Chemical grafting of Co9S8 onto C60 for hydrogen spillover and storage

Confined Space Dual-Type Quantum Dots for High-Rate Electrochemical Energy Storage

Owing to the quantum size effect and high redox activity, quantum dots (QDs) play very essential roles toward electrochemical energy storage. However, it is very difficult to obtain different types and uniformly dispersed high-active QDs in a stable conductive microenvironment, because QDs prepared by traditional methods are mostly dissolved in solution or loaded on the surface of other semiconductors. Herein, dual-type semiconductor QDs (Co9S8 and CdS) are skillfully constructed within the interlayer of ultrathin-layered double hydroxides. In particular, the expandable interlayer provides a very suitable confined space for the growth and uniform dispersion of QDs, where Co9S8 originates from in situ transformation of cobalt atoms in laminate and CdS is generated from interlayer pre-embedding Cd2+. Meanwhile, XAFS and GGA+U calculations are employed to explore and prove the mechanism of QDs formation and energy storage characteristics as compared to surface loading QDs. Significantly, the hybrid supercapacitors achieve a high energy density of 329.2 µWh cm-2, capacitance retention of 99.1%, and coulomb efficiency of 96.9% after 22 000 cycles, which is superior to the reported QDs-based supercapacitors. These findings provide unique insights for designing and developing stable, ordered, and highly active QDs.

Protonated g-C3N4 coated Co9S8 heterojunction for photocatalytic H2O2 production

Photocatalytic H₂O₂ production is an eco-friendly technique because only H₂O, molecular O₂ and light are involved. However, it still confronts the challenges of the unsatisfactory productivity of H₂O₂ and the dependence on organic electron donors or high purity O₂, which restrict the practical application. Herein, we construct a type-II heterojunction of the protonated g-C₃N₄ coated Co₉S₈ semiconductor for photocatalytic H₂O₂ production. The ultrathin g-C₃N₄ uniformly spreads on the surface of the dispersed Co₉S₈ nanosheets by a two-step method of protonation and dip-coating, and exhibits improved photogenerated electrons transportability and e^--h⁺ pairs separation ability. The photocatalytic system can achieve a considerable productivity of H₂O₂ to 2.17 mM for 5 h in alkaline medium in the absence of the organic electron donors and pure O₂. The optimal photocatalyst also obtains the highest apparent quantum yield (AQY) of 18.10% under 450 nm of light irradiation, as well as a good reusability. The contribution of the type-II heterojunction is that the migrations of electrons and holes within the interface between g-C₃N₄ and Co₉S₈ matrix promote the separation of photocarriers, and another channel is also opened for H₂O₂ generation. The accumulated electrons in conduction band (CB) of Co₉S₈ contribute to the major channel of two-electron reduction of O₂ for H₂O₂ production. Meanwhile, the electrons in CB of g-C₃N₄ participate in the single electron reduction of O₂ as an auxiliary channel to enhance the H₂O₂ production.

Confinement Catalyst of Co9S8@N-Doped Carbon Derived from Intercalated Co(OH)2 Precursor and Enhanced Electrocatalytic Oxygen Reduction Performance

Oxygen reduction reaction (ORR) is an important cathode reaction in fuel cells and metal-air batteries. Composites of transition-metal sulfides (TMSs) and nitrogen-doped carbon (NC) are promising alternative ORR catalysts because of their high catalytic activity. However, the agglomeration of TMS particles limits practical applications. Here, a confinement catalyst composed of Co₉S₈@NC with a flower-like morphology was derived from metanilic intercalated Co(OH)₂ through interlayer-confined carbonation accompanied with host-layer sulfidation. The surface of the Co₉S₈ particles is covered with a few layers of nitrogen-doped graphene, which can prevent the Co₉S₈ particles from agglomeration and also produce catalytic activity affected by internal Co₉S₈. Thus, the Co₉S₈@NC material achieves excellent ORR performance with a half-wave potential of 0.861 V_RHE. In addition, an oxide layer on the surface of Co₉S₈@NC is fabricated shortly after the ORR starts. Further tests and density functional theory calculations indicated that this cobalt oxide layer can increase the electrochemically active area of Co₉S₈@NC as well as reduce the ORR energy barrier, thereby providing more catalytic active sites and enhancing the intrinsic catalytic activity, thus achieving a self-activation effect during the electrochemical reaction process.

