Realizing the Synergy of Interface and Dual-Defect Engineering for Molybdenum Disulfide Enables Efficient Sodium-Ion Storage

Engineering-rich electrocatalyst defects play a critical role in greatly promoting the charge storage/transfer capability of an energy storage/conversion system. Here, an ingenious and effective two-step strategy was used to synthesize a bimetallic sulfide/oxide composite with a coaxial carbon coating, starting from mixing well-dispersed MoO3 nanobelts and Co-PAA compound, followed by a selective etching process. The simultaneous formation of dual defects of interlayer defect and sulfur-rich vacancies as well as MoO2/MoS2-x/CoS heterojunctions noticeably enhances both electron transfer and ion diffusion kinetics. The ultrathin carbon protective layer on the surface of the composite ensures its high conductivity and excellent structural stability. The composite electrode shows a high reversible capacity (158.3 mAh g-1 at 10 A g-1 after 4000 cycles) and outstanding long-cycle stability (0.04% per cycle over 2100 cycles at 20 A g-1). A full cell based on MoO2/MoS2-x/CoS@N, S-C anode, and Na3V2(PO4)3 cathode can maintain a reversible capacity of 128.1 mAh g-1 after 600 cycles at 1 A g-1, surpassing that based on MoO2/MoS2 and is very comparable in performance with the state-of-the-art Na-ion full cells. Moreover, density functional theory (DFT) calculations, electrochemical kinetics analysis, and in situ Raman and ex-situ X-ray diffraction characterization were carried out to elucidate the involved scientific mechanisms of sodium storage.

One Stone, Three-Birds Approach: Ultra-active Ru/N, S-MoO2/CNTs Electrocatalyst for Overall Water Splitting in Wide Electrode Applications (NF, GC, and CC)

The construction of exceptionally multifunctional electrocatalysts is essential for various applications, but it poses significant challenges. A novel electrocatalyst, denoted as Ru/N, S-MoO2/CNTs, was successfully synthesized using a combination of mechano-grinding and hydrothermal/calcination techniques. The Ru/N, S-MoO2/CNTs demonstrates ultrasmall overpotentials of 12 and 163 mV in NF, 51 and 167 mV in GCE, and 54 and 173 mV in CC for HER and OER, respectively, at a current density of 10 mA/cm2 in alkaline medium. To accomplish electrocatalytic OWS, a current density of 10 mA/cm2 can be obtained by using a cell voltage of 1.446 V. Theoretical studies demonstrated that the inclusion of Ru, N, and S triggers a change in the composition of MoO2; produces oxygen vacancies; and forms Ru, N, and S-oxygen-Mo catalytic centers. The combination of Ru, N, and S nanoclusters; Ru, N, and S-oxygen-Mo catalytic centers; and OVs-enriched MoO2 would position it among the top electrocatalysts.

In-Plane Mott-Schottky Effects Enabling Efficient Hydrogen Evolution from Mo5 N6 -MoS2 Heterojunction Nanosheets in Universal-pH Electrolytes

Cost-effective electrocatalysts for the hydrogen evolution reaction (HER) spanning a wide pH range are highly desirable but still challenging for hydrogen production via electrochemical water splitting. Herein, Mo₅ N₆ -MoS₂ heterojunction nanosheets prepared on hollow carbon nanoribbons (Mo₅ N₆ -MoS₂ /HCNRs) are designed as Mott-Schottky electrocatalysts for efficient pH-universal HER. The in-plane Mo₅ N₆ -MoS₂ Mott-Schottky heterointerface induces electron redistribution and a built-in electric field, which effectively activates the inert MoS₂ basal planes to intrinsically increase the electrocatalytic activity, improve electronic conductivity, and boost water dissociation activity. Moreover, the vertical Mo₅ N₆ -MoS₂ nanosheets provide more activated sites for the electrochemical reaction and facilitate mass/electrolyte transport, while the tightly coupled HCNRs substrate and metallic Mo₅ N₆ provide fast electron transfer paths. Consequently, the Mo₅ N₆ -MoS₂ /HCNRs electrocatalyst delivers excellent pH-universal HER performances exemplified by ultralow overpotentials of 57, 59, and 53 mV at a current density of 10 mA cm^-2 in acidic, neutral, and alkaline electrolytes with Tafel slopes of 38.4, 43.5, and 37.9 mV dec^-1 , respectively, which are superior to those of the reported MoS₂ -based catalysts and outperform Pt in overall water splitting. This work proposes a new strategy to construct an in-plane heterointerface on the nanoscale and provides fresh insights into the HER electrocatalytic mechanism of MoS₂ -based heterostructures.