High Turnover Frequency of Hydrogen Evolution Reaction on Amorphous MoS₂ Thin Film Directly Grown by Atomic Layer Deposition

Abstract

Recently amorphous MoS2 thin film has attracted great attention as an emerging material for electrochemical hydrogen evolution reaction (HER) catalyst. Here we prepare the amorphous MoS2 catalyst on Au by atomic layer deposition (ALD) using molybdenum hexacarbonyl (Mo(CO)6) and dimethyl disulfide (CH3S2CH3) as Mo and S precursors, respectively. Each active site of the amorphous MoS2 film effectively catalyzes the HER with an excellent turnover frequency of 3 H2/s at 0.215 V versus the reversible hydrogen electrode (RHE). The Tafel slope (47 mV/dec) on the amorphous film suggests the Volmer-Heyrovsky mechanism as a major pathway for the HER in which a primary discharging step (Volmer reaction) for hydrogen adsorption is followed by the rate-determining electrochemical desorption of hydrogen gas (Heyrovsky reaction). In addition, the amorphous MoS2 thin film is electrically evaluated to be rather conductive (0.22 Ω(-1) cm(-1) at room temperature) with a low activation energy of 0.027 eV. It is one of origins for the high catalytic activity of the amorphous MoS2 catalyst.

Atomic Layer Deposition of Crystalline MoS2 Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

“…Increasing the MoCl 5 dose decreased the film thickness close to the precursor inlet, which hints toward etching of the deposited film by MoCl 5 . Later, we also found that Mo(CO) 6 , the other molybdenum precursor used for ALD of MoS 2 , [47][48][49][50][51][52] suffered from heavy precursor decomposition in our reactor already at 110 °C. This was avoided by lowering the temperature below 100 °C, but no film deposition was found in this case.…”

“…[34,36,37] Other bottom-up techniques used for the deposition of thin MoS 2 films include sputtering, [40] physical vapor transport, [41] pulsed laser deposition, [42] and atomic layer deposition (ALD). [43][44][45][46][47][48][49][50][51][52] Atomic layer deposition is an inherently scalable technique that can be regarded as an advanced modification of CVD. It is based on self-limiting surface reactions of vapor-phase precursors that are alternately pulsed to substrates.…”

“…[53][54][55] So far, ALD of MoS 2 has been reported using MoCl 5 with H 2 S, [43][44][45][46] as well as Mo(CO) 6 with H 2 S, [47,52] H 2 S plasma, [48] or dimethyl disulfide. [49][50][51] The films deposited with Mo(CO) 6 have mostly been amorphous due to the low deposition temperatures of 100-200 °C, [47,[49][50][51] although the films deposited with H 2 S plasma were polycrystalline. [48] Using MoCl 5 and H 2 S, crystalline MoS 2 films have been deposited by ALD, [43][44][45][46] but a postdeposition annealing [43,46] or high deposition temperatures in excess of 500 °C [45] have still been required, in most cases, to obtain films of sufficient quality.…”

Solvent-Assisted Oxygen Incorporation of Vertically Aligned MoS2 Ultrathin Nanosheets Decorated on Reduced Graphene Oxide for Improved Electrocatalytic Hydrogen Evolution

“…6,21,54 We then further compared the Turnover frequency (TOF) of different catalysts, which is an effective way to determine the active sites of the catalyst 10,16 ( Figure S11 for more information). The calculated TOF for OMoS 2 /rGO catalyst is 1.74, 5.15, and 7.37 s −1 at the overpotential of 220, 300, and 350 mV, respectively, which is much higher than those of our prepared O-MoS 2 (3.24 s −1 at η = 300 mV) and pristine MoS 2 /rGO (1.47 s −1 at η = 300 mV) catalysts (Table S1) and those of MoS 2 -based catalysts, such as defect-rich ultrathin MoS 2 nanosheets 4 (0.70 s −1 at η = 300 mV), amorphous MoS 2 films (0.80 s −1 at η = 220 mV) 51 and 3D MoS 2 nanospheres (0.89 s −1 at η = 350 mV). 57 Although pristine MoS 2 /rGO has lower TOF than O-MoS 2 , it exhibits better catalytic ability ( Figure 6) due to the various exposed vertically aligned edges.…”

Top‐Down Integration of Molybdenum Disulfide Transistors with Wafer‐Scale Uniformity and Layer Controllability

“…[1][2][3][4] MoS 2 is an attractive and most widely studied TMDC due to its unique properties. [5][6][7] Layered MoS 2 consists of a vertical stack of 0.65 nm thick single layers, which are held together by van der Waals inter actions. Few layer MoS 2 exhibits a band gap ranging from 1.2 to 1.9 eV depending on its thickness, which is favorable prepare high quality large area TMDCs with excellent con tinuity.…”