Self-Supported and Flexible Sulfur Cathode Enabled via Synergistic Confinement for High-Energy-Density Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted much attention in the field of electrochemical energy storage due to their high energy density and low cost. However, the "shuttle effect" of the sulfur cathode, resulting in poor cyclic performance, is a big barrier for the development of Li-S batteries. Herein, a novel sulfur cathode integrating sulfur, flexible carbon cloth, and metal-organic framework (MOF)-derived N-doped carbon nanoarrays with embedded CoP (CC@CoP/C) is designed. These unique flexible nanoarrays with embedded polar CoP nanoparticles not only offer enough voids for volume expansion to maintain the structural stability during the electrochemical process, but also promote the physical encapsulation and chemical entrapment of all sulfur species. Such designed CC@CoP/C cathodes with synergistic confinement (physical adsorption and chemical interactions) for soluble intermediate lithium polysulfides possess high sulfur loadings (as high as 4.17 mg cm^-2 ) and exhibit large specific capacities at different C-rates. Specially, an outstanding long-term cycling performance can be reached. For example, an ultralow decay of 0.016% per cycle during the whole 600 cycles at a high current density of 2C is displayed. The current work provides a promising design strategy for high-energy-density Li-S batteries.

Remarkably improved electrochemical hydrogen storage by multi-walled carbon nanotubes decorated with nanoporous bimetallic Fe-Ag/TiO2 nanoparticles

Nanoporous bimetallic Fe-Ag nanoparticles (NPs) were synthesized using a facile chemical reduction method and used to decorate the surface of multi-walled carbon nanotubes (MWCNTs) for hydrogen sorption and storage. The effect of TiO2 nanoparticles on the hydrogen storage properties of Fe-Ag/CNTs was further studied in detail. For this purpose, several nanocomposites of nanoporous bimetallic Fe-Ag/TiO2 nanoparticles with different amounts of bimetallic Fe-Ag NPs were prepared via a hydrothermal method. The hydrogen storage capacity of the as-prepared nanocomposites was studied using electrochemical methods. The Fe-Ag/TiO2/CNT nanocomposite with 0.04 M bimetallic Fe-Ag NPs showed the highest capacity for hydrogen storage, which was ∼5× higher than that of pristine MWCNTs. The maximum discharge capacity was 2931 mA h g-1, corresponding to a 10.94 wt% hydrogen storage capacity. Furthermore, a 379% increase in discharge capacity was measured after 20 cycles. These results show that Fe-Ag/TiO2/CNT electrodes display superior cycling stability and high reversible capacity, which is attractive for battery applications.

A Novel Type of Battery-Supercapacitor Hybrid Device with Highly Switchable Dual Performances Based on a Carbon Skeleton/Mg2Ni Free-Standing Hydrogen Storage Electrode

The sharp proliferation of high power electronics and electrical vehicles has promoted growing demands for power sources with both high energy and power densities. Under these circumstances, battery-supercapacitor hybrid devices are attracting considerable attention as they combine the advantages of both batteries and supercapacitors. Here, a novel type of hybrid device based on a carbon skeleton/Mg₂Ni free-standing electrode without the traditional nickel foam current collector is reported, which has been designed and fabricated through a dispersing-freeze-drying method by employing reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) as a hybrid skeleton. As a result, the Mg₂Ni alloy is able to deliver a high discharge capacity of 644 mAh g^-1 and, more importantly, a high cycling stability with a retention of over 78% after 50 charge/discharge cycles have been achieved, which exceeds almost all the results ever reported on the Mg₂Ni alloy. Simultaneously, the electrode could also exhibit excellent supercapacitor performances including high specific capacities (296 F g^-1) and outstanding cycling stability (100% retention after 100 cycles). Moreover, the hybrid device can switch between battery and supercapacitor modes immediately as needed during application. These features make the C skeleton/alloy electrode a highly promising candidate for battery-supercapacitor hybrid devices with high power/energy density and favorable cycling stability.

A three dimensional sulfur/reduced graphene oxide with embedded carbon nanotubes composite as a binder-free, free-standing cathode for lithium–sulfur batteries

The free-standing electrodes are synthesized by an eco-friendly method with sulfur/carbon nanotubes embedded in the basal plane of graphene oxide.