One-Step Hydrothermal Synthesis of Phase-Engineered MoS2/MoO3 Electrocatalysts for Hydrogen Evolution Reaction

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.