Interfacial Mo-N-C Bond Endowed Hydrogen Evolution Reaction on MoSe2@N-Doped Carbon Hollow Nanoflowers

In Situ Carbon-Confined MoSe2 Catalyst with Heterojunction for Highly Selective CO2 Hydrogenation to Methanol

The synthesis of methanol from CO2 hydrogenation is an effective measure to deal with global climate change and an important route for the chemical fixation of CO2. In this work, carbon-confined MoSe2 (MoSe2@C) catalysts were prepared by in situ pyrolysis using glucose as a carbon source. The physico-chemical properties and catalytic performance of CO2 hydrogenation to yield methanol were compared with MoSe2 and MoSe2/C. The results of the structure characterization showed MoSe2 displayed few layers and a small particle size. Owing to the synergistic effect of the Mo2C-MoSe2 heterojunction and in situ carbon doping, MoSe2@C with a suitable C/Mo mole ratio in the precursor showed excellent catalytic performance in the synthesis of methanol from CO2 hydrogenation. Under the optimal catalyst MoSe2@C-55, the selectivity of methanol reached 93.7% at a 9.7% conversion of CO2 under optimized reaction conditions, and its catalytic performance was maintained without deactivation during a continuous reaction of 100 h. In situ diffuse infrared Fourier transform spectroscopy studies suggested that formate and CO were the key intermediates in CO2 hydrogenation to methanol.

Interfacial Chemical Bond Engineering in a Direct Z-Scheme g-C3N4/MoS2 Heterojunction

The Z-scheme heterojunction shows great potential in photocatalysis due to its superior carrier separation efficiency and strong photoredox properties. However, how to regulate the charge separation at the nanometric interface of heterostructures still remains a challenge. Here, we take g-C₃N₄ and MoS₂ as models and design the Mo-N chemical bond, which connects exactly the CB of MoS₂ and VB of g-C₃N₄. Thus, the Mo-N bond could act as an atomic-level interfacial "bridge" that provides a direct migration path of charge carriers between g-C₃N₄ and MoS₂. Experiments confirmed that the Mo-N bond and the internal electric field promote greatly the photogenerated carrier separation. The optimized photocatalyst exhibits a high hydrogen evolution rate that is about 19.6 times that of the pristine bulk C₃N₄. This study demonstrates the key role of an atomic-level interfacial chemical bond design in heterojunctions and provides a new idea for the design of efficient catalytic heterojunctions.

Cu-Mo Bimetal Modulated Multifunctional Carbon Nanofibers Promoting the Polysulfides Conversion for High-Sulfur-Loading Lithium-Sulfur Batteries

High sulfur loading is essential for achieving high energy density lithium-sulfur (Li-S) batteries. However, serious issues such as low sulfur utilization, poor cycling stability, and sluggish rate performance have been exposed when increasing the sulfur loading for freestanding cathodes. To solve these problems, the adsorption/catalytic ability of high-sulfur-loading cathode toward polysulfides must be improved. Herein, based on excellent properties of cationic MOFs, we proposed that Cu-Mo bimetallic nanoparticles embedded in multifunctional freestanding nitrogen-doped porous carbon nanofibers (Cu-Mo@NPCN) with efficient catalytic sites could be prepared by facile MoO₄^2- anion exchange of cationic MOFs. And, the sulfur embedded in Cu-Mo@NPCN was directly used as self-supporting electrodes, enabling a high areal capacity, good rate performance, and decent cycling stability even under high sulfur loading. The freestanding Cu-Mo@NPCN/10.3S cathode achieves a high volumetric capacity of 1163 mA h cm^-3 and a decent areal capacity of 9.3 mA h cm^-2 at 0.2 C with a sulfur loading of 10.3 mg cm^-2. This work provides an innovative approach for engineering a freestanding sulfur cathode and would forward the development of cationic MOF-derived bimetallic catalysts in various energy storage systems.

Interlayer Spacing Regulation of Molybdenum Selenide Promotes Electrocatalytic Hydrogen Evolution in Alkaline Media

The construction of heterostructures is a versatile tactic to enhance catalytic activity. However, it is still elusive to realize the modulation of the interlayer spacing in this way to further improve the performance. Here, strong interfacial coupling between CoSe₂ and MoSe₂ by constructing CoSe₂ /MoSe₂ heterostructures is achieved. The interlayer spacing of MoSe₂ is compressed by 0.3 Å. The enhanced charge transfer is validated by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. Coupled with the morphology of hollow microtubes, which can facilitate the exposure of active sites, CoSe₂ /MoSe₂ heterostructures reported here exhibit high activity (119 mV at 10 mA cm^-2 ) and excellent stability with small degradation after 50 h operation, surpassing other analogous powdered electrocatalysts. This work sheds light on the importance of tuning the interlayer spacing to improve electrocatalytic activity.

Graphitic Carbon Cloth-Based Hybrid Molecular Catalyst: A Non-conventional, Synthetic Strategy of the Drop Casting Method for a Stable and Bifunctional Electrocatalyst for Enhanced Hydrogen and Oxygen Evolution Reactions

Hydrogen energy production through water electrolysis is envisaged as one of the most promising, sustainable, and viable alternate sources to cater to the incessant demands of renewable energy storage. Germane to our effort in this field, we report easily synthesizable and very cost-effective isoperthiocyanic acid (IPA) molecular complexes as electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under acidic and alkaline conditions. The Pd(II)IPA, Co(II)IPA, and Ni(II)IPA complexes were synthesized and were evaluated for HER and OER applications. These complexes when embedded onto graphitized carbon cloth (GrCC) exhibited a significant enhancement in the HER activity in contrast to their pristine counterparts. The hybrid electrocatalyst Pd(II)IPA among the three showed an extremely low overpotential of 94.1 mV to achieve a current density of 10 mA cm-2, while Co(II)IPA and Ni(II)IPA complexes showed overpotentials of 367 and 394 mV, respectively, to achieve a current density of 10 mA cm-2. These complexes on carbon cloth showed decreased charge transfer resistance compared to that of pristine metal complexes. The enhanced catalytic activity of the complexes on carbon cloth can be attributed to the porous and conducting nature of the graphitized carbon cloth. For OER activity, the Pd(II)IPA complex showed an excellent performance with an overpotential value of 210 mV, while Co(II)IPA and Ni(II)IPA exhibited overpotentials of 400 and 270 mV, respectively, to drive a current density of 10 mA cm-2 in 0.1 M KOH. This work further widens the scope and application of molecular complexes in combination with an excellent carbon support for renewable energy storage applications.