Abstract
The development of suitable approaches for the synthesis of ultrathin transition-metal dichalcogenide (TMD) catalysts is required to engineer phases, intercoupling between different phases, in-plane defects, and edges and hence maximize their catalytic performance for hydrogen production. In this work, we report a simple one-step hydrothermal approach for the synthesis of a three-dimensional (3D) network of self-assembled metallic MoS2/MoO3 nanosheets, using α-MoO3 and thiourea (TU) as the Mo and S precursors, respectively. A systematic structural/property relationship study, while varying the precursors’ molar concentration ratios (TU/MoO3) and reaction temperatures (TR), revealed a kinetically controlled regime, in hydrothermal synthesis, that enabled the formation of ultrathin branched MoS2/MoO3 nanosheets with the highest metallic content of ∼47 % in a reproducible manner. Importantly, the work established that in addition to the rich metallic MoS2 phase (1T), the electronically coupled interfaces between MoO3 and MoS2 nanodomains, profusion of active sites, and tuned electrical conductivity significantly contributed to hydrogen evolution reaction (HER)-catalytic activity, affording a low overpotential of 210 mV (with respect to the reversible hydrogen electrode) at a current density of 10 mA/cm2, a small Tafel slope of ∼50 mV/dec, and high stability. Overall, this work demonstrated a controllable one-step hydrothermal method for the rational design and synthesis of a 3D network of MoS2/MoO3 nanosheets with high 1T-MoS2 metallic yield, simultaneous incorporation of MoO3/MoS2 heterointerfaces, sulfur vacancies, and tuned electrical conductivity, which are highly beneficial for clean energy conversion applications that can potentially be expanded to other two-dimensional TMD materials.
Highlights
Electrochemical generation of hydrogen (H2) is considered as a green and sustainable way for producing clean alternatives for fossil fuels
A detailed study has been carried out to explore the role of sulfur-to-molybdenum (S/Mo) molar ratio and reaction temperature (TR) on the formation of different phases (1T-MoS2, 2H-MoS2, and molybdenum oxide phases, denoted hereafter as Molybdenum Oxide Phases (MoOx)) and resultant hydrogen evolution reaction (HER) electrocatalytic activity in an aqueous acidic medium (0.5 M H2SO4)
We found that 3D networks of ultrathin nanosheets synthesized at a TU/MoO3 ratio of 2.5 and a TR of 200 °C exhibited the highest metallic 1T phase contribution of ∼47 %, which was directly connected to the best HER performance, reflected by a small overpotential at 10 mA/cm[2] (η10) of ∼210 mV and a small Tafel slope of ∼50 mV/dec in 0.5 M H2SO4
Summary
Electrochemical generation of hydrogen (H2) is considered as a green and sustainable way for producing clean alternatives for fossil fuels. Large-scale industrial application of water dissociation is highly dependent on the development of robust electrodes, loaded with active catalysts, that can provide large current densities at low potentials.[1] Pt-based catalysts are undoubtedly the most active for hydrogen evolution reaction (HER) and used as a benchmark; the high cost and scarcity of Pt have greatly impeded their widespread applications To this end, many efforts have been devoted to creating cheaper and earth-abundant alternatives. The 2H-MoS2 is the most stable but owing to limited unsaturated S active sites[9] located at its edges and inherently low electrical conductivity of the inactive semiconducting basal plane (S sites in the basal plane are inert), it provides a modest activity for electrochemically catalyzing the hydrogen production To this end, various efforts[6,10−13] have focused on creating catalytically active sites on the basal plane by introducing sulfur vacancies/ defects. This study provides new insights into rationally designing efficient electrocatalysts via appropriate modulation of phases and crystalline structures and integrating different functional active sites into material systems
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