system 30 ). There are also reports that suggest that the combining of Ni-based catalysts with MoS 2 significantly improves the hydrogen adsorption/desorption process (at the Mo and S edge sites) with more near to zero ΔG H* values (−0.06 eV) for Ni−MoS 2 and Ni(OH) 2 /MoS 2 systems.…”

“…The hydrogen adsorption free energy (Δ G H* ) values are reported to be −0.25 to −0.36 eV for the Mo and S edge sites of MoS 2 . , Despite the great HER activity in acidic solutions, MoS 2 nanosheets are HER inactive in alkaline medium due to unfavorable (high barrier) water dissociation on the surface. The kinetic energy barrier of the initial water dissociation step (Δ G H 2 O ) on MoS 2 is reported to be high up to 1.17 eV. , The unfavorable charge interactions and unsuitable orbital orientation are reported to be the major reasons for the unfavorable water adsorption and dissociation characteristics of MoS 2 . , Doping or heterostructure engineering with suitable low-barrier water adsorption/dissociation components can be performed to activate the alkaline HER activity of MoS 2 . ,,, Past studies have shown that the kinetic energy barrier for water dissociation is effectively reduced by the incorporation of Ni sites into MoS 2 (Δ G H 2 O = 0.66 eV for the Ni–MoS 2 system, 0.81 eV for the NiO–MoS 2 system, and 0.05 eV for the Ni­(OH) 2 /MoS 2 system). There are also reports that suggest that the combining of Ni-based catalysts with MoS 2 significantly improves the hydrogen adsorption/desorption process (at the Mo and S edge sites) with more near to zero Δ G H* values (−0.06 eV) for Ni–MoS 2 and Ni­(OH) 2 /MoS 2 systems. , Further, the introduction of plasmonic Au nanoparticles on MoS 2 nanosheets effectively increases the number of active hydrogen adsorption/desorption sites with more optimal (near-zero) Δ G H* values to improve the HER activity. − Taken together, we have developed a plasmonic–excitonic Au–MoS 2 /NiO/Ni foam catalyst through a simple in situ strategy to achieve both the favorable hydrogen adsorption and low-barrier water dissociation sites for exhibiting highly active alkaline HER.…”