Porous Cobalt Sulfide Selenium Nanorods for Electrochemical Hydrogen Evolution.

A key process in electrochemical energy technology is hydrogen evolution reaction (HER). However, its electrochemical properties mainly depend on the catalytic activity of the material itself. Therefore, it is important to find efficient electrocatalysts to realize clean hydrogen production. As a typical kind of catalytic materials, transition metal dichalcogenides (TMCs) play important roles in the field of energy catalysis. As a representative of TMCs, cobalt disulfide (CoS2), recently has raised much research interest owing to its abundant reserves, environmental friendliness, and excellent electrochemical stability. Meanwhile, given the fact that doping is one of the effective methods to improve the electrochemical catalytic property, various means of doping have been researched. Here, we report for the first time that porous-like Se-CoS2-x (or Se:CoS2-x ) nanorod can be facilely synthesized via a controllable two-step strategy. It is demonstrated that doping Se can greatly improve the catalytic performance of CoS2 electrode. The electrode can obtain a current density of 10 mA cm-2 at overpotential of only ∼260 mV. And the current changes with the applied bias voltage in an obvious stepped pattern, in the chronopotential (CP) curve of Se-CoS2-x , indicating its outstanding mass transfer property and mechanical stability.

Interface engineering of cobalt-sulfide-selenium core-shell nanostructures as bifunctional electrocatalysts toward overall water splitting.

The number of active sites and stability of the structure of electrocatalysts are the key factors in the process of overall water splitting. In this paper, cobalt-sulfide-selenium (Se:CoS2-x) core-shell nanostructures are prepared by a simple two-step method, including hydrothermal reaction and chemical vapor deposition. The resulting product exhibits excellent electrochemical performance, owing to the synergistic effects between CoS2 and CoSe1-x, as well as the plentiful active sites in the electrode structure. The Se:CoS2-x material shows a more improved hydrogen evolution reaction activity compared to CoS2 and Co(OH)Cl precursor catalysts, with a low overpotential of only 240 mV achieved at 10 mA cm-2. Meanwhile, Se:CoS2-x as a bifunctional water splitting catalyst also shows remarkably improved oxygen evolution reaction activity, with a low overpotential of only 1.32 V at 10 mA cm-2. The above results show that selenide/sulfide materials provide a new research direction for discovering high-performance and cheap electrode materials.

Composition and Interface Engineering of Alloyed MoS2 x Se2(1- x ) Nanotubes for Enhanced Hydrogen Evolution Reaction Activity.

Hierarchical MoS2 x Se2(1- x ) nanotubes assembled from several-layered nanosheets featuring tunable chalcogen compositions, expanded interlayer spacing and carbon modification, are synthesized for enhanced electrocatalytic hydrogen evolution reaction (HER). The chalcogen compositions of the MoS2 x Se2(1- x ) nanotubes are controllable by adjusting the selenization temperature and duration while the expanded (002) interlayer spacing varies from 0.98 to 0.68 nm. It is found that the MoS2 x Se2(1- x ) (x = 0.54) nanotubes with expanded interlayer spacing of 0.98 nm exhibit the highest electrocatalytic HER activity with a low onset potential of 101 mV and a Tafel slope of 55 mV dec(-1) . The improved electrocatalytic performance is attributed to the chalcogen composition tuning and the interlayer distance expansion to achieve benefitting hydrogen adsorption energy. The present work suggests a potential way to design advanced HER electrocatalysts through modulating their compositions and interlayer distances.

In Situ Carbon-Doped Mo(Se0.85 S0.15 )2 Hierarchical Nanotubes as Stable Anodes for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are promising energy storage devices, but suffer from poor cycling stability and low rate capability. In this work, carbon doped Mo(Se0.85 S0.15 )2 (i.e., Mo(Se0.85 S0.15 )2 :C) hierarchical nanotubes have been synthesized for the first time and serve as a robust and high-performance anode material. The hierarchical nanotubes with diameters of 300 nm and wall thicknesses of 50 nm consist of numerous 2D layered nanosheets, and can act as a robust host for sodiation/desodiation cycling. The Mo(Se0.85 S0.15 )2 :C hierarchical nanotubes deliver a discharge capacity of 360 mAh g(-1) at a high current density of 2000 mA g(-1) and keep a 81.8% capacity retention compared to that at a current density of 50 mA g(-1) , showing superior rate capability. Comparing with the second cycle discharge capacities, the nanotube anode can maintain capacities of 102.2%, 101.9%, and 97.8% after 100 cycles at current densities of 200, 500, and 1000 mA g(-1) , respectively. This work demonstrates the best cycling performance and high-rate sodium storage capabilities of MoSe2 for SIBs to date. The hollow interior, hierarchical organization, layered structure, and carbon doping are beneficial for fast Na(+) -ion and electron kinetics and are responsible for the stable cycling performance and high rate capabilities.