Dongman Hou

Three-Dimensional Hierarchical Frameworks Based on MoS2 Nanosheets Self-Assembled on Graphene Oxide for Efficient Electrocatalytic Hydrogen Evolution

Advanced materials for electrocatalytic water splitting are central to renewable energy research. In this work, three-dimensional (3D) hierarchical frameworks based on the self-assembly of MoS2 nanosheets on graphene oxide were produced via a simple one-step hydrothermal process. The structures of the resulting 3D frameworks were characterized by using a variety of microscopic and spectroscopic tools, including scanning and transmission electron microscopies, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman scattering. Importantly, the three-dimensional MoS2/graphene frameworks might be used directly as working electrodes which exhibited apparent and stable electrocatalytic activity in hydrogen evolution reaction (HER), as manifested by a large cathodic current density with a small overpotential of -107 mV (-121 mV when loaded on a glassy-carbon electrode) and a Tafel slope of 86.3 mV/dec (46.3 mV/dec when loaded on a glassy-carbon electrode). The remarkable performance might be ascribed to the good mechanical strength and high electrical conductivity of the 3D frameworks for fast charge transport and collection, where graphene oxide provided abundant nucleation sites for MoS2 deposition and oxygen incorporation led to the formation of defect-rich MoS2 nanosheets with active sites for HER.

MoO2 nanobelts@nitrogen self-doped MoS2 nanosheets as effective electrocatalysts for hydrogen evolution reaction

Advanced materials for electrocatalytic water splitting are central to renewable energy research. In this study, MoO2 nanobelts@nitrogen self-doped MoS2 nanosheets are produced by nitridation and sulfuration treatments of MoO3 nanobelts. The material structures are characterized by a variety of techniques including scanning electron microscopy, transmission electron microscopy, Raman scattering, X-ray photoelectron spectroscopy, and X-ray diffraction spectroscopy. It is found that because of nitrogen doping and the abundance of exposed active edges, the heterostructures exhibit high electronic conductivity, and more importantly, enhanced and stable electrocatalytic activity in hydrogen evolution reaction (HER), as manifested in electrochemical studies. The onset potential is found to be only −156 mV (vs. RHE), which is 105 mV more positive than that of pure MoS2 under identical experimental conditions. The corresponding Tafel slope is estimated to be 47.5 mV dec−1, even slightly less than that of commercial 10 wt% Pt/C (49.8 mV dec−1), suggesting that the reaction dynamics is largely determined by the electrochemical desorption of hydrogen. This is accounted for by nitrogen doping that leads to an enhanced electronic conductivity of the heterostructures as well as a high density of spinning electron states around the N and Mo atoms in MoS2 nanosheets that are the active sites for HER, as manifested in density functional theory studies of a N-doped MoS2 monolayer.

MoS2 nanosheet-coated CoS2 nanowire arrays on carbon cloth as three-dimensional electrodes for efficient electrocatalytic hydrogen evolution

The design and engineering of low-cost and high-efficiency electrocatalysts for the hydrogen evolution reaction (HER) has attracted increasing interest in renewable energy research. Herein, MoS2 nanosheet-coated CoS2 nanowire arrays supported on carbon cloth (MoS2/CoS2/CC) were prepared by a two-step procedure that entailed the hydrothermal growth of Co(OH)2 nanowire arrays on carbon cloth followed by reaction with (NH4)2MoS4 to grow an overlayer of MoS2 nanosheets. Electrochemical studies showed that the obtained 3D electrode exhibited excellent HER activity with an overpotential of −87 mV at 10 mA cm−2, a small Tafel slope of 73.4 mV dec−1 and prominent electrochemical durability. The results presented herein may offer a new methodology for the design and engineering of effective multilevel structured catalysts for the HER based on earth-abundant components.

Flexible and porous catalyst electrodes constructed by Co nanoparticles@nitrogen-doped graphene films for highly efficient hydrogen evolution

The development of electrodes composed of non-noble-metal catalysts with both excellent activity and high stability for the hydrogen evolution reaction (HER) is essential for hydrogen production. In this work, a flexible and robust film electrode based on cobalt nanoparticles embedded into the interlamination of N-doped graphene film (Co@NGF) is fabricated by simple vacuum filtration combined with subsequently controlled calcination. This flexible three-dimensional (3D) nano-architecture film directly used as the electrode shows a low onset potential of only −14 mV (vs. RHE) with a small Tafel slope of 93.9 mV per dec for the HER in 0.5 M H2SO4. Stability tests through long term potential cycles and extended electrolysis confirm the perfect durability of Co@NGFs in acid media. The remarkable HER catalytic activity is derived from the electron penetration effect of cobalt nanoparticles as the core protected by N-doped graphene as the shell. It is worth noting that the Co@NGF electrodes, for the first time, used as both the anode and cathode in a two-electrode system open up new possibilities for exploring overall water splitting catalysts in an acid electrolyte. This development offers an attractive HER film electrode for large-scale water splitting technology.

Metal–Carbon Hybrid Electrocatalysts Derived from Ion‐Exchange Resin Containing Heavy Metals for Efficient Hydrogen Evolution Reaction

Transition metal-carbon hybrids have been proposed as efficient electrocatalysts for hydrogen evolution reaction (HER) in acidic media. Herein, effective HER electrocatalysts based on metal-carbon composites are prepared by controlled pyrolysis of resin containing a variety of heavy metals. For the first time, Cr2 O3 nanoparticles of 3-6 nm in diameter homogeneously dispersed in the resulting porous carbon framework (Cr-C hybrid) is synthesized as efficient HER electrocatalyst. Electrochemical measurements show that Cr-C hybrids display a high HER activity with an onset potential of -49 mV (vs reversible hydrogen electrode), a Tafel slope of 90 mV dec(-1) , a large catalytic current density of 10 mA cm(-2) at -123 mV, and the prominent electrochemical durability. X-ray photoelectron spectroscopic measurements confirm that electron transfer occurs from Cr2 O3 into carbon, which is consistent with the reported metal@carbon systems. The obtained correlation between metals and HER activities may be exploited as a rational guideline in the design and engineering of HER electrocatalysts.